How to Treat Small Room Acoustics

[jim1961]

jim1961: Wow, 0.16 s. That is truly dead - too dead for comfortable conversation for most people. Why?

Not as dead sounding as you may think.

In this case, rt60 is misleading. I have significant reflections at 25ms (@120 degrees) and to a lesser extent at 27ms (@60 degrees)

A RFZ ISD + Termination model.

 

[Floyd Toole]

Jim1961 At least the reflections are high frequency - one-inch fluff will kill them. Is this a stereo room or HT - or both?

 

[jim1961]

Jim1961 At least the reflections are high frequency - one-inch fluff will kill them. Is this a stereo room or HT - or both?

I dont want to get rid of them. They are there by design (ISD termination).

This is a 2 ch. dedicated listening room. Not a casual conversation room.

https://www.gearslutz.com/board/studio-building-acoustics/817205-my-listening-room.html

 

[TheWarrior]

Warrior: I don't know about localization precision with QRD reflections. More research, I guess. Because these are secondary to the direct sound, normally suppressed by the precedence effect, it might be a moot point. If the precedence effect breaks down for some reason, the the reflections will be localizable, but the most probable reason for breakdown in our small rooms is that the spectrum of the reflection is different from that of the direct sound. - i.e. either bad off axis loudspeakers being specularly reflected, or reflections that are spectrally distorted. That is why I tend to favor acoustical treatments of two kinds: absorb it all, or reflect it all. Anything else adds risk of degrading good loudspeakers. That said, there are some manufacturers of engineered diffusers who publish reflection spectra for their devices. If that is good, they are an option, remembering that we now know that they may not change the audibility of the reflection as we once thought. Confusing, eh?

I asked about QRD because I do not have any experience with diffusion. It makes sense to me, as you stated, that a diffusor makes an absorber work harder. Is it for that reason that you 'treat' rooms as either absorptive, or reflective? Are there any broad examples of where you would be inclined to use both?

Curious. Is there a measurement for how diffuse a QRD is, or how well it scatters? I am still questioning the relevance of this new data you cited. As I understand it, a diffusor should not dampen but rather, redistribute a sound wave so that it is more difficult to localize. So to a microphone, the sound wave should read the same dB with or without the diffusor in place, but a microphone does not use the signal to create a 3-D image the way the brain does.

Or is it really just a matter of knowing when to use diffusion, or absorption?

 

[Floyd Toole]

OK Jim, you win. This is truly a DEDICATED room! I like your "throne" chair. If it works for you, that's great. BTW, what is ISD termination?

If we had multichannel recordings, most of what you have done would not be necessary. But it's a lost cause. Pity.

 

[Floyd Toole]

First, spelling: diffusers are devices that diffuse or scatter sound. Diffusors are made by RPG - it is a brand name. RPG has set the pace for developing high performance diffusers, and they have gone so far as to have developed the methods now standardized for measuring their performance. I discuss this in Chapter 21 and show examples. There you will see that simple inexpensive semi-cylinders are very effective diffusers, so long as you don't place them side by side - there must be space, preferably randomized, between them.

Diffusion in a concert hall is essential to deliver sound to all parts of the hall. In a recording studio it helps to blend the sound from multiple instruments. In a small listening room it is really of limited value because we are in a ritualized geometric arrangement and all of the sound comes from relatively directional loudspeakers. We don't want or need a diffuse sound field for stereo or multichannel listening. Multichannel audio generates it when it is needed, and not, when it is not. That is one of the advantages.

The microphone will show a collection of returns from a QRD, lower in amplitude than from a flat surface, but the brain appears to add them up. Again, psychoacoustics intervenes - what we measure is not always what we hear. But when it is, that is powerful medicine.

 

[jim1961]

BTW, what is ISD termination?

Seriously?

 

[whatthedileo]

''Many people in recreational listening actually preferred early reflections''

The word 'recreational' is a caveat that agrees early reflections are artifacts, and I concur. That's why, ideally, I don't want any reflections anywhere in my theater!

