Paul Hales on room equalization on Soundstage! Network

[audiofooled]

Assuming time alignment accross frequency is the goal DSP can help or hinder. Most DSP focus is on smooth FR which can conflict with time alignment. Similarly distributed subs certainly can help smooth FR but you lose the ability to somewhat recreate the original wave front and even for pure time alignment distributed subs have a small sweet spot compared to semi point source full range speakers. Chasing "slam" is hard and can conflict with other priorities.

Setting aside stereo bass for this discussion, but thinking in terms of energy in vs. energy out, it's not only about pressure. IMO this is where it gets complicated.

This is filtered impulse response where the right channel is inverted and vector sum (average in green and not visible under the sum in yellow for the normalized plot) of the channels not being inverted.

80Hz:

63Hz:

50Hz:

 

[SigbergAudio]

The bass impact is more about the “punch in the chest”, which the overtones and transients have nothing to do with.

The question is if the lack of impact the guy is talking about in the podcast is simply because of the lesser energy happening when the peaks are shaved off, or if it indeed has something to do with the direct sound losing the impact in favor of equalizing the problems with the room acoustics.

I think it is because of the reduction in energy (which is what we do with EQ after all).

As a side note, I often find the opposite to be true: When evening out the bass and reducing it to a proper level, the sense of impact is INCREASED, because the deeper bass no longer overpowers the midbass.

 

[SigbergAudio]

I doubt that long-term resonance has much\exessive impact. Or maybe this is not the right impact))

If I understand you correctly; When we EQ down, we don't only reduce the long term resonance, we reduce the initial level of the sound as well. It's natural that this will feel like less bass / impact because that's exactly what is happening.

How it is experienced depends on how much excessive energy we had to begin with + how much it was reduced + which frequency it was of course.

 

[singular]

I assembled and EQ tuned active system, which works allright in non treated listening room opened to apartment on one side of stereo triangle...compensated.

It is not Brutte Force EQ.
But I think it works quite allright due to a large bed surface in the middle.

You can enjoy music for hours, but after long sessions there is tiny feeling that it is not good enough as it could be if the room is very well treated to about 18dB on all surfaces.
Some of DSP EQ will go out then.

 

[Flaesh]

less bass / impact because that's

It's obvious that the amplitude is higher before the peak is equalized. As I understand it, the resonance amplitude doesn't immediately reach its maximum. The perceived impact\kick\punch can be qualitatively different for this reason.

 

[GL1zdA]

It's obvious that the amplitude is higher before the peak is equalized. As I understand it, the resonance amplitude doesn't immediately reach its maximum. The perceived impact\kick\punch can be qualitatively different for this reason.

The question remians: has this been researched? Can we really hear it or is it one of these unquantifiable things like „microdetail”. I assume it would be hard to ABX test on a real system.

 

[singular]

It's obvious that the amplitude is higher before the peak is equalized. As I understand it, the resonance amplitude doesn't immediately reach its maximum. The perceived impact\kick\punch can be qualitatively different for this reason.

I do not know exactly, but...

To me "belly hearing" is around 400Hz ( somebody please refute ) neccessary for feel of "impact".

Try to put 2 pillows in the front.

It is obvious that feedback ( control ) is neccessary for right feel of impact, however system without feedback can manage feel of impact too.

The non equalized system could be perceived as more rhythmic sometime, with inadequate feeling of impact where it is not natural or recorded - phase shorted.

We all talk about ideal system, but few of us listen to music in ideal treated room 18dB.
From simulations it looks that it is still not ideal room then, and we get phase distortion around 400Hz, but probably the right way for impact feeling - from listening tests.

 

[Flaesh]

The question remians

Yeah. Probably someone has already researched it and it can be researched further.
Extremely sketchy, possibly with mistakes(?). Normalized. Others can seriously simulate something like this:

Even in this obscene pic we can see that the kick is no longer the same .
A flawless test seems like a daunting task. For example, what do with amplitudes for a blind test?

p.s.: Don't forget that there is a simple solution to this problem - just believe that at low frequencies in room we hear sound power only:

 

[kemmler3D]

The question remians: has this been researched? Can we really hear it or is it one of these unquantifiable things like „microdetail”. I assume it would be hard to ABX test on a real system.

I guess it would be hard to test because the change overall should be easily audible but the specific effect, less so.

I suppose you would have to do ABX tests on just short transients, like a few ms long?

I think amplitude would need to be normalized either way.

Or possibly you'd need one of those spatial audio simulator rigs with a sphere of studio monitors around the MLP, so you could eq the direct sound and the room sound separately, in a sense.

I do think it would be an interesting test. On one hand eqing out peaks is not some kind of subtle change. We're talking about multiple 10dB cuts sometimes. It's can make a dramatically audible difference in many rooms. On the other hand I'm not sure whether the impact perceptible just from direct sound is overwhelmed by the room or not, especially in small rooms.

 

[SigbergAudio]

It's obvious that the amplitude is higher before the peak is equalized. As I understand it, the resonance amplitude doesn't immediately reach its maximum. The perceived impact\kick\punch can be qualitatively different for this reason.

I think I need to back up a bit to ensure we are discussing the same thing.

We are discussing whether or not we have less impact post EQ.

Less impact than what exactly? What is the reference?

 

[Flaesh]

whether or not we have less impact post EQ.

My point\question is, is there a perfect kick (impact\punch etc) before equalization?

What is the reference?

Linkwitz proposed using "pings" (tone burst with Hann or similar window) for measurements as they better correlate with ear\brain perception. Situation can be even worse by trying a rectangular window))

Or may be https://www.audiocheck.net/audiotests_matt.php (although the main goal there is articulation)

P.S.: One young man said:

I put a Hertz subwoofer in the car, and when I turned on the music, my nose started bleeding, and the wench started vomiting.

