Re: Focused sound
From: Carl Lowenstein (cdl_at_deeptow.ucsd.edu)
Date: 08/28/04
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Date: Sat, 28 Aug 2004 00:50:29 +0000 (UTC)
In article <412f8c70$0$62398$5fc3050@dreader2.news.tiscali.nl>,
Dmitri Vikawtsky <Eddow@gmx.net> wrote:
>Mok-Kong Shen wrote:
>
>>
>>
>> Dmitri Vikawtsky wrote:
>>
>>
>>> Sound is nothing more than a wave, while you can "reflect" it with
>>> some material, you can make orientation-shaped 'sound-mirors', like
>>> mirors used in your torch, where a parabola mirror direct light beam.
>>>
>>> These mirrors intended to give a unique orientation are just given a
>>> parabola shape.
>>
>>
>> Do you happen to have an explanation why the firm concerned
>> does it in another, apparently much more complicated, way?
>> Thanks.
>>
>> M. K. Shen
>>
>Indeed, I forget a detail about sound :) That wave is a particles wave,
>while light is an electro-magnetic one. The point here is that 'perfect'
>mirrors for sound are kinda impossible at a pocket-torch size. Sound are
>for now well-reflected by walls of about 1 or 3m width. In other words,
>all is, even a bit, 'transluent' to sound. So, if you try to make a
>light-director with transluent paper, you'll have to put several papers
>in a complex way in order to achieve the best directing.
A short explanation of the complicated way of generating directed sound:
A beam of high frequency (much higher than audible) sound has a much
shorter wavelength so it can be directed by reasonable-sized 'mirrors'.
The would-be audible message is carried as the difference frequency
between components of the high-frequency beam. Nonlinearity of the
medium causes sum and difference frequencies to be generated, and
you hear the difference frequency.
Not at all sci.crypt unless you think of it as acoustic steganography.
carl
--
carl lowenstein marine physical lab u.c. san diego
clowenst@ucsd.edu
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