Here are two papers that look very useful for this discussion, but I don't want to spend $25 to buy them, does anyone here have them or access to them?
A. Celestinos and S. B. Nielsen, “Controlled Acoustic
Bass System (CABS) A Method to Achieve Uniform
Sound Field Distribution at Low Frequencies in
Rectangular Rooms,” J. Audio Eng. Soc., vol. 56, pp.
915–931 (November 2008).
A. Celestinos, “Low Frequency Sound Field Enhancement
System for Rectangular Rooms, Using Multiple
Loudspeakers
A. Celestinos and S. B. Nielsen, “Controlled Acoustic
Bass System (CABS) A Method to Achieve Uniform
Sound Field Distribution at Low Frequencies in
Rectangular Rooms,” J. Audio Eng. Soc., vol. 56, pp.
915–931 (November 2008).
A. Celestinos, “Low Frequency Sound Field Enhancement
System for Rectangular Rooms, Using Multiple
Loudspeakers
IMO, the jury is still out about that method. I'm very interested to learn more about this method for the low bass.
This method do nothing for the bass where your subwoofer cuts off, so around 80hz and up so you definitely need absorption for 80hz- 500hz.
and you do need first reflections panels on side walls, back wall, ceiling for mids/highs reflection.
I'm a bit of a purist at heart. all those subwoofer and delay would stress me. I prefer living with those huge bass traps and be done with it. They work well if you have the space to make them big enough and if you do them yourselve isnt expensive at all.
I'll follow the thread at gearslutz also. keep his posted about the method, very interesting stuff. thanks!
so you simply ignore the need to control and absorb the upper bass and lower midrange?
This method do nothing for the bass where your subwoofer cuts off, so around 80hz and up so you definitely need absorption for 80hz- 500hz.
and you do need first reflections panels on side walls, back wall, ceiling for mids/highs reflection.
I'm a bit of a purist at heart. all those subwoofer and delay would stress me. I prefer living with those huge bass traps and be done with it. They work well if you have the space to make them big enough and if you do them yourselve isnt expensive at all.
I'll follow the thread at gearslutz also. keep his posted about the method, very interesting stuff. thanks!
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Here's a link to the CABS paper for rectangular rooms. This one is more useful to this discussion:
http://vbn.aau.dk/files/62729209/LF_sound_field_control.pdf
http://vbn.aau.dk/files/62729209/LF_sound_field_control.pdf
Not at all, in previous replies I think I've already mentioned (about 3X, in fact!!) that for critical applications the room still needs to be treated for the frequencies not covered by the DBA or CABS...
The fact that your room and decor and financial situation allows you to use massive amounts of damping material and bass-traps is great. Not everyone here has that kind of situation!
Also, this part of the discussion wasn't just about YOUR room, it was about whether active bass absorption can work instead of having to use huge bass traps...
I think the papers and research we have cited prove it, and we've established, beyond any reasonable doubt, that it can and DOES work.
That you want to keep your doubts? Well, OK, I too believe in freedom of religion, even when it is self-created.
In my case, because I had a very critical WAF to deal with, I ended up placing my mains in near-field and delaying the signal so it was in sync with the bass from the front sub. Having the mains so close to listening position radically reduced the audibility of the remaining room modes between 100Hz and 500 Hz...
With the simple sub-in-front/active bass absorption in back and near-field placement of my mains (small satellites, crossed in at 100Hz), I was able to achieve a stunning level of quality. So yes, even with the simplistic sub in front, active absorb in rear, I got it to work exceptionally well.
So, OK, by now it is obvious you've heavily tweaked your room and are now very satisfied...
Listen, we all KNOW that with enough material, money, time, expense and expertise, a great room can be had. That's great.
But don't let that make you believe it is the ONLY way... and potentially mis-inform dozens of others who are building their rooms now, and who may greatly benefit from applying the DBA or CABS method... it is THEY who can still save a lot of money and time, and still attain an exceptionally high level of quality, for a LOT less money.
