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Subwoofer Selection Criteria

DonH56

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miniDSP... I think the Harman system. Most room correction programs work better treating them as a group, but some of that has to do with how the manufacturers implement the algorithm, out of the control of say Audyssey or Dirac Live. I use my processor in dual-mono mode so it supposedly sets the delay and level for each pair independently, but in practice I found I still had to dial in the delay/phase to get the best integration.
 

March Audio

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Hi all

Which digital room EQ software or hardware can work their magic with 4 subwoofers, each sub independently? Both frequency and time domain response room EQ.

I know of solutions that can work with 2 subs independently, but which can do 4 subs independently?
I think accurate will work with as many channels as you like (within reason) but its not an automated system along the lines of dirac/audyssey etc.
 

Music1969

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I think accurate will work with as many channels as you like (within reason)

Thanks. Are all your 4 subs each integrated independently? Or as two pairs?

Which software / hardware do you use for digital room EQ?
 

March Audio

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Thanks. Are all your 4 subs each integrated independently? Or as two pairs?

Which software / hardware do you use for digital room EQ?
Right at the moment just a single channel! Left and right mixed together, rear duplicate of front.

You can't localise in theory below 80Hz, so stereo is a bit pointless, but accounting for listener distance front to rear should be done. I am closer to the rears. Im just rehashing the setup at the moment and will try this............ I wonder what effect it will have on the mode cancellation...... Mmmm....
 

Dimifoot

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Hi all

Which digital room EQ software or hardware can work their magic with 4 subwoofers, each sub independently? Both frequency and time domain response room EQ.

I know of solutions that can work with 2 subs independently, but which can do 4 subs independently?
Trinnov?
I hope so, it’s on the way :)
 

Soniclife

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Right at the moment just a single channel! Left and right mixed together, rear duplicate of front.

You can't localise in theory below 80Hz, so stereo is a bit pointless, but accounting for listener distance front to rear should be done. I am closer to the rears. Im just rehashing the setup at the moment and will try this............ I wonder what effect it will have on the mode cancellation...... Mmmm....
So those measurements were effectively one mono bass channel, but distributed around the room? And then with overall correction applied on top. They looked so go I'd assumed they were all being addressed individually.
 

March Audio

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So those measurements were effectively one mono bass channel, but distributed around the room? And then with overall correction applied on top. They looked so go I'd assumed they were all being addressed individually.
Yep one channel. They are measured at close range to get a driver linearisation. That is then convolved with the crossover filter so what's coming out should be flat.

That is then convolved with the measurement at the listening position.
 

Music1969

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Yep one channel. They are measured at close range to get a driver linearisation. That is then convolved with the crossover filter so what's coming out should be flat.

That is then convolved with the measurement at the listening position.

All with Accourate?
 

Willem

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These graphs were truly illuminating. They showed that at least in this case, moving from one to two brings the biggest improvement. Moving up to three only gives marginal improvements, but going up to four brings some meaningful additional improvement. The improvement from the dsp eq is not to be ignored either. Therefore, the practical lesson is that two small subs with dsp eq should be the baseline for quality low bass. If there is any additional budget, it can go to another two small subs for best quality bass, or to two bigger subs if louder and deeper bass is required, as perhaps for HT. But your experience in your room may vary. Since with four subs signal cabling may become a practical issue, a wireless connection may be a practical help.
 

andreasmaaan

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Because only half the energy is being reflected from a single wall alongside the speaker -- the other side is open and subject to normal acoustic propagation. In a corner you get reinforcement from two walls thus 6 dB.

Unless it is suspended in space or in an anechoic chamber you do not start out in 4pi space; the floor is already there. Thus the gain is 3 dB with one wall, 6 dB in a corner. Maybe I misunderstood your original response, sorry.

No need to jump out on a long tangent on this one, but I’ve always struggled with this question. Firstly, my starting point is 4pi space which explains the difference of opinion regarding the floor; not much needs be said about that.

But putting that to one side, how to conceptually reconcile +6dB baffle step as a baffle transitions from full space to half space (standard definition) with +3dB boundary reinforcement for each additional boundary, ie halving of space (also the standard definition)?

In each case we have a halving of space, yet a disagreement on the resultant increase in SPL.

