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Old 24th January 2010, 03:31 AM   #1
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Default bandpass sonotubes

I recently finished building these 4th order bandpass subs, which I designed to complement my Abbeys.

Click the image to open in full size.

The port opening is at the top end, covered by grill cloth. I laminated a ¼” layer of cork between the sonotube (14” diameter) and veneer to smooth out the surface and to add some extra dampening. The drivers are B&C 12TBX100s (same as the Abbey woofers) and are mounted vertically with a 4” port and a fairly small front chamber (thanks for the idea, PB).

Click the image to open in full size.

I am using a Behringer 2496 and external amps to drive them (the amps are from Class D Audio). They sound great… providing a subtle (but deep) foundation for music – but also capable of room-shaking response on movies or bass-heavy music. I was planning to add one more sub, which I was originally going to tune lower, but since these ended up measuring somewhat lower than expected I might just add a smaller one instead to level out the 80-150 Hz region a bit (suggestions welcome).

Subs only in-room (average of 4 measurements across the main listening couch; I added several tight EQ filters in the DCX to knock down the peaks; the stuff at ~300 Hz is ambient noise from my heating system, not port resonance):

Click the image to open in full size.

Broadband response with the Abbeys (also averaged across the main seating area):

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Old 24th January 2010, 07:47 PM   #2
Pallas is offline Pallas  Pakistan
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VERY nice, both in concept and execution! The cork is a very smart idea, and I bet it made veneering much easier.

I think a third lower-tuned one is still a good idea. (Or at third one tuned this low.) Not because I think you need more low-end, but because then you can cut the ports of these two a little bit and maybe get more fill in the 80-160 Hz octave that way. IMO, better to have as many drivers working in that octave as possible.

It's really amazing how low those B&C 12TBX100's, which on paper shouldn't do much less than 50 Hz, perform in room.

Last edited by Pallas; 24th January 2010 at 07:54 PM.
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Old 24th January 2010, 08:32 PM   #3
freddi is offline freddi  United States
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those look great! - May I ask the chambers' volumes and port spec? have you run near xmax in loud situations? (it looked to me at first that the rear of the woofer fed the "front" chamber that exits to the external world and that wave came up though the bottom of the semicircle bulkhead to exit into the room - I'm confused) is the foam hiding the port's entrance? response looks deep enough to allow room ambiance to bloom in good recordings

Last edited by freddi; 24th January 2010 at 08:38 PM.
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Old 24th January 2010, 11:59 PM   #4
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Thanks, folks,

The chamber dimensions are 40 liters (rear) and 12 liters (front). The rear chamber has a fair amount of fiberglass fill in it and the front chamber has ~1/2" synthetic felt stuck to the top and bottom surfaces to reduce standing waves and port resonance; I also wrapped the port with ~1.4" of closed sell neoprene foam since the material it was made of seemed a bit thin (4" Precision port with flared ends). The port is around 13" long with a ~1.5" gap between the port end and bottom of small chamber. Here is a shot looking "up" into the rear chamber after installing the baffle.

Click the image to open in full size.

I used silicone caulk to seal the cracks between the chambers (not glue) so it would be possible to pull it apart again if I really wanted to. I tested them assembled before sealing and decided I would leave them as is. The response had a broad peak at ~70 Hz, as designed. The nearfield response I measured from one of them had the peak closer to 50, which is a pretty significant difference (I too am surprised how low these pro dirivers can go).

I have been thinking of using an IB for the third sub (there is a ~4' half basement beneath the room, which is mostly closed off from the rest of the basement - except for a 3' square opening). That would take care of both the top and bottom ends of the sub spectrum, using appropriate filters, etc.. I am a bit concerned, however, about where the back wave will go, since there are some large heating ducts in that area.

The B&C drivers have ~95 db sensitivity, and these subs can play plenty loud, but I haven't tried measuring them when playing that way yet. Something worth doing, I think (I just need an SPL meter so I know how loud they are actually playing). I suppose I could try using dynamic EQ in the DCX if that would help (but I may not need it).

- Doug
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Old 30th January 2010, 05:42 PM   #5
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Default brief update

Hi folks,
I spent a bit more time optimizing my system response. I got the following after playing with the phase and adding some more PEQ filters on the DCX for the subs, I also ended up pushing the response of the Mains in the 80-200 Hz regions with some additional PEQ filters on my receiver. Overall I'm pretty happy with it. Looks like a third sub is not really necessary after all (I can probably live without the sub-20 Hz stuff).

Click the image to open in full size.

Click the image to open in full size.
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Old 19th March 2010, 08:20 AM   #6
seanny is offline seanny  United States
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Hi Doug,

does it jumping around during playing?
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Old 19th March 2010, 12:39 PM   #7
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Not at all (they are heavy enough and have four rubber feet on the bottom).
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Old 20th March 2010, 05:23 AM   #8
FlipC is offline FlipC  United States
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Nice build.
Now how do they actually sound in a room?

Did you have to time align them to get them in phase with the rest of the system?
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Old 20th March 2010, 06:31 AM   #9
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Think out of the box
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Old 20th March 2010, 08:12 AM   #10
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Lovely subs, amazing that they still have some output at 16Hz.

Hope you enjoy them
My work:
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