Twelve 12" driver dipole subwoofer build thread - diyAudio
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Old 11th August 2015, 09:54 PM   #1
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Default Twelve 12" driver dipole subwoofer build thread

I found a great deal on some 12" subwoofer drivers, so I bought a bunch (12 of them to be exact). I'm using them to build a 12-driver dipole subwoofer that will be eventually used in conjunction with some open baffle 3-way speakers. I plan to crossover to the sub around 80-100Hz depending on where in frequency the first dipole peak is located.

The design is a new twist on existing themes, although it's nothing all that innovative. I like to think of it most simplistically as a U-frame or an H-frame that has a longer "line" to the rear compared to the front. In order to fit all 12 drivers in a small space they are nested one on top of the next. This creates a cavity and is similar to the dipole subwoofer that Siegfried Linkwitz used in his Phoenix project a few years back, although my design has additional line length to the back. In some ways it is like Nelson Pass' "Slot Loaded" open baffle, except its a slot loaded U-frame. Some of the same resonance issues (related to the cavity depth) of that design will be present in this one. My design also has some relationship to the Ripole (with the addition of the rear line), since the close nesting results in openings to the front and rear that are equal to about 0.4*Sd for each driver. As a result, I expect that the resonance frequency will lower and Q will increase compared to the free-air values.

The overall dimensions of the enclosure are about 18"H, 60"W, and 30" deep. The cabinet will be used horizontally, like a bulky AV cabinet or credenza thingy. This will be located between the main speakers.

So far I have built the outer cabinet and cut wood to form the inner dividers that direct the radiation to the front and rear. Below are a couple of pics taken while I was dry fitting the interior pieces. I have decided to glue everything together, although this will mean that I will likely never be able to take the sub apart without damaging the drivers unless I am able to get creative and carefully saw everything apart like a surgeon while at the same time not creating any dust... Since I am a terrible woodworker I used some inexpensive and lightweight honeycomb panels for the exterior shell from my favorite local supplier, IKEA. Even so, after I add the interior wood and all 12 drivers the weight will probably be over 100 pounds. Hopefully it will turn out to be sufficiently mechanically rigid and strong to not snap in half when looking at it cross-eyed.

In the attached pics the cabinet is standing upright, however, this is just for the moment and done out of convenience. In this orientation all the drivers would be facing the ceiling and this might cause cone sag and increase distortion a bit. When it is in use the cabinet will be oriented horizontally and the axis of the cone motion will be parallel to the floor. The left picture is a view from the rear and the right is looking at the front. In each cavity there will be the magnet of one driver nesting into the cone of another. Drivers will operate in push-pull within each cavity, which should cancel some even order distortion products.
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File Type: jpg IMG_2644.JPG (109.3 KB, 548 views)
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Old 12th August 2015, 01:11 AM   #2
Zero D is offline Zero D  United Kingdom
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12 x 12" jeepers ! Different anyway.

You don't say what the drivers are ?

Curious to hear how it turns out. Will you be taking measurements & posting them ?
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Old 12th August 2015, 05:15 AM   #3
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Interesting design. Looking forward to the results!
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Old 12th August 2015, 06:07 AM   #4
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Pretty clever way to use a lot of drivers. The total cone area should be equivalent to about 5.3 18" drivers, since 18s are a pretty easy to visualize metric of driver size. I'm very eager to see the measurements if you can produce some.

I've always somewhat wondered how well that kind of dipole design really works for subs.

My intuition is never really satisfied that the front and back are both open. Then again I am one of those electronic high spl sub junkies. 6th order resonant systems are my thing.
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Old 12th August 2015, 03:08 PM   #5
Octavia is offline Octavia  United States
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Charlie you better bring these beasts to Burning Amp!
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Old 12th August 2015, 03:37 PM   #6
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Quote:
Originally Posted by Zero D View Post
Curious to hear how it turns out. Will you be taking measurements & posting them ?
Yes. Give me a chance to finish building it first!
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Old 12th August 2015, 03:47 PM   #7
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Quote:
Originally Posted by zettairyouiki View Post
Pretty clever way to use a lot of drivers. The total cone area should be equivalent to about 5.3 18" drivers, since 18s are a pretty easy to visualize metric of driver size. I'm very eager to see the measurements if you can produce some.

I've always somewhat wondered how well that kind of dipole design really works for subs.

My intuition is never really satisfied that the front and back are both open. Then again I am one of those electronic high spl sub junkies. 6th order resonant systems are my thing.
These particular drivers work well for close nesting because the magnet is not all that large and the dustcap is the inverted variety. If you touch the back edge of the magnet of one driver to the cone of the next the distance is only 3.5 inches (although this would not allow any cone movement). I am using a spacing of about 4.25", which would allow for up to ~20mm of cone movement (Xmax is 8.5mm). This allows me to pack quite a few drivers in a relatively small space.

I recall listening to some large open baffle DIY dipoles that used three 18" low-Xmax drivers. These were playing some carousel organ music, and the bass was quite impressive. In my design the upper end will be strictly limited to around 80-100Hz, however, the dipole loss at the lowest frequencies will not be as severe as some other systems.

In any case, the number of drivers used is not any kind of effort to make a high SPL system. I am only trying to make up for the losses that the dipole loading will create.
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Old 12th August 2015, 03:50 PM   #8
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Originally Posted by Octavia View Post
Charlie you better bring these beasts to Burning Amp!
See:
The Burning Amp 2015-Schedules & Info
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Old 14th August 2015, 07:50 PM   #9
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If anyone's in socal, heres a couple of ideas:

1) go to apex Jr and pick up a dozen of the cerwin Vega twelves. For $264 you'll have more displacement than four eighteens.

Or

2) check out the Alpine sws-15. It'll need some power to get loud, but there aren't many drivers with more displacement at the price. I paid something like $125. A lot of car stereo shops sell this driver.
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Old 16th August 2015, 01:05 AM   #10
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After a bunch of routing, gluing, screwing, then yet more gluing, and gluing, and gluing, I have about 85% of the assembly completed. See attached pics for evidence of this. I still need to glue the last driver into place but I ran out of glue so I'm all done for today. I need to cut a couple last pieces once I know the dimensions of the last cavity.

In the pics you can see the assembly and a closeup showing the nesting of the drivers. Not shown is the rear view with lots of dangling wires that will eventually be connected in three parallel banks of four drivers in series. If I believe the datasheet sensitivity numbers, this arrangement will end up around 4.5 Ohms (DC impedance) with a voltage sensitivity of about 97dB@2.83v. Not bad.
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File Type: jpg IMG_2646.JPG (175.1 KB, 355 views)
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