Axiom Home Page Forums General Discussion Technical Questions Room acoustic question

Can the room acoustic affect the sound differently at different volume levels?
The reason I am asking is because my room is acoustically very bad, it's 20x11x8 ft, hardwood floors, plain walls and very little furniture. At the beginning it was pretty bad, then later, after putting a high pile rug on the floor, it became much better. Up to know, I only listened at moderate levels but this weekend, I had a friend over, I put on the Dave Matthews BD concert and as usual, it sounds very good. My friend then asked me to turn up the volume. At high volume, the imaging became pretty bad, the sound became more "blurry", and it sounded almost the same as before I had put the rug. When going back to lower volumes, it sounds good again. Is that possible or is it just me since I am not used to the sound of these speakers at this level?

Volume levels are hard to discern over the internet as well as listener preferences during that moment but I would also look into the possibility that it might not be the room acoustics but rather that you are clipping the amp or at least starting to push it to its limits when you start turning it up to "high volume" which is causing the negative impact on the sound quality.

Thanks Dr but I don't think it's clipping or at least I cannot hear it. For reference I was still at -8 dB on the receiver, the only time I've ever heard clipping was when I first got the speakers and I had it at +5dB (insanely loud). This sounds more like the sound is not as clear, not as detailed.

I think it is a combination of room acoustics and that the M80s don’t roll off the highs. One of the several reasons I bought he M80s was that unlike most other speakers that do roll off the highs the louder the M80s get the highs still keep up. In a potentially “bright” room this can sound quite harsh IMO.

Before installing my curtains I had a similar experiences with my M80s here in my house even with a carpeted floor. However, now with the curtains up 270 degrees around the room there is no harshness no matter how loud I push them as long as their not distorting.

Until I installed my curtain I just used the “front treble” to reduce the high end when playing them loud.

Can you explain what does that mean? I am not familiar with the terminology, sorry.

Also, the fact that the highs increase with volume, would that make m perception of the sound being less detailed, I don't find it harsh, I find the sound blurry. I had the same feeling before I put the rug, even at low volumes. I understand that the rug removes the first reflections, could it be that at higher volumes it is not enough and that what I am experiencing is just the sound bouncing from the floor and the walls at high volume which I don't hear at low volumes?

Hi Bruno. Dean would be referring to the frequency chart of the M80 vs some other brands as some manufacturers deliberately attenuate the higher freq's because they feel, well, that's what their customers prefer. Co's like Axiom, Paradigm and PSB, for instance, will try to maintain a flat freq response right up to 20khz as that is their design philosophy. Their testing has shown that this is preferred by listeners to the "rolled off" or attenuated highs that Dean aluded to.

(don't mean to butt in and answer for Dean, btw. Okay, yah I did...)

I think I understand, thanks. But if these manufacturer have lower highs, this will also be noticeable at lower volumes, not just at higher volume, correct?

Correct.

Also many speakers don't have tweeters which can keep up. As the volume level increases their dynamic range compresses. So at different levels the high frequency response is different. With two tweeters the M80s can play much louder without compression.

I think I partly misunderstood what you were saying and thought that you were perceiving the high frequencies as harsh. Getting a “blurry” sound as the volume increases sounds like distortion to me. Though I think it could also be related to the following, which I didn’t explain very well. To much Tequila?



Thanks for explaining what I was actually trying to say.

When I demoed speakers, besides the outstanding bass, the thing that actually struck me the most about the M80s was exactly what Chris describes. The M80s were the only speaker I demoed who’s highs “kept up” with the mids and lows as the loudness increased. With all the other speakers I heard the mids and lows became dominant as the loudness increased.

So there is very little chance that my problem is room related?

Without hearing exactly the same thing you were, it's impossible to say.

No, we're talking about would lead to it being a room problem. We're saying that because the M80s don't roll off the highs, as the room loads up, they become over-bearing. Where as other speakers that don't have highs which can keep up with the level of the rest of the music range won't have the same effect.