To make it explicitly clear, the amount of material and money needed to reduce the main longitudinal mode in a room is ridiculous, and making it look even halfway acceptable is nearly impossible (yes IMO and YMMV, etc.). Users can save themselves a LOT of hassle, time, money and suffering by adopting the full DBA/CABS approach or even subsets of it like I did with my two subs.
In closing: It's clear I can't convince you, so I hereby resign from that job!
But for all others, my recommendation would be:
1) build the bass system as a DBA/CABS
2) Judiciously apply small bass traps, absorbers and deflectors to handle the remaining room issues.
3) Make sure your ceiling is properly treated as well, and perhaps build a coffee table/deflector system to keep the floor bounce from getting to your ears.
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I think this one would be a good one to link in... it's still not the full monty one I previously found and lost, but it's a good start.
Having the mains so close to listening position radically reduced the audibility of the remaining room modes between 100Hz and 500 Hz...
You still absolutely need quite deep absorption to be able to control those FREQ. You need at least 8 inch thick for 100hz, ideally even thicker. so your point about reducing the WAF apparence is not really one since only pressure based bass traps can be really effective under 100hz (unless you use 20-30 inch thick velocity based bass traps.) and pressure based bass traps can be relatively small.
no matter how close you are to your main, you still will hear the room resonance as much as the direct source without treatment for at least up to 400hz.
We need much more then those papers to establish without doubt that the method work.
I still think this can be very valuable for many here! thanksJack Caldwell;4568838 Also said:
This next link is well worth reading, it's where Todd Welti compares DBA vs his SoundField Management system...
Comparison of Double Bass Array to Sound Field Management: THE MEATY PART!!!!!!
Here's an interesting comment/hint from what Todd Welti wrote, I lifted it verbatim:
"SUMMARY
I would summarize by saying that in rectangular rooms, if you don’t know where the seats will be, and you can get the subs located in/on the front and back walls, use DBA. Also if making impulse response measurements is too difficult, use DBA. "
Also, to be fair, he DOES go on to say that DBA is ONLY for rectangular rooms...
Comparison of Double Bass Array to Sound Field Management: THE MEATY PART!!!!!!
Here's an interesting comment/hint from what Todd Welti wrote, I lifted it verbatim:
"SUMMARY
I would summarize by saying that in rectangular rooms, if you don’t know where the seats will be, and you can get the subs located in/on the front and back walls, use DBA. Also if making impulse response measurements is too difficult, use DBA. "
Also, to be fair, he DOES go on to say that DBA is ONLY for rectangular rooms...
Applicability to non rectangular rooms
SFM will work in any room, since it is based on actual room measurements and does not care about the shape of the room. DBA is based on the acoustics of a rectangular room and wont work in a non rectangular room. It also may not work as advertised in rooms which are acoustically non-rectangular. This could be the case for rooms with very different wall construction on different walls, for example.
Like in 99% of rooms, walls will show complex impedence which will make it very hard to implement that method.
Hmm... In some cases not all that true, or even much at all!
Let's play with some math. With the mains 1m away from my listening seat, they were 1m away from the side walls.
The minimum distance for the first reflection was 3m away.
1) The amplitude level of that reflection was MUCH lower than if the speaker was near the wall - in theory it would be about 1/9th, in practice the measured level was about 6dB lower. So the ratio of direct vs reflected was VERY different.
2) The time difference was such that the reflections from the walls arrived 2 meters later which equates to about 5.8m Sec or greater. Our brain does some interesting things with delayed reflections in that range, and the sonic contribution becomes much less audible.
Yes, with steady-state tones we would hear some frequency difference, but not so much or even at all with regular music as a source. I gave up on the many pleasures of listening to steady-state tones a long time ago.
3) Floor bounce: I did strategically place a coffee table with a deflector panel at the back in such a way as to nearly eliminate the floor issue.
Umm, really? Where do you get your numbers?
Oh come on! If you're going to go to the effort of building a dedicated room, it's bloody easy to make sure it's acoustically symmetrical !
Look, why are you fighting this? It's pretty obvious DBA/CABS will work and work very well in rectangular rooms, and even fairly well in non symmetrical rooms according to the the other paper from the Aalborg guys.
