Are my bass traps not working? Some changes in var smoothed frequency response, but not much in ERB smoothed one.

[Sigberg Audio]

First of all, people can decide for themselves whether it's impractical or not. And not sure why it should be less practical then multiple subwoofers in many cases.

Secondly, I have several subwoofer designs I plan to release. Will I speak differently when I do? No, because to me it's about recommending the better approach and just not selling products. And you simply don't deal with many of the important issues with only subwoofers or EQ for that matter.

Acoustic products to home market generally doesn't generate much income. And I often recommend people to build their own products.

I resent the implication that I'm just here trying to sell products rather than recommend the better approach.

The listening room I'm currently in has acoustic treatment for several thousand dollars (among other things four of the broadsoarber panels you mention). I always recommend people to treat their room, but I also know most people have a living space and must make some compromises.

 

[Justdafactsmaam]

You're asking a lot of questions here and this is waste topic. We can only scratch the surface here.

Not sure how it’s a waste topic. It is complicated for sure but I think we can dig well below the surface

First of all posted data/measurements of acoustic products are not necessarily to be trusted. There are several reasons for that but one is that the measurement method for lowest frequencies isn't always trustworthy.

Depends on who is testing and how. Some measurements are trustworthy

Secondly, they can be based on reverberation, and which means it isn't something you can automatically transfer to small rooms. Said in other words, the unit will not absorb as well in a small room.

Never heard that before. How would an absorption panel be less absorptive based on room size? How would that change its absorption coefficient?

Thirdly, when someone says it works down to a specific frequency, this doesn't mean it's very efficient to that frequency. It may be that it only absorbs 30 %, 20 % or 10% there. And we need a lot more for a good result.

The good data on absorption coefficients address that. What they don’t and can’t address is accumulative effects of multiple absorbers in the room. Put a single 4” rockwool absorber on one wall its rated coefficient will be accurate. Cover every square inch of the room and the accumulative effect will reach much lower frequencies than its coefficient would suggest. And this is a function of the complex geometry of the panels on the walls. It’s 4” thick at a 90 degree angle but much thicker at various other angles. It really is more a function of volume than thickness of the absorption. Using 4” on the side walls and 6” on the front and back I have about 200 cubic feet in my “small” room. Of course I also have that 2,000 cubic feet of absorption in the attic that my room is open to (with a faux ceiling made of acoustically transparent cloth) so mine is an extreme example. But it brings down the bass reverb in a way that nothing else can.

There’s a lot that can be done in the frequency domain with subwoofer arrays, EQ and DSP room correction. But only absorption and cancellation works in the time domain. And it does matter

There are new measurements out there today that suggest that a 10 cm panel can be very effective to about 80 Hz. But it's only a certain material. Or a product that uses multiple cores like the Broadsorbor from RPG. I have seen great effect to 110 Hz with only a few such panels and to 80 Hz with more panels.

As for air gap, too much of that with openings and the effect will actually become worse.

All good points. Materials do matter

While pressure based traps can be far more effective at the lowest frequencies, they generally tend to be band limited and not addressing the most sensitive area great. So often a combination is the better approach.

Pressure traps really need to be tailored to the room to work their best

 

[Bjorn]

Matthew Poes, acoustician, on multiple subs versus bass traps (from a video recorded years before he became a dealer for Perlisten):

"I've installed a lot of bass traps in people's rooms, I've filled every corner, the ceiling, you name it, and it didn't make anywhere near as big a difference as four subs did."

Here's the video, cued up to that part. He gets his point across within about 30 seconds:

Of course multiple subs, bass trapping, and EQ are NOT mutually exclusive! They can be used in combination, and imo that would be ideal.

Considering many acousticians are able to get excellent response with treatment, doesn't that tell us more about Matthew Poes and the products he has used rather than about acoustic treatment itself?

It's also quite odd. Because it means he is basically only considering the frequency response, and is overlooking the time domain behaviour and the higher frequency area where multiple subwoofers don't function in but treatment addresses. To most acousticians that wouldn't make much sense.

