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In the Forum: Audio Discussions
In the Thread: Big room vs small room

Post Subject: Big room vs small roomPosted by rowuk on: 7/12/2012

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

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