Do bass traps produce noticeable audible difference? - Page 6

since i've quoted Toole a multitude of times and you still won't accept it (who are you to argue against toole) ... let's quote Ted Schultz (of which Toole himself cites repeatedly):




so not only are you attempting to argue against Toole, but you're also going against Ted Schultz (and Leo Berenek, as he also concurred).

and not only that, but you are also attempting to imply there exists a critical-distance (at 3.2ft, mind you!!!) in your home theater! utterly laughable.

if only as much time and energy were spent on actually learning acoustics as is spent on googling and copy-pasting out of context word searches in some frantic and desperate attempt to find contradictions.


what do you think, amir ... is Ethan's use of RT60 in a 37.75 by 22.5 by 14.5 inch box acceptable use?
http://www.realtraps.com/art_surfaces.htm

and it's any wonder then, while in attempt to determine whether RTxx would be acceptable use in his garage, that i have repeatedly asked Ethan to provide clarity on whether a critical-distance exists in his garage - of which he has blatantly ignored any such response to me. the silence is deafening. maybe we should go through his published book to determine how and when he uses RT60, for clarity.
Edited by localhost127 - 3/7/13 at 6:11am

conclusion? you have yet to respond or even answer any questions presented to you in an attempt to clarify your statements. all of your commentary has been with regards to "sounding like" reverb.
you do not seem particularly interested in whether it is a reverb-field ..


are you attempting to imply that because long decay times that "sound like reverb" exist in a small space, that such energy flows are actually reverb?

and i'm glad throughout this conversation you specifically ask us to "ignore official definitions"...

I contacted Greg offline and he kindly provided some additional detail on the dimensions of the room and specifics of the material on the surfaces. I thought it would be a useful exercise to walk through the math and science we have discussed and see what that gets us.

Recall the Sabine formula: RT60 = K * V / Sa. Let's see if we can compute RT60 using this and compare it to the actual measurement posted by Greg. V = 785 for Greg's room. K is 0.049 for Imperial system (feet). Sa is the surface area times the absorption coefficient(alpha). In the case of Greg's room, he used dissimilar material so we have more than one alpha. There is an easy solution for that. We can simply multiple the surface area for each type by its corresponding alpha and then sum them up all up. That gets us the total Sa which we can then use in this formula.

Turns out Greg's room is not a simple rectangle. So I had to do some rough estimation of actual surface areas. The right numbers are probably somewhat different than these but I think they are close enough to run with them. He has three types of material in the room:

1. Carpet on the floor. Coefficient of absorption for household items is hard to come by but we have some data that points to it being around 0.5 at 500 Hz, our frequency of interest for RT60.

2. Linacoustic. Greg used 1 inch thickness which the manufacturer shows to have 0.6 absorption coefficient at 500 Hz.

3. Bass Traps he built. I don't have an exact number for this but the material is thick enough that I used 1.0 for 500 Hz (i.e. total absorption).

Now let's multiple the surface area times the above alpha coefficient for each part of his room:

Front Wall 33.6
Back Wall 39.9
Left and Right Walls 67.2
Floor 56.25
Ceiling 48
Traps 16
Soffit 12.6

Total = 273 Sabines

Putting that in the sabine formula, we get an RT60 at 500 Hz of 0.14. Eyeballing the actual measurement above, I see values in the 0.11 to 0.12 in the graph at mid-frequencies. We see that this 120 year old formula is proving remarkably accurate! It certainly good enough to tell us if our room is on the dead side (at or below 0.2) or live side (> 0.5). The fact that Greg thinks his room is dead provides additional validity to the computation and measurements confirming the same.

As I noted and quoted Dr. Toole, for the purposes of estimating how much absorption we need to have in a room before building it, the formula can be quite useful. It is also useful for Greg to look at the above break down and decide how much impact each can have if he shrunk their amounts. The actual difference there may be more in error because the room is highly dead right now but is enough to make some reasonable decisions. For example we can see that the traps are not contributing much due to their much smaller surface area.

Useless/Meaningless data? I think not .