The other likely candidate, is the receiver is running out of power. That will cause a sort of dynamic range compression too, and also cause the sound field to shrink. This one is slightly more likely from your description, in that you mentioned a blurriness, that may be the onset of clipping, or a gross amount of harmonic distortion.

I guess you could buy bigger amps, and see what happens, if that doesn't solve the problem, go with more absorptive room treatments (although that may dull lower listening levels). Or just don't play it that loud.

Where were you on the volume knob anyway? -9, 0, +3?

Hi Bruno,

Agreed, extremely unlikely that it's room related. What you might be hearing is "incipient" clipping. That's when the amps in the Denon aren't actually chopping off the tops of the waveform, but getting close, so distortion has risen to audible levels.

Keep in mind that all amplifiers driving 4-ohm loads will have higher measurable (not audible) distortion because of the increased current flow through the output transistors---more heat, more distortion. If you look at the distortion curve on an amplifier as the power output increases, you'll see the distortion figures ramp up just before the amplifier reaches the "knee" of the distortion curve when it actually clips.

I suspect that you were pushing the Denon into this territory that precedes actual clipping, when audio may become somewhat edgy, mushy and unpleasant. I've heard similar qualities from both tube amplifiers (the stereo soundstage collapsed into mono and the sound became mushy) and transistor amps when pushed to levels at almost-clipping.

There is also a psycho-acoustic effect wherein your ears may have reached their limit in terms of loudness tolerance. When that happens (to me and to others I know), the sound subjectively is intolerable and may simply sound "distorted" even when technically it's clean.

Regards,
Alan

Thanks Alan and Chris.

The power might very well be the reason I experiencing this blurriness. Just for reference, my knob on the AVR was around -8dB and is was driving 2xM80s and the VP180, the Denon was pretty hot. I usually don't have it at this level unless in another room. I wasn't aware of this "incipient clipping", I just knew of the chopping clipping that I experienced once when I had the knob at +5dB and since then I set the receiver to the max on the knob being 0 in case the teenage daughter decides to crank it up as I never heard chopping at this level. I understand that the chopping can damage the tweeters but can this incipient clipping damage them too? Should I lower even more the max level on the receiver?

Bruno,

No, not usually, but remember that the "0 dB" point on a given receiver's volume setting is only approximate. I'd view anything close to 0 dB as dangerous territory in terms of rising distortion levels that may become audible prior to actual clipping. If certain levels sound mushy, edgy, harsh to your ears, I'd lower the level.

To determine a particular receiver/amplifier's point of actual clipping, you'd have to measure it on the test bench driving a fixed 4-ohm load with a distortion analyzer and follow that up with actual listening tests with a music program signal and a panel of listeners, noting the level at which everyone agreed that the playback signal seemed harsh. It's a very complex process, complicated by the fact that there is individual variation from one person to the next as to what is subjectively perceived as "too loud."

There are cultural factors as well. Have years of listening to over-amplified rock concerts conditioned or prepared some of my friend's and colleague's ears to tolerate much louder playback levels than I can tolerate? (I grew up with largely unamplified music, both in the instruments I play and the concerts I've attended). There are cetain kinds of highly amplified and distorted "grunge" guitar/heavy metal that I can't stand (TomTuttle likes it, because I presume his ears are "used to" or conditioned to like it, as are some of my Axiom colleagues.)

It's really interesting territory.

Cheers,
Alan

One thing I don't understand though, Many times I've read on this forum that the M80s actually will play very loud using not too much power (from my understanding, 60W will get them to play very loud) and the the extra power is overhead. I don't think that I had them to extreme levels, so shouldn't my 105W/ch have enough overhead for me to play them loud without distortion?

Keep this in perspective what Alan wrote and that you are driving 3, 4 ohm speakers.

Keep in mind that all amplifiers driving 4-ohm loads will have higher measurable (not audible) distortion because of the increased current flow through the output transistors---more heat, more distortion. If you look at the distortion curve on an amplifier as the power output increases, you'll see the distortion figures ramp up just before the amplifier reaches the "knee" of the distortion curve when it actually clips.