Just take a deep breath and admit the point: say it after me - active bass absorption CAN work very well in SOME cases, and in MOST rectangular rooms.
Great! Now you can continue telling me why you would still prefer to do conventional treatments. That is a choice, and it is your prerogative. It doesn't inherently make it better.
You are far from the well establish -10db within the first 20ms for early reflections.
Read about SBIR.
TBH, you seem to not fully understand room acoustic. you absolutely need, even in near field setup, to control those early reflections.
now if you dont believe that first reflection in LF is detrimental, thats your religion
''Make the panels as deep as possible, at least about 6” but preferably 12” or deeper. A 3” panel will only be effective down to about 300-400 Hz and this will only EQ the reflection leaving the lower frequency range unattended, and this will mess up the lower part of the response due to SBIR.
I always try to make the first order reflection panels at least about 8” but often 14-20” if possible. Needless to say, you need to select an appropriate wool (with suitable flow resistivity) deepening on the thickness used for optimal performance. Multi-layer Absorber Calculator
In small room acoustics, we are primarily concerned with lower order reflections and these will always be at specific angles of incident, so relying on absorption coefficients sourced from random incident measurements (reverberation chambers) might be hazardous. First order reflections usually occur at between 0 to about 30 degrees incident angel to the boundary. Ideally, you want a panel that absorbs all the way down to the cutoff of the speaker, but if the monitor is positioned close to the boundary, you might get away with a thinner panel (not effective at low frequencies) since the difference in travel distance between the direct sound and the reflection from this boundary will be small and a constructive phase relation between direct and reflected sound will occur fairly high up in the frequency range, and assuming you can compensate of this low frequency boost by adjusting your monitor, this might not be a big problem.
Also, one needs to consider the directivity of a normal monitor. The energy hitting the reflection points at the sides, ceiling and behind the speaker is mostly made up of low frequency energy since the monitor is close to omnidirectional at low frequencies but becomes more directional at higher frequencies, so there might not be a strong need to absorb the highest range at these points relative to the lower frequency range depending on where they are located in relation to the source and the directional properties of it
>>
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im talking about the walls themselve will show complex impedance.
Im not fighting at all and I already admitted that it may seem to work but that we need more information and measurements. I<m not fighting, but tone down your attitude. ive come up with many problems in your setup and in your argument.
you need thick absorption to treat the 100hz to 500hz. so DBA wont remove the need for absorption.
Sigh. This is starting to make me angry.
OK, so now that we've pretty much shown you research that proves the point about active bass absorption below 100Hz (in rectangular rooms)...
I wish you would stop taking this out of context. Stop avoiding the point.
As I explained, I am well aware that IDEALLY we need to absorb the reflections, and also of WHAT we need for that. As I ALSO explained, there was a major WAF issue to deal with, so I did not implement that.
But to make my position clear, YET AGAIN
I have REPEATEDLY stated that I too believe we need to treat the room for the range from 100Hz up.
Now can we PLEASE focus on the MAIN issue I have been trying to discuss?
which is: can active bass cancellation work well?
YES, it CAN
It is in the range BELOW 100 Hz that the active bass cancellation systems like DBA/CABS work best, and provide a superior solution in rectangular rooms.
So now I have two questions/requests for you.
1) Would you PLEASE stop coming back at me with the 100Hz and up issue when I have REPEATEDLY agreed and stated it is necessary to treat for those?
2) Would you be willing to address ONLY the 100Hz and below issue? Are you STILL going to sit there and insist that even in rectangular rooms passive absorption just HAS to be better ?
Otherwise I'm pretty much done here.
sorry that you get mad.
I have said many times that the method you describe may work.
Ive mention the need to treat the first reflection for LF from 100hz to 500hz because youve made that comment.
Let's play with some math. With the mains 1m away from my listening seat, they were 1m away from the side walls.
The minimum distance for the first reflection was 3m away.
1) The amplitude level of that reflection was MUCH lower than if the speaker was near the wall - in theory it would be about 1/9th, in practice the measured level was about 6dB lower. So the ratio of direct vs reflected was VERY different.
