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Ported - 4th Order Vented

technical


Basic Theory



Widely popularized by Acoustic Research back in the 50's. The driver is mounted in a totally sealed and airtight enclosure, generally with the front of the driver facing outward but is not restricted to this method only. The system is designed to achieve a desired Q factor which controls the response characteristics of the driver/enclosure combination and usually ranging between 0.5 and 1.5.   The total system Q (also known as Qtc) is dependent upon: volume of enclosure, T/S parameters of driver and internal treatment compounds including all types of insulation, stuffing and wall-deadening materials. Best suited for drivers with an EBP of 50.0 or lower and drivers with Qts values above 0.40 but is not restricted to these exact alignments always.  Cutoff rate is about 12 dB/octave below f3.  However higher system Q's result is a somewhat sharper roll-off while lower system Q's result in a slightly more shallow roll-off varying by about +- 2 dB.  Better damping and better transients is achieved by shooting for a lower system Q which can be accomplished by either making the enclosure larger or by adding stuffing/damping material such as polyfill, Dacron, fiberglass, acoustic foam, or any other suitable type of fill material.  Box stuffing will also affect f3 by either raising it or lowering it depending upon the type and amount of stuffing used.

Advantages

Sealed enclosures are the simplest of all designs. Easy to model with speaker software and easy to achieve predicted results. Box size and shape are generally the least complex.  Great for both beginning and advanced DIY'ers. The exact response characteristics which are desired can be achieved by simply designing for a particular Qtc. You can alter its performance only varying the size of the enclosure and the amount of stuffing material used. Qtc ranges from 0.5 to 1.5 while 0.7 is generally considered ideal. Read about Qtc by clicking on Sealed above. Slowest of all cutoff rates below fB of 12 db/octave. This results in much quicker group delay responses ranging from 1ms - 10 ms. Fast, quick, natural, smooth, tight, accurate, controlled and warm are some common terms that audiophiles use to describe sealed enclosures. Transient response is the best of all enclosure types. The excursion of the driver increases as the frequency applied decreases until fB is reached after which the driver excursion begins to decrease once again. No need for subsonic filtering due to the enclosure's natural tendency to inhibit extremely low frequencies.  This results in less bottoming out of drivers at subsonic frequencies.  More extended low frequency response than vented enclosures given the same f3 for both.  Phase shift is minimal between its normal operating frequency range.

 Disadvantages

Very low frequency output is minimal. The -3dB down point (also know as f3) is usually fairly high, above 30 Hz in most applications. Less power efficiency by about -3 dB as compared with ven 13513c21n ted enclosures. Lower over SPL capabilities. Strong need for drivers with very large Xmax in order to ensure safe operation at least down to fB.  Any enclosure volume that models the system Q larger than 0.707 results in higher f3.  Lowest f3 is achievable only under an ideal Q = .707 alignment which may require unusually large and sometimes unacceptable enclosure volumes.

Best Applications

Where a completely uncompromised sound quality is desired. Best for classical music and most rock and pop type music. Most widely used in car stereo systems where cabin gain can make up for its lack of real low end. Where size is an issue. Sealed boxes can be half the size of vented boxes yet can be made even smaller. May also be use for small to moderately sized Home Theaters. Usually is the easiest box to pass SAF (spouse acceptance factor).  You should also go with sealed when the driver's T/S parameters dictate that the driver should be housed in a sealed enclosure due to a high Qts (above 0.4) or an EPB of 50 or lower.

Ported - 4th Order Vented

Basic Theory

Also known as bass-reflex.  The driver is mounted into an enclosure which exhibits a large opening, port, vent or slot that extends into the cabinet a specified length. The length and size of this vent are extremely critical to the proper function of this enclosure. The port and driver contribute together to provide the desired response characteristics. The driver is generally mounted with the front facing outwards, but is not restricted to this method only. The vent which extends into the cabinet tunes the enclosure to a specific frequency (known as fB) thereby acting as a high pass filter on the driver. Driver excursion is at its minimum at fB where the vent then takes over and does most of the work. Cut-off rate below fB is 24 dB/octave but can be varied up or down 5-6 dB depending upon the exact tuning frequency and volume of the enclosure. There are various types of alignments that all fit into the ported 4th order category. Some common types are QB3, EBS, SBB4 and SC4. By varying the enclosure size and the tuning frequency, it is possible to achieve a variety of distinct low frequency performances from a single driver. The vent acts by damping the load produced by the driver above fB causing it to behave somewhat as if it were in a sealed enclosure.  Best suited for drivers with an EBP near 100.0 or higher but is not restricted to this number only.

Advantages

Extended low frequency response. 3 dB down points (f3) are capable of being near or even below 20 Hz. Increased power handling above fB due to reduced driver excursion at and while nearing fB. More efficient system. Generally 3dB increased output over sealed enclosures due to the combined output of driver and port. More overall SPL capabilities. Deep, powerful, full, loud, inspiring, incredible, and earth shattering are common terms associated with vented enclosures. 

 Disadvantages

Larger enclosure size. More difficult to accurately achieve predicted results. Misaligned enclosures can result in very poor bass quality. Very accurate T/S parameters of actual driver is required. Although sometimes you can get away with using manufacture's specifications. Driver unloading or bottoming out below fB is very common. Xmax is reached easily below fB and may cause sever damage the the driver's suspension, voice coil or cone. This usually requires the need to install additional high pass filtering below fB. But is not a always a necessity as long as power levels and frequency content are kept within reason. Transient response is degraded, yielding typical group delay curves as high as 50 ms. Muggy, boomy, sluggish, one-note, slow, and inaccurate are common terms associated with vented enclosures.

Best Applications

Where the deepest and loudest bass is necessary. Where size is not a huge issue but may still be a definite factor. For Home Theater and music.  May be best suited for sound reinforcement, theater, live performances, DJ and other situations where lots of loud deep bass is needed and transient response is less critical.

 Bandpass - Dual Chamber Vented/Sealed 4th Order

Basic Theory

The front and the rear of the driver are housed in their own separate and distinct enclosures.  The front of the driver is in a ported enclosure while the rear of the driver is in a sealed enclosure.  The driver may be mounted the other way around however as long as one chamber is sealed while the other is vented.   The enclosure is designed as a sealed enclosure but with the addition of an acoustic filter (the port) in series with the front of the driver that acts to limit the driver's bandwidth and therefore increase its SPL capabilities within its bandwidth.

Advantages

Very low f3 is possible at the expense of lower efficiency and increased ripple.  Extremely high SPL is also possible at the expense of a higher f3 and narrower bandwidth.  Less overall driver excursion.  More control over cone movement.  Bandwidth and efficiency are inversely proportional.

Disadvantages

Combined volume of both chambers results in large overall enclosures.  Difficult to design properly.  Results may vary substantially due to misalignment of both front and rear chambers as well as tuning frequency.  Tend to have "one-note" bass, especially if designed or built poorly.   In order to achieve a wide useable bandwidth, there must be some amount of mid-band ripple as well as decreased efficiency.  Drivers can be easily blown due to high compression factors because of lowered cone motion and thereby exceeding the thermal limits of the driver before exceeding its mechanical limits.  Bandwidth and efficiency are inversely proportional.

Best Applications

Where the large size of enclosure is of little concern.  In cars where the design calls for high SPL where the limited bandwidth which results can be increased due to cabin gain.  The cabin gain will help achieve a flatter and wider bandwidth across the desired range while maintaining the increased SPL of the enclosure.  Very popular in car applications for this reason.

Bandpass - Dual Chamber Vented 6th Order

Basic Theory

 

The front and rear of the driver are mounted in separate enclosures and tuned to specific calculated figures.  Resultant output is suppose to be better than any of the other designs mentioned previously.   Bose owns the rights to the exact details behind this design.  They explain the theory like this, "The low-frequency speaker drivers are located between separate acoustic compression chambers inside a patented Bose Acoustimass module. As each speaker cone moves, it excites air in the chambers. Trapped in the chamber, this air acts as an acoustic spring, which interacts with the air in the port to produce more low-frequency sound with less power.  The system is more efficient and requires less cone motion, which in turn produces less distortion. In the event that any otherwise audible distortion is produced, the patented design traps it inside the acoustic chambers -- so it never enters the room. The result is an Acoustimass module with no audible distortion that can be located anywhere in the listening area."  www.bose.com

Advantages

 

More efficient system within its bandpass.  More control over cone movement.   Less audible distortion.  This doesn't mean that there is a true reduction in distortion, but that any distortion that is present form the driver can't be heard as well due to the chambers acting as filters on any unwanted noise. 

