Acoustic Weirdness..

I'm in my room, putting up about the 30th 12"x12" piece of sound deadening foam on my back wall I've hung so far, eventually I'm going to cover nearly the entire wall, or more with it. I put in a Beatles CD one of the two disk greatest hits ones, and hear the usual, annoying midrange to lower treble range it normally has, at least so far. It's better by far than it was, but the room seems to really be a problem. Playing a test CD, the low end seems fine, no real complaints, my sub could be a lot better, but it's ok. Higher freqs around 4-10k seem ok too, it's the vocal range that's really bad.

I even drug my old AR 83's into the room, and they were just as annoying as my SBS-01 front and center speakers, and they are as "laid back" as it gets. Anyway, the CD is playing in 2 ch stereo mode, and I had to go to the bathroom, and just walked out with it playing at about -12db level. I sat down and a few seconds later, it hit me. It sounded GREAT! The bass was mostly the wall between the bathoom and the TV room thumping, but the vocals were perfect! I sat there for a long time, listening, and wondering what was going on exactly. No edge, smooth as could be. If I could get it to sound like that when I was in the room, I would be overjoyed.

I've lived in the house for almost 25 years, and it always sounded really bad in there before, regardless of how good it sounded in the living room, or the bedroom I'm using now. The two rooms are next to each other, so the sound has to come out the door of the bedroom, make a 90 degree turn, go down the hall about 10 feet, and make another 90 degree turn into the bathroom. As a goof, I walked into the living room, and it was pretty good, not as good as the bathroom, but close. In the bedroom at the end of the hall, it was slightly dead sounding compared to the bathroom, but still 10 times better than in the room itself! In 7 Ch mode, the back bedroom was great, and the bathroom slightly hot. In the TV room, it's ear bleeding..

Anyone got any ideas as to why this is happening? I sure wish the sound quality approached the picture quality..

System as of today:

Yamaha RX-V659
SVS SB-01 Fronts
SVS SC-01 Center
Sony 12" active sub, can't remember the model.
RS Minimus 77 surrounds, with xover mods (soon to be replaced with another pair of SB-01s) the mod made the high end really come alive, and they annoy me no end now. I should have left them alone.
RS Minumus 77's rear surrounds, these are stock, and are ok right now, but will soon be gone too..
Philips Upconverting DVD player DVP5960 Audio uses coax connection to reciever.
Sharp LC37D40 HDTV

> just walked out with it playing at about -12db level. I sat down and a few seconds later, it hit me. It sounded GREAT! <

It's not clear what you're describing. Are you saying the sound is better when you leave the room and go to another room, with the speakers still playing in the first room?

--Ethan

Be careful with overtreating your room. Dr. Toole just released a new paper to AES on acoustics in small rooms where he proves there are benefits in vocal intelligability from early reflections. Overtreating the first reflection points could be responsible for your dislikened vocal response in your room.

Ethan Winer said:

> just walked out with it playing at about -12db level. I sat down and a few seconds later, it hit me. It sounded GREAT! <

It's not clear what you're describing. Are you saying the sound is better when you leave the room and go to another room, with the speakers still playing in the first room?

--Ethan

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Yes, it's amazingly better in the other rooms, the bathroom and the back bedroom! I can't take it too long in here with the volume anywhere close to where I normally want it. It gives me a headache. Vocals, and violins, etc are very edgy in here, in the bathroom, it's great.

gene said:

Be careful with overtreating your room. Dr. Toole just released a new paper to AES on acoustics in small rooms where he proves there are benefits in vocal intelligability from early reflections. Overtreating the first reflection points could be responsible for your dislikened vocal response in your room.

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Well, it's a whole lot better now than it was a couple weeks ago, when I started putting the foam panels up. I had to run the treble on the 659 all the way down just to keep my ears from bleeding!

All I've done so far is to do the areas around the front and center speakers, at least a foot on all the sides that are possibe. Before I started it, it was just horrible. I wish I had my old Audio Control RTA, I bet there's a huge peak in here around 1 K or so..

