Wanted: Proof of multiple subs and sub EQ

[h.g.]

I’m not aware that anyone has ever claimed that multiple subs reduce ringing. Can you or someone point me to that?

​

​

See my replies and link in this thread.

 

[NorthSky]

Each room must have some resonances @ some frequencies no?
Using a frequency sound generator, and say from 10Hz to 300Hz in o.5Hz increments, there will be a frequency where the room vibrates in unison with the frequency generator, no? Yes. And it'll make the glasses, the windows, the paintings on the walls, the doors, the walls all dancing @ that specific frequency of that particular room. I did not read that, I've heard it, from some music recordings with strong bass content. ...Tracy Chapman's first album...Mountain o' Things.
A subwoofer is a room exciter, multiple subs have the advantage of balancing the energy with less resonances; I've heard it too, with three subs instead of one.

If you play a mono recording through a mono speaker, with 20Hz content and anywhere from there up higher, can that mono speaker (with good bass reproduction in the low 20s) have more resonances with the room (untreated) than a pair of stereo loudspeakers (also with good bass reproduction in the low 20s)?

I don't know too many people who have a mono hi-fi sound system setup. ...The imaging must be the best, in the center.
I'm just theorizing. And I don't think that a mono center channel speaker can disperse the sound to its left and right, unless DSP sound manipulation.
But the point is with a mono (single) sub versus stereo, or quad (multiple) subs.

Modal ringing = Frequency resonance from the subwoofer and room @ which the room vibrates @ that specific low frequency.
My own wording...and that frequency can vary by few hertz in different rooms, or more.

It's just a post in an audio science forum discussion where we're here to learn? You betcha.
__________

 

[Ethan Winer]

Is that an assumption on your part because they show different things or do you know how they are measured differently?

Room measuring software sweeps a sine wave and records that through your speakers, then it processes the sweep into the equivalent of an "impulse" sound source like a gun shot or balloon pop. Once it has the impulse it can display many types of data: frequency response, modal ringing, individual reflections, and more.

I was asking if you had observed a correlation between the type of person/publication that tends to use waterfall plots and those that don't. It looks like the answer is probably no.

That question (and your answer) makes no sense. Which type of graph someone uses to make a point in a technical article depends on what they're trying to show.

As mentioned earlier, unless we know what "modal ringing" means to you it will involve guesswork. I have already guessed once and got it wrong by referring to graphs that would have answered your questions for many.

You're really losing me here. I can't tell if you're being sarcastic, confrontational, or genuinely want to know what modal ringing is. Assuming the best, modal ringing is the propensity to continue a sound (not unlike reverb) after it stops, but only at frequencies related to the dimensions of a room. In practical terms small rooms have modal ringing, very large rooms have reverb.

--Ethan

 

[Ethan Winer]

http://www.acousticfrontiers.com/20...ow-to-use-parametric-eq-to-flatten-your-html/

Yes, Nyal Mellor claims that multiple subs and EQ both reduce decay times by a useful amount around the room. I can believe it for EQ at one location at very low frequencies, even though my own tests showed barely any reduction in ringing. Nyal promised to send me an REW data file "when he gets a chance" and that's all I'm waiting for to complete my Bass Traps Myths article. I want to be as fair as possible to multiple subs and EQ proponents, so if anyone can prove the point it's Nyal. I can't for the life of me imagine that either can reduce ringing even half as much as a bunch of bass traps! But I'm willing to be convinced if Nyal or someone else shows me hard proof. But it has to be at multiple locations.

--Ethan

 

[amirm]

Ethan, the question of multi-subs cannot be asked outside of EQ. The ideal configuration of multiple subs is one that gets rid of nulls but allows the peaks actually get worse! That is fine because we can then use EQ to pull those down and have our smooth response. And that response by definition results in less ringing because we do not have excess energy anymore at those frequencies.

Now, there are methods where we can use multiple subs to also smooth out the peaks as I linked to earlier but in the simpler context you are asking, the above is the answer.

 

[h.g.]

Room measuring software sweeps a sine wave and records that through your speakers, then it processes the sweep into the equivalent of an "impulse" sound source like a gun shot or balloon pop. Once it has the impulse it can display many types of data: frequency response, modal ringing, individual reflections, and more.