Ethan's 37.75" by 22.5" by 14.5" empty, glass-lined box has an RT60 of approximately 0.3, which according to you is just about right, or perhaps slightly on the dead side. Is Ethan's RT60 measurement providing useful information?

yep: mickey mouse acoustics. but what more do we expect from the salesman in this thread who:

0) learns of a new term or name and becomes an over-night expert via google searches, and comes back here to provide us with book-reports and "history lessons" in an attempt to appear knowledgeable.
1) confuses Schroeder/Davis transition frequency with Schroeder Large Room frequency (!!!)
2) confuses (interchangeably uses the terms) echo and reverb --- of which are logical contradictions of each other (!!!)
3) ignores the use of an omni-directional source of which is required for RTxx to be considered valid (see quote from Schultz as well as from Toole himself) .. yet then claims "Therefore we have met the conditions of reverberant space even though our speaker was not omni-directional." (!!!)
4) implies they have critical-distance in their home theater (!!!)
5) preaches that "references to Schroeder and conditions for reverberant field are inappropriate in this context." ... then turns around and does the opposite.
6) unable to demonstrate further and expand for us just what these "conditions for reverberant field" are - and resorts to quoting dragonfyr (!!!)
7) claims that: "The demonstration shows that late reflections can be reduced and that effect shows up in RT60 calculations. Do we care if the relationship is 1:1? No. This is a rough measure with wide latitude of 0.2 to 0.5. We are not after precision." ... and then turns around and preaches about the "accuracy"

but what more do you expect from these "experts" that are clearly only interested in "ball-parking".



isn't it a bit strange that the professionals and self proclaimed acoustical experts here are publically displaying such blatant misunderstandings of even the most fundamental concepts of acoustics? going against Toole, Davis, Schroeder, Beranek, and Russ Berger? we should rename this sub-forum the "ball-parking audio theory and chat".

ah, but enough of doing their homework for them. let's see how deep they can dig their holes.

Thanks for doing the math, Amir. I'm sure the fireworks are being loaded as I type.

I guess I'm a little unclear as to what is being argued in this thread. Is it the validity of the measurements, because that illustration gets pretty close to what I measured. Or is it the range of live to dead? Or both. I am just looking for ways to use different tools to try and make my little theater room perform better.

Apparently what's being argued is who can copy / paste more snippets from books they don't actually own or have read in the shortest amount of time.

--Ethan

Some posters are trying to help someone improve their room. Others are not trying to be helpful. Feel free to choose which discussion you wish to join.
If this proves useful to Greg, the customer's satisfied. You've done the thread a service. Thanks!

HAve fun,
Frank

I appreciate the breakdown and the explanation very much!

And I did find some more info to copy and paste from here (http://blog.acousticfrontiers.com/whats-new/2011/10/13/acoustic-measurement-standards-for-stereo-listening-rooms-pu.html:

This paper seems like a must for anyone interested in measuring and shooting for taget values. There is also an interesting acknolegement at the end of the paper:

Thank you Amirm for the incredibly helpful explanations.

Thank you for your question. Before I answer it, I hope you join me in commending Ethan for taking the time to set up such elaborate fixtures to test the notions posted on the Internet. I always give him kudos for having an inquisitive mind that wants to prove to himself that his understanding of the science is correct.

Back to your question, the breadcrumbs are in this thread to answer that. Let’s review them again as a refresher.

The box, and let’s be clear that it is a small one given those dimension in inches, has very small amount of volume:


By my math it is only 6.5 cubic feet. In one of my earlier posts (http://www.avsforum.com/t/1453370/do-bass-traps-produce-noticeable-audible-difference/90#post_23008908) I talked about the Schroeder transition frequency. This is the frequency below which the modes are too separate making our room response more location specific. For our typical home listening spaces, that frequency is usually in the 200 to 300 Hz region so you almost don’t need to do the math there. This little box however is far smaller than a real room so let’s do the math for it:

Fc = 11885*SQRT(RT60/V); let’s plug 6.5 in there for Volume and stated 0.3 RT60 time. That gives us the Transition Frequency of 2,535 Hz. Alas, the Schroeder’s formula was arrived at empirically (working backwards from measurements) and never tested against such a little box. The way we compensate for that is to instead think of this as somewhere in the middle of a much wider range of frequencies (much like I did in my “200 to 300 Hz” statement above). I don’t have direct data on how wide we need to make it in this small space but I think it is safe to say that the transition region could easily range from 2000 Hz to 3000 Hz. Let’s park this for a moment.