Disadvantages

 

Combined volume of both chambers may result in large overall enclosures.  Very difficult to design properly.  You may have to experiment for months before getting this design to sound acceptable.  Results may vary substantially due to misalignment of both front and rear chambers as well as tuning frequency of each chamber.   Drivers can be easily blown due to high compression factors because of lowered cone motion and thereby exceeding the thermal limits of the driver before exceeding its mechanical limits.  The driver may in fact tear itself to pieces.   There are no exact parameters or calculations for designing 6th order bandpass enclosures due to the patent owned by Bose.  So if you build one, you're basically on your own.

Best Applications

 

For more information on 6th order bandpass enclosures please visit www.decware.com

EBS - 4th Order Large Vented Enclosure with Low Tuning

Basic Theory

 

EBS- Extended Bass Shelf.  This is only one of the various different types of vented alignments which are possible and follows many of the same characteristics of vented enclosures.  The idea is to intentionally design the enclosure to be 125-175% larger than the optimal calculated volume and then tune the enclosure much lower than optimal as well.  The result is a significant amount of extended low frequency response.  When the response curve is simulated, a visible "shelf" can be seen in the curve just above the tuning frequency before it sharply rolls off.  The LEAP manual explains EBS theory like this: "The name [EBS] was derived simply from the visible appearance of the response curve. The bass response is extended to a lower frequency than would be possible from the QB3 alignment, but at a lower level or shelf relative to the mid band level. Although the EBS alignment is not a nice neat flat alignment such as the QB3, it is very often a much better choice than the QB3. The EBS alignment has some interesting features. Consider a loudspeaker with a Qts of 0.30, the QB3 alignment would have about 2dB more output at a frequency of twice the Fs, while the EBS alignment would have over 2db more output at Fs.  In most cases the EBS alignments will have far more subjective [low] bass than the QB3 alignments. Also, if you were to equalize the responses flat to Fs, 10db more boost would be required for the QB3 versus the EBS. This can dramatically consume large amounts of headroom in the power amplifier, and may also far exceed the linear excursion limits of the speaker.  The EBS alignment will maintain much lower cone excursion at frequencies near Fb than is possible with the QB3 alignment. This can be very important for high power systems." 

Advantages

 

Extended low frequency response down into the teens.  Subsonic earth shattering bass response.  Increased efficiency at the lower frequencies (below 25 Hz) but decreased efficiency at higher  frequencies (above 30 Hz).  This is a rough figure since many different combinations can be designed to yield specific results.   In general, low frequency is extended and efficiency increased at the expense of reduced efficiency at higher frequencies. 

Disadvantages

 

Cut-off rate can be as high 36 dB/octave below fB.  Transient response is degraded as a result of this.  However it may be argued that because the tuning frequency is so low, that is it far enough out of normal operating range that it may be considered a negligible downside.  The enclosure size is huge.  Anywhere from 5-15 cubic feet depending on the size of the driver being used.  Power handling capability of driver is reduced anywhere from 25-50%.  Driver may reach Xmax sooner above fB even if it never reaches Xmax right at or below fB.  Lack of real presence.  Lack of kick or punch.  The overall impact of the bass is much softer.  Signals between 40 and 60 Hz are significantly reduced.  Harder to "sell" because most people are more receiving to a pronounced upper bass response rather than an incredibly low and deep bass response .  It takes 8 times as much power (as well as moving air) to make 20 Hz sound as loud as 40 Hz.

Best Applications

 

Where the truly deepest of all heavenly deep bass is desired.  For drivers with a large Xmax and the ability to consume large amounts of power.  For drivers whose T/S parameters dictate an optimal enclosure size that's smaller than what the designer wants to build.  Large Home Theaters and varying kinds of music with heavy bass tracks would take the best advantage of this enclosure alignment.

PR - Passive Radiator

Basic Theory

A passive radiator is used in conjunction with an active driver and its purpose is to replace the port or vent of a typical 4th order enclosure.  A passive radiator is sometimes referred to as a drone cone.  A passive radiator (PR) enclosure is most similar to a vented enclosure in that they behave very much the same.  Response characteristics include: there is a notch at the Fp of the passive radiator (resonant frequency of PR) and the typical cut-off rate below fB is 36 dB/octave.  The resonant frequency of the PR is intentionally altered by the designer in order to achieve the proper fB of the enclosure.  In other words, it is used to tune the box to the desired frequency and for optimum performance.  This is done my adding or removing calculated amounts of mass from the cone of the PR.  More mass = lower tuning.  Less mass = higher tuning.  The increases mass also helps to lower the Fp of the PR which in turn moves the undesired notch out of the passband resulting in improved transient response.  In theory, the Vd (volume displaced by PR) should be at least 2 times the Vd of the driver it is being used with.  Yet in practice, a good rule of thumb to go by is to have anywhere from 3-4 times as much displacement in the PR.  This is to ensure the longevity of the PR's by preventing excessive continual over-excursion. 

Advantages

Simplicity of tuning.  By merely adding and removing small amounts of mass (usually measured in grams) the tuning frequency of the enclosure may be changed up or down by as much as 15 Hz or as little as 0.1 Hz.  Precision tuning is very possible.  Ability to tune small enclosures to very low frequencies without the loss of volume due to internal ports taking up enormous amounts of precious space.   No port noise or any kind of air- turbulence mach levels to worry about.  Pipe resonances and port standing waves are non-existent because there are no ports or vents in this system.  Better driver stability below fB due to increased damping on the driver below fB.  This is because of specific compliance characteristics of the PR which help to keep the driver under better control at subsonic frequencies.

Disadvantages

Steepest of all cut-off rates with a roll-off 36 dB/octave below fB.  Given the same size volume and tuning frequency of its vented counterpart, the PR alignment would result in a slightly higher f3.  The expense of of PR's can be quite high when compared to a simple piece of PVC pipe.  Especially when 2 or more PR's is needed, which is usually the case when using high-power high-excursion drivers.

Best Applications

Best suited just about anywhere a regular vented enclosure would be used.  May be used in applications where a smaller box is desired while wanting to maintain a 4th order alignment.  The PR alignment can be made half the volume of the same vented alignment and still be designed to have the same tuning frequency.

TL - Transmission Line

Basic Theory

 

The driver is mounted in a type of acoustical labyrinth or long pipe commonly referred to as a transmission line.  The length of this transmission line is usually somewhere between 4-8 feet and is dependent upon the Fs of the driver and the fill material used in the labyrinth.   This t-line may have a tapered effect or maintain the same cross-sectional area throughout its length and may also contain various folds which help reduce the overall size of the enclosure.  The length of the transmission line corresponds to the 1/4 wavelength of the resonant frequency of the driver.   The t-line is almost always filled with various types of stuffing material which help reduce the speed of sound through the t-line allowing shorter line lengths while still achieving  the proper tuning.  For example, a transmission line for a given driver with an Fs of 25 Hz without any fill would need to be nearly three times longer than the same driver in a transmission line that was damped with 8kg/m^3 of wool.  

Advantages

Transient response is considered equal to (and sometimes better than) a 2nd order sealed enclosure and is considered far superior to that of a vented enclosure.  The cut-off rate is somewhat shallower than a typical sealed enclosure and may be as low as 10 dB/octave or lower.  This results in improved deep bass performance.  Less upper bass coloration due to reduced impedance peaks.  A more pure, cleaner, and deeper bass.

Disadvantages

 

Difficult to design as well as build.  A transmission line is every carpenter's nightmare.  Extensive knowledge of wood working is required.  Not all drivers will work well for a TL enclosures, yet there is no specific guideline for which drivers may work well.  There are no concrete methods or formulas for designing TL's.  It's mostly trial and error.  Not recommended for the novice DIY'er.   Enclosure size may be very large.

Best Applications

 

Where you've got a ton of room, a ton of time, and a ton of patience.   TL's will work well basically wherever any of the other alignments would work.  It's unique performance characteristics make it suitable for even the most serious audiophile.

Isobaric - Dual Drivers
 

Basic Theory

Two drivers are mounted together in an enclosure with a cavity of air between the two drivers.  The drivers must operate in phase with each other.  The cavity of air between the drivers should be made as small as possible without compromising the operation of either driver.   The modeling for this type of enclosure is done just as you would any other speaker enclosure except you take the Vas of the driver and divide by 2.  This will in effect make all your speaker enclosures half as big as they would normally be for any particular driver.  

