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Re: Digest Number 1285

Subject: Re: Digest Number 1285
From: Walter Knapp <>
Date: Mon, 01 Mar 2004 11:46:33 -0500
>    From: Klas Strandberg <>
> Subject: Re: the nature of parabolic reflectors
>
> I think it will be very difficult to make polar patterns:

Yes, it will be difficult without a proper soundproof chamber that's
long enough. But it can be done with fair accuracy.

> Suppose you move the sound source in a wide circe - diameter 50 meters or
> more, how do you do that, practically, and how to prevent that the
> loudspeaker works in different acoustics all the time?
>
> Suppose you move the parabol around. It will "see" drastically different
> acoustics, for each degree, in fact. Nevertheless, with common sense one
> with draw better conclusions from such a test than without it.

Were it me I'd turn the parabola, calibration would be easier.

You'd need a site that was as even as possible acoustically. Like a very
large mown field, dry lake bed or such like.

Then I'd place the parabola and sound source very high. Like the high
tripod I have. To avoid the irregularities close to the ground as much
as possible.

For each measurement you'd still need to do two measurements, one with
the sound source, and one without. So you could compensate for any other
sound sources the parabola was picking up.

I'm sure there would be more involved, which you would find when you got
into it. But something like the above should give a fairly reasonable
polar pattern.

The main use of a polar pattern is to look for ways you can improve
actual recording, so anything you find there you would be confirming
when actually out recording. And not in just one recording session.
You'd have to confirm it, because real recording is not very often in
such a simplified environment.

That's what I'm looking forward to, hints to try in real recording. And
maybe some confirmation of things I've already found.

Walt




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