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Topic: I think it is about harmonics and decays.

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Posted by rowuk on 07-12-2012

I have been lurking here for a while and am fascinated at the discussions of TONE. I play trumpet professionally in Germany and have many opportunities to experience big rooms and big pipe organs as well as symphony halls with various degrees of acoustic treatment.

When I have a rehearsal in an acoustic space that I have never had experience with, I normally come an hour early and just sit to feel the room. Sometimes there is activity in the church (cleaning people, tourists), many times I am by myself. During this acclimatization I make decisions about how I need to play: with great projection and power or to gently stroke the acoustics. Even the paint on the walls makes a huge difference in how reflective the reverberation and decay is.

I think that the tactile feeling of these big spaces cannot be "reproduced" or simulated with "conventional" techniques (like 2 ULF channels). The reason is that in a smaller room, the TRUE standing wave cannot be created. The bass wave "folds" at the wall behind the listener and the reflection mixes with the direct wave at the listening seat and makes a funny sound. The ultimate funny sound is bass in an automobile where we only have folded waves.

I have thought about this for about 20 years now and suspect that a solution can only be to employ "anti-sound" behind the listener so that the bass wave cannot be reflected back to the listener. This would effectively make the room unlimited size at ULF (or perhaps tunable to a specific defined virtual acoustic size)! An acoustic sump would be my name for this device.

Some primitive forms of anti-sound are found in the noise reducing headphones like from NoiseBuster, Bose or Sony. I use them when I travel.

Romy, I think that you currently have a room that is a resonant enclosure with the ULF located somewhere away from a boundry. This is almost like tapped horn concept, except that you are sitting in the (big) speaker box. Granted, your space is very generous, so it is a very big box compared to the compression chamber of an automobile interior for instance. Moving the box changes the distance before the bass wave "folds" the first time.

If someone can turn the Sunfire sub into a noise cancelling box, we may have a solution............ If this can get DSP support, many of us with small listening rooms can benefit. Now my only personal solution is to listen at volume levels that the room can handle.......

Here some interesting ULF links that I have not seen published here at your site before. None offers a "sound" solution but perhaps inspiration:

http://www.earthbreathing.co.uk/sr.htm
http://www.prosoundweb.com/article/church_audio_basics_dealing_with_standing_waves/
http://www.interferencetheory.com/Articles/files/544e307e7c540c745a0340683695d1a0-3.html

Posted by Romy the Cat on 07-13-2012

Rowuk,

I think you take the subject of acoustic in listening room a bit wrongly, would it be for audio or for your trumpet. The reflection of bass wave back to the listener is not the problem at all, at least in my assessment. The key is in decay patter at different frequencies or something that we call reverberation time. The size of performing space or listening room is primary responsible for reverberation time at lower frequencies and there are zillion other factors that are responsible for reverberation time at higher frequencies. Depends of the music playing and playing techniques you want to have 1 to 2 seconds of reverberation time or room decay at lowers produced frequency. The patters with which the higher frequencies decay (it will be shorter of cause) is something that describes the sound of the given acoustic space. I do think that if you read about management of reverberation time in halls instead of reflection of bass cancelation than you will be closer to the answers you are looking for.

Rgs, The Cat

Posted by rowuk on 07-13-2012

Reverberation time is surely a part of it but I think that there is more. If I am in the quiet church alone and close my eyes, I know how big the space is. If I am in a concert hall with managed acoustics and close my eyes, I know nothing. I believe that the difference is a standing wave that is in the unmanaged room always and never decays as long as there is a draft, activity, wind or other at least minor acoustic excitement. the finest halls have a characteristic sound before anyone plays a note.
I do not know of many recording engineers who try to capture the "space" (except perhaps Mr. Johnson from Reference Recordings and certain recordings from John Eargle at Delos). This could be a reason why you can increase ULF to extreme in your system without it being a "problem".
Maybe this is a factor for hearing a difference between a musical event in a listening room or in the original hall. I often think about how we can squeeze this standing wave into listening room. Physics is hard to beat.

Posted by Romy the Cat on 07-14-2012

Well, rowuk, I still do not think that when you are talking about what you are taking about then you are talking about standing wave. The standing waves are nothing more than persistent room gain. I think when you are talking about what you are talking about then you mean the specific of room harmonics and the reverberation time across the whole bandwidth. There are some headphone software that allow you to “write” in ANY reverberation pattern and to mimic ANY concert hall in the whole. You can push a single button and get the acoustic environment of Carnegie Hall, Hungarian Opera House, Vienna's Musikverein or Vienna State Opera. It works very well and it use no standing waves but just refactoring harmonics and decays.

Posted by skushino on 07-14-2012

Last week in a different thread I posted:

"I've been reading about the acoustic characteristics of the world's great symphony halls, like Boston and the Concertgebouw. Did you know that Sabine, Berenak, and Cyril Harris mathematically defined those characteristics, using metrics like RT-60, clarity, intimacy, warmth, spaciousness, and background noise? The reverb time for the great halls is around 2 sec for symphonic music, around 1.5 sec for opera (due to voice clarity). For smaller rooms used as monitoring studios (~ 3000 - 15,000 ft^3), the suggested reverb time is around .35 - .9 sec.