2) The time difference was such that the reflections from the walls arrived 2 meters later which equates to about 5.8m Sec or greater. Our brain does some interesting things with delayed reflections in that range, and the sonic contribution becomes much less audible.
that comment made me think that you think you dont need to treat the LF early reflection, which is false. you do need to treat the LF early reflection and to treat all early reflection that are not -10db at 20ms. So why say that in your setup you dont need early reflection LF
It is in the range BELOW 100 Hz that the active bass cancellation systems like DBA/CABS work best, and provide a superior solution in rectangular rooms.
why superior?
weird that you now think with the limited amount of research on the DBA method that your able to be certain that DBA method works better then pressure based absorption and velocity based bass traps under 100hz. seriously, you jump to conclusion to support your biased view. I mean this respectfully.
2) Would you be willing to address ONLY the 100Hz and below issue? Are you STILL going to sit there and insist that even in rectangular rooms passive absorption just HAS to be better ?
I dont insist that its better to use absorption, simply that we still have very limited of comparison and information on DBA method.
anyways, Im out.
I have said many times that the method you describe may work.
Ive mention the need to treat the first reflection for LF from 100hz to 500hz because youve made that comment.
Let's play with some math. With the mains 1m away from my listening seat, they were 1m away from the side walls.
The minimum distance for the first reflection was 3m away.
1) The amplitude level of that reflection was MUCH lower than if the speaker was near the wall - in theory it would be about 1/9th, in practice the measured level was about 6dB lower. So the ratio of direct vs reflected was VERY different.
2) The time difference was such that the reflections from the walls arrived 2 meters later which equates to about 5.8m Sec or greater. Our brain does some interesting things with delayed reflections in that range, and the sonic contribution becomes much less audible.
that comment made me think that you think you dont need to treat the LF early reflection, which is false. you do need to treat the LF early reflection and to treat all early reflection that are not -10db at 20ms. So why say that in your setup you dont need early reflection LF
It is in the range BELOW 100 Hz that the active bass cancellation systems like DBA/CABS work best, and provide a superior solution in rectangular rooms.
why superior?
weird that you now think with the limited amount of research on the DBA method that your able to be certain that DBA method works better then pressure based absorption and velocity based bass traps under 100hz. seriously, you jump to conclusion to support your biased view. I mean this respectfully.
2) Would you be willing to address ONLY the 100Hz and below issue? Are you STILL going to sit there and insist that even in rectangular rooms passive absorption just HAS to be better ?
I dont insist that its better to use absorption, simply that we still have very limited of comparison and information on DBA method.
anyways, Im out.
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When it comes to acoustics, it appears that very few people have a good practical understanding of all the variables involved in the real world. Any time someone suggests a rule of thumb (38% rule for ex.) I want to know exactly WHY... Why do they think that can be a general truth in more than one case? Way too many half baked opinions have been mis-leading audiophiles in recent decades.
Multiple woofers necessarily improve the room ringing situation just because it becomes likely that a woofer becomes closer to your ears. Since sound pressure falls off logarythmically with distance, the difference between perceived room ringing and the direct sound out of a given woofer increases. Room ringing is effectively pushed down in amplitude. Room ringing by itself may not be improved at all (although it could be for a given spacial location), but if a woofer is now closer to your ears...
Is that good enough? maybe not. With parallel walls, there will be resonances, besides all the comb filter effect cancellations. Bass traps dissipate energy, possibly at a tuned frequency (depending how they are designed). My experience is that bass absorbers need a lot of mass (weight) to be effective at low frequencies, rather than necessarily needing to be large.
At mid and high frequencies, I found that nailing 2 inch cotton rope into all 2 and 3 surface corners of my living room (except at the floor in a carpeted room) virtually eliminated the rather noticeable ringing from clapped hands. You would think that the large parallel surfaces would need more treatment, but what I found is that it's actually the corners that are the much bigger problem (Since cotton rope is very flammable, I recommend fire resistant foam instead, such as Auralux).