We are often advised to use a combination of absorption and diffusion to avoid an unnatural 'dead' room where you go into sensory deprivation when the system is not turned on. But I don't care how people feel before the movie starts... I'm interested in the performance.

Doesn't a perfectly dead room give you the envious purity of sound that we love in a great pair of over-ear headphones?

 

[Goliath]

Hi Floyd,

Great admirer of your work and I've read many of your papers. Since we are discussing acoustics, I thought I might show you a pic of my room :

My room is quite small (apartment) so I've added 4" thick absorbers on the rear wall, two for the front to tackle possible SBIR and two for the ceiling to address early reflections there.

No diffusion. What do you think of my treatment plan, and would you suggest I keep things as is, or would you recommend a different approach? Please be brutally honest. I can take it.

Sorry for the thread hijack.

 

[TheWarrior]

First, spelling: diffusers are devices that diffuse or scatter sound. Diffusors are made by RPG - it is a brand name. RPG has set the pace for developing high performance diffusers, and they have gone so far as to have developed the methods now standardized for measuring their performance. I discuss this in Chapter 21 and show examples. There you will see that simple inexpensive semi-cylinders are very effective diffusers, so long as you don't place them side by side - there must be space, preferably randomized, between them.

Diffusion in a concert hall is essential to deliver sound to all parts of the hall. In a recording studio it helps to blend the sound from multiple instruments. In a small listening room it is really of limited value because we are in a ritualized geometric arrangement and all of the sound comes from relatively directional loudspeakers. We don't want or need a diffuse sound field for stereo or multichannel listening. Multichannel audio generates it when it is needed, and not, when it is not. That is one of the advantages.

The microphone will show a collection of returns from a QRD, lower in amplitude than from a flat surface, but the brain appears to add them up. Again, psychoacoustics intervenes - what we measure is not always what we hear. But when it is, that is powerful medicine.

Thanks for the clarification on diffuser. And for pointing out the brand name whom also has established testing!

I have not reached Ch.21, I keep re-reading the first 150 pages or so, and going over it with a hi-liter. It's being treated as a textbook, And my room sounds better for it!

It just amazes me though, even with all this data, there is still so much we don't understand.

 

[Floyd Toole]

whatthedileo: In double blind tests done by me and several other independent researchers, a high proportion of listeners, including recording engineers, preferred reproduction with significant lateral reflections when listening for pleasure. Not everybody though - it is a free world, so if you like the room dead, that is entirely your privilege. Where dead rooms appear to have a strong following are with recording engineers during the mixing operation. They say it makes the job easier. With so many of them having hearing impairments (it's an occupational hazard) there is logic to it because of deteriorated binaural discrimination. People with normal hearing can deal with reflections much more easily than those with hearing loss - something I know about from personal experience. Take away reflections though, and you hear the enormous interaural interference dip in the phantom center image sound. It's about an octave wide, 10 dB deep around 2 kHz. See Figure 9.7 in my book. This is one reason why, when a comparison is made, the sound quality improves - at least for the featured artist - when there are some reflected sounds. The speech intelligibility goes up too. This interference dip does not happen in headphones, but then you sacrifice stereo. It is entertaining, but not the soundstage and space that the artists created.
Now, though, there is some new data from McGill University's tonmeister program where they examined the performance of recording mixers in situations where early lateral reflections were absorbed, reflected or diffused. The interesting result was that they quickly adapted to whatever situation they were in and carried on working with no apparent impairment. When asked which they preferred, there was a nearly equal split among the three conditions. The tests were blind. So, as I said, if you like it, go with it. In my recommendations for room design I specify the adjacent wall area as "optional" for treatment.

