Room size and dynamics?

[Rip Van Woofer]

I have read -- from reliable enough sources to accept that it's true -- that one of the limitations a small room imposes on a system is the apparent dynamic range; in particular, the subjective loudness of dynamic peaks.

Since upgrading to larger speakers in the same small room, and also temporarily setting up the speakers in a larger room for comparison, I have experienced this first hand.

So just out of curiosity: What is the underlying mechanism? Has it been studied?

As I am aware that acousticians often treat some acoustical phenomena as analogs of electronic principles I wonder if the acoustic impedance of various air volumes has something to do with it?

It almost seems as if a smaller room becomes "saturated" with sound sooner, for want of a better description.

Like I said, just wondering. Meanwhile, I have to build a larger room.

 

[Ethan Winer]

Rip,

> one of the limitations a small room imposes on a system is the apparent dynamic range; in particular, the subjective loudness of dynamic peaks. <

Unlikely. If it were true the underlying mechanism would be distortion. But rooms don't create distortion, other than perhaps rattles and buzzes.

> I have experienced this first hand. <

There are many acoustic problems in small rooms, but I have to assume what you're hearing is something other than distortion.

> It almost seems as if a smaller room becomes "saturated" with sound sooner, for want of a better description. <

Perhaps what saturates earlier is your ears? Otherwise I'd chalk it up to the badly skewed response, multiple early reflections, comb filtering from the many nearby surfaces, and so forth, typical in all small rooms.

--Ethan

 

[Rip Van Woofer]

Ethan;

Thanks, that makes sense. I was hoping you or another pro would answer! I was careful of course to to say "apparent" dynamic range, meaning subjective.

So basically, the myriad distortion mechanisms at work (skewed response, comb filtering, etc.) in a small room make large dynamic peaks less clean, thus giving the impression of less "easeful" (to use a word I've seen) dynamics - not an actual compression of dynamic range.

Yes, I have heard other colorations in my smaller room vs. the larger one (and I suspected comb filtering for those) so that fits with your explanation too.

 

[Ethan Winer]

Rip,

> So basically, the myriad distortion mechanisms at work (skewed response, comb filtering, etc.) in a small room make large dynamic peaks less clean <

Well, all that stuff makes everything less clean. Soft clipping, which is really what "compression" would imply, adds new content in the form of THD (the frequencies added are related to the source) and IMD (frequencies are not related). But none of that happens in a room. Lots of other nasty stuff happens in a room though!

I'll also add that audiophiles seem to have invented a lot of their own nomenclature for things that are already well understood and defined. Like noise, distortion, frequency response, etc. It's always a challenge for me to understand what the heck they mean by "rhythm" and "pace" and all the other buzzwords those flowery magazine writers like to use. As a musician, the words rhythm and pace are already used for something else. Then again, obfuscation is not new or limited to audiophilia.

--Ethan

 

[Buckle-meister]

One of the limitations a small room imposes on a system is the apparent dynamic range; in particular, the subjective loudness of dynamic peaks.

Unlikely...

What about decay? Whilst sound decays at the same rate in air regardless of the room it's present in, simply by virtue of the fact that in a small room one is always close to a boundary and therefore subject to a greater degree of reflected sound before it decays to inaudibility, wouldn't this result in reduced as-heard dynamic range? After all, absorbent room treatment reduces ringing time or 'lingering' sound. Doesn't it then follow that if the sound doesn't 'linger' as long, the as-heard dynamic range would increase?

Just a thought.

 

[tbewick]

I've heard it's called echo clutter.

"A living room 19 feet 8 inches long by 9 feet 3 inches wide with an 8-foot ceiling (6 by 2.8 by 2.4 metres) has the same dimensional ratios as Boston's Symphony Hall on a 1:8 scale. For a centrally located listener in Symphony Hall the first reverberant echo from the rear wall arrives 140 milliseconds after the direct sound is heard: in the lining room it arrives in only 17.5 milliseconds and can bounce back and forth seven additional times before the first echo is heard in the concert hall. The multiplicity of closely spaced reverberant echoes experienced in home music reproduction seems to give rise to an exaggerated sense of loudness that has been called "echo clutter." With foresight in microphone placement and various tricks... it is possible to create a very plausible illusion of "concert-hall sound" in the home. To do even this, however, demands much of the high-fidelity components."