Do you have pre-outs on the 890? You might want to look into a separate amp stable down to 4 ohms for the front 3.

Since you said it is running pretty hot, you should take a temperature reading on the Denon during normal use and see what it is running at.

Correct, Bruno; unless the level was extreme, say above about 105dB, distortion in your 890 wouldn't have been an audible factor.

Dr, on the 890 I don't have pre-outs, but even if I did, I am not sure I would go with a separate amp in my current sized room. As I said, I rarely have them play at these levels. I'll try to get a temp measurement though.

John, I don't have a SPL meter but I don't think the volume was extreme, loud yes but not extreme. Extreme levels were once when I turned the knob to to +5 and started to experience clipping.

I still think it might be room related, the highs seem to have an accurate sound but both channels seem to get mixed together rather than well defined as at lower levels. Tomorrow I'll try to cover the rest of the hardwood floor with bed sheets and pillows and see if it helps.

How about the walls? Do they have any sort of covering? If you're loading the room, reverberations from the walls will be a big contributing factor.

Bruno, I just did a quick search for lab test results on the 890 and didn't find any, but I did find these on the Denon 2309(889), which should be close enough. Generally on music distortion has to be above about 1% to be audible, and the Denon unit is capable of driving both 8 ohm and 4 ohm loads cleanly to beyond safe listening levels. It appears that what you describe is unlikely to be related to amplification.

It's good to have an SPL meter for determining the sound levels that are actually present during listening even if(as I do)the calibration of levels is done by the receiver auto-calibration system. We should always be cautious about sound levels which cause hearing loss. This also allows more accurately judging actual power requirements at various moments.

Your situation may be due at least in part to room effects, so experiment. It may be difficult for you(and impossible for us, of course)to come up with the best solution.

Nothing on the walls as well and this will be harder to experiment, at least for now. I'll try covering the floor and let you know.

A different scenario all together, I know. However, I'll add that with my Denon, a small room, and M60s, I don't have to go anywhere zero or sub zero to hear 105db peaks in some material. In louder material, I've experimented and roughly "maintained" 100db with much higher peaks at only about -7.

All scenarios differ but my point is that unless you have a db meter, you might not realize just how loud or, to be fair, not loud it really is.

I'll add a similar data point. With Sony mains (which are probably less efficient than the M60s), and Pioneer receiver at -6 I was maintaining a 100 dB level playing Bjork's Vespertine DVD-A.

Murph is right about the meter. I bought one a few days ago and it is very interesting to find out how how loud something really is.

If you have an iPhone or an Android phone, you can get a free app that will measure SPL. It might not be quite as accurate as a dedicated RS meter, but it's "something".

Bruno, you have a lot more area on the walls than on the floor, so you might want to consider a temporary experiment, even if it is only tacking a sheet on the back wall or something. The floor represents a relatively small percentage of the surface area of your room, and the furniture is going to diffuse the sound a lot there anyway.

OK, maybe the amplifier has something to do with it but the room has definitely something to do with what I am experiencing. First I tried covering the rest of the hardwood, it sounded a bit better. Then I tried hanging some bedsheets and piling up all the pillows that I could find and it also improved a bit, the highs were still a bit high but they didn't seem to mix both channels has much. Finally, I turned Audyssey ON (it was OFF) and even though it didn't sound as natural to me, the highs were tamed down a bit, so less blurriness. Well, unlike some people, I have the WAF factor and I don't think she will enjoy all the drapes in the living room and all the pillows on the floor , so I guess I'll just keep it down for now (it was too loud anyway) and one of these days I'll get at least some curtains which will help a bit. One day I'll also get a SPL meter as I am curious now to how loud it was playing. Thanks all for your input.

Bruno

You can get panel treatments (which tame treble, not so much bass), with photos printed on them. Designed specifically for the WAF.