Advantages

Improved sonic bass response.  Bass is claimed as being tighter, faster, more accurate and more pure.  Vas of the driver is cut in half.  The volume of enclosure required to obtain a specific frequency response can be achieved in only half the volume.  This is where isobaric enclosures have their biggest advantage.

Disadvantages

Wasted amplifier power to driver the internal sub.  Efficiency of the system is down 3 dB as compared to a single driver due to the added cone mass and the reduced Vas.  When you compare isobarics to a system which houses two drivers each in their own enclosure, this system would actually be 6 dB less efficient.  

Best Applications

Where size is a big issue.  When you want the box to be very small.  Where more accurate bass is more important than lots of bass.  If you have a hefty amplifier with plenty of juice to spare and a driver that can handle a good amount of power.   Suited for music, home theater and car.

Compound ~ Push/Pull Dual Drivers

 

Basic Theory

Two drivers share an acoustic volume of air within a single enclosure.  The best way to take advantage of this alignment is to mount one driver facing outwards with the other driver inverted and facing inwards.  The drivers are then wired so that they are electrically out of phase while remaining mechanically still in phase with one another.  Odd ordered harmonics are cancelled out by using this approach according to Vance Dickason.  According to M&K who specialize is push/pull subwoofers claim that this approach cancels out even ordered harmonics.  So take your pick.  Either way, harmonic distortion is reduced in that any anomalies or variations in the two driver's spider, cone or suspension characteristics are canceled out by the other driver's inversely proportional anomalies and variations.  The sound is as accurate and pure as it can possibly be with each driver "correcting" the other driver.   Of course many times two drivers will share the same acoustic volume of air while maintaining the more traditional look of having both drivers fire forward into the listening environment.   Though this does not have the same harmonic cancellation effect, all other characteristics between the two alignments is identical.  Box volume must be twice that of a single driver.  This can be easily modeled by taking the Vas of a single driver and multiplying it by two.  The system has an increased efficiency of 3dB over a single driver.  Power handling for the system is twice that of single driver.  Frequency response is the same for a single driver in an enclosure excaly half the size.

 

 

Advantages

Increased output and power handling.  Very high SPL capability.

 

 

Disadvantages

One single huge speaker enclosure that may be both unattractive and hard to move.  Response it essentially identical to building two smaller enclosures of exactly half the size but without the versatility of placement of two separate subs.  If one of the drivers blows due to too much power, the whole speaker will no longer perform because the blown driver will begin to act like a passive radiator.  If your enclosure is already ported, then this will only cause more problems.  If it is sealed, then bass response will be reduced dramatically.  There are no real disadvantages to building this kind of enclosure as the speakers will behave just as they would in enclosures by themselves.  It's very common to make MMT style speakers and use the two drivers in the same enclosure.

 

 

Best Applications

 Where one sub just isn't enough.  High power high output applications.  If you choose to do the push/pull configuration, the sonic advantage may make this sub more suitable for audiophile music and critical listening experiences.

 

 

Out With the Old, In With the New

Ultimately I wanted my center channel to match all the speakers I'm currently working on, so I decided I'd better get cracking on a design soon.  So today I spent some time cutting and drilling and, well this is what I came up with.  I will be using my same exact drivers from my old center channel.  Which consists of a 6.5" Vifa M17SG-09-08 shielded woofer and Morel's DMS-29 shielded 1-1/8" soft dome tweeter.  I love the way these two drivers sound together.  I believe they are a very good match and have enjoyed their performance over the last year I have been using them.  I recently upgraded the cheap 1st order filter with an L-R 2nd order filter and lowered the crossover point to just above 2KHz.  There is also a Zobel network on the woofer and was calculated from standard Zobel equations.  Now their response is even better than before.  Vocals sound natural and uncolored.  Upper midrange is clear and blends well with the lower end of the tweeter.  I've never had any complaints...except that the enclosure was ugly as all sin.  So that's what I'm determined to fix.  Here are the first few pictures.  More details will follow.

The Details

Okay now it's time for the details that follow.  As you can see from the pictures to the right, the speaker is almost to final completion.  When I first started this page only 1 week ago, I only had 4 pictures posted.   Now I've got about 30 pictures and it's almost totally done and ready to sit on my entertainment center.  I haven't explained in any detail any part of the building process on this speaker.  I suppose that's what this whole web site is suppose to do!  But I will explain a little bit about how I have achieved the final look on this new center channel speaker just in case someone decides they actually do like the way it looks and wants to replicate it.  Now most of the pictures speak for themselves.  But I'll walk through some of the procedures taken and tools required to accomplish it.

The first thing I did was build a plain, ugly rectangular MDF box.  There is nothing fancy about the enclosure in any way.  All the cuts were made with a circular saw and a poor-man's-table-saw rig.  I put a standard shelf brace between the woofer and tweeter for added strength and support to the front baffle.  I cut the holes with a B&D jigsaw.  Not even an expensive one.  Probably the cheapest you find at Home Depot - around $30.00.  Who says you need expensive tools to build great speakers?  You don't!  But what I used was a good compass, to draw the circles where I wanted the drivers to be located.  Then I very carefully and slowly, cut the driver holes.  Now I usually try and cut the holes exactly the right size the first time, but if there's any mistaking in the cut, I try to make it smaller, and not bigger.  Then I just use some course sandpaper or a course tooth file and shave off any excess until the drivers drop right in.  

Not Your Ordinary Flush Mounting

Now the next trick is the flush mounting of the drivers.  Once again here's a trick for those of you who don't have a router.  Besides, it's just one more expensive tool you don't really need (but I sure do want one!).  I call it the flushed-baffle board. In order to flush mount both drivers exactly, and I mean totally exactly, you need to use a flushed-baffle board that is the same depth as the thickest gasket on your drivers.  The Vifa woofer was 3/16" thick and the tweeter was just over 1/16".  Ideally I should have used a 1/4" flushed-baffle board, and then raised the woofer 1/16" by using extra thick weather stripping.  The tweeter I could have done the same as used super extra thick weather stripping, or made a 1/16" ring to fit inside the hole and then used some thick weather stripping.  Well that seemed too complicated and I didn't want all my drivers sitting on 2" of weather stripping (to exaggerate a little).   Not only that, but the drivers should be mounted as firmly and as closely as possible to the enclosure baffle to help eliminate basket ringing or other resonant effects the the drivers may exhibit if given too much play against the baffle they're bolted to.  With the tweeter, it's not as big an issue, because the moving force of the dome is so minute compared to the weight of its faceplate and surrounding structure.  But with woofers, the cone can create some fairly large amounts of force, which are radiated into the basket and enclosure.  And a 40 lb. enclosure does a lot better job of dampening those resonances than a 1/2 lb. cast aluminum basket.  Anyway, I decided to use 1/8" hardboard to make my flushed-baffle board.  This way the woofer's gasket would just barely sit over the top, and I could easily raise the tweeter with weather stripping to the exact height of the baffle, making a seamless extension of faceplate-to-enclosure.  The fact that the woofer is not totally flush mounted won't have any significant effect since it operates in a frequency range much lower than the tweeter.  The wavelengths coming from the driver are much longer than the 1/16" overhang it has.  So effectively, they (the sound waves) won't even know it exists.

So with the hardboard thickness determined, I went ahead and measured the exterior dimensions of the drivers and cut my holes in the flushed-baffle board.  Also using my jigsaw and cutting very carefully and very slowly.  This cut is very important because it will be an exposed cut.  If it's not exactly circular, you will definitely be able to see it.  Also if it's too large, you will see it.  I ended up cutting two baffle boards because the first one I cut was just a hair too big and I didn't like so much gap between the tweeter edge and the baffle.  So the next hole cuts I made much smaller and then sanded them till the drivers slipped inside nicely, leaving just about 1/64" all the way around. 

