How to Treat Small Room Acoustics

[jim1961]

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.

Wondering if this is a case of favoring what one is used to.

 

[Floyd Toole]

jim1961 You are right. There is absolutely no doubt that humans adapt to existing circumstances - just as well because so much of what we hear isn't close to perfect. Good music seems to prevail in spite of it. However, over the 40 years of being involved with these double-blind tests with hundreds of loudspeakers and hundreds of listeners, the monotonous result continues to be that the highest rated loudspeakers are flatfish on axis, with uniformly wide dispersion, which can only be beneficial if those reflections are audible.

Still, there are people who are habituated to dead rooms and they like them, in which case loudspeaker directivity is not a factor, but other side effects creep in, like the acoustical crosstalk issue that I mentioned earlier. But after a while even that becomes tolerable to the point where those people don't like center channels because the interference error and spatial distortion is missing. Life can be complicated if you let it be.

Just sayin'

 

[jim1961]

jim1961 You are right. There is absolutely no doubt that humans adapt to existing circumstances - just as well because so much of what we hear isn't close to perfect. Good music seems to prevail in spite of it. However, over the 40 years of being involved with these double-blind tests with hundreds of loudspeakers and hundreds of listeners, the monotonous result continues to be that the highest rated loudspeakers are flatfish on axis, with uniformly wide dispersion, which can only be beneficial if those reflections are audible.

Still, there are people who are habituated to dead rooms and they like them, in which case loudspeaker directivity is not a factor, but other side effects creep in, like the acoustical crosstalk issue that I mentioned earlier. But after a while even that becomes tolerable to the point where those people don't like center channels because the interference error and spatial distortion is missing. Life can be complicated if you let it be.

Just sayin'

Do you mean this?

Seems a +9db gain at 2500hz is as equal a problem as a -9db one at 1600hz.

 

[Goliath]

Floyd, if I may ask - do you use any room correction in your own system/room? If so, only for the bass range or full frequency correction?

 

[Floyd Toole]

Jim1961 The curves in (c) are measured at the entrance to the ear canal, and include the HRTFs (Head Related Transfer Functions). The solid curve is exactly what the ears normally hear - to our hearing system it is "flat and smooth", neutral and uncolored. The center speaker delivers the sound we want to be delivered. The dotted curve is what happens when there is acoustical interference - it is not what we want to hear from a center located sound source, but it is what we hear from a "phantom" center image. The curve in (d) is the difference - the error caused by listening to a pair of "mono" loudspeakers instead of a single "mono" loudspeaker.

This is another advantage to upmixing - you get a real center image from a real loudspeaker. But, as I said earlier, it does not work equally well with all recordings. Stereo is such a serious compromise! I wonder at times why it has endured - it can only be because we tap our feet to the rhythm and can whistle the melody. The music industry is simply backward. I exaggerate, but only slightly. I was recently at McGill university, where I recorded my YouTube lecture, and witnessed recording engineering students creating 5.1, 7.1 and 20.2 mixes. They sounded great. With streaming it might be possible for us to get to hear them, but otherwise, they will languish in a hard drive somewhere.

Goliath: my subwoofers are Sound Field Managed as shown in Figure 13.18 in my book. The four subs are each signal processed in an optimized configuration. When that was done, as luck would have it, I did not need global EQ. But the whole point of multiple subs is to reduce seat-to-seat variations so that global EQ works for several listeners, not just one. Slight EQ was necessary in the crossover region between the subs and satellites. Above about 200 Hz nothing is done - I have very good loudspeakers and I leave them alone. Look at my recent AES paper for explanations: go to AES.org, click on Publications, click on "open access", type in "Toole" and download my paper - it is free to all. It basically says that full range EQ is a risky business, likely to degrade good loudspeakers, and incapable of fixing bad ones.

 

[Goliath]

Thanks for your feedback, Floyd! Thanks again for participating on Audioholics.

 

[jim1961]

Jim1961 The curves in (c) are measured at the entrance to the ear canal, and include the HRTFs (Head Related Transfer Functions). The solid curve is exactly what the ears normally hear - to our hearing system it is "flat and smooth", neutral and uncolored. The center speaker delivers the sound we want to be delivered. The dotted curve is what happens when there is acoustical interference - it is not what we want to hear from a center located sound source, but it is what we hear from a "phantom" center image. The curve in (d) is the difference - the error caused by listening to a pair of "mono" loudspeakers instead of a single "mono" loudspeaker.

This is another advantage to upmixing - you get a real center image from a real loudspeaker. But, as I said earlier, it does not work equally well with all recordings. Stereo is such a serious compromise! I wonder at times why it has endured - it can only be because we tap our feet to the rhythm and can whistle the melody. The music industry is simply backward. I exaggerate, but only slightly. I was recently at McGill university, where I recorded my YouTube lecture, and witnessed recording engineering students creating 5.1, 7.1 and 20.2 mixes. They sounded great. With streaming it might be possible for us to get to hear them, but otherwise, they will languish in a hard drive somewhere.

