Re: Question for you scientific types.


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Posted by jeff on August 27, 2003 at 17:49:13:

In Reply to: Question for you scientific types. posted by Tom C. on August 26, 2003 at 17:52:54:

I have read a few acoustics books, and found 3 facts worth mentioning here:

1) Different frequencies of standing wave will reflect back at different points along the bell expansion, depending on the change in impedance of wave progation (this is vaguely analagous to throwing rocks at a still pond at different angles - depending on speed, angle, etc, some will skip, some will sink. The ones that skip are analagous to reflected waves)

2) A standing wave vibrating at the fundamental frequency of a tube will include air vibrating somewhere outside of the opening of the tube into the surrounding airmass. This is dependant on the shape of the bell flare, but for a cylindrical tube with no flare, is equal to something like one half of the diameter of the bell. It's called "end correction"

3) Most acoustics books demonstrate almost no applied knowledge of the way that brass instruments behave, and therefore most acoustics books use over simplified or even incorrect models of brass instrument acoustical behavior, resulting in statements such as "A brass instrument could be covered in 4 feet of concrete with no effect whatsoever on the playing characteristics of the instrument". (That's a paraphrase, but is essentially an accurate one).

I hope that's somewhat interesting and maybe even somewhat correct.

I will say this - not all acoustics books are created equal (see num 3, above). Check out several before buying one. Dover published a good one - I think it's by Benade, but that could be a different text entirely.

Good luck,

Jeff


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