Sound Propagation

[Richard Brekne]

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John Delacour wrote:

> At 5:22 PM +0100 1/9/02, Richard Brekne wrote:
>
>> Well, see the reason I ask is that your "radiate" seems to
>> correspond pretty good with Olsons description of sound board
>> radiation in which case I see almost the exact same description when
>> it come to Benades description about the longitudinal nature of
>> transverse like surface waves. In all this you could sort of look at
>> these as a huge collection of tiny  ... Olson uses the word "pumps"
>> pushing away at the air in his description of sound board
>> radiation.... btw.. I read your stress waves reply to Phil and this
>> also points in this same direction. You said then
>>
>>      "Acoustic radiation is caused by minute pressure
>>      differences at the surface of a body."
>>
>  Interesting that Olson should have used such a very similar analogy.
> You've mentioned him before but given no details.  Who exactly are
> Olson and Benades or what are the books in question?
>
> RB:
>
> Arthur H. Benade "Fundementals of Musical Acoustics" ISBN
> 0-486-26484-X, Dover press New York
> Harry F. Olson "Music, Physics, and Engineering" ISBN 0-486-21769-8,
> Dover press New York
> Neville H. Fletcher & Thomas D Rossing "The Physics of Musical
> Instruments" ISBN 0-387-98374-0, Springer
> W.V. McFerrin "The Piano, Its Acoustics"
>
> All available at Amazon.com
>
> McFerrins book is interesting enough, tho contains the least
> information of these four and is the oldest of them. Benades book
> should be a must for anyone who is really interested in these aspects
> of pianos, and is the easiest to comprehend for the layman. Olson is a
> bit heavier, a bit more math intensive.... more for the engineer with
> a few years of college level math and engineering behind him. Fletcher
> and Rossings book like Oslo requires that you can relate a good deal
> of math. I havent read a whole lot in that book yet so I will reserve
> further comment.
>
> JD:The analogy of his tiny pumps or my little pulsating fountains is,
> of course, an extreme simplification.  The final picture will be
> vastly more complicated.  What I hope we can eventually arrive at is a
> good basic understanding of the principles involved and the nature of
> the wave forms generated.  As I've recently said, I think it would be
> helpful in the early stages to consider the system as composed of one
> homogeneous isotropic solid body (which would, I guess, actually work
> after a fashion) and to avoid discussion of the behaviour of fluid
> bodies.
>
> RB:
>
> I agree that a good understanding of these principles, and adherence
> to a common terminology based on that understanding would be really
> helpfull. My insistance on the fluid bodies examples is as much to
> build my own understanding of wave mechanics in general as it is
> anything else. Actually Benade puts the soundboard in the catagory of
> a 2D plate where longitudinal waves and transverse waves both occur.
> And it looks to me like he is saying that one cannot exist without the
> other and that where one exists the other must occur.
>
> Personally I find the whole discussion fascinating and there are lots
> of little peices of information that pop up out of nowhere.... For
> example...some months ago there was a discussion about something
> refered to as para-inharmonicity and there has been quite a bit of
> speculation as to what it is and isnt, or indeed if it does exist.
> Benade describes some aspects of how soundboard and string modes (as
> in partials) effect each other when each have modes whose frequencies
> nearly coincide. The description could explain to a "T" the whole
> concept of para-inharmonicity.
>
>
>
> JD:We have a lot of studying to do.
>
> Yup...but its fun really. JD




--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no


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