 

[Bjorn]

Put a single 4” rockwool absorber on one wall its rated coefficient will be accurate.

I can't address as it's too broad of a topic. But what you saying above is incorrect. The rated coefficient is not based on one panel. Measurements are conducted with several panels and a large surface area.

Plus, the measurement's isn't necessarrily applicable to a small room wither because there is no isotropic sound field in such room, hence there's no diffuse sound field and this greatly effects the absorption.

But it becomes more complicated than this as well since there can be, and there often is, mistakes in the measuring method also. Just ask Ron Sauro of NWA labs.

 

[Duke]

Considering many acousticians are able to get excellent response with treatment, doesn't that tell us more about Matthew Poes and the products he has used rather than about acoustic treatment itself?

This is an example of argument by innuendo. No actual argument about the relative merits of room treatments and multiple subwoofers is being made.

If "many acousticians are able to get excellent response with treatment", this tells us nothing about the results with multiple subwoofers intelligently distributed.

Nor, in my opinion, does that statement justify the implication that Matthew Poes lacks competence in this area.

... it means he is basically only considering the frequency response, and is overlooking the time domain behaviour...

My understanding is that Toole and Geddes also focus on the in-room frequency response in small rooms, which do not have true reverberant fields.

Also, my understanding is that Toole and Geddes both consider speakers + rooms to be "minimum phase systems" at low frequencies, and this implies that the frequency response and the time-domain response track one another. So when we improve the time-domain behavior (by reducing ringing via bass trapping) we simultaneously improve the frequency response; and when we improve the frequency response (via multiple subs and/or EQ) we simultaneously improve the time-domain behavior. Ime in practice the correlation between the frequency response and the time domain in the bass region is not perfect.

And, Toole reports research indicating that it's primarily the frequency response peak that we perceive, rather than the ringing, though I must admit my instinct is that it's both.

... and the higher frequency area where multiple subwoofers don't function in but treatment addresses.

Elsewhere in the video Matthew Poes talks about and recommends acoustic treatment above the subwoofer region, where it is more effective because the wavelengths are shorter.

 

[dasdoing]

multi-subs don't address the ringing. also subs only cover half the bass

 

[Duke]

multi-subs don't address the ringing. also subs only cover half the bass

To the extent that a multi-sub system smooths the in-room response at low frequencies, it also reduces the ringing. As does EQ. Quoting @Floyd Toole:

"Low-frequency room resonances also behave as minimum-phase phenomena so attenuating the bump, attenuates the ringing. However, as I said, evidence indicates that human listeners respond mainly to the spectral bump, not the ringing."

 

[Justdafactsmaam]

My understanding is that Toole and Geddes also focus on the in-room frequency response in small rooms, which do not have true reverberant fields.

Look at any before and after waterfall plot using room treatments in a small room and tell me that with a straight face. Bass traps reduce RT substantially in the bass regions.

You may not get a uniform diffuse field in a small room but you sure do get a reverberant field. And it has a huge impact on the sound.

Also, my understanding is that Toole and Geddes both consider speakers + rooms to be "minimum phase systems" at low frequencies, and this implies that the frequency response and the time-domain response track one another.

Hate to be blunt but they are wrong.

So when we improve the time-domain behavior (by reducing ringing via bass trapping) we simultaneously improve the frequency response; and when we improve the frequency response (via multiple subs and/or EQ) we simultaneously improve the time-domain behavior.

Again check any waterfall plot. You can EQ a bass peak in the frequency domain but it still rings in the time domain.

Ime in practice the correlation between the frequency response and the time domain in the bass region is not perfect.

And, Toole reports research indicating that it's primarily the frequency response peak that we perceive, rather than the ringing, though I must admit my instinct is that it's both.

Now you’re talkin.

With all due respect to Dr. Toole the focus of his career has been on speaker design, specifically speaker design for every day rooms.

I don’t think his take on the subject of small room acoustics is the last word.