If however the room is large enough to have delay times between 50mS and 150mS (according to David Griesinger), intelligibility of words can be a problem, and in these larger rooms, significant damping of opposing parallel walls may be required. If you live in a typical apartment, this is not likely to be an issue. If you are rich and have a giant living room, it could be. In a typical church it will be a huge issue.
You might say, gee Bob, how can you think that large un-treated surfaces in my small listening room aren't going to destroy the acoustics with comb filter effects? Good question. It's because there is no way to avoid comb filter "mechanisms" in any kind of typical living room, so you're better off to work with them, not against them. In fact, the more you get rid of some reflective paths, the worse the bottom line result. Heh???
The best case scenario for maximum fidelity might be the anechoic chamber, where there are no reflections at all. The worse case scenario is the anechoic chamber where you've introduced only one reflection, which will produce deep nulls all across the entire F response. If you then add in a 2nd reflection that's different than the first (different delay time), although it creates its own set of nulls over frequency, it will do that at different frequencies than the first reflection did, so where one reflection created an almost total cancellation, the other reflected path somewhat fills in that cancellation. In the real world you actually benefit from more different room reflections, so its more likely that any severe cancellations will be largely filled in. As long as they all have different time delays. Random works fairly well, strategic (time delays) could be significantly better, but maybe only for one spacial location in the room.
I agree with Linkwitz, that there are too many variables in the real world for acoustics softwares to be very useful. Above the Schroeder frequency, more random room reflections is a good thing. Below the Schroeder frequency, you might be able to improve things with "bass traps" or tuned dissapators and/or electronic EQ (that's all I use), but in my understanding, the real definition of "the Schroeder frequency" is where you've gone low enough in frequency that the room reflections are no longer varied enough to effectively fill in each others comb filter nulls.
Multiple woofers necessarily improve the room ringing situation just because it becomes likely that a woofer becomes closer to your ears. Since sound pressure falls off logarythmically with distance, the difference between perceived room ringing and the direct sound out of a given woofer increases. Room ringing is effectively pushed down in amplitude. Room ringing by itself may not be improved at all (although it could be for a given spacial location), but if a woofer is now closer to your ears...
Is that good enough? maybe not. With parallel walls, there will be resonances, besides all the comb filter effect cancellations. Bass traps dissipate energy, possibly at a tuned frequency (depending how they are designed). My experience is that bass absorbers need a lot of mass (weight) to be effective at low frequencies, rather than necessarily needing to be large.
At mid and high frequencies, I found that nailing 2 inch cotton rope into all 2 and 3 surface corners of my living room (except at the floor in a carpeted room) virtually eliminated the rather noticeable ringing from clapped hands. You would think that the large parallel surfaces would need more treatment, but what I found is that it's actually the corners that are the much bigger problem (Since cotton rope is very flammable, I recommend fire resistant foam instead, such as Auralux).
If however the room is large enough to have delay times between 50mS and 150mS (according to David Griesinger), intelligibility of words can be a problem, and in these larger rooms, significant damping of opposing parallel walls may be required. If you live in a typical apartment, this is not likely to be an issue. If you are rich and have a giant living room, it could be. In a typical church it will be a huge issue.
You might say, gee Bob, how can you think that large un-treated surfaces in my small listening room aren't going to destroy the acoustics with comb filter effects? Good question. It's because there is no way to avoid comb filter "mechanisms" in any kind of typical living room, so you're better off to work with them, not against them. In fact, the more you get rid of some reflective paths, the worse the bottom line result. Heh???
The best case scenario for maximum fidelity might be the anechoic chamber, where there are no reflections at all. The worse case scenario is the anechoic chamber where you've introduced only one reflection, which will produce deep nulls all across the entire F response. If you then add in a 2nd reflection that's different than the first (different delay time), although it creates its own set of nulls over frequency, it will do that at different frequencies than the first reflection did, so where one reflection created an almost total cancellation, the other reflected path somewhat fills in that cancellation. In the real world you actually benefit from more different room reflections, so its more likely that any severe cancellations will be largely filled in. As long as they all have different time delays. Random works fairly well, strategic (time delays) could be significantly better, but maybe only for one spacial location in the room.