Encylopaedia Britannica, 15 edn, Vol 27, p624-625.

The bibliography has many references for further information, including:

Lord Rayleigh, Theory of Sound, 2 vol. (1877-78; rev. ed., 1926; 1-volume ed., 1945)

Wallace C. Sabine, Collected Papers on Acoustics (1922, reprinted 1964)

The BBC R&D page has some white papers on studio acoustical design.

 

[Rip Van Woofer]

Hmmm...I'm not sure of the decay hypothesis myself as it relates to dynamic range. Except that very live rooms can indeed sound "louder" with all the sound jangling around. But that goes for shower stalls as well as cathedrals.

So more accurately, my (and others') subjective impression of less dynamic range in a smaller room is a psychoacoustic response to the many inherent defects of a smaller room...not necessarily a real reduction in dynamic range.

In fairness to us audiophiles (but not to audio writers who should know better!), it is difficult for the layperson to put what one is hearing into words if the underlying causes such as noise and distortion are not apparent or easily isolated. It takes training and experience to go from "the midrange sounds recessed" to "there's probably a broad dip centered at about 2.5kHz". Our language seems inadequate to describe many sensory phenomena, so we reach for similes and metaphors. Quick: describe "red" to a person who has been blind since birth.

But I never got "rhythm and pace" as applied to audio gear myself either. How can a speaker or amp change tempo??

EDIT: Seems tbewick and I were posting at the same time. "Echo clutter", huh? Interesting...

 

[tbewick]

I've referred to this book several times in a few posts - Practical Hi-Fi Sound, R. Driscoll, Hamlyn. He was (and maybe still is) a lecturer in acoustics.

"A well-planned listening room must be one which produces an unobtrusive sound field, both under steady-state and transient conditions."

For dynamics, I think that the transient conditions are what can be problematic. I find that this is very noticeable with instruments that have an important transient contribution to their character. Solo violins and female vocals tend to sound too bright and piercing in my living room.

He also says that steady-state conditions are often not reached in a normal domestic living room.

"Ideally, the sound field in a small room should be as it is in a larger room, random and diffuse at all frequencies, for then changes in sound level will be smooth and unobtrusive."

Really the whole chapter on acoustics in this book is interesting and it is quite difficult to summarise. Sabine's qualitative description of acoustics given in the book does resemble some of the things Bucklemeister was talking about.

I do think that scale has something to do with it. It's easier to accept there being a loud noise when it is perceived to be coming from further away, this being the case in larger rooms.

 

[Ethan Winer]

Robbie,

> What about decay? Whilst sound decays at the same rate in air regardless of the room it's present in, simply by virtue of the fact that in a small room one is always close to a boundary and therefore subject to a greater degree of reflected sound before it decays to inaudibility, wouldn't this result in reduced as-heard dynamic range? <

I don't see why. The key is that room echo and reverb are linear. The louder the source, the louder the echoes. For sure, all that echo can have you putting your hands over your ears and yelling "Stop!" when it gets too loud. But this is not the same as "compression" that responds nonlinearly.

Another factor is the frequency response of the echoes. In most too-live small rooms some echo frequencies - often harsh midrange stuff - are emphasized more than others. So that's another reason the sound is more irritating in an untreated room.

--Ethan

 

[Ethan Winer]

Rip,

> It takes training and experience to go from "the midrange sounds recessed" to "there's probably a broad dip centered at about 2.5kHz". <

Indeed. My background is in recording, so I learned 35+ years ago what the various frequency ranges sound like by playing around with graphic and parametric equalizers.

Maybe I should hold a workshop for audiophile magazine writers to teach them about this stuff.

Seriously, I've also toyed with the idea of writing and recording a pop tune and making the raw tracks available to audiophiles along with a freeware multi-track DAW program. I think it would be very valuable - and humbling! - for some of these "golden ears" to experience first-hand what's involved in the music recording process. They'd also learn just how bad auditory memory really is, as they fuss for three hours to make a perfect mix only to realize the next day that it sounds like total crap.

