The Design: The maximum available space was more than sufficient, however, the client was looking for something relatively compact, particularly in terms of height. A balance of space-efficiency and acoustic in-cabin efficiency (along the target passband) was arrived at with this common chamber rear-loading horn design:
This is another example of a design where the horn wraps around it's own compression chamber, achieving it's target axial length without the need for any abrupt 180 deg. U-bends.
The Build: A pretty straight-forward assembly routine making use of the now customary "screwless" panel joining technique. A 1.5" radius flare is routed away from the double-stacked face baffle, softly curving out the horn mouth:
Special care was taken to make optimal use of the face the baffle surface area which has to accommodate both the 12.625" outer diameter woofers as well a 6" wide horn mouth (flared to well over 7".)
The woofers are offset toward the mouth of the horn in order to sustain adequate mounting clearance; the throat of the horn terminates directly behind the face baffle on the side opposite of the mouth.
A pair of DD3512s is test-fitted into the enclosure to assure proper fit, spacing, and clearance:
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( 3.6 / 52 )The Goal: The client was interested in a very compact solution for delivering a versatile low-end fill in his 1994 Chevy Silverado. The woofer decided upon was the 6W3v3 from JL Audio:
The woofer was sent to me directly by the client for more precise T/S parameter measurements (and thus, a more accurate design.) The woofer was also to be wired up and loaded in to the enclosure so that it's plug 'n' play ready immediately upon receipt.
The Design: The most immediately apparent characteristic of the available working space was it's lack - a wedge shape allowing for roughly 0.39 cubic feet internally... Anything beyond a sealed enclosure would require a very careful balance of volume alignment, tuning, and compression control. In the end, an off-axis bass-reflex design was chosen.
The Build: Our target tuning / compression profile called for a substantial amount of air to travel along a relatively small cross-section. To maintain a suitably linear velocity profile, very large entry and exit flares were required; three times the internal vent diameter along the outside and two times along the inside. Obviously, no such vents are readily available so one had to be fabricated.
You can think of the picture above as a block of MDF from which a very heavy-duty port (similar to the type used in my audiophile HT builds) is "chiseled" out. In front of the block, there is a single cross-sectional template layer of the port.
Moving right along, the port is beginning to take shape (mainly in length.) Behind it is a partially assembled wedge shell that will make up the body of the subwoofer enclosure:
Once all the rings are stacked and traced to the proper length, the port is attached to the side baffle and beveled to the target geometry along both ends:
The side baffle is also routed to accept a flush-mounted terminal cup--seen covered in saw dust behind the enclosure, further back along the table saw:
As a finishing touch, the sides of the wedge were beveled with a 0.375" radius round-over and the woofer mounting hole was inset for a flush alignment with the outer edge height of the woofer's mounting ring.
Finally, the woofer and the terminal cup is mounted onto the enclosure. As you can see in the picture below, both components' mounting rings are shallow enough to where a flush inset is possible even with just 0.75" wood thickness:
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( 3.1 / 106 )The Goal: The client was looking to achieve a balance of sound quality and loudness within the 30Hz - 80Hz response range inside of a 1998 Chevy Corvette.
The Design: The biggest challenge here was the target enclosure placement; right behind the seats--quite a ways away from the rear of the cabin. This design required some additional modeling time because of the phase discrepancies between the waves radiating forward directly from the enclosure versus the waves traveling toward the rear of the cabin and returning several degrees out of sync. In the end, this off-axis rear-loading horn design turned out to offer the optimal balance of in-cabin efficiency, bandwidth, and minimal brake-up.
The Build: Pictured below are the two faces of the inner waveguide. The same two baffles also make up the rear and the driver side wall of the compression chamber:
What started out as a somewhat challenging loading scenario was solved with a relatively straight-forward looking design. As the picture below illustrates; the enclosure is, in essence, a simple L-bend horn. In looking at something like this, it's easy to forget how much math and fine-tuning goes into arriving at even the simplest of shapes:
For what it's designed to be capable of, this is an extremely compact enclosure--and very rudimentary in spirit. As a finishing touch, I used a 0.375" radius round-over along all the exterior edges:
Luckily, I happened to have a DD2510 on hand to use for a test-fit and some post-assembly photos. Once in the vehicle, the woofer will fire forward and the mouth of the horn will fire toward the passenger side.
Just for personal amusement, once a build is done, I sometimes wire the sub into my test amp and feed it test tones. It certainly doesn't serve to gage what the enclosure will sound like in it's target environment but it's impressive none the less.
In looking at this enclosure, it's rather difficult to accept the effects around the house with just a few watts of power fed into the woofer: At ~21Hz, the medicine cabinet in the guest bathroom spilled it's contents onto the sink counter. That, more or less, concluded my portion of the quality assurance process.
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( 3.3 / 120 )The Goal: The client was looking for a loud and accurate performance in his '96 GMC Suburban. The woofer of choice for this project was the DD3515.
The Design: After some plotting, I arrived at a variation of a rear-loading horn. With the size and the shape of the cabin, this was the optimal candidate for a flat headrest response along with high sensitivity along the entire response bandwidth.
