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In the Forum: Audio Discussions
In the Thread: Big room vs small room
Post Subject: Not too far apart but different reasoning.Posted by Romy the Cat on: 7/18/2012

 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.

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.

Romy the Cat

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