I agree with Linkwitz, that there are too many variables in the real world for acoustics softwares to be very useful. Above the Schroeder frequency, more random room reflections is a good thing. Below the Schroeder frequency, you might be able to improve things with "bass traps" or tuned dissapators and/or electronic EQ (that's all I use), but in my understanding, the real definition of "the Schroeder frequency" is where you've gone low enough in frequency that the room reflections are no longer varied enough to effectively fill in each others comb filter nulls.
The 38% rule is a starting point. 19% is also recommended. you really need to avoid 25/50/75 % of the room.
You absolutely dont want to listen in a anechoic chamber, we need reflection but not early reflection, secondary. you dont want any reflection at the listening position that are early reflection that are at least -10db within 20ms .
I think that when you refer is toole when you say:<<In the real world you actually benefit from more different room reflections, so its more likely that any severe cancellations will be largely filled in. As long as they all have different time delays. Random works fairly well, strategic (time delays) could be significantly better, but maybe only for one spacial location in the room. ''
we do not want to overly treat our room as a dead sounding space sounds horrible. Listening in a anechoic chamber would be a nightmare actually.
I did the mistake myself and treated my room overly and the sound was very claustrophobic. The best solution is LEDE design, or false wall with huge bass traps all around but false wall to allow the mid and HF back into the room and allow them as secondary reflections.
you need to create a free reflective zone and treat the early reflections at your listening position (ceiling, side walls, back wall, floor) and allow only reflections that are secondary reflection. you can then use LEDE design, ect.
You absolutely dont want to listen in a anechoic chamber, we need reflection but not early reflection, secondary. you dont want any reflection at the listening position that are early reflection that are at least -10db within 20ms .
I think that when you refer is toole when you say:<<In the real world you actually benefit from more different room reflections, so its more likely that any severe cancellations will be largely filled in. As long as they all have different time delays. Random works fairly well, strategic (time delays) could be significantly better, but maybe only for one spacial location in the room. ''
we do not want to overly treat our room as a dead sounding space sounds horrible. Listening in a anechoic chamber would be a nightmare actually.
I did the mistake myself and treated my room overly and the sound was very claustrophobic. The best solution is LEDE design, or false wall with huge bass traps all around but false wall to allow the mid and HF back into the room and allow them as secondary reflections.
you need to create a free reflective zone and treat the early reflections at your listening position (ceiling, side walls, back wall, floor) and allow only reflections that are secondary reflection. you can then use LEDE design, ect.
it's my contention that if an anechoic chamber sounds claustrophobic or bad in any other way, it's a reflection of the shortcomings of the recording process. Playing it back in a LEDE room adds some reverb, and if the live end is behind the listener, now you've got surround sound. It may sound more pleasing, but seems a step away from "fidelity", if that's a priority. The point I was trying to make is that a single reflection created in an anechoic chamber would result in deep comb filter cancellations, and nothing to fill them in at all. Hence, worse case. Actually, even worse case would be a frequency selective resonance, since its start up and decay times will vary with program material, and therefore be hard to compensate for. impulse response might need different correction than longer envelop bursts
It has been claimed that acousticians care more about the energy-time curve than about the frequency response. Acousticians are focused on the energy-time curve rather than the frequency response curve because that is their domain. Their job is not to fix the frequency response of the speakers; their job is (among other things) to prevent the room from screwing it up by letting the energy decay significantly more slowly or rapidly at some frequencies than at others.
Back to the subject of low frequencies in rooms. The ear has very poor time-domain resolution at low frequencies. We cannot even detect the presence of bass energy from less than a single wavelength, and we must hear several wavelengths before we can detect pitch. So by the time we can even hear the bass, the energy has already bounced off of several room boundaries and the room's effects are already all over the frequency response. The implication is, it's the in-room the steady-state frequency response that matters at low frequencies because we can't hear the first-arrival sound apart from it. The decay time matters, but primarily because the ear/brain system perceives a longer-duration signal to be louder than a shorter-duration one. Once we shift our focus to the steady-state frequency response, we are including all in-room decays, both long and short.