Quick update! I added another 10 panels of foam, 4 on top so I'm almost to the ceiling, and 6 under the speakers. This made a huge difference. It's tolerable on CDs now at normal listening volume running the 2 fronts and the sub, not great, but ok, and fine on HDTV DD audio in the more reasonable effect modes. I'm going to get another box of the foam panels, and order another pair of SBS-01's.

I tried an experiment just before I left for work and took my left and right surrounds and turned them so they were facing forward ( They are normally wall mounted, but there are shelves nearby, so I set them on the shelves to try it out). This helped a lot to tame the insane high end they have, and then I went into the back bedroom and bathroom, switching modes to see what it was like. In 7 ch stereo, it sounded all right, but a little dull in the bathroom, and really dead in the back bedroom. In 2 ch, it sounded pretty muffled in both rooms, like a cheap AM radio with thumping bass.

This is more like it!

I think with the second pair of SBS-01s, the 7 channel mode will be good, and a few more panels should get it where I want it finally. I actually listened for about 20 minutes tonight, in the room the speakers are, without shaking my head..that's big progress!

Hemi,

> I added another 10 panels of foam, 4 on top so I'm almost to the ceiling, and 6 under the speakers. This made a huge difference. <

I'm sure it made a big improvement, but understand that throwing absorption around willy nilly isn't the best approach, as Gene pointed out. Generally speaking, absorption is needed at the first reflection points on the side walls and ceiling. Then, additional absorption should be placed around the room more or less uniformly, especially on opposing parallel surfaces to avoid *flutter echo. This is better than putting the absorption all in the front, or all in the rear, etc.

--Ethan

* Flutter echo is that "boing" sound you hear when you clap your hands in an empty room.

Gene,

> Dr. Toole just released a new paper to AES on acoustics in small rooms where he proves there are benefits in vocal intelligability from early reflections. <

Well, "prove" is a strong word, especially in this context where opinion, personal preference, and science fact aren't always easy to separate. I think it's generally accepted that absorbing first reflections increases intelligibility. It certainly does in both of my rooms, and in customer rooms I've treated personally.

It may well be that certain types of early reflections can improve some aspect of sound reproduction. I haven't heard every room in the world, and "early" encompasses a pretty wide range of delays. If anything is made "better" with the presence of early reflections, it seems likely to me to be the result of inevitable comb filtering caused by the reflections. For example, if the distance / delay creates a null in the tubby range around 200 Hz, I can see how that might make a vocal seem clearer. Especially if it was recorded too tubby to begin with.

Just some food for thought.

--Ethan

Well, "prove" is a strong word, especially in this context where opinion, personal preference, and science fact aren't always easy to separate. I think it's generally accepted that absorbing first reflections increases intelligibility. It certainly does in both of my rooms, and in customer rooms I've treated personally.

It may well be that certain types of early reflections can improve some aspect of sound reproduction. I haven't heard every room in the world, and "early" encompasses a pretty wide range of delays. If anything is made "better" with the presence of early reflections, it seems likely to me to be the result of inevitable comb filtering caused by the reflections. For example, if the distance / delay creates a null in the tubby range around 200 Hz, I can see how that might make a vocal seem clearer. Especially if it was recorded too tubby to begin with.

Just some food for thought.

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You should really read Dr. Toole's latest contribution to AES on acoustics in small rooms. In it he makes a strong argument for NOT treating first reflections with absorption if you use speakers with uniform on/off axis response and constant directivity. I can see how a compromise can be made here however and in the end it all boils down to preference. In my room I have the ceiling reflections treated with absorption and feel its too much. Thus I will soon change it to a combo of absorption/diffusion soon.

It has been a widely accepted fact - both subjectively and objectively - that early reflections improve speech intelligibility. As Dr. Toole points out:

Dr. Floyd Toole said:

It has long been recognized that early reflections improve speech intelligibility, so long as they arrive within the “integration interval” for speech, about 30 ms [45].