Goliath: you have done a very sensible job. The biggest problem would be the wall immediately behind the listeners. You have done exactly what I recommend - 4-6 inches of fiberglass. Eliminate that reflection. The wall behind the speakers is optional, but again, your panels are thick (good!). The enemy of good sound is thin absorbers - 1 to 2 inches - which just turn the tweeter down, degrading the performance of good loudspeakers. You appear to have sidewall reflections on one side, if the drapes are open, which as I just said are optional in any event. You are in a dominantly direct sound field, like the one preferred by "whatthedileo". Even though I am routinely accused of promoting early lateral reflections, my own listening room has none, the right wall is open to the rest of the house, and the left wall balances that with thick drapes

Warrior: The originator of RPG, Dr. Peter D'Antonio, and Dr. Trevor Cox (Salford University) have published what I believe to be the definitive book: "Acoustic Absorbers and Diffusers" (note the spelling of diffuser), now in its second edition. There is real science behind some of this stuff.

 

[gene]

Even though I am routinely accused of promoting early lateral reflections, my own listening room has none, the right wall is open to the rest of the house, and the left wall balances that with thick drapes

Floyd;

We have a similar situation. No right wall in my room and absorption and thick drapes on my left wall.

Perhaps you can address a question in my mind.

When you have absorption stretched over fabric, does that NOT make the absorption panel a poor off-axis absorber? In other words, it's better suited to deal with flutter echos but won't be as effective absorbing off-axis sound from a speaker?

Also, how does placing thick drapery over an absorptive area affect the absorption of the panels?

 

[gene]

Hi Floyd,

Great admirer of your work and I've read many of your papers. Since we are discussing acoustics, I thought I might show you a pic of my room :

My room is quite small (apartment) so I've added 4" thick absorbers on the rear wall, two for the front to tackle possible SBIR and two for the ceiling to address early reflections there.

No diffusion. What do you think of my treatment plan, and would you suggest I keep things as is, or would you recommend a different approach? Please be brutally honest. I can take it.

Sorry for the thread hijack.

Very nice room, very cozy. That is a massive center channel! Where is/are the sub(s)?

 

[Goliath]

Very nice room, very cozy. That is a massive center channel! Where is/are the sub(s)?

Hi Gene. I have an SVS SB2000 hidden on the other side of the couch. : )

In my previous place I had dual MFW-15 subs, but I downsized and had to sell them.

Problem is, bass response (to me) is still crappy. Bass still booms, even above 100 Hz. I can't employ any additional broad band traps otherwise it will make the room even deader than it already is, and it's already a little too dead for my liking.

So to my way of thinking the only approach I have left is to use DSP on the bass range (150 Hz and down). My objective was not to have a (largely) "reflection-free" space, it just turned out that way, and I'm just understanding now that small rooms like mine just suck, no matter what.

Oh the speakers are Paradigm Studio 20 v5, using the CC690 center and ADP590 surrounds. Yep, it's a big one. The Studio 20's were used in a surround role in my previous place with the Studio 100's taking front duty.

Reluctantly sold them, downsized (once again), but I decided to keep the center. Very happy with dialog intelligibility, plus it's a conversation piece.

 

[Goliath]

Goliath: you have done a very sensible job. The biggest problem would be the wall immediately behind the listeners. You have done exactly what I recommend - 4-6 inches of fiberglass. Eliminate that reflection. The wall behind the speakers is optional, but again, your panels are thick (good!). The enemy of good sound is thin absorbers - 1 to 2 inches - which just turn the tweeter down, degrading the performance of good loudspeakers. You appear to have sidewall reflections on one side, if the drapes are open, which as I just said are optional in any event. You are in a dominantly direct sound field, like the one preferred by "whatthedileo". Even though I am routinely accused of promoting early lateral reflections, my own listening room has none, the right wall is open to the rest of the house, and the left wall balances that with thick drapes

Hi Floyd,

Thank you very much for your feedback and comments, much appreciated! If I could do it all over again I might have opted for diffusion/absorption, but then I'm not sure if diffusion can work effectively in spaces as small as mine.

Interesting to know that your listening room doesn't have lateral reflections. I actually thought the opposite would be true! Thanks again for your feedback!