The idea behind a target reverberation time is to balance two needs: 1) speech intelligibility which is important in both movies (dialog) and music (singer) and 2) nice feeling of space we get from room reverberations. These two factors kind of fight against each other to some extent as ideally we like to have both. That is why we have a range specified of 0.2 to 0.5 rather than a single number. This range however is not computed but based on industry's collective experience of what the value should be based on countless in field experiences in home listening spaces. That experience has been formed from typical home spaces, not a small box like this or an auditorium. The latter actually has its own set of recommended RT numbers which are larger than this. There has been no interest in characterizing how good speech sounds in such a little box so hence, there is not a recommended range for it.

Ignoring the above fact for a moment, we can walk through the analysis anyway and see where that gets us. We have an RT60 time of 0.3. Numerically 0.3 is in that range but there is a problem: our transition frequency has shot up by a factor or 10 over a typical room. Recall that I said in the research and industry our target frequency of interest is 500 Hz although that is often stretched to 1K to 2K Hz. One of the reasons for this was the fact that we would be free of the modal issues (large response variations) below transition frequencies of 200 to 300 Hz of our rooms. We immediately see a problem here. We can’t use RT60 @ 500 Hz since a) Ethan did not test that frequency and b) it would be below the transition frequency.

You might be asking why we don’t look at higher frequencies since they would be above transition range for this box and we do have the data for that. That does not work either. Look at the spectrum of speech in this sample spectrogram as the person pronounces “Rice University:”



This is a nice visualization of the problem with speech intelligibility and late reflections. It is clear from the time graph at the bottom that the intensity of speech changes every 0.2 seconds or so in English language (it may be faster or slower in other languages). The larger colorful graph shows the frequency spectrum at any moment and color coding of the energy/strength. Red means very strong, blue means very week. It is pretty clear that the bulk of vocal energy is below 2,000 Hz. It therefore matters not what higher frequencies are doing as they don’t have a lot of energy at the start. Evaluating RT60 times well into Khz region therefore is not material to this analysis. It is like trying to figure out engine idling problems in a car with a tachometer that starts at 2000 RPM.

Fortunately there are no applications for dollhouse sized home theaters or listening spaces so there will be no riots in the streets that we can’t perform such an analysis.

BTW, there is a small listening space of high interest to us: cars. Their smaller volume means that the modal region climbs up to 500 Hz or even higher. Getting smooth response is hard in our homes below 100 Hz. Now imaging that problem multiplied and moves up in frequency, now impinging on low range of even voices! Inversely, as I mentioned before, larger performance spaces have much lower transition frequencies usually below 20 Hz, which eliminates the modal concerns altogether. These are the factors that are important as we look at “small” and “large room” acoustics, not some worry about RT60 measurement being wrong.

Back to Ethan’s box and experiment, he was simply comparing two surface materials against each other: MDF vs. glass. We know glass is smoother than MDF resulting in theoretically less absorption in higher frequencies. Less absorption means higher reverberation time (what doesn’t get absorbed, gets reflected). Since the measured RT60 time tracked this difference correctly, we have yet another validation point that this measure is accurate! Here is his RT measurement:



If RT60 measurements were useless then we should have arrived at random data and not have experiment after experiment, showing the correlation with amount of absorption introduced in the space.

BTW, the whole argument is circular anyway. You can’t prove RT60 measurement is meaningless using RT60 measurement itself! You have to have an independent metric that is believed to be true that shows RT60 to be wrong. This is how we showed error in the *computed* RT60. We trusted RT60 and showed that the formula must be in error.

Thanks Amir. I'm probably going to re-do my garage reverb test too, without my car, and do a proper measurement with REW.

To be clear, that photo was originally made for a different article on my site:

Ethan's Failed Reverb Live Room Project

The idea was to shift all frequencies up by a fixed 10 KHz offset, apply reverb in a tiny "room," then shift the audio back down to restore the original frequencies. With frequency shifting the "room" became equivalent to 100 feet long at normal frequencies! So your calculated Schroeder Transition Frequency of 2.5 KHz is perfectly appropriate and acceptable. Indeed, this is another example of obtaining real reverb in a tiny space - but only for very high frequencies. Too bad it didn't work for other reasons as explained in the article.