I once dragged my queen size mattress into my living room. It worked wonders. Do you think your wife will let you do that?

Good idea, I'll have to google that! I bet this was designed by men

LOL! I'm sure she'll love it!

Here's a couple I had bookmarked (not that I was interested in these, being a single male, but other products from the same makers).

http://www.asc-home-theater.com/picture-panel.htm
http://www.auralex.com/sonicprint/
http://www.gikacoustics.com/gik_artpanel.html

When I asked a friend who’s an audio engineer I might benefit from room treatments on my back wall. He said I should throw a mattress up against the back and if that made a difference then I probably would.

Hi Bruno and all,

This has been a really interesting discussion, however, without an SPL meter and actually visiting your room, it's very difficult to determine what's going on. I threw out some of my own speculations as to what might be happening, and here's another one to "chew" on:

I do know that in our hearing system there is a muscle in the ear that attenuates hearing sensitivity when we are chewing food so we won't be deafened by the sound of our teeth grinding away on food. I once talked about this with Dr. Floyd Toole and I seem to recall him saying that our ears actually go into distortion when confronted with extremely loud sounds. I don't have Dr. Toole's book with me and I don't recall if he deals with this subject, however, I will email him and run this subject by him to see what he has to say.

In my own experience with loud sound or music, if I don't cover my ears, use ear plugs or get away from the very loud sound, what I subjectively experience is a kind of intolerable blurring and "distortion" if you will, of the music.

Regards,
Alan

I've heard that ear distortion too at loud concerts, it does sound a lot like clipping.

That muscle you're talking about, it can also attenuate continuous loud sounds. But something like a hammering, gun shots, or other sudden, loud bursts don't cause the muscle to tighten up at all, or else too late. Those types of sounds can be very damaging.

You're absolutely correct, Club Neon.

Hi all,

Dr. Toole replied to my email, and has gone into considerable detail about Bruno's situation and the non-linear nature of the ear with high-volume playback.

Floyd Toole responds:

"The following comments assume that no clipping or distortion is being generated within the power amp. Several comments in the forum correctly note that a 4 ohms load impedance is close to the current limiting spec for lots of receivers, so this is a very real possibility. BTW, when listening to music clean clipping is hard to hear until it exceeds about 6 dB, which allows us to get away with undersized amps for non-critical applications. However, when it does become audible virtually all aspects of sound quality are seriously degraded. Also, some amps don't "clean clip", Power supply voltages sag, causing several problems, or they can revert to a protective mode that does strange things.

Let's look at what room acoustics can do. Bruno's addition of the rug obviously reduced the overall reverberation time in the room, making it more acceptable (ideally the reverberation time should be less than 0.5 s at mid frequencies). However, being on the floor, it can do nothing to change reflections in the horizontal plane - i.e. among the walls. Our ears are in the horizontal plane, and therefore are more sensitive to these reflections than to those in the vertical plane, where the new rug would have it dominant effect..

Now, to get into imaging we need to be aware that imaging will be most "clear", most "sharp" when the direct sound is the dominant factor. The more reflections in the horizontal plane that are audible, the more decorrelated, or confused, are the sounds arriving at the two ears. A certain amount of this is highly desirable, adding a pleasant sense of ambiance, or "air" around the instruments, called in the scientific literature "ASW - Apparent Source Width". However, too much of this results in what Bruno describes: "the sound became more "blurry". Why does this occur when the volume is turned up? Because more of the lower level reflections become audible; they have been elevated above the audible hearing threshold. Grunt's comment about the highs being annoying in a live room are part of this. Most high frequency sounds are transient in nature and they draw attention to themselves, making the reflections more distracting, and the soundstage more "blurry".

Also, as Alan points out, the ears become increasingly non-linear at high sound levels and we are less able to discriminate fine details, both spectral and spatial. In the reverse direction, as you turn the volume down, the soundstage gets progressively more simplified, until almost all sense of "air", space and envelopment is gone. This is why we recommend that serious listening - foreground listening - be done at a moderately high level; but not too high, obviously.