In contrast to the ear's poor time-domain resolution at low frequencies, the ear actually has a heightened ability to hear loudness differences at low frequencies relative to the rest of the spectrum. An examination of equal-loudness curves will show that they bunch up at low frequencies, which implies that a small change in actual SPL results in a disproportionately large change in perceived loudness at those frequencies. So if we go by what matters most to the ears, in the bass region, the steady-state frequency response matters more than the time-domain behavior.
That being said, decay time is very closely correlated with modal behavior. A modal peak is associated with low damping, and a modal dip is associated with high damping. Because loudspeakers are minimum-phase systems, as we fix the steady-state frequency response, we also fix the time-domain response, at least to a good first approximation. As a distributed multi-sub system improves the smoothness of the in-room frequency response, it is also improving the in-room time-domain behavior. The advantage over relying on equalization alone is, this improvement tends to be global rather than local.
Damping is pretty much always desirable at low frequencies, but too much damping quickly becomes undesirable at high frequencies. So it has to be done in a way that adequately preserves the shorter-wavelength reverberant energy.
A bigger room is pretty much always better, but the shape of the room doesn't matter much at low frequencies if the damping is uniformly distributed. So a good place for damping is in the walls themselves.
If we accept the in-room steady-state frequency response curve as correlating well with perception at low frequencies, and I think this is reasonable, then the amount of improvement we can expect from adding subwoofers (widely distributed) is greater than the amount of improvement we can expect from adding damping. To put it another way, you are not likely to transform +/- 9 dB bass region frequency response to +/- 3 dB simply by adding damping material, but you can reasonably expect to do so by adding subs intelligently.
Back to the subject of low frequencies in rooms. The ear has very poor time-domain resolution at low frequencies. We cannot even detect the presence of bass energy from less than a single wavelength, and we must hear several wavelengths before we can detect pitch. So by the time we can even hear the bass, the energy has already bounced off of several room boundaries and the room's effects are already all over the frequency response. The implication is, it's the in-room the steady-state frequency response that matters at low frequencies because we can't hear the first-arrival sound apart from it. The decay time matters, but primarily because the ear/brain system perceives a longer-duration signal to be louder than a shorter-duration one. Once we shift our focus to the steady-state frequency response, we are including all in-room decays, both long and short.
In contrast to the ear's poor time-domain resolution at low frequencies, the ear actually has a heightened ability to hear loudness differences at low frequencies relative to the rest of the spectrum. An examination of equal-loudness curves will show that they bunch up at low frequencies, which implies that a small change in actual SPL results in a disproportionately large change in perceived loudness at those frequencies. So if we go by what matters most to the ears, in the bass region, the steady-state frequency response matters more than the time-domain behavior.
That being said, decay time is very closely correlated with modal behavior. A modal peak is associated with low damping, and a modal dip is associated with high damping. Because loudspeakers are minimum-phase systems, as we fix the steady-state frequency response, we also fix the time-domain response, at least to a good first approximation. As a distributed multi-sub system improves the smoothness of the in-room frequency response, it is also improving the in-room time-domain behavior. The advantage over relying on equalization alone is, this improvement tends to be global rather than local.
Damping is pretty much always desirable at low frequencies, but too much damping quickly becomes undesirable at high frequencies. So it has to be done in a way that adequately preserves the shorter-wavelength reverberant energy.
A bigger room is pretty much always better, but the shape of the room doesn't matter much at low frequencies if the damping is uniformly distributed. So a good place for damping is in the walls themselves.
If we accept the in-room steady-state frequency response curve as correlating well with perception at low frequencies, and I think this is reasonable, then the amount of improvement we can expect from adding subwoofers (widely distributed) is greater than the amount of improvement we can expect from adding damping. To put it another way, you are not likely to transform +/- 9 dB bass region frequency response to +/- 3 dB simply by adding damping material, but you can reasonably expect to do so by adding subs intelligently.