If we have the frequency response (with phase) can we work out the impulse response? If so, what does that tell you about the relationship between the frequency response (with phase) and the other plots derived from the impulse response? Do you perhaps want to revise what types of plot contain the information you seek?

That question (and your answer) makes no sense. Which type of graph someone uses to make a point in a technical article depends on what they're trying to show.

It may make no sense to you but I think you will find it makes sense to those that have learnt the basics about how linear systems respond and are familiar with how they tend to be discussed.

You're really losing me here. I can't tell if you're being sarcastic, confrontational, or genuinely want to know what modal ringing is. Assuming the best, modal ringing is the propensity to continue a sound (not unlike reverb) after it stops, but only at frequencies related to the dimensions of a room. In practical terms small rooms have modal ringing, very large rooms have reverb.

I want to know what "modal ringing" means to you. It is not an expression people with a technical background would tend to use because it seems to combine two separate things in a somewhat vague manner. I am asking because I am interested in how you as an "audiophile objectivist" see and reason about things. Your answer is interesting, thank you, and of a similar type to the answers given by Amir when I was asking him the same sort of thing.

 

[h.g.]

I can't for the life of me imagine that either can reduce ringing even half as much as a bunch of bass traps!

Why not? You must have some familiarity with active noise cancellation and how effective it is at low frequencies. Passive devices at low frequencies are rarely viable because of the size.

The physics is simple and works just like timing the pushing or pulling of a child on a swing to slow them down rather than speed them up. When the subwoofer is surrounded by positive pressure it moves inwards to reduce the sound and when surrounded by negative pressure it moves outwards to boost it. From school physics recall that work is the product of force and the distance moved in the direction of the force and so by moving in the opposite direction of the force work is extracted. It removes the energy in the sound far more effectively at low frequencies than squeezing the relatively slow moving air through small spaces to use the product of viscosity and velocity gradients to dissipate the work as heat. Note the velocity gradients are relatively small at low frequencies.

 

[NorthSky]

1. Two subs, on top of each other @ the same location...I'll look into that...if it can reduce modal ringing, ans also improve frequency response...better linearity.
2. Two, three, four or more subs are in themselves some type of EQ (without actual EQ), as they help to smooth the low frequencies by cancelling some nuls and peaks. ...By judicious positioning @ different locations. And, I also believe that without EQ they can diminish/reduce the room's main resonance (modal ringing).
3. With EQ like from Dirac Live, Audyssey, ARC, etc. included in a receiver or/and pre/pro or a separate EQ box, or even with a parametric EQ integrated in the sub...they all further improve the overall performance...including modal ringing...indispensable in my opinion.
4. The phase is very important, with one or multiple subs. ...It's an EQ too, to the room and between speakers, subs and listener's ears.
5. The sub's low pass filter...another important aspect in the phase, interaction, by its own function of its slope and exact frequency point. The crossover between the sub(s) and main speakers. ...Even more important in a stereo system setup, for the highest fidelity and blending.

Those are just my best assumptions; not from measurements but from listening and readings.
Yes, folks like Nyal and Wayne and Richard 'Dick' Hardesty (RIP) are among my readings in regard to a single sub versus multiple. Richard was like a mentor in my learning apprentissage from his various writings. ...Doctor Boom. And the doc was using five subs in his home theater setup. But only one large sub (Energy 18") was reproducing the .1 LFE channel (behind his couch). The other four subs (all Vandersteen, and so all his main speakers) were one for each main channel (FL, FR, SR and SL), and none for the center channel speaker. I'll have to look again if he was redirecting the bass from his center speaker (he had too because it was a smallish speaker - I think it was distributed between the FL and FR speakers, then to their respective subs, not sure).

I have several articles of him from when he was a reviewer and writer for Widescreen Review.
When I have the chance I'll look @ his article on multiple subs; their several advantages, to see if resonance reduction is also one of them. I was a subscriber for many many years and I kept those reference articles from my WR mags.

http://www.theabsolutesound.com/articles/richard-dick-hardesty-19442014/

Ethan, you have one sub or two; if only one get a second one.

 

[Ethan Winer]

Ethan, the question of multi-subs cannot be asked outside of EQ.