The audio community standard wisdom for treating listening rooms seems to be as much bass trapping as possible. This seems completely opposite of efforts to prolong reverb time. Given a desire to extend bass reverb time, wouldn't it be better to minimize bass treatment, while treating some reflecting surfaces for MF and HF absorption? In other words, even if it is physically impossible to recreate symphony hall acoustics at home, if one wants to at least suggest longer reverb at LF, compared with MF and HF, bass trapping seems to be the wrong direction.

From the pictures of your listening room, and your past experiments with RT60, is this consistent with your experience? bty, I posted in this thread because it seems like a room with some effort at recreating symphony hall acoustics would also be a wonderful venue for live chamber music."

I'm not a headphone guy, and this is the first time I heard about hardware or software to replicate the acoustics of the great symphony halls. Question - do you have direct personal experience with these devices? What are the downsides, if any? Can you point me to a specific device / product / software? The power to define acoustic space, being able to dial in the acoustics of a small intimate lounge for jazz, or a large reverberant church for choir, or a treated hall for orchestra, is very appealing.

I'm interested in having this kind of control for my home listening, although it seems to defy the laws of physics.

Posted by Paul S on 07-14-2012

Can/Does this stuff take it into account when the recording in question already includes some sort of native or contrived ambience? In any case, the generic version of this stuff is routine in a typical recording/mixing studio, just pass band +/- delay, +/- volume, and why not an algorithm for a given set of pre-engineered criteria, such as the Loudness button? A rudimentary version might be done with nothing more than venue dimensions. Of course there is much more that influences sound at a particular venue, even attendance at a given performance.

Paul S

Posted by Romy the Cat on 07-15-2012

skushino wrote:
I'm not a headphone guy, and this is the first time I heard about hardware or software to replicate the acoustics of the great symphony halls. Question - do you have direct personal experience with these devices? What are the downsides, if any? Can you point me to a specific device / product / software? The power to define acoustic space, being able to dial in the acoustics of a small intimate lounge for jazz, or a large reverberant church for choir, or a treated hall for orchestra, is very appealing. I'm interested in having this kind of control for my home listening, although it seems to defy the laws of physics.

Skushino, nope I do you have direct personal experience with these devices but I know that they are out there. I know that they do very good job as I personally heard bits and pieces of it and I do not feel that it would be any problem with technology they use to mimic the sound of great concert halls. I also know a guy to whom I trust who did heard the demonstration of the devises a few years back, he did report very positive result.

If you look to evolve in this direction then look for Recursive Ambiophonic Crosstalk Elimination. This technology actively manipulates crosstalks IN the reverberant fields under the Ambiophonic umbrella and allows writing unimaginable things. They have the preconfigured acoustic snapshots of various concert halls and you can play music while synthesing any given concert hall’s Sound Fields.

Sure it is very appealing but unfortunately only as prove of concept. It will not work well for acoustic systems, only for headphone and it is just DSP manipulation with all expected negative consequences. Also, I hope you understand that basic Ambiophonics is not comparable with standard Stereo, it is like PAL, NTSC and SECAM – just different systems.

Posted by Romy the Cat on 07-16-2012

Rowuk, yesterdays I was attending the Jennifer Koh concert (a stunning concert BTW) and no, I was not thinking about you. Still, suddenly an interesting argument comes to my mind that a bit defeats your notion of standing waves. A standing wave is frequency-dependant category and modulated by lowest reproduced octave and the geometry/volume of space. If the “space” reproduction might be described by standing waves then the acuteness of what you saying would be less significant for sound of single flute in large space. The irony is that sound of a single high-pitch instrument in large acoustic space is subordinate of the same rule of perception and a large orchestra with 12 contra-bass and 4 contra-bassoons placing in your closet.

If you want to think further about it then you might to think a bit about the subject that was taking 8 years back when. If you go to “My playback” section then you will find the flowing image and the following annotation:

http://www.goodsoundclub.com/Playback/Site_images/SpaceIlustration.jpg

“Let pretend that a Zone "B" (gray zone) is a representation of some king of musical signal (in fact it represents nothing except a brutal projection of Reality to a cruel mathematical approximation but for the sake of illustrations let accept it "as is"). The behavior of Sound in the Zone "B" generally describe what we Hi-Fi sound. I very much disagree with it. Sound (in context of a scientific language-approximation) might be described only as distance from the beginning of a coordinate system to the end of the entire boundary of measurements. (The sum of the distances "Distance A" and "Distance B") What is named Zone "A" at the illustration is something that I call X-Space. X-Space is totally overlooked property of Sound reproduction but it hugely important. The processes that take place in X-Space hugely affect what happen in the Zone "B" and those processes modulate many perceptional properties of our consciousness to recognize/identify the messages from the Zone "B".”