--Ethan

I don't understand this at all. The time graph at the bottom seems to show that the intensity is changing all the time. What's special about how it changes at 0.2 second intervals? What does speech intelligibility have to do with late reflections?

Sorry, now that I read it, it seems I left out a sentence that explained that. Remember that late reflections anything after 0.1 seconds. If we have an RT60 time of say, 1.0 second, then we have a ton of late reflections. These reflections terminate at 1.0 seconds and as such, they contain a lot of their energy left in the earlier part of the time cycle. As that graph shows, English language has a cadence of around .2 to .25 seconds as far as quiet vs louder parts. The late reflections can stomp on those quieter parts as kind of a background noise. You are smearing an earlier louder sound (usually a vowel) over the sound of a quieter portion (e.g. a consonant). All else being equal you diminish intelligibility when that happens.

So you're talking about syllables, I guess, and saying that intelligibility will sink to a minimum when an echo of the last syllable is heard at the same time as the current syllable? Sounds plausible, but on the other hand, you know, humans are probably well adapted to understanding each other in reverberant spaces. So maybe not. This is less plausible. Consonants ordinarily do assimilate to following vowels, anyway, so I doubt that this "smearing" would affect intelligibility much.

Yes, it's like measuring water using a tape measure (instead of a measuring cup). Textbook definition of a meaningless measurement. Or is it? Once you get your head out of the textbooks and into the real world, you routinely see inches used to measure water when it is falling from the sky. Does that number tell you how much water has fallen? Nope. But is it helpful? Yes: if the weatherman says 2 inches of rain, you know to grab an umbrella; if he says 22 inches of rain, you know to brace for a flood. The number itself might be meaningless when it comes to measuring the actual amount of water, but that doesn't mean people don't use it routinely, since knowing that number is useful to them.

Same with RT60. Of the various definitions of reverberation mentioned in this thread, one of them makes RT60 a meaningless measurement for small rooms. But that doesn't stop international standard organizations (ITU, BBC, EBU) from recommending target RT60s for small control room designs. If you're uncomfortable calling it RT60, then do what some people have done and refer to it as a T60 measurement (look, no "R", so no need to argue over definitions of reverberation). If you want to label it a meaningless measurement, then I'm fine with that too ([whisper] but if you can get that meaningless measurement between .2 and .4 ms in your room, then that will help speech intelligibility [/whisper]).

Not being a technical person, I'm less concerned with textbook definitions than practical usefulness. Rather than get into the reverberation vs reverb debate, I think of it as a measure of decay time: whatever sound you believe is being measured (or not measured), that sound is going to decay in the room. If the measurement can be used as an indicator of that, then it can be helpful in getting within a range that improves conditions for people listening in the room; at least as helpful as measuring water in inches. Yup, the Mellor/Hedback paper is my go-to for general set-up recommendations. And even though it is written for 2-speaker layouts, I still find many of the recommendations useful for multi-channel set-ups: e.g., using highly smoothed, band limited ETCs to check consistency between left and right main speakers; same approach should be used to check consistency between left/right side speakers and left/right rear speakers (L/R heights, L/R wides, etc). Like you said, a must read.

^+100

([whisper] love the whisper part, too [/whisper])

Also on my list of goto references is the Bass Integration Guide from Hifizine: http://www.hifizine.com/2011/06/bass-integration-guide-part-1/

. . . and of course Ethan's website is absolutely fantastic!

You definitely have the right concept. It is just that it applies to early reflections (less than 0.1 seconds), not late. Early reflections “fuse” together with the direct sound to help increase the total power of the source, hence resulting in better effective signal level/intelligibility. Late reflections are not helpful in this regard. The brain stops accumulating such data after certain amount of time. If it did not do that, then it would not be able to hear clearly separate audible events. See the graph in my first post in this thread that shows this phenomena and levels/distances (i.e. delay) where it occurs: http://www.avsforum.com/t/1453370/do-bass-traps-produce-noticeable-audible-difference/30#post_22977312

Here are some quick references:

Journal of ASA paper: Prediction of the influence of reverberation on binaural speech intelligibility in noise and in quiet

"…that reflections may be useful for the listener if they arrive within a certain time interval te after the direct sound, but disturb intelligibility if they arrive later (for details, see Sec. II B 3 or Bradley, 1986; Bradley et al., 2003; Bradley, 1998; ISO, 2009). These measures are widely applied in room acoustics, although the optimum limit (te) for the useful part in the range of about 50 to 100 ms may differ between studies."