 

[Floyd Toole]

In the listening rooms where we evaluate loudspeakers we usually allow lateral reflections because the quickly reveal loudspeakers with crappy off-axis performance. It is this that most people either ignore or don't know about: that the effect of lateral reflections is different depending on the dispersion characteristics of the loudspeakers. If you have loudspeakers with uneven off-axis performance, it is highly probable that you will think less favorably about lateral reflections. That said, when we gave listeners the preference between almost no lateral reflections and some imperfect ones, they tended to prefer imperfect reflections to none at all. Not my opinion - that's what the listeners in blind tests said. See section 8.2.1 in my book. Incidentally when interrogated about imaging, soundstage and the like, the descriptions tended to favor having some reflections. Two ears and a brain are a marvelous instrument, sometimes preferring complexity to simplicity. Think about the complexity of the sound field in a concert hall - a reference listening experience. Stereo alone does not contain enough information.

 

[gene]

Hi Gene. I have an SVS SB2000 hidden on the other side of the couch. : )

In my previous place I had dual MFW-15 subs, but I downsized and had to sell them.

Problem is, bass response (to me) is still crappy. Bass still booms, even above 100 Hz. I can't employ any additional broad band traps otherwise it will make the room even deader than it already is, and it's already a little too dead for my liking.

So to my way of thinking the only approach I have left is to use DSP on the bass range (150 Hz and down). My objective was not to have a (largely) "reflection-free" space, it just turned out that way, and I'm just understanding now that small rooms like mine just suck, no matter what.

Oh the speakers are Paradigm Studio 20 v5, using the CC690 center and ADP590 surrounds. Yep, it's a big one. The Studio 20's were used in a surround role in my previous place with the Studio 100's taking front duty.

Reluctantly sold them, downsized (once again), but I decided to keep the center. Very happy with dialog intelligibility, plus it's a conversation piece.

I think you can certainly do some improvements with manual PEQ for your situation. However you will need to pull some measurements at your seating location to see where the problems are. Definitely don't add more passive treatments if you feel your room is already too dead. My theater room was initially over treated and it wasn't pleasant to have a conversation in. I actually scaled it back and added a hardwood flooring and now its a much more pleasing environment.

I think you did a great job given the size of the room. You may want to consider adding a second sub in the back left corner to see if that helps things out a bit. Again you need to pull some measurements.

 

[Goliath]

I think you can certainly do some improvements with manual PEQ for your situation. However you will need to pull some measurements at your seating location to see where the problems are.

Done the measurements at the LP. Used my trusty UMIK-1 with REW. Ringing is pretty bad below 100 Hz, but then my entire FR is pretty bad below 100 Hz. I have a peak in the 100-200 Hz region as well, otherwise it's smooth sailing, relatively speaking.

The solution I've been considering is the MiniDSP/Dirac Live. Have you used it before?

I think you did a great job given the size of the room. You may want to consider adding a second sub in the back left corner to see if that helps things out a bit. Again you need to pull some measurements.

Encouraging to hear, thanks for your comments! I'm already getting complaints from the neighbors with one sub. Two subs, well.... I definitely want to add a second sub later to smooth things out, just need to find the funds.

Thanks for your comments.

 

[nickboros]

Encouraging to hear, thanks for your comments! I'm already getting complaints from the neighbors with one sub. Two subs, well.... I definitely want to add a second sub later to smooth things out, just need to find the funds.

I think you were kind of joking about this, but you can never be sure, since all I am reading is text. But, adding a second subwoofer won't do much give you more headroom. I guess you could get the most benefit if you stacked the subs. But, it is more about getting even response throughout the room. Finding the best location in the room to minimize the seat to seat variation. Again, I don't think this is what you meant, and the article clearly explains this. But, on various forums I can see many people have this point of confusion.

 

[jim1961]

The solution I've been considering is the MiniDSP/Dirac Live. Have you used it before?

My measuring setup is Umik/REW/miniDSP. Only got the miniDSP a month or two ago. Was a big help in smoothing my subs FR. May or may not help with ringing. Depends on the primary source of it.