Whats are the different theories on room acoustics to create a great sounding room?

Kal Rubinson

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One reason very, very few loudspeaker manufacturers use an all solid-wood construction is that the wood you buy this year will sound different from the wood you bought last year. I could even argue that the wood from one tree on the South side of the hill will sound different from the wood from another tree on the North side of the hill.
I just completed a review of a speaker that has a front panel laminated from Maple hewn only in November from a specific stand of trees in Hokkaido. However, the rest of the enclosure is made from Finnish Birch to balance what would have been an "excessively rigid and hard sound" had the entire structure been made from Maple.

I can believe that a wood floor will make a specific room sound warmer and more full-bodied, but I won't use that as a theory to treat every room.
Warmer and more full-bodied than what?
 

garylkoh

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I just completed a review of a speaker that has a front panel laminated from Maple hewn only in November from a specific stand of trees in Hokkaido. However, the rest of the enclosure is made from Finnish Birch to balance what would have been an "excessively rigid and hard sound" had the entire structure been made from Maple.

That will be interesting. I've heard wood speakers sound good, but they have mostly been DIY affairs where the designer took great pains to specifically tune the crossover to the cabinet. That's artisan craftsmanship, not manufacturing.

Warmer and more full-bodied than what?

Sorry, I was referring specifically to the post made by AudioNMe that his room was warmer and more full-bodied having converted from a laminate floor to all wood.
 

Nyal Mellor

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Of interest to all in this thread may be the fact that Jeff Hedback of HdAcoustics and I are working on a white paper that will lay out measurable targets based on at least two acousticians experience of what good looks like for a two channel reproduction environment.

We are taking into account:
- noise characteristics of the room
- bass frequency response
- mid and high frequency response
- bass time decay
- reverberation time
- room size
- room construction

I do hope we bring something interesting to the space and my hope is that longer term there will be more acousticians who will contribute to the standards we are developing.

Stay tuned...
 

KlausR.

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I am not sure I understand your point about the differences between the radiations patterns of real instrument they are bound to be different in reproduction...

Many musical instruments radiate certain frequencies or frequency ranges in a particular direction, other frequencies or frequency ranges in another direction, whereas loudspeakers radiate all frequencies indiscriminately in all directions,within their area of radiation. Researchers at IRCAM (Institut de Recherche et Coordination Acoustique/Musique) have investigated the trombone, which possibly comes closest to loudspeakers in terms of radiation behaviour, and used 12 loudspeakers mounted on the faces of a dodecahedron for simulation, and found that it is possible to approximate the perceptual characteristics when the simulated directivity is close to that of the real instrument.

The goal is to simulate, I am not sure it is to replicate such is to be impossible with any number of speakers.

Maybe that wave field synthesis does the trick, no idea. What about jj’s 7-channel recording, 5-channel playback system ? At least for 2-channel, it never will sound like the real thing, no matter how much money you throw at it. Once you realize this fundamental limitation of 2-channel, it may shift your goal and your reference.

KlausR. said:
At least with 2-channel, that is a battle lost right from the start, because of the very different radiation patterns of musical instruments as compared to loudspeakers and because two channels cannot create stuff such as listener envelopment.
This, luckily for all, is completely wrong. The few people who have experienced the counter to this know that it's wrong. The battle is still very much alive, it just has to be fought more intelligently ...

Well, perceptual differences between instrument and loudspeaker have been shown for the trombone, which has a rather simple radiation behaviour. Of course, comparison has to be direct A/B, not from auditory memory, which IS bad, at least for simple tasks such as matching pitch or intensity.

In concert halls you have listener envelopment which is caused by late reflections, i.e. >80 ms. Do such reflections exist in domestic listening rooms? According to Earl Geddes the only chance to get some sort of live-like experience is when the performance room is of similar size and acoustical properties as the playback room. So yes, those few people you are mentioning might have experienced some sort of real-thing feeling with recordings of that type, but I seriously doubt that they got the feeling of being in a concert hall with full size symphony orchestra live recordings.

Klaus
 

microstrip

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In concert halls you have listener envelopment which is caused by late reflections, i.e. >80 ms. Do such reflections exist in domestic listening rooms? According to Earl Geddes the only chance to get some sort of live-like experience is when the performance room is of similar size and acoustical properties as the playback room. So yes, those few people you are mentioning might have experienced some sort of real-thing feeling with recordings of that type, but I seriously doubt that they got the feeling of being in a concert hall with full size symphony orchestra live recordings.

Klaus

I understand the argument, but do not recording engineers add extra microphones to capture these late reflections and mix them in the recording? I think that our room does not need to be larger than the acoustic space - I have heard systems where the soundstage was much larger than the room. IMHO, the most difficult thing to get in the reproduction of a symphony orchestra recordings is the sense of power - loud but without overloading the room and us.
 

fas42

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IMHO, the most difficult thing to get in the reproduction of a symphony orchestra recordings is the sense of power - loud but without overloading the room and us.
Exactly. Most systems seem to fail in this regard, and the recent conversation about the MATT test demonstrates that. The expectation is that every speaker based system will do badly in the exercise, unless substantial reconstruction of the room environment is undertaken. My very modest setup had no trouble, as far as I was concerned, with absolutely no fiddling of the physical acoustics, on the other hand.

