Bass and subwoofers

[levimax]

Capably setup "stereo bass" systems should be fully adept at producing mono bass without compromise. Just a different set (or preset) of DSP parameters and signal routing. You should be able to have both easily if your system is flexible enough, just may not be both at the same time.

I think this issue is that subs would most likely be placed differently for a stereo bass system than a summed to mono bass system.

 

[ShadowFiend]

With just two subwoofers, then having both stereo bass and mono bass can be compromised. But if we have 4 subwoofers and more, IMHO the problem will be non-issue

 

[MayI]

I also don't listen to the music listed here so far.

I acknowledged previously very few audiophiles listen to classical/symphony etc where this sort of bass is present, so they actually have zero idea/experience with the effect live. Simple preference.

It's simple. If you understand the benefits of a multi sub system, using proper placement and EQ to reduce frequency response variation, you will understand what you lose when chasing this bassciousness effect.

So you have zero technical, scientific studies evidence etc. whatsoever. Ok.

using proper placement and EQ to reduce frequency response variation.....t's clear that you don't understand the modal issues I'm talking about. Every frequency has a different wavelength. Study up on how that relates to distances in your room. Decay times are irrelevant to what I'm talking about.

That's hilarious. You have no understanding that by smoothing modal peaks you have simultaneously lowered your decays times. As I suspected all along, this topic itself may be way beyond the ability for many to digest. Proof is in the pudding/responses.
For those who can understand, there is no known law preventing multi subs and EQ for stereo bass. The subs can be placed along the left and right walls, supplement full ranged mains etc. The spatial displacement along the side walls, with EQ will drive the rooms modes in multiple spots, result in greater averaging...aka multisub/EQ smoothing . The channels themselves will remain decorrelated for appropriate material.
The only question then is how to further reduce decay times, via treatment, dipole/cardioid subs and possibly DSP, since Dirac claims to be able to do so also. maybe a combination of all three.

 

[MayI]

LF noise in immediate judgment of spaciousness has been practiced for more than 30 years, e.g. by Jens Blauert and David Griesinger. We use noise to specifically study basic sense of space in humans, i.e. auditory envelopment (AEV).

More than just being repeatable, LF noise is a neutral stimulus, compared to music or atmosphere, and it comes with built-in maximum inter-aural movement velocity (change rate). All relevant qualities when studying elementary sensing. To rely on brainstem physiology rather than cortical.

However, we have still just scratched the surface. More studies are needed, and with music, to connect the inter-aural dots; also when slow listening and social factors (e.g. bonding) are included.

Agree, though expect fierce resistance from some who reject scientific evidence in lieu of what they believe, as seen here. Strange indeed.
What would be nice to know is actual decay times in the McGill test

 

[MayI]

Capably setup "stereo bass" systems should be fully adept at producing mono bass without compromise. Just a different set (or preset) of DSP parameters and signal routing. You should be able to have both easily if your system is flexible enough, just may not be both at the same time.

100% agree. It could be as simple as using 2 smaller subs to the sides/back of listening area, with large mains or 2 spaced subs up front. This gives 4 LF sources spatial smoothing for monophonic signals

 

[Chromatischism]

Capably setup "stereo bass" systems should be fully adept at producing mono bass without compromise. Just a different set (or preset) of DSP parameters and signal routing. You should be able to have both easily if your system is flexible enough, just may not be both at the same time.

...if you're lucky that your "stereo bass" placement gets you the best modal results, which is unlikely.

 

[Chromatischism]

So you have zero technical, scientific studies evidence etc. whatsoever. Ok.

I find your responses passive aggressive and really unfortunate. The studies of modal behavior and how to get your room under control using multiple subs and EQ is well established. You can look for names such as: Toole, Welti, and Devantier.

 

[Keith_W]

...if you're lucky that your "stereo bass" placement gets you the best modal results, which is unlikely.

Please take note that for stereo bass, the optimal position for the subwoofer is LR - to the left and right of the listener.