Here is a useful graph from the referenced Bradley paper:



This graph is for larger spaces and hence the elevated RT values than what we are talking about in our home spaces. Still, you see that the shorter the RT time, the better the speech comprehension. An interesting observation from that data is that at some point, increasing the volume of the source no longer helps to improve audibility! The likely reason for that is that increasing the source volume also increases the level of late reflections so the net gain becomes zero (right side of the curves).

I should note that there is a lot of food fights in the literature on how proportional the intelligibility is to the numerical value of RT60 and other similar formulas. So don't go by this data religiously. We don't care what happens if you go from 0.31 RT to .037. We care that there is difference between that and say, 0.7.
Following vowel? The scenario was the other way around. RT60 must be too high in this forum.

Imagine if I said: “take the cat” vs. “take the cab.” The plosive consonants “t” and “b” are the only difference in those sentences and by definition are very quiet relative to vowel “a” preceding it. The late reflections from that vowel can impact the audibility there. Contextually you may be able to compensate between these two sentences but not always.

Here is a quick reference on that. Journal of AES [peer reviewed] paper: Audio Engineering and Psychoacoustics: Matching Signals to the Final Receiver, the Human Auditory System”

”Using the loudness exceeded in 10% of the time as an indication of the perceived loudness, it can be expected that the speech is 1.2 times louder in the room with 0.6-s reverberation time and about two times louder in the room with 2.5-s reverberation compared with the loudness produced in the free-field condition. This increment in loudness is often very helpful for the intelligibility of speech in rooms as long as the reverberation time does not produce temporal masking, which reduces the audibility of faint consonants appearing in sequence to loud vowels.”

Temporal masking means that an event earlier in time, steps on a later audible event which is what I explained.

This why we like to have certain amount of general absorption in the room, but not too much as to eliminate the good benefit of them helping with intelligibility and feeling of spaciousness/being in a real space. It is a balancing act and hence the recommended range.

I agree, and ever since it was published, it really hasn't received the mentions it deserves. It's not groundbreaking, it's just a well executed reference.

The problem with that reasoning is that you don't hear the difference between "cat" and "cab" by listening to the quiet parts, at least not primarily. The vowel before a syllable final voiced stop, like "b", is longer than before a voiceless stop, like "t", so just the length of the vowel tells you whether it's a "b" or a "t". And the oral cavity is more divided for a "t" than it is for a "b", so the quality of the "a" as your tongue positions itself for the syllable final stop also tells you the place of articulation of the upcoming consonant.

So, what you say about the consonants "t" and "b" being the only difference in those sentences is only true of the spelling, not the pronunciation.

I don't see how that distinction is important here. We are not discussing how words are pronounced. You need to show that if you can't hear the last letter, it doesn't matter and you can still tell what I said. Are you saying that with respect to the words cat and cab? I assume not as otherwise, you are a better man than the rest of the population .

I also cited a bunch of research to back what I said, including from top five experts in psychacoustics, Zwicker (my last quote). Would you kindly confirm if you are disputing those and your own references to prove the same?

To change the subject a little...

This is why I think it makes sense to employ multichannel surround sound rather than just 2 channel. My AVR has a mode where it takes a 2ch input and duplicates the same left or right signals into additional speakers. (centre is a mix of the two) The user has the control to alter the signal strength going to those additional speakers in 1% increments from 0 to 100%. No other alteration to the signal is made unlike with most other upmix utilities.

So instead of relying on reflections off the walls for that sense of space, where the distance to the walls dictates timing, construction and material of the wall dictates the reflected frequency response and the dB level of reflection. Instead, using a wide and/or a side surround speaker to duplicate the signal at a volume and frequency response and delay that the user can control and adjust to taste.

