Ported - 4th Order Vented

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.

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 4^th 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.

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.

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

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.

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.

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.

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.

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

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