Now take a look at Welti's 2002 paper. The link can be found in the first post of this thread. I have highlighted the relevant configuration from the conclusion:

Welti's paper assumed that both subwoofers were reproducing the same signal. But this essentially proves that @NTK is correct. If you set up your subs at the midpoint of the wall on either side of the listening position, a simple flick of a switch can load a different DSP profile and you can decide for yourself if you want stereo bass or mono bass.

 

[Tom C]

If I recall correctly, there is a Welti paper that shows two on the sides in front, and two on the sides in back is one of the better arrangements. Not the best, but not bad. Also, if I understand correctly, no matter what you do, you cannot eliminate all seat-to-seat variation in bass response. One of the goals in the Welti papers I’ve read is to minimize seat-to-seat variation, but it cannot be eliminated altogether, so it’s not like mono bass is a perfect solution. Certainly adequate or excellent results can be obtained, given its stated goals, but still, there are inevitably imperfections.

 

[Tom C]

Please take note that for stereo bass, the optimal position for the subwoofer is LR - to the left and right of the listener.

Now take a look at Welti's 2002 paper. The link can be found in the first post of this thread. I have highlighted the relevant configuration from the conclusion:

View attachment 524423

Now Welti's paper assumed that both subwoofers were reproducing the same signal. But this essentially proves that @NTK is correct. If you set up your subs at the midpoint of the wall on either side of the listening position, a simple flick of a switch can load a different DSP profile and you can decide for yourself if you want stereo bass or mono bass.

That’s why I was considering the four at the mid wall arrangement, with the front and back wall subs mono, playing only the LFE channel, and the left sidewall sub playing only the low end from the left channel speakers (no LFE), and the right sidewall sub playing only the low end from the right channel speakers. One in each corner with total of four ought to work also. What do you think?

 

[kyuu]

I don't think anyone was doubting that it exists. At least, if we are talking about the same thing--the spacious bass effect described by David Griesinger.

It just doesn't seem worth compromising your system's optimization for only a small percent of content.

This is definitely something where the juice isn't worth the squeeze for most people with normal setups, who aren't in the business of arranging their entire domestic space around chasing small gains. It's also interesting that a lot of the people who really seem interested in this aren't even invested in multichannel, where the benefits are way more obvious and the necessary setup requires quite a bit less investment.

At the least, I suppose, those few who have capable full range speakers for surrounds (*cough* Kal Rubinson *cough*) should be able to test this out quite easily. The frequency range where subs are truly necessary are where even proponents of this appear to acknowledge that there is no spacial information available to the human perception system (~40Hz and lower).

 

[Keith_W]

Also, if I understand correctly, no matter what you do, you cannot eliminate all seat-to-seat variation in bass response.

I don't think that is correct. You CAN eliminate all seat-to-seat variation in the bass response ... if you have a double bass array. StigErik (RIP and dearly missed) posted some measurements of his DBA here. I don't recall if he posted measurements from multiple seating positions or not. If he didn't, @Flaesh is our other member with a DBA. Maybe he could share his measurements if we ask nicely

That’s why I was considering the four at the mid wall arrangement, with the front and back wall subs mono, playing only the LFE channel, and the left sidewall sub playing only the low end from the left channel speakers (no LFE), and the right sidewall sub playing only the low end from the right channel speakers. One in each corner with total of four ought to work also. What do you think?

I don't "think", I regurgitate what I read from studies What you are proposing sounds a lot like what Welti proposed in his paper. It's the second link on the first page. Go take a look.

 

[levimax]

the necessary setup requires quite a bit less investment.

I think one of the reasons this subject is so controversial is because many people have a large investment in MC systems built around the "summed to mono bass" concept. For stereo all that is required for AEV is 2 full range speakers.

 

[3ll3d00d]

For stereo all that is required for AEV is 2 full range speakers.

How can you assess stereo Vs mono bass without equalising the response across channels? If you need to do that, how do you do it without spacial distribution of the subs? Or is the assumption that this is strictly for a pure stereo single listening position setup?

 

[levimax]

How can you assess stereo Vs mono bass without equalising the response across channels? If you need to do that, how do you do it without spacial distribution of the subs? Or is the assumption that this is strictly for a pure stereo single listening position setup?