Now comes the tricky part.  This baffle has be mounted directly over the other two holes, completely centered, and then glued into place.  This is how I did it.  I dropped the drivers into their respective openings, and then placed the flushed-baffle board on top.  I moved the drivers around what I could, since there was some tolerance in the original cut made for them, so that they sat in place directly in the center of the exterior holes.  When the 1/8" hardboard was positioned in its final resting place, drivers aligned, I nailed two small 1" finish nails into each opposite corners to hold it in place.  Then I pulled out the drivers, and pulled off the hardboard making sure to leave the nails attached but sticking out so I could eventually stick them back into their holes.  I covered the front baffle with Liquid Nails, and then placed the hardboard back onto the baffle, making sure to get each nail to go back into its original hole.  Then I hammered them down, leaving just enough so I could pull them out later.  Next I cut a small scrap piece of PB and used that to clamp down the flushed-baffled board tightly to the enclosure front.  And that was that.  A few hours later I pulled off the clamps, pulled out the nails and my enclosure was now complete with a 1/8" recessed cutout for each driver.  And I didn't even use a router!  Not only that, but my front baffle is nearly 1" thick with the extra wood.  So it's stronger and more dense and helps the enclosure have a total, overall more deadness to it.

Oak on MDF

Now that the front is done, it's time to work on the oak sides.  This is a new technique I just picked up recently.  I may have seen it on a few speakers and decided to replicate it.  Wow does it look good when it's done!  I took a piece of 3/4" oak veneer (not solid oak, just oak veneer, much less expensive) and cut it out to exactly 3/4" smaller than the width and height of each side.  Then I used pieces of solid oak 3/4" quarter rounds to complete just the top and front of the speaker.  I figured with this being a center channel, the back and bottom of the speaker would never be seen, as well as for simplicity sake, I only covered the front and top with the oak quarter rounds.  On my Monitor M690, I did all four sides with the oak rounds.  And on my Swans M3 I plan on only doing the front with the quarter rounds.  I guess I'm just mixing up the mix.  Once those were are all cut, and the 45 degree angle was cut using my cheap-o miter box, it was time to glue them on.  Once again I used small 1-1/2" finish nails to hold the 3/4" oak on the sides in the exact position they needed to be in before I clamped them.  This did put a small hole in the nice side of wood, but with a tiny bit of putty afterwards, it's totally unnoticeable. 

Now I still haven't found a really good way to glue on the quarter rounds.  My technique to date is to use regular wood glue, place the quarter round in place and then strap duct tape from the top over the quarter round and down the other side.  I've found this to work very well, as it doesn't damage any of the nice wood when you're done with it.  Since the quarter rounds are mostly for aesthetics, there is no need for 100 lb. per square inch force tearing into them to get them to stay on the enclosure.  They will stay on there just fine.  The picture to the right shows this awesome poor-man's technique.

Once the glue was all dry, I whipped out my 100, 150, and 220 sandpaper and just went to town.  I sanded till my arms about fell off and sweat was dripping from every pore of my body (I suppose a 90 degree garage didn't help matters any either).  Once everything was nice and smooth, I took the box inside the house to do the rest of the finish work.  After all, the garage was covered in saw dust, which to this moment is probably still floating around in the air in there.  Unsafe conditions for staining and painting.  Oh yeah before this, I puttied up all the holes left by the screws.  So up in my computer room, I was able to stain each of the sides the color I liked in a dust free environment.  The stain color I chose to go with was Special Walnut by Minwax.  This stuff went on so dark the first time, that I ended up only using one coat.  Now that it's been finished with the clear polyurethane, it darkened up even more, so I'm glad I didn't talk myself into doing another coat (which I almost did).

Once the stain dried, it was time to begin prepping for the black finish which would take care of the other 4 sides to this enclosure.  So I taped the edges with a very high bond type lacquer tape.  It provides a good bond without peeling up and leaves a sharp edge when your done painting.  Home Depot sells it and it's actually called lacquer tape and is meant for doing exactly what I'm doing here.  Along with the tape I used a couple sheets of paper to protect the rest of the newly stained wood.  Now I can spray paint, brush paint, and do any kind of light sanding I need, without disrupting the stained portion of the enclosure.  So first things first, a few coats of primer, with a little light sanding between and I was ready to put on the black paint. 

How Do You Paint Again?

The paint I used in this case wasn't even a lacquer.  It's not even oil based, which I thought it was originally, until I dipped my used paint brush into a bowl of paint thinner and nothing happened.  Okay so I'm a little slow in some areas.  Painting never has been my forte.  It turns out to just be a generic water based style paint intended for around the house crafts and hobbies like chairs, doors, kids toys and furniture.  Well I guess you could fit speakers into the list.  At any rate, the stuff worked out great!  It's thick as all snot, but brushed on smooth and dried very quickly.  Much quicker than any lacquer.  My paint brush wasn't the greatest however so it did leave a few brush strokes.  But after it dried I sanded those out with 220, and put on another coat, somewhat thicker than the last trying to leave less brush strokes.  I think I succeeded.  After 2 coats, I was happy with the finish and was ready to do Dan's patented final finish.  I sanded the last coat with 400 till it was nice and smooth.  There were a few brush strokes, but I knew they'd be gone by the time I was done with the next step.  This is where I whip out the ole spray paint and spray the entire enclosure over three or four coats till it's as black and as smooth as can be.  So spray paint is my patented second to final coat.  I think it works great, and it literally takes out all of the flaws the brush leaves behind.  Well, my brush anyways.  After the spray paint dries, you're left with a somewhat grainy feeling on the speaker.  I remove this with just a sheet of ordinary computer paper.  It acts as a very fine sandpaper and removes all the little grainy spray paint residue.  It's so fine in fact that it will turn your hands black with a fine black powder that is so fine you have to wash your hands with soap and water to get it off.  It's almost like black toner from a copy machine or printer.

Well now that the black finish is complete, I can take off the green tape and expose once again the beautiful dark oak stain below.  This is where you will get your first glance at the final beautiful overall finish of the speaker.  Where the dark satin black meets the the deep brown oak, it just looks awesome.  But not as awesome as it will look once the whole thing has been painted with several coats of a clear polyurethane.  That's the stage I am at right now.  I've got one coat on and 2 more to go.  Between coats I let it dry about 5-6 hours before I will sand it with 220, and redo again.  The final coat requires 24 hours before light use and 72 hours before heavy use.  And that's it it!

Next I will discuss the new crossover I will be implementing and show off the final pictures.  Until then!

The speaker is done and I finally got the finished pictures!  I was borrowing the camera from a friend and he's been using it to take some pictures of stuff to sell on  e-Bay.  So I borrowed it again and took the final three pictures.  My first impressions?  Wow, this speaker looks amazing.  This is the most beautiful speaker I have made to date.  Yes, I impressed myself.  Hard to do, because I'm such a perfectionist in areas such as this.  So I spent 5 days straight on just the finish alone.  It got as good as I could get it and I left it at that.  I ended up doing so many coats of the satin polyurethane, with so much sanding between, that the finish actually ended up being glossy.  Not super glossy, but definitely not satin.  I still like it though.  I even like it better glossy.  The finish is very, very smooth all the way around and has a good deal of depth to it.  In my effort to sand out the brush strokes (reverting back to 150 sandpaper on my nice black finished speaker), I did manage to sand out all the paint brush strokes to the point that they were very, very small.  So small that they longer looked like brush strokes.  But then moving onto 220 sandpaper, I had a hard time removing the markings left form the 150 without going all the way through the original coats of paint to bare wood.  So I was left with these very thin lines, like scratches on the surface of the black paint.  Now with the polyurethane on top, it actually becomes buried into the finish and barely noticeable, yet it gives a lot character to the speaker.  The result can only be seen under certain light and at certain angles.  It just screams out at you, "Many long, hard hours went into my production!"  Otherwise, the finish looks flawless.  I actually prefer this look to just buying a sheet of boring high gloss black Formica and gluing it on the top.  Call me old fashioned.  I finished off the speaker with a few sprays of that Howard's Orange Oil Furniture Polish.  It basically gives the wood a glossy, new, very slick feel to it and takes out most of the finger prints which easily build on the surface.

Now for the sound, I popped in Gladiator and watched a few scenes.  Now since I'm a married guy living with neighbors on either side of me who are also married and have kids and stuff, I never get the opportunity to play movies very loud.  I respect other people's right to have a peaceful, happy home as I like my home to be.  So it's hard to give a really good review.  It does sound much fuller in the low end, since the enclosure is larger than the previous one.  I believe I'm very close to a Qtc of 0.71.  There are no air leaks whatsoever.  The inside walls are lined with egg crate foam and the enclosure is 100% filled with a pollyfill type batting.  The kind your wife buys at the craft store.  So the midrange still sounds very smooth and uncolored.  The cabinet almost has no resonances.  If you place your hands on the cabinet when Russell Crowe talks, there is very little to none vibration artifacts.  I noticed the treble sounds a bit different.  It is perfectly flush mounted (which looks awesome) so I assume that's what is accounting for the tonal difference, but I can't make out what it is just yet.  I almost think I need to pad it 1-2 dB.  It feels a hair brighter than it used to be.  It also could have been the DTS audio track on that movie.  I know it's a bright one.   I also have plans to re-do the crossover once again.  I like the new 12 dB L-R one that I crudely constructed to replace the old 6 dB one, but my inductor values are guestimated and poorly wound.  They have high DCR values and my caps are standard electrolytes.   I want to rebuild it with all 18 gauge air core inductors, polypropylene caps, 14 gauge silver plated internal speaker wire, and drop the x-over frequency to 1950 Hz, which will make for standard values for L-R design.  Then I think I will be officially done!  You think?