 

[Justdafactsmaam]

I can't address as it's too broad of a topic. But what you saying above is incorrect. The rated coefficient is not based on one panel.

It is if it was one panel that was tested

Measurements are conducted with several panels and a large surface area.

Sometimes. Sometimes they are conducted with one panel

Plus, the measurement's isn't necessarrily applicable to a small room wither because there is no isotropic sound field in such room, hence there's no diffuse sound field and this greatly effects the absorption.

It’s still applicable. He physics of kinetic energy into heat happens regardless off the size of the room

But it becomes more complicated than this as well since there can be, and there often is, mistakes in the measuring method also. Just ask Ron Sauro of NWA labs.

I agree it is complicated in real world application. But the principles are pretty easy to understand

 

[Duke]

Bass traps reduce RT substantially in the bass regions.

You can EQ a bass peak in the frequency domain but it still rings in the time domain.

I never said that (adequate) bass traps don't reduce RT substantially in the bass region. I said that a distributed multi-sub system has a greater effect on the in-room frequency response, and that the in-room frequency response is perceptually dominant in the subwoofer region.

It is true that an EQ'd peak still rings, but not for as long.

When the ringing associated with a peak starts out at a significantly reduced SPL, whether due to EQ or multisubs, it takes correspondingly LESS TIME for the ringing to decay into inaudibility. The rate of decay is not changed by these two techniques. Sufficient bass trapping can substantially increase the rate of decay.

As I mentioned previously, the ideal would be to combine all three techniques, if feasible.

 

[Justdafactsmaam]

I never said that (adequate) bass traps don't reduce RT substantially in the bass region. I said that a distributed multi-sub system has a greater effect on the in-room frequency response, and that the in-room frequency response is perceptually dominant in the subwoofer region.

What you said that I was responding to was “My understanding is that Toole and Geddes also focus on the in-room frequency response in small rooms, which do not have true reverberant fields.”

I offered no mention of the relative importance of the two.

Dr. Toole seems to advocate that all one has to do is fix the problem in the frequency domain and the problem will disappear in the time domain. I think HE is wrong about that and I think the measurements support my position

It is true that an EQ'd peak still rings, but not for as long.

Of course not. Nothing that is lower in level will ring as long. But it will ring as long relative to the reduced level. EQ does nothing to fix the bass reverb.

When the ringing associated with a peak starts out at a significantly reduced SPL, whether due to EQ or multisubs, it takes correspondingly LESS TIME for the ringing to decay into inaudibility.

Yes, but if it is a room mode the ringing will be extended accordingly. Again measurements show this. The peaks caused by room modes will still ring longer than the rest of the other frequencies even when the peak is flattened out.

The rate of decay is not changed by these two techniques. Sufficient bass trapping can substantially increase the rate of decay.

Exactly! Which was all I was trying to say. You can’t fix time domain issues with EQ

As I mentioned previously, the ideal would be to combine all three techniques, if feasible.

Whatever it takes!


Attacking bass reverb with room treatments isn’t easy. I know that first hand. But it fixes aspects of the reverb that nothing else other than active cancellation can fix. A lot of folks here take Dr. Toole’s claims that you can fix it all in the frequency domain as gospel and dismiss the value of bass trapping.

Not putting that on you. You just happened to be the one who brought up Dr. Toole’s opinions on the subject.

 

[Keith_W]

Also, my understanding is that Toole and Geddes both consider speakers + rooms to be "minimum phase systems" at low frequencies, and this implies that the frequency response and the time-domain response track one another. So when we improve the time-domain behavior (by reducing ringing via bass trapping) we simultaneously improve the frequency response; and when we improve the frequency response (via multiple subs and/or EQ) we simultaneously improve the time-domain behavior. Ime in practice the correlation between the frequency response and the time domain in the bass region is not perfect.