I do thank you for your responses. It is a pleasant surprise to get to interact with those at the cutting edge in the field.

My setup is 2 ch. audio only. Ive never heard a center channel. Never had one. So all my queries are with this in mind.

 

[Floyd Toole]

jim1961 I rarely participate in internet forums because so many of them turn into shouting matches among people who don't seem to know or care about "truths". Opinions reign supreme. This group has been more serious minded. Thanks.

The 'stereo' topic is interesting to me. I grew up with it, did my PhD research in sound localization so I know a lot about how it functions. It was never ideal. Bell Telephone Labs did research in the 1930s showing that we needed a minimum of three channels: L, C and R to create a credible soundstage. We ended up with two only because that was the maximum number we could get into and out of an LP. That limitation is long gone (RIP), but spatially- and directionally-deprived stereo hangs on. And, the elephant in the room issue goes substantially ignored - the fact that the sound of the featured artist, the picture on the album cover, is significantly less good than it could be. The 2 kHz hole is part of it, changing the timbre of the sound and reducing speech intelligibility. The less obvious part is that waveform fidelity is impossible, and any concept of phase linearity is negated for any image panned between the loudspeakers. Funny how so many people in the audio business don't know or admit this. Fortunately, humans are not phase sensitive, so that aspect really doesn't matter except in marketing So, when I hear/read people talking about stereo "purity" and multichannel mediocrity, I simply sigh. Ignorance can be bliss . . . it seems. Adaptation at work.

Fortunately the movie people realized that more channels could do more things, starting with communicating a sense of envelopment, being in a space with the performers - in their case being in the space portrayed on the screen. Later multichannel developments allow much more flexibility - Atmos, Auro3D and DTSX are the latest over-the-top offerings. Of these, Auro3D is perhaps the most relevant as it was created by a music person. I heard it reproducing dedicated recordings, and you were "there", able to walk around in a concert hall or cathedral - awesome - no sweet spot. Space aliens flying overhead, gunshots and ricochets are easy, this is difficult.

 

[jim1961]

For me, a person trying to improve the sound I get in my room, one thing frustrates me more than anything. Lack of published measurement data of high end rooms.

Knowing how to treat small rooms acoustically (thread title) relies (partly) on targets in the measurement domain. I dont mean to imply that there is only one target everyone should shoot for. But rather, it would be nice (hugely helpful) to have several room data measurements to look at from rooms considered the best of the best. Not just FR, but the whole enchilada (mdat's).

I do understand that designers cant publish or share data from their clients. The clients themselves have no such ethical restrictions though. Certainly those who manage great results on their own dont have any conflicting interests in this regard.

I scour the net looking for such data. Once in a while, I find something from an intermediate hobbyist, but mostly, its data from novice and first time folks that are at the very beginning of the journey, not those at the end of it.

 

[highfigh]

The missing fundamental is almost certainly a factor from the perspective of pitch, but not "kick in the gut" bass energy. It is not there.

Loudspeakers with substantial low-frequency output energize room modes, which make things sound "slow". Tame the modes, and things speed up considerably. For many years the Brits had a love affair with small bookshelf loudspeakers, on stands. They were even the "reference" loudspeakers for some prominent journalists. Why? No low bass = no boom in the often thick plastered or masonry walls in many homes. Rather than address the problem, they seemed to accept a compromise - insufficient low bass.

But, there is more. As I discuss in great detail in my new 30 page AES paper - a free download - bass is not constant among recordings. Figure 2.4 in my book is a scary look inside recording control rooms. So I really believe that tone controls are essential if you are fussy.

An anechoic flat on-axis speaker will not be flat in a room - the bass will rise. The task of multi-subs, bass traps, and equalization is to get rid of resonances. Once that is done you need to find a suitable bass level. It very likely won't be flat, and it cannot be the same for all recordings or movies. Hence the tone controls. The problem is that the industry has no standards that work, and most recording engineers think they know better . . .

in my room the bass is very smooth and flat down to about 23 Hz, still going at 17 Hz. Figure 13.18 in my book. Five listeners hear almost exactly the same bass and it is clean, deep and 'tight'. You can walk around the room and the bass is remarkably consistent. It should be ideal. Yet, when I listen to music in the foreground, I sometimes have to resort to tone controls. The system is fine, the recordings are what they are - not all the same, and not all good.