So, how can this situation be improved in Bruno's room?

Nowhere in these discussions did I learn where Bruno's head is with respect to the rear wall. If there is a bare wall close behind the listener, all bets are off. The first thing to do is to place a broadband absorber behind the head - something fibrous (a cushion, fiberglass, etc. that is not less than 4 inches thick). Reflections from the back wall corrupt the perception of the front soundstage. We tend to get tied into knots worrying about where we put the loudspeakers, and then sit down in a chair backed up against a rear wall. This is not logical, right?

If this is not an issue, I suggest more furniture, or more acoustical treatment, mostly on the side walls. Either or both will be beneficial. In general, surface irregularities - bookcases, display cases, tilted pictures, etc - are useful, as are purchased "diffusers", so long as they are moderately thick (ignore the "toy" diffusers that are only 2-3 inches thick - they only work at tweeter frequencies). A certain amount of absorbing material may be needed if the room is too live, but don't overdo it; excessively dead rooms are not pleasant places in which to spend time. Scattering the sound using furniture or irregular surfaces makes whatever absorption that is in the room work harder, and the sound energy is preserved.

Of course, all of this and more is explained in my book: "Sound Reproduction", Focal Press 2008."

Good luck,
Floyd

So now I've learned from the top guy that not only does my room suck because it's square, but also because my couch is up against the rear wall.

Someday, I'm gonna build me a room....

No, you're not.

Thanks for posting that Alan. Very informative as always!

Its time to get down to business.

Very interesting Alan(and Floyd). Tks.

It makes me wonder how many people have spent so much more $$ on "upgrading" speakers, when all they needed were some simple room treatments.

Alan, it's great that your former association with Dr. Toole at the NRC has allowed us to have the benefit of his knowledge here.

Okay Bruno, you heard Dr. Toole; get that mattress out of the bedroom and put it up on the wall behind you!

Incidentally Alan, the "auditory reflex" which you mentioned above, in which the ear tries to protect itself against very loud sounds(only partially successful, unfortunately)is briefly discussed by Dr. Toole at pp. 437-438 of Sound Reproduction.

Page 437. I'd have to be reading tolkien or something interesting to get that many pages in!

This is true and could probably be the case with Bruno. However, Dr. Toole and Dr. Olive also stress when buying a system is to spend money on quality speakers above all else and just not put them in too live of a room to begin with. Minimize room treatments. In recent postings by Dr. Olive stresses over treating a room as waste - the same point Dr. Toole was making towards the end about Bruno's situation.

Very cool to see the response from Dr. Toole, thanks Alan. I was going to post a couple follow-up questions but instead I ordered the book. I love/hate Amazon.

If WAF is a consideration, you might try a large plant or ficus tree in each corner behind your listening spot as well as a bookshelf on your side wall.

How lucky are we here that we have so many experts but also experts who are friends with experts. Best of all, things mostly stay light and entertaining while we learn.

Back when I used to be more "hands on" in computers and networking, I would frequent a few technical forums and while they were extremely good places to learn and have assistance from top minds in the business, there was always zero entertainment value and you only asked question that was "worth" of their expertise or that was probably going to be a thread with zero replies.

Sorry, I've been away for a few days. Thanks Alan and Dr Toole, what a great explanation!

I also thought it had more to do with reflections more than the amp, specially after playing around with bed sheets and pillows, but wasn't really sure why, now I know

Unfortunately, I don't have a dedicated room, I use my living room that is 20x11 ft. To answer Dr., I seat in the center of the long side wall and my TV and speakers are across. My couch is against the wall and on top of that, behind the main listening position is a bay windows so no acoustic panel can be there. As for the sides, they also unusable for acoustic treatment, one side is open towards the hallway, the other has a bay window. The only thing that could really be done (on top of bringing the mattress, pillows, bed sheets, etc.. into the living room ) is adding a bit of furniture and putting thick curtains on the bay windows.

Thank you all for your help, this has been great.