Sure it can! Either multiple subs can reduce ringing, or only seem to because they lower the level of peaks. Likewise, either EQ can reduce ringing because "minimum phase" or it can't. And by "reduce ringing" I mean at more than one location, for every seat in the house. And if ringing is reduced around the room, by how much is it reduced? These are questions I have been asking for for years but never gotten satisfactory answers. Hopefully Nyal Mellor's REW data will settle this.

we can then use EQ to pull those [peaks] down and have our smooth response. And that response by definition results in less ringing because we do not have excess energy anymore at those frequencies.

Simply lowering the level of peaks does not change the rate of decay, which is what I mean when I say "ringing."

I recall you showed some waterfalls where EQ reduce ringing decay times. But unless I missed something, I didn't see waterfalls for anywhere other than the one place the microphone was placed when the EQ was calibrated.

--Ethan

 

[NorthSky]

I also want to learn more from Nyal. I'll PM him and give him this thread's link.

 

[Ethan Winer]

If we have the frequency response (with phase) can we work out the impulse response?

I'm not a math guy so I don't know the specific details of the convolution process. I do know that modern room measuring software sweeps a sine wave, then processes that into an equivalent impulse. Then from the impulse all graph types are derived. Are you asking me how this works because you don't know and want to learn?

I want to know what "modal ringing" means to you. It is not an expression people with a technical background would tend to use

Modal ringing is absolutely an established technical term. Google reports "About 236,000 results" though many are references to me. But not all are. These guys are all professionals:

http://www.sengpielaudio.com/calculator-roommodes.htm
http://www.weslachot.com/new/articles_scales_content.html
http://www.acousticfrontiers.com/20...ow-to-use-parametric-eq-to-flatten-your-html/
https://www.soundonsound.com/sos/apr09/articles/studiosos_0409.htm

I probably first heard the term from my friend, high-end studio designer Wes Lachot, one of the links above.

--Ethan

 

[Ethan Winer]

You must have some familiarity with active noise cancellation and how effective it is at low frequencies.

Noise cancellation deals with attenuation of level, not a reduction in decay times which is what I'm asking about.

--Ethan

 

[h.g.]

I'm not a math guy so I don't know the specific details of the convolution process. I do know that modern room measuring software sweeps a sine wave, then processes that into an equivalent impulse. Then from the impulse all graph types are derived. Are you asking me how this works because you don't know and want to learn?

I am asking in order to help work out what you do and do not understand and how you reason about things. This question was asked to determine if you knew that the impulse response can be calculated from the frequency response (with phase) and vice-versa. If you knew that (which you didn't) then you would know they are the same thing. This explains how you can be lead to think things that are the same are different but I still don't know why you plump for "they are different" rather than "don't know" or "they are the same".

Modal ringing is absolutely an established technical term.

But you are not familiar with the technical side, do not understand it and do not want to understand it. As you explained in your first reply you want the answer, a plot, but not the scientific reasoning. You have ignored the school level physics and told me you do not understand the maths even at the level of a frequency and impulse response. This would not be a problem if you recognized that scientific knowledge exists, you don't know it and need to be cautious around it. Yet you go about get things wrong with the confidence of a subjective audiophile and, I suspect, for some of the same reasons.

Simply lowering the level of peaks does not change the rate of decay, which is what I mean when I say "ringing."

For example, what supports this? Is it perhaps obvious without requiring any supporting reasoning?

I would like to add that I am genuinely interested in how you and Amir see things. It hadn't occurred to me until I posted here and looked at a couple of Amir's posts and saw your two questions that people would be interested in scientific answers to the extent that both you and Amir clearly are but without being interested in the science itself. It's weird but then so is the whole of the audiophile world.

 

[amirm]

I would like to add that I am genuinely interested in how you and Amir see things. It hadn't occurred to me until I posted here and looked at a couple of Amir's posts and saw your two questions that people would be interested in scientific answers to the extent that both you and Amir clearly are but without being interested in the science itself. It's weird but then so is the whole of the audiophile world.

I see your comment weird in that no matter how much explanation of science is given, you still think it is some audiophile rendition than the science itself. So why don't you explain what the science is that you think we are missing? Would appreciate proper references to back what you are going to say.