This next little portion I'm dedicating to the, "How I wished I'd done it." section.  Tips on how I could have done it better and what I have learned from doing it wrong.

How I Wish I'd Done It

"Measure twice, cut once".  I love this one.  It's a classic saying but you can't go without.  I made at least three bad cuts that caused me to have to toss good wood for scrap.  Granted it was a small speaker, so not much was wasted, it is frustrating to go try and pop and piece of wood in place and find you cut the short side even shorter instead of the longer side to fit just right.  I also mounted the terminal cup off center towards the top instead of off center towards the bottom how I wanted it.  Now I measure 27 times and cut just once.

"Don't take off the lacquer tape before you've completed all the sanding on the lacquer."  Once my paint dried I was so anxious to see what it looked like in contrast with the stained oak, that I tore right off the tape and paper protector.  I ooooed and aaaaawed at how cool it all looked.  The seam from black to stain was perfect.  Then I started sanding away at that newly dried paint and, well remember how I said it left such a fine powder it was like toner from a printer?  Well it works in the same manner too.  I ended up getting that fine black powder inside the tiny cracks of grain in my oak (just on the top) and no amount of blowing inside there was getting it out.  It was very subtle but it did tend to darken up the overall look of the brown stain in a couple of spots.  Lucky for me I had chosen such a dark stain to begin with.  Any lighter a color could have easily been ruined.  So keep that in mind!  The only hard part is sanding the paint without tearing up the edges of the tape.

"Thicker coats of paint are better than thinner ones."  This may sound contrary to what you've always heard, but this is why I say that.  My first coat I put on very sparingly, just enough to cover the surface and make everything black.  Well, the brush strokes were huge and there wasn't enough paint to fill them in as it dried.  Not only that but it dried so fast, since it was so thin, that it didn't give any paint a chance to fill in the brush strokes.  As I later learned, I gobbed on the paint, brushed it all the way out the sides, it took about 5 seconds to paint one whole side, and then after I quit brushing, there was enough paint on the surface, that it dried slower and within minutes had filled up all the brush strokes.  Now this technique only works on flat surfaces, so you can only do one at a time.  Don't try painting the top and front, because the front will drip.  You don't want drips, but you do want to use lots of paint, so do only flat surfaces.  It only needs like 30 minutes before it's set enough to not drip and you can move onto one of the other sides.  My disclaimer - I am not a painter.  I know absolutely nothing about paint.  Paint your own speakers at your own risk.  =)

That's it for now.  I know I have more stupid lessons to be learned, but this is all I can write at this time.

  

Getting Sidetracked When You're Already Sidetracked

I'm sure I'm not the only one who gets a little distracted by other projects while trying to work on just one.  My intentions about 4 months ago was to kick off a pair of Swans M3 tower speakers.  Then about 1 month ago I began working on a pair of mini monitor speakers.  Then about 1 day ago, I built myself a pair of bipole surround sound speakers.  I pretty much designed them, built them and finished them all within one weekend.  Who says I can't finish a project when I start one?  So without going into any detail on its design, I'll just show off all the pictures of it.  Tomorrow I'm going to paint them and finish them entirely.  For now, this is what I've got.  Now I'm not sure exactly if they're really dipoles, or what kind of surround category they fit into.  They've kind of got the Bose direct-reflecting thing going on.  Similar design to PSB's 10S surround sound speakers also.  They should work great for just basic surround sound and ambient effects.  I suppose they'd really suck for just music.  But then that's not they're intent.  Enjoy the pics.  They're big in size but small in bytes.  Well around 50K small.  The fleck paint was totally my wife's idea.  I've wanted to use the stuff it the past, but never wanted it to totally mess up a pair of speakers that were months in the making.  These were a good pair to try it out on.  My initial thoughts are that this stuff is awesome!  It goes on so easy, and has a very rustic look to it.  It should also fit the decor of the room.  More to come later!

 

 

 

Some Theory on Bipolar Surrounds

First thing everybody is wondering is, "So are the drivers wired in phase or out of phase??"  Right now they are wired in-phase.  There is no acoustical null when listening directly over the center of the speaker.  This is why they are bipole surrounds and not dipole surrounds.  I will not be placing them exactly to the left and right of my couch either.  So to explain why I have gone with a bipolar design and not a dipolar design, I will look towards PSB and their 10S surround speakers which I mimicked in my design here.

"... It is a bipolar design that combines two identical panels that employ the Image 5-1/4-inch woofer and the Image 1-inch aluminum-dome tweeter. The angling of these two panels outward creates a diffuse soundfield, and the connection of the two speaker arrays in phase also aids localization of sound when sharply placed effects are present on a soundtrack or a music recording field.

Over the past few years, the growing dominance of Dolby Digital surround recordings has created a need for a speaker on the surround channel that would be neither a conventional direct radiator nor the dipole design that came into being during the Dolby Pro-Logic era. The dipole created a welcome diffusion of sound, but it was designed and placed to create a "null" at listeners' usual seating position because there were and are no directional effects in Pro-Logic's monaural surround channel. This became increasingly unwelcome to most of us as Dolby Digital took over, because the directional effects that appeared in these recordings weren't sharply registered by the dipole design. And while conventional direct radiator surround speakers do handle the need for pinpointing some surround effects, many listeners miss the ambience of the dipole's diffused surround field.

The Image 10S offers the best of both worlds. Its surround ambience is very convincing, thanks to the way the two speaker panels are angled to radiate indirectly. But because the speakers are wired in phase, in a bipolar design, rather than out of phase in a dipole array, they also provide all the localization needed for soundtracks with directional surround effects. Surround recordings of music also profit greatly from the soundfield of the 10S, and small rooms sound much "larger" than they do with direct radiator speakers. The more demanding you are about surround sound, or the more demanding your listening conditions are, the more we think you will appreciate what the 10S has to offer."

I couldn't have said it better myself.  So bipoles they are.  There are some other factors that go into a dipole as well that I didn't want to have to worry about.  First of all each driver needs its own enclosure.  I didn't place a dividing barrier between the two drivers.  They share the enclosure.  Also the bass response in dipoles is minimal at best unless you place a high pass filter on one of the drivers, so that only the other driver is producing the lower frequencies.  Then there's placement of dipoles and making sure that the in-phase drivers point forward toward the main speakers.  There's just a lot more to the dipole.  I have tried out the speakers as dipoles and they do a marvelous job of creating that "where's the sound coming from" feel.  It's quite amazing actually.  It's as if your ears were deceiving you the way the sound seems to reflect off everything and doesn't appear at all to actually come from the speaker itself.  At any rate, I like the bipole design better.

Updated 09-27-03

After several months of listening to these surrounds in a bipole configuration, I decided to try out the dipole side of things.  This is where the woofer and tweeter that face forward are wired out of phase with the woofer and tweeter that face toward the rear.  This configuration works best when you can mount the speakers at ear level exactly on either side of the listening position, which is how I currently have it set up in my home theater.  Compared with the bipoles, I love the dipole quite a bit more.  They truly do give the real effect of a ((surround sound))).  Since there is little or no directionality to the speaker, due to the out of phase drivers, the surround effects just appear to come out of no where.  It's really pretty awesome sounding.  Not to mention that since the cabinets were so small, the two drivers were constantly fighting for air space.  Now that they are wired out of phase, the nasty hump around 100 Hz (that I could constantly hear) is gone.  There's probably massive dip in that same spot instead, but these speakers were never meant to provide any substantial low frequency anyway.  I'll take the softer sounding dip over the boisterous hump any day.