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Reference [45] is:
P. A. Lochner and J. F. Burger, “The Subjective Masking of Short Time Delayed Echoes by Their Primary Sounds and Their Contribution to the Intelligibility of Speech,” Acustica, vol. 8, pp. 1–10 (1958).

There are numerous other references, including citations of the work of Yoichi Ando, a true pioneer in his studies of early reflections and their beneficial properties. The topic of early reflections improving speech intelligibility is, with all due respect, not up for debate. There have been ample scientific studies for the last 7 or 8 decades that prove this, as Dr. Toole points out in his fantastic paper.

The main difference between the references (Burger, Bradley, Ando, etc.) and Dr. Toole's paper is that Dr. Toole discusses the application (applicability?) to small acoustical spaces. This is where the rubber meets the road. The usefulness of early reflections has been used to great advantage in many a large space - including concert halls, theaters, etc. But little work has been done (as pointed out by Dr. Toole) regarding how useful are similar early reflections in small spaces. Especially considering all the other factors such as construction style and materials, use of room (production or reproduction), music or speech (or both) as the source, etc. In my view, I still believe - even after reading Dr. Toole's paper - that each situation will be unique and that general principles are useful only as guidelines. Are early reflections useful in home theaters? I think it depends on many things. Sometimes yes; sometimes no. I believe that even if we spend another 3 (4? 5?) decades researching small room acoustical behavior, we will still not have definitive answers for designing any small room. Certain design "formulae" can apply to large spaces because of the statistics involved. The same cannot be said, I think, for small rooms.

Suffice it to say, I believe Dr. Toole would concur that there is much debate as to the usefulness of early reflections in small spaces. He does a wonderful job, IMO, of presenting the "state of the science"; a thorough discussion on almost every facet of the facts and science surrounding small room acoustics, and great discussions of how these parameters relate (or not) to subjective qualities of small rooms. To provide another quote from the Discussion and Summary section:

Dr. Floyd Toole said:

If we are looking for hard recommendations (regarding 'the design of loudspeakers and listening spaces for sound reproduction in professional...or consumer...domains'), it is evident that all of the necessary facts are not yet available. ... There are questions that will exercise researchers for years to come. However, there is useful guidance from the research that has been done...

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What follows is a summary of, as I have called it above, the "state of the science." If I might opine further, the paper is a must-read for anyone seriously interested in the topic of small room acoustics. If nothing else, it will provide new perspectives and ideas on how to look at (listen at? ) small acoustical spaces.

Getting back on-topic {apologies for the digression(s)}, I believe that all home theaters would absolutely benefit from the careful control of early reflections. By control, I mean absorption, or reflection, or redirection, or diffusion. No two applications will be alike. The specific solution that worked for one theater won't necessarily work for another (or any other, for that matter).

Well, since I'm using the 3M "command" adhesive tabs, the panels can be removed/moved very easily and for about 25 cents a panel. the first refection points are almost exactly where my surrounds are. I was going to wait to do anything there, as I'm waiting for another pair of SBS-01's to show up and want to see what they sound like first. Of course, since the panels can be easily moved, I might try a couple just to see what happens. If I can just get the fronts to sound like they should, I think the rest will be a cinch.

Gene:

> You should really read Dr. Toole's latest contribution to AES on acoustics in small rooms. <

I have that paper, and started it, but haven't had a chance to finish it. I will make a point to do so ASAP. In the mean time...

Jeff:

> I believe Dr. Toole would concur that there is much debate as to the usefulness of early reflections in small spaces. <

Of course, the only rooms I'm talking about here are small rooms as found in most homes. Research about large venue acoustics is irrelevant for small rooms.

I understand the importance of reflections on a stage and behind an orchestra in an auditorum, having performed in orchestras hundreds of times. This is also why reflective floors are common in recording studios. But while that sort of added presence and sense of "being there" is appropriate in a performance venue, I disagree that it's useful in a living room. This is one of the "great debates" in audiophilia - whether a listening room should attempt to duplicate the acoustics of a venue, or be relatively void of reflections and ambience so the acoustics of the venue as captured in the recording can come through. I am strongly on the side of the latter. Small room ambience is generally lousy boxy sounding ambience, and anything that reduces such ambience (or diffuses it) is most welcome as far as I'm concerned.