Why can this be so? Because IMO the key is getting clean sound out of the speaker drivers in the first place: as soon as you have dirty, that is, distorted sound emerging into the room then you have a huge battle on your hands making the sound emulate a realistic event. There was no trouble with my system overloading the room, because the electronics weren't overloading. I note that most satisfactory solutions people have evolved are based on massively over powered systems, that is, the systems can go vastly louder than the volume they are normally listened to at.

So, by far the easiest way to have good room acoustics is to only allow "good" sound to enter into it ...

Frank
 

KlausR.

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I understand the argument, but do not recording engineers add extra microphones to capture these late reflections and mix them in the recording?

I think that late reflections are indeed captured and added to the mix, but it is impossible that a 80 ms concert hall reflection from the rear comes with 80 ms delay from the rear of your listening room when all you have is a 2-channel system.

Blauert has discovered that signals in certain frequency bands (he called them directional bands) are perceived as coming from e.g. above or behind with the sound source being in front (Blauert, “Sound localization in the median plane”, Acustica 1969/70, p.206; Blauert, “Localization and the law of the first wave front in the median plane”, JASA 1971, p.466). This means that by spectral manipulation source elevation can be simulated (Bloom, “Creating source elevation illusions by spectral manupulation”, JAES 1977, p.560). By some manipulation (spectral or phase ?) it is also possible to extend the soundstage to beyond the speakers, as can be heard on Chesky JD37.

I don’t know to which extent such manipulations are used in commercial recordings.

I think that our room does not need to be larger than the acoustic space - I have heard systems where the soundstage was much larger than the room.

What were those systems?


IMHO, the most difficult thing to get in the reproduction of a symphony orchestra recordings is the sense of power - loud but without overloading the room and us.

E. Brad Meyer has written a piece entitled “Power, how much do you really need?”, can’t find it any more on the web, could send you a pdf if interested. Depending on your system, personal needs and listening habits, you might need a lot of power indeed. In orchestral pits sound power levels of up to 115 dB SPL have been measured. For very loud rock music (116 dB SPL), Meyer indicates the following: 40 Wpc (99 dB/W/m), 631 Wpc (87 dB/W/m), 2,512 Wpc (81 dB/W/m), figures are for 2 channels driven. A SPL calculator can be found here:

http://www.hifi-forum.de/viewthread-42-61.html

where

Kennschalldruck: Loudspeaker efficiency
Verstärkerleistung je Lautsprecher: amp power per channel
Anzahl Lautsprecher: number of loudspeakers
Abstand zu Lautsprecher: listening distance
Lautstärke: Sound pressure level

Also interesting reading is:

http://www.silcom.com/~aludwig/EARS.htm#Soft_sounds_and_loud_sounds

Overloading the room and us: my active speakers have 2x920 Wpc, which, according to Meridian’s Bob Stuart (Audio 1987, Sept., p.64: The case for active speaker systems) is equal to about 3,000 Wpc in a passive system, maximum SPL at about 135 dB, thus plenty of headroom for whatever comes along. My 2x40 Wpc desktop Genelec begin to thermally compress when being pushed hard, it’s not too loud but very unpleasant and makes you turn the volume down. My main monitors just play loud, very loud, without perceivable thermal compression, so loud without becoming annoying is possible.



Klaus
 

caesar

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Of interest to all in this thread may be the fact that Jeff Hedback of HdAcoustics and I are working on a white paper that will lay out measurable targets based on at least two acousticians experience of what good looks like for a two channel reproduction environment.

We are taking into account:
- noise characteristics of the room
- bass frequency response
- mid and high frequency response
- bass time decay
- reverberation time
- room size
- room construction

I do hope we bring something interesting to the space and my hope is that longer term there will be more acousticians who will contribute to the standards we are developing.

Stay tuned...

This sounds very interesting. I guess to take that to the ultimate level - and I don't know if it is possible - would be to build several sample rooms with varied parameters. That will allow the consumers, who don't always know what they want, to simulate the audio experience.


Please keep us posted.
 

microstrip

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I think that late reflections are indeed captured and added to the mix, but it is impossible that a 80 ms concert hall reflection from the rear comes with 80 ms delay from the rear of your listening room when all you have is a 2-channel system. (...)

Sure, the world (better, the sound reproduction) is not perfect. But here your brain has to do the extra work - you hear the late reflections with proper timing and wrong origin coming from the two speakers and reflections in your room, and, from your previous experience of life music in music halls, you still perceive the wall greatness. I do not remember the exact words of F. Toole in his Sound Reproduction book, but when it works, it is really fantastic what it can do.

Many people claim that an ideal multichannel system would do it better, but where are the recordings?
 

Ron Party

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I am a firm believer in multi-channel, be it a DVD-A, SACD, or something along the lines of Logic 7. Kal, one day I hope to have a visit with you. I would love for you to demo some of those multi-channel SACDs for me.
 

microstrip

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I have a few thousand.