Not meaning to derail the thread, sorry - just reminded of a perennial source of head scratching on my part...
 

RayDunzl

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But putting that to one side, how to conceptually reconcile +6dB baffle step as a baffle transitions from full space to half space (standard definition) with +3dB boundary reinforcement for each additional boundary, ie halving of space (also the standard definition)?

6 + 6 = 9

So +3

?

(in the incoherent/uncorrelated case)
 
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March Audio

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These graphs were truly illuminating. They showed that at least in this case, moving from one to two brings the biggest improvement. Moving up to three only gives marginal improvements, but going up to four brings some meaningful additional improvement. The improvement from the dsp eq is not to be ignored either. Therefore, the practical lesson is that two small subs with dsp eq should be the baseline for quality low bass. If there is any additional budget, it can go to another two small subs for best quality bass, or to two bigger subs if louder and deeper bass is required, as perhaps for HT. But your experience in your room may vary. Since with four subs signal cabling may become a practical issue, a wireless connection may be a practical help.
Yes, 2 subs gets you most of the way there. BTW just for info the room is 6m x4. 5m x2. 7m. One sub is really a non starter for anything like even bass.

What those graphs don't show is how much more even the bass is around the room.
 

andreasmaaan

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6 + 6 = 9

So +3

?

(in the incoherent/uncorrelated case)

Hmm, that's correct, but for the fact that a boundary reflection is actually correlated (for frequencies for which the distance between the radiator and the boundary are small relative to wavelength of course).
 

Music1969

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Yes, 2 subs gets you most of the way there. BTW just for info the room is 6m x4. 5m x2. 7m. One sub is really a non starter for anything like even bass.

What those graphs don't show is how much more even the bass is around the room.

Any measured performance advantage with having all 4 in corners versus centre of each wall?

Or more just practical purposes, due to room layout etc?
 

andreasmaaan

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A baffle occurs all around the driver.

Ok, but so does a floor or wall, I would have thought?

I feel that I must missing something extremely obvious here...

EDIT: having re-read some articles on the topic, it seems that the discrepancy simply comes down to an assumption in the classical theory that the reflection is incoherent with the direct sound. See for example the article that @March Audio borrowed graphics from earlier, which states, "the effective gain realised from incoherent summing is +3dB for each additional boundary..."

This would seem to be a wrong assumption in the case of subwoofers placed against boundaries IMHO, since for frequencies with wavelengths that are short (<1/4 wavelength or so) relative to the distance between the sub and the boundary (i.e. all typical frequencies reproduced by a subwoofer), summing will be coherent, giving a +6dB SPL increase.

This would also seem to me to be consistent with the fact that a halving of the radiation angle should result in a doubling of the % efficiency.
 
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andreasmaaan

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Any measured performance advantage with having all 4 in corners versus centre of each wall?

Or more just practical purposes, due to room layout etc?

According to the Harman research:

1553905028953.png


#10 is 1 sub in each corner, and #11 is 1 sub in the centre of each wall (4 total in each case).

Looking at that graph, 1 sub in each corner gives higher SPL but slightly less uniform response. Both are excellent choices.
 

DonH56

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Ok, but so does a floor or wall, I would have thought?

I feel that I must missing something extremely obvious here...

EDIT: having re-read some articles on the topic, it seems that the discrepancy simply comes down to an assumption in the classical theory that the reflection is incoherent with the direct sound. See for example the article that @March Audio borrowed graphics from earlier, which states, "the effective gain realised from incoherent summing is +3dB for each additional boundary..."

This would seem to be a wrong assumption in the case of subwoofers placed against boundaries IMHO, since for frequencies with wavelengths that are short (<1/4 wavelength or so) relative to the distance between the sub and the boundary (i.e. all typical frequencies reproduced by a subwoofer), summing will be coherent, giving a +6dB SPL increase.

This would also seem to me to be consistent with the fact that a halving of the radiation angle should result in a doubling of the % efficiency.

Correct, I spoke (typed) too quick... The wavelengths are long but reflections also invert the signal so there is local cancellation. As for the gain, I've measured ~3 dB on a wall and ~6 dB in a corner, but YMMV. I need to practice a bit tonight and get ready for another few hours of work tomorrow, don't have time to dig up my text and provide the equations. Any acoustic text should have them.
 
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