Now, Gene may well prefer more ambience in his listening room, and I'd never say that's wrong. I happen to prefer more on the dead side, but that's me. The real point is that having a mostly dead sounding listening room does not mean that playback sounds dead! I enjoy a huge sound stage that's wider than the speakers would imply. Assuming a suitably made recording, there is never a lack of spaciousness or depth etc either.

As for "vocal" intelligibility, that improved enormously in my HT once I treated all of the first reflection points on the side walls and ceiling. So I'm more than a little baffled that anyone would claim that absorbing these reflections is a bad thing. But I respect Dr. Toole (duh) and I'll gladly hear him out.

--Ethan

Ethan,

I'm sure I haven't said this enough in the past; thank you for sharing your thoughts. It is always interesting to read your opinions on these acoustical topics, what with your having such a unique perspective.

Ethan Winer said:

Research about large venue acoustics is irrelevant for small rooms.

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I agree with where you're coming from here. Things like absorption coefficients and RT have no place in the contexts of small rooms. Of course, I'm confident you would agree that much of the research is quite relevant since the industry would be without many useful tools, materials, treatments, etc. without the volumes of research on large rooms. Time Delay Spectrometry, Quadratic Residue Diffusors, Speaker-boundary Interference, and membrane absorbers, to name but a small few; all of these came about either as a direct result of, or as some descendant of, research on sound behavior in large spaces.

As for "vocal" intelligibility, that improved enormously in my HT once I treated all of the first reflection points on the side walls and ceiling. So I'm more than a little baffled that anyone would claim that absorbing these reflections is a bad thing. But I respect Dr. Toole (duh) and I'll gladly hear him out.

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Again, I echo (!) your sentiments, having myself been a long-time champion for absorbing early reflections. It is often the best, most efficient way to take care of problems they cause. Dr. Toole would no doubt sympathize with our feelings on this and I believe he would concur to a degree. As Gene has pointed out, Dr. Toole's paper discusses much of the research that has been done regarding early reflections, and how that research seems to indicate that there are many ways to, shall we say, work with early reflections. While absorption has long been the panacea for early reflection woes, there are many contemporaries of ours, such as David Moulton, that strongly subscribe to the usefulness of early reflection in a listening space. I think you have (once again!) touched upon a very good point. Absorbing early reflections is unlikely to vanish as a control option. Like you, I believe that absorption will remain a significant component in the evolution of the well-controlled small room.

Just a quick update with this. I put two panels on each side wall just to see what would happen (With the furniture in here, it's not possible to do a lot more than maybe 4 or 5 on each side, except along the ceiling), then reset and ran auto setup again. MUCH better, still not right, but a lot less "strident". The only oddity is that the 659 dropped the level of the right surround down about 2.5 db from what it should be (so it's balanced with the left side), and it turned the sub level down to -5, at least 2 steps lower than it needs to be. In 2 ch stereo mode, it's getting pretty good. When playing some classical stuff I'm well familiar with, it's still not quite there, but tolerable now to the point I could live with it, if I had to. On vocal stuff though, it's still annoying as hell to me. Movies seem ok, it's music, either on CD or FM that still has real problems at this point. Thanks for all the replies..

gene said:

You should really read Dr. Toole's latest contribution to AES on acoustics in small rooms. In it he makes a strong argument for NOT treating first reflections with absorption if you use speakers with uniform on/off axis response and constant directivity.

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That's all well and good for the fifteen guys on the planet that have speakers like that.

Rob Babcock said:

That's all well and good for the fifteen guys on the planet that have speakers like that.