I just listened to 'Graceland' (several versions, in fact) and it seems likely that they wanted to allow the fretless bass to come through, rather than use a pounding kick drum because a strong kick drum would have detracted from the song. Since most of what is perceived as "bass" WRT bass guitar is the 1st harmonic anyway, losing the lowest octaves doesn't hurt. Also, it means that song will sound good on a small system and in light of the fact that Simon recorded that album with South African musicians and singers, the people of South Africa, who should be justifiably proud of the performance, were unlikely to listen using big systems that were capable of 20Hz. The bass rise in the listening room further helps, without the problem of sub-40Hz room mode excitement.

 

[Goliath]

Floyd, if you're still posting on the forum, I have a question I'm hoping you can help me with. Do you think treating the early reflections off the ceiling was a good move, in a small room like mine, all things considered?

Unfortunately I wasn't in a position to do any blind listening sans/post ceiling treatment, and it will be difficult to take them down as they are mounted to brackets (4" air gap).

I'm not sure exactly what it's doing to the sound in terms of liveliness/spaciousness, apart from (perhaps) additional bass absorption. I assume it's doing good, but your thoughts on this would be appreciated. Thanks again!

 

[TheWarrior]

Do you think treating the early reflections off the ceiling was a good move, in a small room like mine, all things considered?

I'm glad you asked that, because I had questioned it upon seeing your photo's. Try taking them down, leave the brackets, and try a couple sample tracks. Keep your track list consistent, and try multiple things!

I recently removed two panels and returned the carpet, only to find even better sound. Not because I needed to, but to always keep searching for the best sound.

Its called Audioholics for a reason!

 

[jsrtheta]

Gene, it's "one and the same," not "one in the same."

 

[wgb113]

I know this is an oldie and that many of the conversations center around multi-channel surround but I'm curious what @Floyd Toole and others think about trying to get the bass even in small rooms for only one listening position. So much of the research he and others have done are for larger room and multi-seating positions.

I have the challenge of a room that's only 1080 cubic feet (10W x 12D x 9H)and trying to get the bass even for one listening position. Is one sub enough? Would two subs be any better? Should I add a sub at all if my speakers can play reasonably well down to 50Hz?

The room is dedicated and treated in the form of soffit traps that run the perimeter wall/ceiling junction and "superchunk" style traps in the front corners.

Also curious as to thoughts around using digital room correction like Dirac Live to help.

 

[highfigh]

I know this is an oldie and that many of the conversations center around multi-channel surround but I'm curious what @Floyd Toole and others think about trying to get the bass even in small rooms for only one listening position. So much of the research he and others have done are for larger room and multi-seating positions.

I have the challenge of a room that's only 1080 cubic feet (10W x 12D x 9H)and trying to get the bass even for one listening position. Is one sub enough? Would two subs be any better? Should I add a sub at all if my speakers can play reasonably well down to 50Hz?

The room is dedicated and treated in the form of soffit traps that run the perimeter wall/ceiling junction and "superchunk" style traps in the front corners.

Also curious as to thoughts around using digital room correction like Dirac Live to help.

My room is 11' x 16' x 7'-8", but it opens to the kitchen and hallway to the bedrooms and bath (now that I have removed a wall), so it has benefits and problems from that. I had a deep cancellation in the 80-100Hz area and I found that moving the speakers didn't help, so I brought the panels I had made for a home theater job in and started placing them while I was running RoomEQ Wizard. I could see the difference with each panel and after placing the 1" panels at the first reflection area (where I could- a door is in that spot on one side), I started placing the 2" panels in the corners- the front corners are asymmetrical because I have my LPs stored in the right front, but the left front and rear left were open, so I stacked the panels vertically in the rear left and placed one along each wall in the left front. The response from my speakers is basically flat down to ~36Hz at my listening location and I don't hear the notes disappearing anymore. The panels handled the problem nicely, but I don't operate the system at extreme SPL,. either. I did nothing at the wall/ceiling intersection and don't feel a need to- the bass level is very even, audibly and as seen on the computer display when I run REW.

I haven't used a sub since I built my speakers almost ten years ago- I had great bass in the past and those woofers spoiled me, so I don't really need to frustrate myself by trying to achieve it with small drivers.

I would recommend watching REW to see the changes to the response as you move the mic, then return it to the original location and move the sub and speakers- a little movement can make a big difference. When I started the process of eliminating the problem, I started with the main speakers and that improved the sound greatly- I can walk to a place that's almost even with the line across the two and still distinctly hear the left one because the sound coming from the sides doesn't muddle everything, as it had in the past.

 

[squaleca]

I've read on your site that placing sub's mid room is the worst possible place to place subs

 

[Eppie]

I've read on your site that placing sub's mid room is the worst possible place to place subs

Thanks for bumping this thread. Lots of interesting info here. If mid room you mean the middle of the room, then yes. I think the latest recommendation is to try placing subs in the corners of the room, and if that is not possible then along a wall at either the midway point or 1/4 wall distance. That's only a starting point as all rooms behave differently and usually require some experimentation or testing, along with the placement and angle of the main speakers.