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Double Bass Array (DBA)

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StigErik

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Measurements are here :

 

architect

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have you tried reversing 6 of the 12 subwoofers like a checkersboard?
for the dipole 12” woofers you could do the same
distortion levels should even get lower wouldn’t they ?
 
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StigErik

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I know, have done that before so am familiar with the benefits.
 

neRok

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Sure. It looks like ***, but sounds very nice!

Front end - including MG 3.7 with 4x12" midbass dipoles, MG 3.6 center channel with two 4x10" midbass dipoles. The whole thing is usually hidden behind drapes and a projection screen, so it's a bit less ugly than this (see pic #2).

View attachment 346991


View attachment 346992

Rear end, also showing the surround speakers - MG 3.6 plus 4x12" midbass dipoles - and hush-box for my projector. The large stack of firewood is actually "skyline" diffusors.

View attachment 346989
I came to ask about the installation details, but I can see them here. Very nice. I'm surprised it works so well because this relationship of subs to wall is meant to be the worst option, the best being flush in/with the wall, and next best being subs firing towards wall. But your results show that these minor details are dwarfed by the improvements from having the plane wave.

The actual difference is 5dB, not 9.
You connected 2 subs per channel to the front but 3 per channel at the rear. Perhaps some/all of the SPL difference is load (ohms/wiring) related? Or maybe not, I'm not 100% on the effects of wiring vs ohms vs power vs SPL.

Dips are the result if there are no modes or the ones that are there are not coupled to speakers/LP ("null").
It's all reflections, and modes are reflections where the frequency divides cleanly between 2 surfaces. The speaker or LP location along the mode determines if the overlapping sound/reflections boost each other or cancel each other. These handy visualisations show this.

This particular null might be more of an SBIR problem (which is also reflections), based upon LP to back wall. It's redundant when considering the plane wave because the back subs effectively cancel the reflection.
 
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StigErik

StigErik

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I came to ask about the installation details, but I can see them here. Very nice. I'm surprised it works so well because this relationship of subs to wall is meant to be the worst option, the best being flush in/with the wall, and next best being subs firing towards wall. But your results show that these minor details are dwarfed by the improvements from having the plane wave.

You connected 2 subs per channel to the front but 3 per channel at the rear. Perhaps some/all of the SPL difference is load (ohms/wiring) related? Or maybe not, I'm not 100% on the effects of wiring vs ohms vs power vs SPL.

I can share a little details about the installation. Attached here are two simple drawings of the room layout that should explain most of it. The shape of my room with its cathedral ceiling is not optimal for DBA. The subwoofers should also be placed flush to the front and rear walls, which they are not. There are also five very large speakers in the room that will disrupt the plane wave. Even so, it works very well with some tuning.

I also mentioned that the subwoofers are hung (like a pendulum) from the ceiling using rubber rope and rubber straps. This is done to avoid vibration transfer from the subwoofers to the structure of the room itself. The longer the pendulum, the lower will the resonant frequency of the pendulum itself be as well. Assuming gravity is 1G, a 2 meter pendulum will have a resonance frequency of just 0.35 Hz, way lower than the frequency range of the subwoofers.

I have different number of amp channels and wiring schemes for the front and rear arrays, and the gain of the amps used is also different. That really got me confused! I've always thought that something around 9 dB var the correct attenuation of the rear array in my room, but measurements of the real SPL coming from each subwoofer (done at 1 cm from the speaker cones) showed that is more like 5 dB.
 

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StigErik

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The drawings above are not entirely accurate anymore. I've moved the sofa about 1 meter further back, and moved the front L R C speakers a little further away from the front wall as well.
 
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StigErik

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It's all reflections, and modes are reflections where the frequency divides cleanly between 2 surfaces. The speaker or LP location along the mode determines if the overlapping sound/reflections boost each other or cancel each other. These handy visualisations show this.

This particular null might be more of an SBIR problem (which is also reflections), based upon LP to back wall. It's redundant when considering the plane wave because the back subs effectively cancel the reflection.

I've investigated this a little, and the dip I see at 34 Hz looks like an SBIR thing to me.
 

neRok

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I've been thinking about DBA some more. I'm wondering how the "noise pollution" side of things is? So what is the bass volume like in other rooms, or outside the home, etc? I'm guessing it's a bit lower than it would be with normal multi-sub, but still fairly loud?
 
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StigErik

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My experience is that it can be slightly less loud in neighboring rooms or outside the house than regular single- or multisub solutions, which I've had in the past. Don't have any numbers, just a feeling based on fewer complaints ... :cool:
 

Justdafactsmaam

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Then there would have to be a null for the rear array too.
I think the cancellation of the front array at the rear array prevents the nulls and peaks.

Individually both the front and rear arrays would excite peaks and nulls.
 
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