 

15" Ultimate Attitude Subwoofer

 

 

Speaker Projects    TC Sounds 15"    10Triple10    Shiva    EBS Shiva    UA 15" Sub

 

15" Ultimate Attitude Subwoofer

Planning the Design Goals

Before I design or build any speaker, I like to decide on my design goals.  These would be certain criteria the speaker has to meet when it's completed.  Do I want the lowest 3 dB down point as possible in a size-no-object enclosure?   Or can I sacrifice some space and get away with a higher f3?  Maybe an enclosure that isn't tuned to give a completely flat anechoic response but will yield a flat in room response.  Are looks important?  Can the box be twice as deep as it is tall?   What type of finish will the speaker have?  Will it downfire?  What's  the smallest diameter port can I get away with before port noise becomes a problem?  Should I go PR instead?  How much money am I willing to throw into this speaker?  And the questions go on and on but you get the idea.  This helps me easily decide on what type of speaker I'll end up with and how it will sound.  For many people who are building their first sub, they'll simply state, "I want it to go as low and as loud as possible!"  Well I've been there and done that, so my design goals usually vary a bit more.  I am probably more critical about certain factors than I need to be.  But to me it presents more of a challenge and a greater satisfaction when the final product comes to life after weeks of making it all come together.  So I present you with the UA3504 15" Subwoofer. 

Design Goals     

  • Ported Enclosure
  • Smallest enclosure size possible (and still be suitable for a 4th order design)
  • No active EQ
  • Tight and  punchy, powerful and clean bass between 30 and 60 Hz
  • 3 dB down point near 35 Hz if possible
  • Not a huge bulky ugly box that can hit 18 Hz while ignoring WAF
  • Must be covered in wood and stained in something nice
  • The front I want to be gloss black with a huge flared port
  • Bracing at a maximum to ensure there's no panel vibration 

That was the basic idea.  Small ported box with strong bass between 30 and 80 Hz using in-room effects to smooth response and help out the really low end.  Here's the driver that I had to work with: 15" Attitude AU1576 Subwoofer *350 Watts RMS 500 Watts Peak *2.5" diameter voice coil *4 ohm nominal impedance *Frequency response 20 - 200 Hz* Magnet weight 70 oz. *SPL  92.5 dB 1W/1M *Vas = 9.9 *Qms = 11.25 *Qes = 0.37 *Qts = 0.36 *Xmax = 10.7 mm

Modeling the Enclosure

The specs above are manufactured specs.  I did do my own T/S tests and got very similar results.  I just can't remember where I'd written them down.  The box was designed using the actual T/S parameters.  So the first thing I did was plug and chug some numbers to see what kind of box this driver would really like to be in.  Using various programs from Brian's ported.xls to Bass Box Pro 2.0 to Juha Hartikainen's WinISD.  I found that the driver would work best in a rather large ported enclosure of 4.75 cubic feet tuned to 30 Hz with an f3 of 32 Hz.  That big of a box was not going to pass especially to achieve an f3 of only 32 Hz!  With that you can easily see that low f3 is not this speakers strong point.  This is due to a high Qms and Vas which results in a more efficient driver.  Which is a definite plus for low power amplifiers.   I wanted a small box at the expense of having a relatively high F3 but with the bonus being greater efficiency.  This sub sounds awesome with only a few watts in.   So I took the box down to what was an aesthetically pleasing size for a 15" woofer.  18"W x 17"D x 25"H.  Minus all the bracing  (which was a lot) and the woofer and port, I ended up with a net internal volume of only 2.75 cubic feet.  I thought at first that it would be to small for this woofer, but that was as big as I dared go to still achieve my design goal of a "small enclosure".  So I went ahead and plugged in 2.75 ft^3 and ended up with an enclosure with an f3 of 39 Hz being tuned to 35 at the expense of a 3 dB hump in frequency response.  The hump I surely did not want, so by dropping fB to 30 Hz, the hump is reduced to 0.5 dB, which is much more suitable, especially since the box is so small.  I wanted the box to hit hard in the mid-bass region and this design will certainly do that very well.  You'll notice from the graphs that this speaker will also work perfectly (with a Q of 0.70) in a sealed enclosure of the same volume.  So if you like the sound of sealed boxes better than ported, all you need to do is put a PVC end cap on the other end of the port and your set.  Either way this sub sounds great with DVD movies and most all kinds of music. 

Construction Detail

The box was constructed of 3/4" particle board.  Oh no, I said the 'pb' word.  You're right I didn't use MDF on this box.  I went back to the old school methods and used good old fashioned particle board.  For all you MDF fans (me being one of them) you can get away with using particle board as long as you understand a few things:  particle board is not as dense as MDF.  Therefore bracing technique and panel width must be doubled to reduce panel vibration.  Also particle board is much more difficult to work with than MDF.  Screws tend to split the wood easier.  Bits and pieces can break off corners easily and be difficult to repair.  So taking those factors into consideration, I tried to make the box as thick as I could and use a lot of solid bracing.  I was extra careful in building the box so as to not split or break off any corners.  I had planned to cover the box in 1/8" mahogany which would further strengthen the panels and provide better protection on the corners.  I can safely say that I "got away" with building this sub box out of particle board.  The panels remain motionless during even heavy passages of pounding bass.  By looking at the pictures to the right, you can see how I have two vertical and two horizontal braces that are interlocked to each other in the middle.  Each brace runs to another brace which runs parallel to the panel it supports providing 1.5" of thickness over that particular area.  Now the reason I don't have all the panels 1.5" thick was too maximize the internal volume of this enclosure.  Extra internal bracing would have reduced internal volume.  I had to compromise just a little between maximum internal volume and maximum internal bracing.  I believe I achieved the best of both worlds by using the technique that I did.

Applying the Plywood Veneer

After the box was built and all the bracing in tact, I went ahead and cut out the 4 sheets of 1/8" plywood veneer.  The reason for using 1/8" plywood mahogany in my case, was because I had just enough left over from a previous project to finish up this one as well.  Which is also why I used the particle board.  I already had a bunch of it on hand.  Sometimes that is the deciding factor when building a box - the stuff you've already got.  Okay so I don't like to waste wood.  Anyways, I like to cut my veneer 1/8" too big.  This way I can sand down the edges to ride exactly flush up against the other piece of veneer.  It gives a seamless look.  I used Liquid Nails and a caulk gun and ran a thick 1/4" bead up and down the entire side panel.  I wanted the glue touching every part of both pieces to make a strong bond between veneer and box.  These side panels will never come off in a million years.  

The Finish

After finishing the mahogany panels, I sanded down everything real smooth - first with 120 and then 220 sandpaper.  I went ahead and stained the sides and the top with its first coat of stain.  Then a second, third and fourth until it reached the color I liked best.  After the last coat of stain dried, I lightly sanded all the sides with a synthetic steal wool of 800 grit.   Now it was time to paint the front and back baffles.  This is done by using painters-type 2" masking tape to protect the newly stained sides.  I then sprayed three coats of gray primer on the front and back, while sanding with 400 between coats and after the final coat.  I then brushed on the black lacquer with a fine-bristled, quality paint brush.  After one coat, I sanded with 220 and did another coat.  After the second and final coat, I sanded the front and back down again with 220.  Now I could peel off the paint and apply the final two coats of a high gloss polyurethane to the entire enclosure.  This ensures an even shine throughout the whole enclosure including the black front and the stained top, bottom and sides.  The final look is remarkable.  The speaker enclosure looks absolutely wonderful.  The box feels incredibly smooth and just shines like a light bulb.

The Pictures

To the right are thumbnails of the the different stages of the building process of this subwoofer.  Each one shows how production progressed until the final product was complete.  This speaker I have to say is the most gorgeous of any the others I've built recently.  I really love the way it looks.  Not to mention the way it sounds.  I'd have to say it has a very robust type of sound to it.  It's very heavy and strong.  It doesn't take a whole lot of power to get this sub to start shaking everything in the house.  But when it gets going, it doesn't want to stop.  I really like the unique bass response of this sub - it's tight, it's fast and it's clean.  Most importantly this sub passes SAF by a landslide.  My wife loves this speaker, not only because its small but because it looks so nice.  This sub is also for sale at an incredible price. I'm practically giving it away.  So check out the For Sale page and see if this sub might not suit your needs.  Then give me a call and we can work out the best way to get this sub into your own sound system.