--Ethan

 

[WmAx]

I have read -- from reliable enough sources to accept that it's true -- that one of the limitations a small room imposes on a system is the apparent dynamic range; in particular, the subjective loudness of dynamic peaks.

I am not aware of this being a hard rule. I'm familar with much of the general perceptual research in this area of reverb/reflection effects on human perception[though I can not think of a study that directly addressed dynamic range perception based on room reverb or reflection time], but I can not think of how a small room in itself must cause a problem as you describe, unless it's just a distortion of your perception due to result of using improperly treated or non-treated acoustic listening space. The effect may be simply related to the negative impression/quality an overbearing short reverb/delay time combined with high amplitude vs. direct sound. Refer back to the thread you started about room noise floor perception level. I think this may be a related issue. Looking at it from one perspective: if you have a small room with prominent early reflections, and then compare the same setup in a substantially larger room with more spacing from the walls, the reflection time vs. direct sound will increase. Human auditory system will tend to prefer longer reflection time and reverb time, as compared to shorter time spans, since shorter time differences are percieved as interference, where as longer different times are percieved as ambience enhancement. Perhaps a certain combination of this is causing you to percieve some sort of dynamic range difference. If one applies specific treatments for a room given a specific speaker and listening position/speaker position, most of the inherant room problems concerning midbass to treble should be nullified. The Orion speaker you are using is intended to make use of 1st reflections more so than most other speakers, and as such, this speaker can not be properly[as defined by the designer] used in a small room that does not allow the [rather large] recommended spacings for that speaker. Many speakers can be used in such smaller rooms by use of increased number of room treatments to heavily reduce 1st reflections. But with a speaker such as the Orion use of more treatments to reduce the reflection amplitudes further because of the required close spacings in a small room to improve sound, will in turn be counterproductive and nullify many of the psychoacoustic effects that this speaker is excellent at producing by it's efficient use of the 1st reflections in it's intended environment.

This reply I have provided is rather ambiguous; a result of trying to guess what your specific percieved problem might be. Please address specific points if you desire specific information.

It must be noted that you have two primary delay times to be concerned with: the 1st reflection time vs. direct sound and the overall room reverb characteristic. You also must factor the direct sound SPL vs. reflected/ambient SPL ratio. You can reduce the ambient energy by using absorbers/diffusors within the room at non-first reflection points. Or you can reduce the ambient energy by using absorbers in the path of the 1st reflections, but this is not desirable in certain circumstances[such as the Orion]. You can move the speaker closer to the listening position, thus increasing direct vs. reflected time and reducing the direct vs. reflected and ambient reverb SPL ratios. In a very small room, I don't see how one can ever have proper sound with a speaker such as the Orion, however. By small, I mean for example, 11' x 11'. The minimum spacings could not be achieved. 15' x 15' should be marginally acceptable for proper spacing/setup, if combined with acoustic treatments to control the room reverb characteristics, if it is a room that can be arranged/setup around the speaker system.

-Chris

 

[Rip Van Woofer]

Chris, I think you're onto something. In a larger room with longer delays from reflective surfaces the sound is decidedly more "spacious" than in my den. In part that could also contribute to the impression of greater dynamics. Also, my listening position in the den is decidedly "nearfield", being less than 6 feet from the speakers.

In addition, Linkwitz says that the distance from listener to speaker should be at least double the distance from the speaker to the wall behind the speaker. Otherwise early reflections from the rear wall cause mischief - maybe comb filtering? Plus the usual side reflections.

Anyway, I was wondering if I was hearing what I thought I was hearing and if so, if there was a physical and/or perceptual reason for it.

One "reliable source" was Peter Aczel who once wrote that in a smaller room you must be prepared to give up the "untrammeled dynamics" of a larger room. Some other sensible types have said similar things but I hadn't seen anything truly scientific.

In spite of all that, the low distortion and flat frequency response characterisics of the Orions still mostly come through.

Bottom line: I need a bigger room. Can't use the living room permanently due to WAF.

My planned room will be 13' x 19' x 7.5'.

But tonight I'll be listening in a very large room. Got tix for Midori with the Detroit Symphony Orchestra!