This is what I do and with a decent amount of 6" broadband absorption panels around my room. Remove the variability of a room and use the control that additional speakers give.

I'm saying I can tell the difference between "cat" and "cab" even if the last consonant is removed, or between "cat" and "cad". That's not quite the same as saying I can tell what you said, because there are more possibilities than just the two. The vowel length tells me whether the following consonant in the same syllable is voiced, so I can tell that, even if the consonant is snipped off. In fact, since word final obstruents in English dialects are often devoiced, for such a dialect, I could not tell the difference between "cat" and "cad" by listening for voicing of the last consonant, because the final "d" would not in fact be voiced.

I'm working at finding references for you, but I'm having difficulty finding anything on line, and I don't want to go to the library. Probably Denes, P. (1955), Effect of duration on the perception of voicing, Journal of the Acoustical Society of America, 27, 761--4, would work, but I'm not able to actually look at the article right now. And for using vowel transitions to tell what place a following syllable final consonant has, probably Delattre, P.C., Liberman, A.M., & Cooper, F.S. (1955), Acoustic loci and transitional cues for consonants, same journal, 27, 769-73.

Both these references I found in "Acoustic Cues to the Perception of Segmental Phonemes" by J. Raphael, http://books.google.com/books?id=EwY15naRiFgC&pg=PA202&dq=locus+perception+final+consonant+phonetics&hl=en&sa=X&ei=sLw7UZbaL8idyQHL_IDoDg&sqi=2&ved=0CC0Q6AEwAA#v=onepage&q=locus%20perception%20final%20consonant%20phonetics&f=false.

The second reference above by Pierre Delattre, et al., is relevant to what I said about listening to the vowel to tell the place of articulation of the following consonant. If you will just consider your example modified to end with words like "sack", "sat", "sap", and assume that the last consonant is not released, you can readily tell that there is a problem figuring out how people distinguish those words, since the "quiet" part is completely silent. The only way listeners have available to tell the difference is by listening to the preceding vowel. The consonant part is silent. That is the puzzle that Delattre "locus" theory solves.
I didn't look at your references. Sorry.

If there are more possibilities than one, then we have failed in our mission. Our goal in designing high performance listening spaces is 100% comprehension. If after spending thousands of dollars on your home theater and countless hours on this forum, you have to turn to your significant other and ask, “what did he say?” then you have lost the battle. Think of it as a light switch. It needs to always turn on the light. Even 99% is not good enough as that takes you out of the experience one out of 100 times.

Whether it is in watching a movie or everyday life, we have many clues that help us fill in or guess at the missing parts. The visuals, lips, context, and yes, the previous sounds in a word, all help comprehension. But there comes a time when despite all of that, we slip below the threshold of 100% intelligibility. To the extent we can help that with good room design, we want to do that. And oh, we want to do that in a language independent way: so let’s be very careful as we resort to perception of phoneme that are only true of English language. Again, none of that changes the equation here. You have to show that in no case the addition of (late) reflections is detrimental to 100% speech comprehension. Linguistics science tells us how we are able to understand speech but unless you connect the dots with respect to acoustics, it is not relevant to the conversation we are having. I have the two papers you cite, have read them, and they don’t do that.

Ironically, the text you cite and some of the other references within, do. Here is a sample:

"Under ideal listening conditions, such as when stimuli are presented in quiet, audibility can account for over 80% of the variance in the speech perception abilities of older adults. Under more difficult listening conditions, such as in the presence of background noise or reverberation, the importance of audibility is reduced but can still explain approximately half of the systematic variants in speech perception.

Notice the section I bolded. If [late] reverberations help with speech as you said at the start of this disagreement, then how come it is in the same class as noise and causing “difficult listening conditions?”

The book cites this research from Journal of ASA: Monaural and binaural speech perception in reverberation for listeners of various ages by Anna K. Nábělek and Pauline K. Robinson

”The data of this study show clearly that reverberation alone can cause listening problems. The young adults performed significantly better than the other groups in all conditions, but were still affected by longer reverberation. Children performed poorer than young adults which indicates the importance of good acoustics in classrooms. If reverberation acts similarly to masking noise, children younger than 10 years of age might have even more difficulties with reverberation, than is the case with masking noise (Elliott, 1979). For the adults, the problem with reverberation starts to be more noticeable in the sixth decade of age. Monaural speech perception in reverberation declines rapidly for the elderly, especially for longer Ts [RT60].”