Measuring the Frequency Response

Just a little bit of info regarding  how the frequency response was measured.  The sub was measured in my front yard so as to avoid all reflections from walls and ceilings.  This is about the best anechoic response you can get.  Only the ground is capable of interfering with the results.   I used a precision frequency generator, frequency counter, amplifier, and my trusty Radio Shack analog SPL meter.  The sub was placed in the grass as far way from the house and any walls as possible, while the SPL meter was placed at exactly 1 meter from the front baffle at the same height as the dust cap.  I ran 9.75 volts into the driver which has a nominal impedance of 4 ohms which roughly equates to 23 watts.  Since impedance varies with frequency, we can't say exactly how many watts the driver was dissipating, but we can get an idea of how hard the sub is being pushed.  23 watts is very conservative.  I then plotted the SPL at 5 Hz increments starting at 15 Hz working my way up to 100 Hz.  I then accounted for meter correction and plotted the results in Excel.  That is the graph you see to the right.  The response has a small hump of about 2 dB from 50-80.  Below 50 Hz the response begins to drop off where it's 3 dB down point would be figured around 40 Hz.  The response continues to roll off gradually just as it should dropping to about 93 dB at 15 Hz.  In-room response of the sub would improve the low end by about 10 dB starting at 20 Hz.  For a 15" subwoofer in an enclosure this size, it hits plenty deep and plays plenty loud.

 

The Completed Project

The Driver

Bracing Technique

Stained

Primer

Black Lacquer

Calculated Response

Measured Response


Copyright 2000 © Audio Innovation, Inc.  All Rights Reserved.
This page last updated on January 28, 2005.

The Mind is a Terrible Thing to Waste

I started imagining this design a few months ago while trying to stay awake through the one of my professor's boring lectures.  Though I didn't get much out of class that day, the boredom had caused by brain to wander into the deepest parts of its inventive little caverns.  I was reflecting upon the many recent discussions regarding passive radiator operation.  Especially thinking about DB's The Beast.  So many people have so many different opinions regarding how to make PR-based subwoofers yet I bet more than half of those people have never really sat down and put one together.  I didn't want to be another one of those people.  And since I had some knowledge both from experience and research behind me, I made up this little masterpiece I call the 10Triple10.  

When Four is Better Than One

This subwoofer is a 10" woofer in a small enclosure with 3 10" passive radiators.  That's a total of 4 radiating drivers all bouncing and booming to the rhythm of the beat.  All I can say about this subwoofer is its performance is completely remarkable.  You'll think that either your eyes or your ears are deceiving you to believe that a subwoofer this small can produce such enormous amounts of truly deep bass.   This sub loves low notes.  It's like it physically thrives off them.  It's just playing along having a good time up above 40 Hz, but when those notes start to get into the 20's, it's like the sub drops into overdrive.  So anyway, enough salesman talk, here's the real deal on the design, production, and test results of my all mighty 10Triple10 Subwoofer.  

The Driver

The speaker starts with Ultimate Attitude's 10" AU1040 subwoofer.  A sub designed for car audio, but since I haven't seen many inexpensive home theater subs in the 10" range on the market for DIY, I went ahead with this sub.  The specs are listed here: Attitude AU1050 10" Stamp Frame Woofer.  250 watts RMS/350 watts max *Impedance: 6 ohms per coil *Frequency response: 25-200 Hz *Magnet weight: 50 oz. *Fs: 29 Hz *SPL: 89 dB 1W/1m *Vas: 3.50 cu.ft, *Qms: 8.20 *Qes: .45 *Qts: .43 *Xmax: 9.9mm. *Net weight: 9 lbs. *Dimensions: A: 10-1/16", B: 9-1/8", C: 5-1/16", D: 5-1/4", E: 1-1/4".   It's got a cupped spider too, so rail on the speaker if you must, but I believe it sounds great for the money.

The Passive Radiators

The passive radiators were custom built.  I didn't actually build them from scratch, but they didn't cost me 60 bucks a piece either.  The PR's are just flat pieces of machined MDF with a large thick foam surround giving each PR an Xmax of more than 10 mm.  Imagine a real PR and take away everything but the radiating diaphragm.  These diaphragms originally would have gone into making a full-blown PR, but I got to them before they made it that far down the assembly line (in a sense).  So we're talking really cheap flat PR's but with nice thick surrounds and a solid machined MDF diaphragm.  Each PR had an initial mass of 90 grams.

Some PR Basics

The first step was to design a box for this speaker that would be optimum for a PR design.   A good rule to go by with PR's is keeping in mind that their main advantage is to allow very small enclosures to be tuned very low while keeping compression factors to a minimum.  Small box + PR = very low tuning.  The fact that PR's have such large surface areas (even more with 3 PR's) it has been theorized that this decreases nasty compression factors till they're literally non existent.  The result?  Uninhibited bass response in the lowest octaves which can mean up to and beyond 3 dB increased output.  This is all very good.  So I wanted to stick with the idea of making the box small and tuning the box low and allowing the PR's to do all the work giving the lowest bass possible.  Otherwise I might as well throw a puny three inch round port in the box and call it good.  But where's the creativity in that?  Where's the spunk?  Where's the innovation?  That's what I'm all about...innovation in design.   This sub definitely has satisfied my need for something different.

Modeling the Enclosure

To the right are a few thumbnails of shots taken from Brian's ported.xls.  I chose to make the box the size I did because of both aesthetics and design.  I wanted the box to look proportional with the 4 10" speakers on each side.  A cube seemed the logical choice.  I didn't want too much extra space on either side of the woofers either.  So I decided on 15" all the way around and plugged in the T/S parameters into a few programs to see if this driver would work in a 1.35 ft^3 box.  A lot of times you can get away with making the box smaller than normal if you can tolerate a hump in the frequency response.  But don't forget we're going passive!  I can get rid of any hump by tuning the box much lower than would normally be possible with an ordinary port.  Small Box + Low Tuning + PR = No Hump.  So here's the final Frequency Response Plot, SPL Plot and Excursion Plots of the 10Triple10.  I compared the box to a sealed enclosure just because the program would allow me too.  From looking at the graphs your probably thinking, "So what's so impressive about that?"  Well first off these plots are modeled after a ported enclosure.  Since I'm using passive radiators with an equivalent surface area of a 13" round port, these graphs suddenly go out the window.  I can expect similar response curves but with much more actual output.  F3 will go down and SPL will up.  The problem is excursion goes up too.  But I can get a good idea of where to tune the box and a general idea of how it will sound.

Tuning Frequency

I deciding on a tuning frequency of 30 Hz, since that dropped the hump from +3 dB to only +1.3 dB.  I could have gone as low as 25 Hz for the tuning and probably had acceptable results as well.  But I wanted to keep from having to add too much mass to each PR.  I was afraid that if they were too heavy, they'd cantilever out of control long before I'd want them too.  Since adding mass to a flat PR can be tricky to ensure that each you don't end up massing down one side just a few grams more than the other and in effect making it "lopsided".  I used 9 washers that weighed 18 grams a piece to mass down each passive. 

How to Calculate Tuning Frequency of a PR System

Now your asking how in the world did I know to add 9, 18 gram washers?  I used passive.xls.   Which is available here at my site.  I entered in the parameters of my passives and the fB and size of the enclosure.  I found Sd by measuring across the diameter of the PR plus 1/3 of the surround on either side.  This came out to be really close to 7.50"   See the picture to to the right.  Although you can't see what the ruler says, this shows how it is possible to find the Sd of a driver or PR.  Sd = pi*(D/2)^2.  Then do the proper conversion to cm^2 or m^2.  This is where your HP-48 comes in handy.  I measured from where the 1" starts to 8.5" so don't let the edge of the ruler throw you off.  So from the spreadsheet it looked like I would need to add 160 grams (for a total of 250 g) to each PR for a tuning of 30 Hz in a box totaling 1.35 ft^3.  And that was that.  All the designing was done, now it was time to build the box and put the PR's together.  I won't go into any detail on box construction.  I figure this page is about PR's and such so construction tips I won't be giving.  But you can see quite easily from the pictures how the box was made.  3/4" MDF with 1/8" mahogany plywood and a rad slab of green marble on the top framed by a black border.  Yeah, this sub basically looks awesome.  It's stained in Light American Oak from Minwax.

The Pictures

To the right you'll find pictures of the last stages of building this subwoofer.  That's all I have to say for now.  I do have response plots coming in the near future.   From an initial comparison, this sub was keeping up with a single Shiva in a 3 ft^3 ported enclosure.  Now that was an amazing thing to hear!  But more about that later.