The Build: This particular build illustrates a slightly different approach to folding the horn within the alloted footprint. In this instance the horn is wrapped around it's own compression chamber:
This limits the bends to 90 deg. (as opposed to a more traditional 180 deg. U-bend, which can have an adverse effect on the velocity profile.) Though it may be kind of hard to tell, the throat baffle is beveled with a 0.375" radius round-over, while the mouth of the horn flares out along a 1.5" radius. The client also requested that the enclosure be inset for a flush woofer mount. The face of the enclosure is therefore double-stacked allowing for improved structural integrity as well as more material depth to be cut into.
Once the enclosure is assembled into a solid "block," it is time to "chisel" away the excess, in a sense sculpting the face. No mistakes can be made here; you can't put back what you've taken off:
With the high speed routers and sanders, whatever comes off is turned into fine dust, so proper safety gear is quite essential. On account of the small difference between the woofer's outer diameter and the enclosure's height, I decided to implement a split-baffle approach; preserving the flush-mount look while simultaneously cutting away the insets directly above and below the woofer (which would otherwise have to be very thin and extremely fragile.)
The depth of the inset is just under 0.75" which allows for a perfect flush mount, at the same time preserving almost a full inch of baffle thickness for the woofer to mount to:
At the time, I didn't have any DD3515s to use for a test fit. Instead, I brought out one of my 15" RE Destroyers with a standard 12-spoke basket, the outer diameter of which is almost identical to the outer diameter of DD3515--and it fits like a glove. So there it is:
This is how you flush mount a ~15.375" woofer along a 16" wide face.
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( 3.4 / 130 )The Goal: Derrick, the proud owner of the "Sculpture 101" front stage is back for more; this time upgrading the setup to accommodate a full-blown 5.1 surround sound home theater with three additional pieces: A center channel, rear left, and rear right speakers.
The Design: To keep the new set voice-matched with the original pair, the same Vifa D19TD-05 tweeters and 3kHz high-pass cross-overs are implemented. Unfortunately, the 6.5" Alesis woofers used in the Sculpture 101 are no longer available so, in their place, I've decided to use the new Tang Band W4-1720 4" mid-bass drivers.
The Build: I figured I'd begin by illustrating a fun way to extract small shapes out of MDF. As anyone with router table experience will tell you, the smaller (and lighter) that a piece of wood is, the more likely your bit is to pull it out of your fingers. For this reason, I like each small shape that I'm working with to act like a flush trim guide attached to a much larger, heavier, and more stable cut of wood beneath:
This method also allows for a high degree of precision as there are no loose parts; every shape is quite literally carved out of a single "slab" before it is flush trimmed into individual pieces. These, by the way, are the ring stack guides for a set of 1" internal diameter, 1" thick bass ports:
Here's a couple of the individual ring stack guides flush trimmed away from their sheet pictured along with a frame for one of the rear speaker enclosures. Things are starting to take shape:
The ring stack guides are bonded onto a second layer of MDF and re-traced for proper vent length; in this case 2.25", accounting for the thickness of the rear speaker baffle. Here you see another rear speaker frame being put together and, right behind it, a set of ring stacks being bonded to one of the rear baffles:
The next step is to flare all three sets of the bonded ring stacks to their target vent geometry; in this case a 3" outer diameter flare on the outside and a 1.5" outer diameter flare on the inside. After some test cuts are performed on scrap wood, all the speaker cut-outs are routed into the face baffles:
Once all the panels are bonded, the edges are rounded over to reduce the effects of diffraction: 1.5" radius vertical and 0.5" radius horizontal on the two rear speakers, then 1.5" radius along the entire front / rear face of the center channel with 0.5" round-over along the remaining corners.
Next, it's onto the internal electronics. Since the original (Sculpture 101) build, I've gotten a lot of inquiry about my crossover networks. For the tweeters, I'm using a 2nd order Butterworth high-pass filter (C=4.7uF, L=0.6mH,) resulting in a 12dB per octave cut-off at 3000Hz, while the midbass drivers are left to accept the full bandwidth.
Finally, the only thing left to do is to secure and dampen all internal electronics, mount the binding posts, wire in the drivers and there you have it - a full-fledged 5.1 surround sound upgrade component set:
"Starting from day 1 of their arrival, I didn’t expect much from a pair of 4” drivers. Pete told me I would be quite surprised and urged me to use the rear speakers as my front stage for first impressions. So I turned off the sub and the center channel and played Star Wars Revenge of the Sith. After two hours of movies and a little bit of jazz listening, the Tang Band W4-1720s are the real deal. The imaging was awesome and so was the range. The bass output was really surprising to the point I really don’t need to use the sub. The vifa tweeters do an outstanding job of keeping up with the high action sequences down to the whisper in an ear. I'm thinking about doing another pair of 4” drivers for a perfect voice match. Then use the sculpture 101s in a dedicated listening room.
So now the moment of truth. I connected all speakers to the three Dayton apa150s and turned the volume half way up on each. I tuned the volume up on the subwoofer to ¾. I had just bought Death Race on blu-ray. The hell with watching the movie, I was in the movie. The 5.1 wrapping around my head was absolutely sick. I am spoiled with my new setup. Pete, to no surprise you do it once again. I am not what you would call a seasoned audiophile, but anyone knows what sounds better to the ear when listening to different setups. I got a one of a kind system that I’ll have around for a while. That is until I get audio fever again.
Thanks Pete"
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