The above is the conclusions from a set of listening tests trying to determine the impact of Reverberation time (among other factors). You can easily see reinforcement of the point I made and what is said in the text: that late reflections do degrade intelligibility even though as humans we get pretty good at guessing at what is being said.

Here is another paper referenced in that book: ”Intelligibility of conversational and clear speech in noise and reverberation for listeners with normal and impaired hearing.” by K. L. Payton, R. M. Uchanski, and L. D. Braida:

”Both background noise and reverberation are typically present when people communicate with one another. Such interference degrades speech intelligibility for both normal heating and heating-impaired listeners but at different signal-to-noise and reverberation levels (Nabelek and Mason, 1981; Nabelek and Robinson, 1982).“

This is another set of listening tests which underscores the same conclusion. Happy to quote the specific intelligibility scores if you like with respect to RT values of different rooms simulated.

So as you see, even with the references you provided, the same conclusions are reached. If what I stated was untrue, it would not be so easy to demonstrate that point.

Making sure we have not confused anyone with this detour, let me be clear that we are discussing *late* reflections that occur past 0.1 seconds. Reflections in the first few milliseconds do help with intelligibility as they increase sound power and the brain ignores the fact that they are separated in time. That is not tested in the above studies. So please don’t assume “reflections are bad.” The nature of them determines if they are beneficial or not.

Evidently "the conversation we are having" got split up in two parts. It was natural for you to assume that the point I was making disputed what you were saying about how reflections affect comprehensibility, but that was not my intent. I was just commenting about your example with "cat" and "cab", which I thought, and still think, was wrong. And that's all I was saying.

You said that reflections cause vowels to interfere with perception of following consonants. Maybe. I'm not expressing an opinion about that. But the example you gave has some special properties. In your examples, the vowels are in the same syllables as the following consonants, and the consonants differ only in voicing and place of articulation. You couldn't have chosen a worse example for your point, because under these exact conditions, the vowels already contain almost all the important perceptual information that listeners use to figure out what the following consonants are. They listen for the length of the vowel to get the voicing of the following consonant, and they listen to the formant transitions to get its place of articulation. The vowel can't cover up information about the following consonant in this particular case, because there is virtually no information there to cover up. It's all in the vowel, already.

You need to change examples.

Is this the study of RT60 times of 600-700 living rooms from the 1970's which I seem to remember.

Sorry for the late reply. Did not realize you had answered . For the example to be wrong, you need to incorporate in your reasoning both linguistics and acoustics. The former alone is not going to do it. Please see below. Implicit in your argument above is that the formant transition was heard and perceived correctly. Such may not be the case. In a room with long reverberation times, the steady state part of the vowel/formant does not terminate immediately -- it continues to "play" over the formant transition. To the extent you agree that the formant transition is a necessary part of comprehension, then you have to also accept that degrading it, lowers intelligibility. The fact that the consonant itself is also temporally masked adds to the problem.

To prove that the example is not proper, you need to show that the formant alone would let you unambiguously tell the difference between cat and cab. I hope you agree that can’t be done.

No, this is not based on study. As I said, the determination is based on field experience. The study you are thinking about was from Bradley where he surveyed those Canadian living rooms and found that they happened to have the same reverberation time, 0.4 +-.1 target we like to achieve. That says that you don't automatically need treatment in your multi-function rooms if they have sufficient amount of furnishing/natural absorption.

No, this is not a correct characterization. I don't know what one could tell in the presence of reverberation (and I never said I did). Maybe a listener could distinguish "cat" from "cab", or maybe not, but if not, it couldn't be due to the vowel echo obscuring the sound of the following consonant. Your explanation of this example is incorrect, regardless of the outcome of an experiment with reverberation. I am confident that if you operated on recordings to snip away the final consonant portions of "cat" and "cab", so the consonants were entirely absent from the sound, in the absence of reverberation, listeners would be able to distinguish the two correctly.

Do you have a cite to the field experience to which you are referring.