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I've been thinking more about this - and I reread the Toole paper. One of the concepts I find most interesting is the whole notion of, for consumer listening environments, the fact that a space can be "learned" - that the inherent problems in a small acoustical space can be listened "through" and the true quality of what is being played back (or what it's being played back on) can be faithfully evaluated in a typical living room with no special acoustical treatments. (I am certainly borrowing some of Dr. Toole's terminology here, btw.) I have experienced situations like this - where the sound quality is exceptional despite the fact that there hasn't been a single thing "special" done to treat the room. I would venture to say that there exist just as many treated rooms that sound awful as untreated rooms that sound truly outstanding. I have a strong feeling - based on my own observations of many hundreds (thousands?) of small rooms - that there are plenty of both out there.

However, having said that, I would still agree with the above statement - there simply aren't that many (affordable) loudspeakers out there with an off-axis response good enough to implement what Moulton and LaCarrubba call "wide dispersion" acoustical design. Absorption and diffusion (and combinations thereof) will always have a place near the top of the early reflection control food chain.

And - just so this doesn't seem totally off-topic - I think that philosophy is evident from what hemiram is discovering about his acoustical space. More control of early reflections yields something that sounds "better." In general, I believe this would be the case for many home theaters and listening spaces.

Jeff,

Thanks for your comments. It seems we're in agreement on most things. No surprise there.

The improvement hemiram observed is typical, and I've heard it a hundred times (not exaggerating). That makes it even more strange that someone could claim early reflections are not only not bad, but good.

I always thought my Mackie 624 and (huge) JBL 4430 loudspeakers had a good off-axis response. Maybe I'm kidding myself? Then again, I'm also a realist. My own article on Front Wall Absorption presents polar patterns for ten different speakers, and above 5 KHz they all suck. Then again, none of these are hi-fi speakers. Why didn't I show hi-fi speakers? Because none of the manufacturers publish polar data! And why don't they publish polar data? Well, now you know.

> I find most interesting is the whole notion of, for consumer listening environments, the fact that a space can be "learned" - that the inherent problems in a small acoustical space can be listened "through" <

Someone elsewhere recently posted a link to an interesting article related to this. That article talked about listening "through" lousy amateur mixes and poor piano recordings etc, and noted that after a few minutes we don't notice the poor sound as much. I've noticed that myself too. If I make a mix that's, let's say "less than stellar," eventually it sounds okay, especially if I keep playing it back louder and louder. But man, the next day, in the first two seconds I can hear the lame "tone" all over again.

> I think that philosophy is evident from what hemiram is discovering about his acoustical space. More control of early reflections yields something that sounds "better." In general, I believe this would be the case for many home theaters and listening spaces. <

I agree. Sure we can get used to a lousy room. That's what 99 percent of the people do! They don't even know their room is terrible either. But that's no excuse. Like ignorance of the law is no excuse. And it's even worse when audiophile magazine writers have no acoustic treatment at all and don't even know what they're missing. When I read a review in an audiophile magazine where the author comments on the wonderful "imaging" of this speaker or that, and I know that the author has no acoustic treatment at all (vast majority), I can only laugh smugly.

I'm going to read the rest of that Toole article right now. I promise.

--Ethan

Folks,

I just finished reading the article. Floyd is brilliant and I agree with most of what he wrote. I enjoyed the article tremendously, and learned a lot too. I hope to read it again at least once if not twice.

Perhaps the most important thing I learned is that "Generic 'good' listening room ratios are a myth" for which he makes a compelling argument. However, his point does not seem to apply for a playback system having bass management if the subwoofer is in a corner, as in my living room HT. I never experimented with four subs, one in each corner, but I suspect the same thing applies there too. If all the modes are activated equally, their ratio should indeed still matter.

I did find a few more things to comment on. In the opening Floyd wrote:

At low frequencies the long-standing problem of room resonances can be alleviated substantially through the use of multiple subwoofers, thereby providing similarly good bass to several listeners in a room.

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If you define "good bass" as a flat response, I agree that multiple subs can help. But that does nothing to reduce modal ringing which is at least as damaging as a skewed response, so having multiple subs is not a complete solution. I'm still waiting for proof that modal ringing can be reduced by EQ for an area larger than one cubic inch.