At low frequencies, rooms are mostly minimum phase systems. Toole advocates against trying to fill in dips in the bass response by turning up the volume of the subwoofer if the dip is caused by phase cancellation. The dip is non-minimum phase so it can never be filled. I love the rest of your explanation, nice and clear as always

 

[Bjorn]

Except of course that most of the area below 100 Hz isn't minimum phase in small rooms. You'll generally only find a few frequencies where it is.

But we want to hear what we want to hear don't we.

 

[Paffi]

That

multi-subs don't address the ringing. also subs only cover half the bass

That's wrong and depends on the configuration. I by myself use multiple subs for that.

 

[Paffi]

As I mentioned previously, the ideal would be to combine all three techniques, if feasible.

And that's the way to go!

 

[Bjorn]

Best to combine all three?
If treatment is sufficiently effective there is of course no need for multiple subwoofers or EQ. Would only be a matter of having enough SPL and low distortion and possibly stereo subs if one is into to that.

If we do things correctly from the start, we can achieve a very linear response and great time domain behaviour over the whole bass area plus lower midrange for less then the cost of one single quality subwoofer.

It will not only greatly surpass what can be achieved with multiple subwoofers around listening position but also work everywhere in the room.

While that requires something not everything can do, it's still harder to sell the idea to those can. People are generally draws to items rather then to good ideas. So it's simply a lot easier to sell them 4 subwoofers and a DSP. Despite that the result of this is mediocre compared to what can be achieved for less money.

 

[Paffi]

Best to combine all three?
If treatment is sufficiently effective there is of course no need for multiple subwoofers or EQ. Would only be a matter of having enough SPL and low distortion and possibly stereo subs if one is into to that.

If we do things correctly from the start, we can achieve a very linear response and great time domain behaviour over the whole bass area plus lower midrange for less then the cost of one single quality subwoofer.

ok, than let's talk about facts: what do you mean specific with "less the cost of one single quality subwoofer?" Which price range are you talking about (number)?

So when you don't agree with the approach of combining all three methods together (in my opinion it's the holy grail, because using just one method always has compromises):

- you prefer listening to a perfectly linear frequency response (or whatever your system outputs) instead of adjusting it to human hearing (e.g. harman or toole housecurve) via eq
- you are using nearfield setups or monster speakers for greater listening distance
- you are using dedicated rooms stuffed full of basstraps and absorbers

Really, I don't get why many people only see black and white.

 

[Bjorn]

ok, than let's talk about facts: what do you mean specific with "less the cost of one single quality subwoofer?" Which price range are you talking about (number)?

So when you don't agree with the approach of combining all three methods together (in my opinion it's the holy grail, because using just one method always has compromises):

- you prefer listening to a perfectly linear frequency response (or whatever your system outputs) instead of adjusting it to human hearing (e.g. harman or toole housecurve) via eq
- you are using nearfield setups or monster speakers for greater listening distance
- you are using dedicated rooms stuffed full of basstraps and absorbers

Really, I don't get why many people only see black and white.

Not much to say is there when you bring up strawman arguments or give me opinions I don't have. Nor is your description anywhere correct.

You haven't grasped what's being discussed. Better to ask questions instead of judging incorrectly.

 

[Paffi]

Not much to say is there when you bring up strawman arguments or give me opinions I don't have. Nor is your description anywhere correct.

You haven't grasped what's being discussed. Better to ask questions instead of judging incorrectly.

ok, then lets forget everything else and just concentrate on this question, which refers to your previous statement. I´m sure as an dealer of room acoustic products, you can provide us with reliable numbers:

what do you mean specific with "less the cost of one single quality subwoofer?" Which price range are you talking about (number)?

 

[dasdoing]

Low-frequency room resonances also behave as minimum-phase phenomena so attenuating the bump, attenuates the ringing.

graphs, e.g. OP's in post 25, clearly show that this is not the case.

evidence indicates that human listeners respond mainly to the spectral bump, not the ringing.

It is true, you can't hear it.
BUT once you heard a room without typical ringing you hear a massive difference. You then can't unhear it in typical rooms. I guess this is kind of a case of red pill vs blue pill