Can we call this experience an impact? But there's no doubt amplitude was significant.

 

[olieb]

What cannot be EQed is the non minimum phase part like the deep dips from boundary reflection cancellation and interference between two standing wave modes. This is very position dependent and a short duration phenomenon. the reflections are also part of the experience of space.

What do you mean by “short duration phenomenon“? “Interference between two standing wave modes“ seems not to belong to this category.

And @pma is correct of course. Consider a speaker that is anechoically perfectly flat. It would emit a delta impulse. Now the room has resonances and we EQ the peaks back to flat (more or less).
What does that mean for the impulse that the speaker emits and that will arrive at the listening position as direct sound? The pulse will have less energy in the frequencies that were attenuated and there will be phase rotation from those filters of course.
The room is not exactly minimum-phase, and this becomes noticeable at certain points.
OTOH, if the reflections start after, say, 10 ms, it makes increasingly less sense to talk of ‘direct sound’ going below 100 Hz (as 10 ms corresponds to just one period). Often enough, reflections start even earlier.

And then there is the spatial aspect. The bijection (FR<->time domain) does not define the wavefront. The pressure could be a result from frontal speakers creating something similar to a plane wave or from speakers around the listening position creating something like an inboun cylindrical front or a combination (subs in the room + mid bass in front).

However, what kind of difference does all this make for our hearing? For the bodily perception of a kick drum?
In other words, which part of the spectrum is responsible for hearing/feeling of the impact? And how will this impact perception be changed by some phase rotation in LF? [A kick drum is rather broad band, so the reduced energy from narrow filters might be not so important, as this is exactly at those frequencies where the room tends to convey exaggerated energy.]

But that’s not maths; it’s psychoacoustics - or maybe mechanics, as the chest 'impact' might be a result of exciting the resonance of the chest wall. [In which case the “chest punch“ will take some time to develop as it is coupled to a resonance, too]

So: it's complicated as soon as you delve into specifics like “Perceptual Effects Resulting from the Electronic Attenuation of Low-Frequency Room Modes During the Two Channel Stereophonic Playback of Well-Recorded Kick Drum Beats in Small Listening Rooms through Loudspeakers with Different Arrangements of Subwoofers.”
The simple solution was mentioned above: In LF we tend to hear mostly steady state sound power.

 

[SigbergAudio]

My point\question is, is there a perfect kick (impact\punch etc) before equalization?

It at least isn't perfect in every sense of the word, since it has too much energy (as identified by the peak we wish to equalize).

What could be theoretically interesting is to compare the equalized result compared to fixing the peak with acoustic treatment. But it wouldn't be realistic to do a blind test of something like that, so then we're left with measuring the alternatives. And then again we are mostly speculating about the audible differences.

So it feels like a slightly academic question.

But if I should just speculate from a practical perspective: A kick drum (to use that as an example) is a very broadband sound. Due to interactions with the room, it is currently not represented correctly, let's say we have a peak at 50hz. With EQ we are simply reducing the amplitude of a very narrow part of the broadband sound that is the kickdrum down to a more appropriate level (closer to the source material).

It feels like that should be an improvement, and that we are making it closer to perfect that the pre-equalized sound. At least in the context of what can be reproduced in that room. And that is also what practical experience tells us.

 

[levimax]

IMO this is where it gets complicated.


80Hz:

View attachment 555805

63Hz:

View attachment 555806

50Hz:

View attachment 555807

This is so complicated I am not sure what I am looking at and what is may mean Can you explain, thank you.

 

[Flaesh]

What could be theoretically interesting is to compare the equalized result compared to fixing the peak with acoustic treatment.

I did this a long time ago and for a short time, using one uninformed expert. The "test" was very brief, and the expert said, "Please, do it the way it was*!!"

* - DBA. This is that rare case where an effective low-frequency absorber covering the entire rear wall can be turned off with a button.

 

[levimax]

I did this a long time ago and for a short time, using one uninformed expert. The "test" was very brief, and the expert said, "Please, do it the way it was*!!"

* - DBA.

I see DBA as more similar to room treatments than it is to using DSP amplitude EQ. Both room treatments and DBA eliminate the standing wave by either absorbing or canceling it at the back wall instead of just attenuating the amplitude of the standing wave at the LP. How do you see it?

 

[Lars Risbo]

DSP can eliminate a standing wave by adding a zero smack on top of the mode pole. room treatment is very ineffective below 100Hz. DBA is a simple version of a speaker array. with proper DSP processing you can eliminate N-1 modes using N speakers.

 

[levimax]

room treatment is very ineffective below 100Hz.

How about large tuned Helmholtz resonators in the corners? I have never tried them but I see reports of ~12 dB or more attenuation being achieved. Is that really possible? If so how would you compare this to a DBA or amplitude DSP?

 

[kemmler3D]

How about large tuned Helmholtz resonators in the corners? I have never tried them but I see reports of ~12 dB or more attenuation being achieved. Is that really possible? If so how would you compare this to a DBA or amplitude DSP?

Definitely possible but not always practical as traditional designs for resonators need them to be big.

However, I think "metamaterial" style resonators (with folded necks) can be made physically smaller, tradeoff being you need more of them.

I think a practical way to approach this is whether you can absorb more bass per square foot of room or per dollar with resonators or extra subs. Subs have a big advantage because they can work at multiple frequencies, resonators do one each.

 

[Cbdb2]

Consider a speaker that is anechoically perfectly flat. It would emit a delta impulse.

Only if it had infinite BW and I believe minimum phase.
Heres a quick easy test. Take a kick drum sample with lots of "slam" and EQ down 10db everything under 100hz for the first 6ms. Listen with headphones, does it sound different?