Audio in the way how unfortunate audio people know it is a subject of observation of Zone "B" and Zone "B" only. I can’t even begin to describe how primitive it is. Unfortunately there is no ways how audio people can understand it. There is no tools, no calibrations, no language, not methods to let audio people to deal with events in Zone "A". Reading right books in childhood would certainly help but they were too busy soldering and going to stupid baseball games…. On more serious note – to deal with events in Zone "A" is difficult but administer the Zone "A” buy audio methods is humongously complex human endeavored, and something that distinct online-idiots who just apply currents to loudspeakers from the version of audio that I’m practicing or I am interested.

Rgs, Romy the Cat

Posted by rowuk on 07-17-2012

Hi Romy,
perhaps we are speaking about two different things. English is my first language, but I have been living in Germany for 37 years and perhaps my words are not sufficient.

I had a rehearsal for a church concert last night and as usual, sat in the church to "acclimate". I was alone at first and saw no mice running around to generate "noise". Still, there was a fundemental sound, or breathing of the room. I then started to warm up, listening to my trumpet sound and the decay until only the "fundemental sound" was left. Then I move around in the room. At some positions, the fundemental sounds were very low, at others - much louder. In each area, I play my trumpet and listen to the sound develop, sustain and decay. At he position where the fundemental sound was lowest, my trumpet sound exploded. The room seemed to fill up with sound much faster. In other positions, it sounds nice, but is more work to play and hear.

This is a common experience for me and my assumption was that only standing waves could be of sufficiently low frequency to come and go with this intensity. I wish that I had a position like this in my practice room at home! I NEVER find a position like this on stage with an orchestra.

Posted by Romy the Cat on 07-18-2012

rowuk wrote:
I had a rehearsal for a church concert last night and as usual, sat in the church to "acclimate". I was alone at first and saw no mice running around to generate "noise". Still, there was a fundemental sound, or breathing of the room. I then started to warm up, listening to my trumpet sound and the decay until only the "fundemental sound" was left. Then I move around in the room. At some positions, the fundemental sounds were very low, at others - much louder. In each area, I play my trumpet and listen to the sound develop, sustain and decay. At he position where the fundemental sound was lowest, my trumpet sound exploded. The room seemed to fill up with sound much faster. In other positions, it sounds nice, but is more work to play and hear.

This is a common experience for me and my assumption was that only standing waves could be of sufficiently low frequency to come and go with this intensity. I wish that I had a position like this in my practice room at home! I NEVER find a position like this on stage with an orchestra.

Rowuk, I do not think we are very far apart we juts chose to explain the effect by different reason. Warn you - there is no indication that you or I are right. All that we do just to bring arguments to support own reasoning. I still insist that standing waves themselves no meaning, they add or reduce room gain at LF but it might be done by standing waves as much as by any other means. Therefore your accent of standing waves as some kind of expressive acoustic phenomena is most likely not accurate.

The effect you describe during your acclimation experience in that church is very good one. I did have many time similar experiences in fact you might very simple to model it with any table radio. Take a table radio with let say opening of Mahler 5. Play it with a table radio that has simple 3 band equalizer. Set bass and mid bands to unity gain. Close your eyes and slide your HF band to the setting that you feel the trumpet sound right to you. Mark you setting for high-frequency band – let presume that it will be +2dB (juts for sake of illustration). Now, set the bass band for +6dB and play the same first bars of Mahler 5. Bindley slide your HF EQ band to set your trumpet to sound properly. Open your yeas and read the setting of your HF band. This time it will be a few DB more. The point is that if playback (or concert hall) has more LF then listeners subjectively are able to consume more HF and at higher volume.

This was very simple experiment but the notion is very well know. It is not only the presence of the LF but the londer decay and many other factors into which I will not be going now. In your church event when you hit the location when fundamentals sounded were very low your location was pumped up by LF that made your HF sounding instrument to explode. It was not only “pumped up by LF” but it was active zone in that church.

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=4421

We both do not disagree about the phenomena but we attribute the reason of the phenomena to deferent cause. You feel that it is the standing wave but I feel that it is many other factors, including standing wave. In my view the standing wave is not the reason but juts a mechanism that adds LF harmonics in your current location. You see, a standing wave exists only as a space event and it has meaning ONLY for two locations in the room – sound source and the location of ears. For both of those locations the standing wave does not exist but exists ONLY the LF boost. If the LF boost would be delivered not by standing wave but by any alternative method then you will have the absolutely the same improvement in sound of your trumpet but then you will not be associate it with standing wave. So, the point that I am trying to make is that what you describe is not the standing wave but the LF boost that took place by standing wave and the location-specific prolonging of decay for fixed resonant frequency of your trumpet. That prolonging also comes from standing wave but standing wave is just transport, not the reason. You might accomplish the same by doubling the amount of basses in Allegros of Second Brandenburg Concerto. You might not have the effect of “acoustic explosion” but you might find that you will be able to play “louder” without being too loud. Well, I might be out of depth here with my illustrations but I hope you understand what I am trying to say.

Rsg,
Romy the Cat

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