Kal,
Could you list a few classic SACDs you consider excellent, including some symphonic music recorded in good music halls?
My few experiences buying multichannel were rather deceiving.
 

Kal Rubinson

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KlausR.

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KlausR. said:
I think that late reflections are indeed captured and added to the mix, but it is impossible that a 80 ms concert hall reflection from the rear comes with 80 ms delay from the rear of your listening room when all you have is a 2-channel system. (...)

Sure, the world (better, the sound reproduction) is not perfect. But here your brain has to do the extra work - you hear the late reflections with proper timing and wrong origin coming from the two speakers and reflections in your room, and, from your previous experience of life music in music halls, you still perceive the wall greatness. I do not remember the exact words of F. Toole in his Sound Reproduction book, but when it works, it is really fantastic what it can do.

Toole says on p. 96: “It is not necessary to replicate the sound field of a real space in a listening room; it is sufficient only to provide key cues to elicit a recollection or an emotion.”

But, on p. 97 he refers to the work of Griesinger, in particular to ESI (early spatial impression) : “However, the spatial impression remains frontal.”

and

“Obviously, the longer delays are far beyond those that can be generated by strong individual reflections within small listening rooms. Envelopment therefore requires multiple loudspeakers delivering recorded sound containing the appropiately delayed sounds from the appropriate directions. It is possible that reflections within the listening room may assist in impressions of envelopment by adding repetitions, but they must be initiated by recorded sounds having th large initial delays.” And on p. 98: “It [sense of envelopment] is directional ambiguity of a special kind. For this to happen, the right kinds of sound must arrive at the ears from the right directions, in the right quantities.”

And lastly on p. 110: “Small-room reflections have little to no effect on these phenomena. Illusions of envelopment require delays in excess of about 80 ms, which can only be delivered by multichannel recordings. Small-room reflections may usefully embellish the effect but cannot originate it.”

The size of a room is determined using the delay and amplitude of the strong individual reflections as cues. You can record them and add them to the mix but that is not sufficient, when using 2-channel. I know what concert halls sound like, I never had even remotely the impression of being there when listening to live recordings.

Klaus
 

fas42

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The size of a room is determined using the delay and amplitude of the strong individual reflections as cues. You can record them and add them to the mix but that is not sufficient, when using 2-channel. I know what concert halls sound like, I never had even remotely the impression of being there when listening to live recordings.
You've mentioned this now several times, and I agree that it is difficult to achieve. The barrier to reaching such a level of reproduction is that the system has to behave almost faultlessly, because you need both volume and lack of distortion, something most systems find a very severe undertaking. When the system behaves itself the captured acoustic of the performance takes over, as far as the ear/brain is concerned, rendering the acoustic of the listening room largely irrelevant. With my highly limited current componentry I need to run it at maximum volume to achieve concert hall bigness of sound, and the slightest deficiency or remaining problem area is so very, very obvious. But the key point is that it is possible to get there, provided sufficient care is taken ...

Frank
 

FrantzM

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KlausR

I have read your post with interest and would like you to sum up for us... What's your take on Room Acoustics? We all know we can'treplicate Live... We all also seem to think we get close when the room is well treated. So what is your take on room treatment and which one do you favor and why?

If you also prefer multi-channel that is fine ... I hasten to say , that I am on the fence for MC as I haven't ..yet found it entirely satisfying ...and its logistics are for me cumbersome
 

microstrip

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Toole says on p. 96: “It is not necessary to replicate the sound field of a real space in a listening room; it is sufficient only to provide key cues to elicit a recollection or an emotion.”

But, on p. 97 he refers to the work of Griesinger, (...)

The best thing about the Toole book is that he presents his opinions and the opinions of others that do not agree entirely with him, enabling a critical mind from the reader. As you say he shows a preference for multichannel, but accepts that stereo can also do the "trick".

Considering your comment " I never had even remotely the impression of being there when listening to live recordings" it is difficult to define exactly what is the impression of being there, as many members will happily explain you, as it is a subjective notion. IMHO, primitive appreciations, such as "I close my eyes and would believe I am in the music hall" do not apply here. What I suppose you call "the sensation of being there" is triggered in me by feeling many stimulus that are similar to what I associate with live events, some more important than others, and these delayed reflections seem part of it. Life recordings can help, but are not a necessity for it. Surely others think differently about this subject.
 

JonFo

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... What I have not found a good answer for is the following: Can a room be designed for all speakers? I tend to think that that is a room design that suits a type (not a brand mind you) of speakers i-e what works for a dipole may not for a point source ...

I would agree with that. A room designed and treated for large dipole Electrostats is not really suitable as a host for three-way dynamic driver speakers, and vice-versa.

Specifically, the room dimensions and wall treatments need for speakers with radiating surfaces measured in square feet (e.g my system has 78 sq feet of radiating surfaces) is radically different than what most dynamic speaker rooms might need, even those using large line sources (which are closer).
 

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