Given how many times HG has made this comment, I am going to ask others to withhold any other comments until we see his explanation of science.

 

[h.g.]

So why don't you explain what the science is that you think we are missing? Would appreciate proper references to back what you are going to say.

We were all taught what science is at school and it can be looked up easily enough on the web. Here is the opening sentence from Wikipedia:

Science is a systematic enterprise that creates, builds and organizes knowledge in the form of testable explanations and predictions about the universe.

Not always a reliable source but it will do in this case. Note the explanations and predictions.

Given how many times HG has made this comment, I am going to ask others to withhold any other comments until we see his explanation of science.

I take this to mean I have over stayed my welcome. Fair enough it is your forum and your rules.

 

[amirm]

We were all taught what science is at school and it can be looked up easily enough on the web. Here is the opening sentence from Wikipedia:

Science is a systematic enterprise that creates, builds and organizes knowledge in the form of testable explanations and predictions about the universe.

Not always a reliable source but it will do in this case. Note the explanations and predictions.

Great. Now apply that to the topic and question at hand and provide the answer so that we know what you mean by the word science. As I mentioned, unless you are an acoustic researcher, I like to see references to proper research in whatever you state.

I take this to mean I have over stayed my welcome. Fair enough it is your forum and your rules.

My forum and my rules? What rules? You repeatedly criticized Ethan for not knowing the acoustic science involved in this topic. And threw the same rocks at me. I am giving you the full stage to school us on how it should be done according to your point of view of science. If you can't or unable to do so then I like to understand the motivation for the harsh criticism you have put forward.

 

[Don Hills]

Noise cancellation deals with attenuation of level, not a reduction in decay times which is what I'm asking about.

--Ethan

I believe I understand your point:
- A "modal resonance" has a particular decay time determined by the losses in the room.
- Room treatment can increase the losses, thus shortening the decay time.
- The treatment will also reduce the amplitude of the resonance during the time it is being excited by the source.

- Applying an inverse transform of the "modal resonance" to the signal fed to the exciting source will again reduce the amplitude of the resonance during the time it is being excited by the source. For a simplistic example, a 10 dB peak in the room response might be dealt with by reducing the source output by 10 dB at that frequency.

I believe we agree so far. The fun comes when we get to what happens when the excitation ends. The "modal resonance" will decay. Your argument is that the resonance decays faster with increased room losses, but is unchanged with the "inverse transform" method. I believe you are only looking at half of the system. The "inverse transform" of the resonance being produced by the exciting source does not stop when the source does. It decays at the same rate as the "modal resonance", so its "cancelling" effect continues.

On your other assertion, that room treatment is more effective over a range of room locations than "active cancellation", I partially agree. No modification of the exciting source signal can remove a deep null, for example. Doing so without room treatment requires intelligent physical placement of multiple sources as well as DSP techniques.

 

[dallasjustice]

Ethan,
Is there a proposition hidden somewhere in your obtuse rhetoric? For example, is it your position that multiple subs can be used to reduce/cancel SPL level but cannot be used to reduce modes?

Michael.

Noise cancellation deals with attenuation of level, not a reduction in decay times which is what I'm asking about.

--Ethan

 

[Ethan Winer]

I like to understand the motivation for the harsh criticism you have put forward.

Me too. As best I can tell it's about dick size, or lack thereof. I'll never understand why some people need to elevate themselves by putting others down. I've been as clear and articulate as possible in asking for evidence of reduced modal ringing all around a room, but apparently that's not good enough for some people. Unbelievable. Why is this question even offensive to some?

(LOL that p-e-n-i-s is censored and replaced with *****. I hope I'm not being more offensive than is warranted. )

 

[Thomas savage]

Me too. As best I can tell it's about dick size, or lack thereof. I'll never understand why some people need to elevate themselves by putting others down. I've been as clear and articulate as possible in asking for evidence of reduced modal ringing all around a room, but apparently that's not good enough for some people. Unbelievable. Why is this question even offensive to some?

(LOL that p-e-n-i-s is censored and replaced with *****. I hope I'm not being more offensive than is warranted. )

It's ok Ethan but now you have to provide measurements and photos , subjectivist comments from the wife don't count.. This is a science forum!