I am just going off what Thomas Lund said which is 2 full range monitors could work. I assume stereo would be limited in its image postion size for AEV just like it is for everything else.

 

[MayI]

It just doesn't seem worth compromising your system's optimization
And again you'd be optimizing for a small percent of content, while giving up the modal smoothing benefits of multi-sub at all other times.
Even if I did listen to a lot of music that meets that criteria, my home theater would be compromised. That's why I keep saying that
It's simple. If you understand the benefits of a multi sub system, using proper placement and EQ to reduce frequency response variation, you will understand what you lose when chasing this bassciousness effect.
It's clear that you don't understand the modal issues I'm talking about. Every frequency has a different wavelength. Study up on how that relates to distances in your room. Decay times are irrelevant to what I'm talking about.

The studies of modal behavior and how to get your room under control using multiple subs and EQ is well established. You can look for names such as: Toole, Welti, and Devantier.

Those are name drops, not studies. Not a single one supports your claims above. That's why you can't cite a single one.
None involved stereo vs mono perception etc, except the Welti https://secure.aes.org/forum/pubs/conventions/?elib=12979

The test room used for all listening tests is a 6.4 x 7.3 x 2.7 meter listening room which is fairly live as set up (estimated 500 Hz RT60 = .8 s. 1) . the room
has a modest amount of low frequency absorption consisting of velour curtain (approximately 20% overage) carpet with pad, and some soft furniture

Ooops. Like Poes test, it was over before it began. The McGill and other similar tests shows why.
This isn't a false dichotomy as you've made it. Stereo bass doesn't audibly "compromise" anything until you provide evidence it does. Monophonic bass OTOH, compromises any LF envelopment if it exists in the content.

 

[Tom C]

Based on the 2004 Welti paper, the problem with stereo bass is the cancellations that occur at the modal nulls when playing back correlated material. You can EQ the peaks for each channel separately, but you’re stuck when it comes to nulls during playback of recordings that have mono bass baked in.
I don’t let that worry me, though. For me, once the peaks are tamed with EQ, the system becomes quite listenable and enjoyable. Seems I’m not as picky as some.

 

[bmc0]

I generated a few test signals which may be of some interest. The input is 2-channel uncorrelated periodic (1M) pink noise. This is split into high- and low-frequency paths at 80Hz using 9th-order (54dB/oct) Butterworth filters, then each path is either summed to mono (and corrected for level) or left uncorrelated before recombining. All four combinations are attached:

1. Cross-correlation of 1 at all frequencies (mono_hf_mono_lf)
2. Cross-correlation of 1 above 80Hz and ~0 below 80Hz (mono_hf_uncor_lf)
3. Cross-correlation of ~0 above 80Hz and 1 below 80Hz (uncor_hf_mono_lf)
4. Cross-correlation of ~0 at all frequencies (uncor_hf_uncor_lf)

The use of full-range noise should hopefully reduce the possibility of nonlinear distortion from low-frequency drivers affecting spatial impression (something that has been brought up multiple times).

 

[janbth]

Capably setup "stereo bass" systems should be fully adept at producing mono bass without compromise. Just a different set (or preset) of DSP parameters and signal routing. You should be able to have both easily if your system is flexible enough, just may not be both at the same time.

I don’t think it’s that simple. For mono bass to be effective against a given room mode you would need to locate the L and R subs in high pressure zones of different polarities for that mode. What happens then if you switch to the «stereo preset»? If the signal was truly stereo, we can imagine the sound hard panned to, say, L. This would excite the mode. It would be even worse if L and R played the same offending frequency exactly out of phase.

 

[3ll3d00d]

I assume stereo would be limited in its image postion size for AEV just like it is for everything else.

My point is that there seems an implication that there can be major, difficult if not impossible to correct, imbalances in frequency response in that part of the spectrum so the image presented is inevitably skewed by that. If the q is assessing the degree to which stereo bass is perceptible, surely you have to correct for this, just as you correct for volume differences in other such tests, otherwise you are not just testing stereo Vs mono.

Put another way, how do you even test if what you hear is from stereo Vs mono if you can't normalise the level/response?