The Results

After I put the box together and screwed in all the speakers, I did an fB test to see if I hit my targeted 30 Hz.  Would you believe that I hit the 30 Hz perfectly?  I couldn't believe it either, but sure enough, I was right on the money.  Cha-ching!  Now that's good design.   Just a little bit of info regarding  how the frequency response was measured.  The sub was measured in my front yard so as to avoid all reflections from walls and ceilings.  This is about the best anechoic response you can get.  Only the ground is capable of interfering with the results.   I used a precision frequency generator, frequency counter, amplifier, and my trusty Radio Shack analog SPL meter.  The sub was placed in the grass as far way from the house and any walls as possible, while the SPL meter was placed at exactly 1 meter from the front baffle at the same height as the dust cap.  I ran 9.75 volts into the driver which has a nominal impedance of 3 ohms which roughly equates to 31 watts.  Since impedance varies with frequency, we can't say exactly how many watts the driver was dissipating, but we can get an idea of how hard the sub is being pushed.  31 watts is very conservative but even still I was able to get the PR's to cantilever at 30 Hz and below.  I then plotted the SPL at 5 Hz increments starting at 15 Hz working my way up to 100 Hz.  I accounted for meter correction and plotted the results in Excel.  That is the graph you see to the right.  In-room response of the sub would improve the low end by about 10 dB starting at 20 Hz.   The extra hump you see below 30 Hz I believe was due to a loud knocking sound that the PR's began producing.

The Final Product

The Design

The Driver

The Box in Progress

The Marble Top

The Passive Radiators

The Inside

Dual Binding Posts

The Finished Sub

Measuring the Diameter

Calculating Mass

Frequency Response

Measured Response

 

Shiva Subwoofer - The Destroyer Has Arrived

 

 

Speaker Projects    TC Sounds 15"    10Triple10    Shiva    EBS Shiva    UA 15" Sub

 

Shiva Subwoofer
The Destroyer Has Arrived

What the Heck is a Shiva!

Shiva has been the subwoofer on the minds and drawing pads of thousands of DIY'ers for over a year now.  So what the heck is Shiva?  Probably one of the best 12" drivers in its class for DIY Audio.  I started reading about Shiva when the driver was still under production, early January of 1999.  That's actually around the time this web page came together.  I wrote Dan Wiggins, President of Adire Audio (formerly Avatar Audio) and said, Hey Dan, I want two of your drivers!  At the time I had just finished building a brand new pair of 12" subwoofers for my home theater.  The drivers I had originally bought were made by Aura and cost me a mere 50 bucks a piece.  Yet I didn't let the cost of the driver deter me from building an awesome enclosure for it.  Cheap drivers in a good box can sound remarkable.  However,  the vice-versa of that it true also.

The Original Aura Subwoofer

Using the specs for the Aura sub, which still flaunted 8 mm of Xmax (which used to be considered pretty good), I designed two sub enclosures for each.  The design was basically a QB3 alignment tuned to 28 Hz for a maximally flat response.  The internal volume of the box was targeted for 3.0 cubic feet (80 L).  The 3 cubic feet also came from the fact that it's the largest enclosure you can build two of out of a single sheet of 4' x 8' MDF.  I maximized every cut and every side so that not a single piece of wood went to scrap.   Even all the little pieces I used to brace all the panels to reduce any and all unwanted vibration.

The Results

After I finished the enclosures and painted them in a piano black lacquer I dropped the drivers in and gave the new system a whirl.  I was totally blown away by these sub's performance.  I had never heard such powerful and deep amounts of bass in my life.  The subs were being driven with a Craver M1.5t capable of pushing 600 watts RMS into each sub.  I lived in a small apartment complex at the time and the bass was so intense it physically shook nearly all of the 24 surrounding apartments to the point that every one would come barging out of their quiet dwellings to find out why their flatware was falling out of the cupboards and shattering on the floor.  Yes, and most of these people lived all the way down the hall from me.  After that, I was hooked.  Hooked on the power of deep, teeth-shattering, mind-boggling bass.  Using my Radio Shack SPL meter, I was able to hit 120 dB almost anywhere in the room with various rap artists and boom CD's.

Never Satisfied

That was when I decided I needed more.  I needed more power.  I had an amp that wanted to push these speakers too far.  If I wasn't careful I could get those subs to bottom out like mad.  Very loud popping sounds would protrude from the cone often times.  It was a nightmare.  I knew the only way to combat the problem would be with a driver that could handle more power and had more xmax.  That's when I ran across Shiva.  A driver that would beat out my old Aura's by a landslide.   I drooled and drooled until 8 months later I had two of them arrive on my doorstep.  That's some patience I tell you.  I was very impressed with the looks of these drivers.  I'd never seen anything so big, massive, and just plain huge.  Although I do have some gripes with this driver now, that I've worked with it for various projects, I still believe it to be a great driver and subwoofer that will work awesome for many applications.  And the price is definitely right.

Moving on to Shiva

By the time my new Shiva's had arrived, I had moved to a small condo with only 2 other condos on either side of us, so the worry of bothering the neighbors was reduced to a minimum.  Well, as opposed to having a hundred people mad at me there would only be a dozen or so.  The Shivas frame was a smidgen on the large side and didn't quite fit in my 11" cutout I'd made for the Auras.  It wasn't that the frame edge was too large, it was that the frame edge was too deep.  The cutout I had made with a jigsaw had the slightest inward taper on the cutout, reducing it's interior dimension to just under 11".  So I took a file to it and 10 minutes later my new Shivas were resting nicely in their new little homes.  They looked beautiful and beefy as could be.  I wired the coils in a semi-permanent 4 ohm load because I only had one binding post terminal on the enclosure.  There was no need for wiring it any other way, since I'd planned on running a stereo amp into each sub at 4 ohms.

The First Few Runs

The first few test runs were something impressive.  By this time I had moved on from just listening to music to watching movies on my DVD player with my brand new Sony ES receiver.  So I fired up some of my favorite movies and watched and listened to my new Shiva subwoofers.  I believe it was The Mask of Zorro that impressed me most.  The intro with the fast tap dancing and Zorro walks out and cuts a Z in the screen.  The bass was so intense.  It shook everything in the house and completely blew me and my family who was watching totally out of our seats.  The bass seemed to envelope the entire listening area.  It crept in from all around and surrounded you.  It shook the floor, it shook the seats, it caused your hair to vibrate on your head and your pants to shake on your legs.  There was not a part of your body that didn't hear and feel the extreme low frequencies that came out of those subs.  I also remember watching Last Man Standing with Bruce Willis (no, I didn't actually watch the movie with Bruce) and feeling the powerful impact of gunshots blasting through the room at life-like levels.  As anyone whose ever shot a .44 Magnum knows, when you pull the trigger on that sucker,  not only is it loud as all hell, but the acoustical shock almost puts a whole through your chest.  I've felt it in real life, and I've re-lived it with these speakers and this movie.  Some other great movies that I enjoyed thoroughly with my Shivas were The Mummy, The Rock, Terminator, Godzilla, Backdraft, 5th Element, and the list goes on and on.

The Shiva Driver

For anyone who is serious about subs and home theater, the Shiva gets 4 stars in my book.  Of the two enclosures I've used Shiva in, I'd say that these performed the best in the smaller ported enclosure versus the larger EBS passive radiator enclosure.  They can handle a lot of power, they're loud and play plenty deep, and the enclosure doesn't take up half my living room. Each sub was cable of delivering well up to 120 dB SPL within a few feet and both subs together delivered an impressive 121 dB average SPL for overall in-room response.  Yes, they sounded great.  Yet every great sub still has its pitfalls.  With Shiva, I'd have to say the few downsides were only little things that Adire intentionally skimped on to make the driver less expensive.  Such as the paper cone, the stamped frame, the foam surround, the flimsy spider and especially those dang, horrible tinsel leads that would slap against the spider-riser-frame and make rather loud and obnoxious noises.  Other than that, this driver has set a new standard for long throw subwoofer on the market today.  Keep your eyes peeled for the new Shiva Mark II Subwoofer which Avatar is developing right now.  Which may cost a little bit more, but if they've re-engineered any of their previous designs, and don't skimp out on anything, I'm sure for anyone who is serious about DIY will be happy to pay the extra pennies to get a driver that's totally and completely top-of-the-line.  

 

The Making Of

Almost Done

Painted with Auras

New Drivers...Shiva!

Measured Response


Copyright 2000 © Audio Innovation, Inc.   All Rights Reserved.
This page last updated on April 15, 2005.


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