Acoustic Weirdness..

[Ethan Winer]

Gene,

Also:

You deserve to be made aware of your obvious biases and agenda to promote the only solution you know which you incidentally sell on your website.

I'm really not here to fight or to sell products. As we both know, there's a lot of snake oil out there, and just as much sincere but wrong information. My only "agenda" is to discuss the science of audio and try to separate truth from fiction for the benefit of all. Am I hopelessly naive? Could be! But I persist anyway because getting to the truth is so important.

[edit:] Also, I apologize if I come off as combative, or as an insufferable know-it-all (mea culpa), or as a shill for my company. That is not my intent.

Thanks.

--Ethan

 

[krabapple]

It just came out this year:
Loudspeakers and Rooms for Sound Reproduction—A Scientific Review by Floyd E. Toole, J. Audio Eng. Soc., Vol. 54, No. 6, 2006 June, pp. 451-476

This one from the same (next-to-last) issue looks interesting too

Evaluation of Sound Quality, Boominess, and Boxiness in Small Rooms
Adam Weisser and Jens Holger Rindel 495
Subjective listening tests were conducted in seven small rooms to investigate those physical attributes that correspond to the perception of boominess and boxiness. Three new acoustic metrics-small room bass ratio, small room early decay time ratio, and low-high ratio-proved to be better predictors of sound quality than conventional measures. However, the type of audio, namely music or speech, influenced preference and quality judgments. Speech was best in rooms with weak reverberation, whereas a preferred range of reverberation was found for music.


And this from the May issue

Low-Frequency Optimization Using Multiple Subwoofers
Todd Welti and Allan Devantier 347
The acoustic environment of a sound system has a strong influence on the sound quality at low frequencies, especially in small spaces. As a result there is an interest in solutions that improve the performance. While conventional approaches tend to focus on signal processing, the proposed solution introduces the location of subwoofers as the major variable, with the addition of minimal signal processing. Using a metric that optimizes performance in multiple seats, a robust solution becomes available.


http://www.aes.org/journal/toc/

 

[krabapple]

Forgive me if this hasn't been asked, but where can I download this PDF document of Dr Tooles ?

Thanks.

--Sincerely,

As it is from a recent issue, I expect you eventually will be able to purchase it from the JAES website, like other JAES articles. For now you'll have to find it in your local university/engineering school library.

 

[Savant]

This one from the same (next-to-last) issue looks interesting too

The other two papers you listed are also well worth reading. Welti works with Toole. And research like that being conducted by Weisser and Rindel is truly fascinating.

 

[Savant]

It has been proposed that EQ can reduce ringing. In my experience it cannot. To back up my claim I have posted graphs showing the RESULTS of a professional consultant attempting to do exactly this and failing. So I don't see why it's unreasonable for me to ask for proof that EQ can reduce ringing in practice, by a meaningful amount, and over a useful physical area. For all the research and theoretical technical papers out there, you'd think somebody would have performed the simple tests I am asking to see!

Perhaps we should all let the topic rest? You have been provided with references to papers discussing the research that has been done on the topic of active correction. Your reciprocative sharing of the findings of others on this topic is commendable. Now, instead of jumping to conclusions about the work others have done (which you have not read and reviewed), having others provide you with "graphs" (as if that would "prove" anything - I have yet to see a graph truly "prove" anything), and generally contributing to the hostility over something quite insignificant in the grand scheme of things...why don't we just forget about it? If there's anything I've learned over the years, it's that no one can force feed you, Ethan. You've got your mind made up on this and that's just the way it is. Fine. We get it and that's AOK.

Gene, I think we should let this one go - it is clear that we are not able to provide the proof Ethan requires. Therefore, there's not much use in and nothing to be gained from continued back-and-forth.

Of course, it should be noted that no one here is really saying you're wrong, Ethan—just under-informed, perhaps? There are plenty of folks that feel just as you do about active correction. And, in fact, for many situations I share those exact feelings and opinions.

However, let's just let this one rest, agree to disagree, and move on.

> This reminds me of the issues we had years ago with Jon Risch on exotic cables <

Are you really suggesting that bass traps and acoustic treatment are in the same snake oil category as exotic cables?

I don't think that is what Gene's suggesting. I believe he was simply making a comparison between your strong convictions, and those of someone else - a comparison that Audioholics readers can relate to.

I don't see why "how we hear" bass should be glossed over with averaging.

I think there is some miscommunication going on here. Again - perhaps we should let it rest since we are not all on the same page. A 1/12th octave display is, arguably, more representative of how bass is heard. Nothing is being glossed over.

If a null that aligns with the frequency of a bass note really is 25 dB deep, then that's exactly how far down it will sound when that note is played.

Very few listeners would be able to listen to anything and say, "Oh, that's 25 dB down." Also, 25 dB down from what, exactly? From a peak 10 Hz lower? Hardly a valid reference point. Finally, how a null is perceived cannot be fully understood unless the nature of the problem - modal, boundary-interference, loudspeaker, other? - is understood. And even then, it's still being perceived, it is a subjective "thing," and it cannot be equated "exactly" to something objective like a difference in sound level.

In short, I would - for the third time - request a break from all this. People are starting to say (with all due respect) some pretty silly things here and it's not going to do anyone any good.

That's a difference of 11 dB over a distance of only four inches. And yes, I was surprised too, so I measured both places again just to be sure it wasn't a glitch. It was not a glitch.

Perhaps you should ask yourself why you were surprised...

> Check out Robinson and Dadison curves which well establish this point. <

This is why I'm such a strong proponent of empirical evidence rather than relying on theory alone. Since I have proven (above) beyond all doubt that the low frequency response can change substantially over very small spans, it's clear the theory needs to be modified.

The Robinson-Dadson curves are the results of experiments. They are not "theory." Check out Figure 2.1 (pp. 13) of Newell's book (Recording Studio Design). Since Newell didn't provide them, I'd be happy to provide references if you need 'em.

Also, no one is arguing against low frequency response being position dependent. Rayleigh understood this over 100 years ago and it's his math that is used (in most acoustics texts that cover the subject) to derive the equations governing the spatial response of a room. There is no "theory" that says otherwise.

 

[gene]

In many cases, addressing the amplitude (frequency) domain issues does indeed have a positive benefit on the time domain response. Otherwise, bass traps wouldn't work at all. However, modal problems can be non-minimum phase. I.e., they are not consistent in the the amplitude domain when measured spatially in the room. Therefore, they are not consistent in the time domain either. This means active controls are less effective - the eloquent "one cubic inch" issue brought forth above.

Room modes that are much larger in amplitude than room noise behave in a minimum phase manner. The more it is attenuated or corrected in amplitude, the less problematic and inaudible they become. Again the one cubic inch argument has little relevance at low frequencies as bass doesn’t drastically change (at least within our audible capabilities) between the distance of our ears at a fixed seated position.

Gene, I think we should let this one go - it is clear that we are not able to provide the proof Ethan requires. Therefore, there's not much use in and nothing to be gained from continued back-and-forth.

Agreed as I have bigger fish to fry. We will be publishing several articles shortly on the benefits of active room correction and multiple subwoofer integration with spatially average measurements. You will be amazed at how linear the bass response is in my reference room with almost no passive treatments in effect below 100Hz. I of course cannot wait till my Auralex bass traps show up so I can further fine tune my room response.