I also think his comparison of music in a concert hall in the context of why we don't mind longer reverb decays is flawed. That's fine for opera and symphony concerts, but it's not relevant for pop music or jazz where the bass instruments are recorded either direct or with a microphone very close. In that case you do not want excess ringing or decay because bass notes can run together losing clarity and articulation.

Likewise, he seems to equate "good" but very late reflections in a concert hall that make the orchestra appear wider than it is, to side wall reflections in a home listening room. This defies my own experience, where absorbing those reflections makes the sound stage wider, rather than the other way around.

Strong directional features were associated with early reflections.

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Sure, and this returns us to whether the listening room should impart its own character onto the playback, versus all desired ambience is already in the recording so the room should add nothing further. The latter approach is the only way a recording can be heard as intended in different rooms. I contend that all needed and desired localization is (or should be) already present in the recording through the use of panning and reverb and ambience effects added by the mix engineer.

All of this is clearly relevant to localizing the real sources - the loudspeakers. However, success in doing this may run counter the objectives of music and film sound, which is often to "transport" listeners to other spaces.

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Exactly. In a listening room you do not want to localize the sound as coming from the loudspeakers. Untamed reflections defeat this goal. It is very easy to demonstrate that in my own living room, and I do this all the time for visitors. If you stand behind the couch outside the Reflection-Free Zone you can clearly identify the speakers as the sound source. If you then lean forward over the couch the sound stage opens up, becomes wider, and you no longer hear the speakers as the source. (Except maybe for instruments panned all the way left or right.)

Another thing he seems to miss is why a small room seems to sound better than the measurements would imply. As I see it, the reason we can enjoy music in a room that measures excessive comb filtering is because the comb filtering is very different for each ear. He keeps trying to make it sound like the brain is some mysterious processor that is able to make sense of sound even when the comb filtering response is so poor. As Occam would say, I have a simpler explanation: The frequencies missing in one ear due to comb filtering are mostly present in the other ear simply because the ears are far enough apart. Later in the article Floyd seems to recognize this because he observed:

Gilford ... concluded: "The fact that the listening room does not have a predominant effect on quality is very largely due to the binaural mechanism." ... we measure differences that we seem not to hear.

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Were we to measure at two locations six inches apart (ear spacing) and combine the results, I believe that would more closely resemble what we hear.

Anyway, all and all this has been most enlightening for me, and hopefully for others here too. Comments?

--Ethan

Folks,

Wow, no comments? That's either very good or very bad.

As an experiment, last night I placed heavy cardboard sheets on the carpet, all the way across the room left to right, between me and the front three speakers. Independance Day was on HDTV in 5.1 so I watched that. With the cardboard in place the sound seemed to come from the speakers more than from a phantom sound stage. So the "illusion" was definitely better without the cardboard, having only the absorbing carpet.

Also, I've read many interviews with movie mix engineers who confirm that all ambience and directional cues are embedded in the sound tracks. They all seem to agree that direct reflections are not desirable in a room because that just competes with what they're doing.

Thinking further on all of this, it occurs to me that you can have your cake and eat it too. A room with absorption at all the first reflection points will still have a sound and character of its own. Not all reflections are early!

--Ethan

If you define "good bass" as a flat response, I agree that multiple subs can help. But that does nothing to reduce modal ringing which is at least as damaging as a skewed response, so having multiple subs is not a complete solution. I'm still waiting for proof that modal ringing can be reduced by EQ for an area larger than one cubic inch.

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Oh geez! If you flatten bass response in the frequency domain, you reduce the ringing. If you never heard a correctly implemented multi sub system, you don't know what you're missing.

I have almost no passive treatment in my room for bass yet I am achieving +-5dB response from 20Hz to 20kHz at the listening position averaged over 6 seats! This was an impossible feat without having 4 subs in my room.

If you want proof, attend some of Dr. Toole's CEDIA classes and/or read his white papers on this topic. It is well proven and most installers worth their salt are now implementing multi-sub systems for the better installations.