From: steve <whitaker@p...>
Date: Tue Jan 9, 2001 6:42 pm
Subject: Re: Structure-born noise
problem is, structure born noise travels *faster* than air born, so the
wavelength will be dramatically less than the 5m you refer to.
As for use/applications, broaden your vision a bit. In the 5000 price
range, large 'sound reinforcement' situations would use the device too.
there are plenty of those.
I remember working on a classical FM radio station where that would have
been useful. There was a parking lot nearby and the cars would cause a
structure born noise which would be picked up by the record stylus.
not so many record players in use today, but once a device is developed,
applications come out of the woodwork ;-)
I wouldn't be surprised to find the device being used to cancel the noise
inside jet airplanes. I haven't been around Boeing's acoustical lab since
around 1980, so they might have one, but if they develop it, it'll likely
remain in-house. (they'll probably publish a paper on how they did it tho).
Technologically, the 3-axis method wouldn't work as each material used has
an inherently different acoustic velocity, meaning that the device would
have to add the materials and distance of each material into the
calculation... ugly :-( not to mention the variability of each material.
Finally, are you suggesting this be used with a loudspeaker which would
cancel the sounds once they again become airborn, being radiated from the
various surfaces, or as a replacement for a good decoupling/isolation of
the microphone from its mounting?
Interesting idea :-)
>Train, subway, truck, etc. noise would be the primary
>candidate -- and while this would present some
>difficulties, I doubt that it would be insurmountable.
>With wavelengths (in air) on the order of 5 meters
>(and, in the structure, probably on the order of 10
>meters) a single structure-noise pickup would not
>suffice. But many pickups are practical. Just to
>put some numbers on it, let's assume each structure
>pickup consists of a 3-axis accelerometer. It would
>be easy enough to package such a widget, complete
>with A:D conversion (ten or twelve bits should be
>plenty over the frequency range of interest) for a
>manufacturing cost of about $10US (let's say a
>street price of $50). Such a widget could be
>easily daisy-chainable. In a small to moderate
>sized recording studio, three such widgets per
>surface would probably suffice to provide a mapping
>that would allow 20dB post-processing attenuation of
>structure-born vibration -- even given processing
>electronics, we're probably talking about a street-
>price on the order of $5000. It doesn't take too
>many 3 A.M. recording sessions at union overtime
>rates to pay off $5000.
>But, do enough studios exist that treat recording
>as a business to support the several million
>dollar development cost of such a system? (That
>development cost, by the way, is part of the
>difference between the $10 manufacturing cost and
>the $50 street price.) Putting numbers to it
>again, let's assume a "per-installation" street
>price of $5000, with $1000 going to pay for the
>development. With a development cost of $2e6,
>that would (using back of the envelope estimates)
>make the break-even point somewhere around 2000
>Of course, there are plenty of ways of playing
>with the numbers, and of playing with the cost
>of the electronics. (Given a big enough
>quantity, the distributed "widget" could probably
>get down to $1 manufacturing cost.) Let's say
>that the system could sell for any number you
>pick -- just so long as the total sales (street
>price) amount to $1e7. Is there a ten million
>dollar world market for a machine that does not
>reduce room vibration, but that does remove it
>from recordings, or sound reinforcement systems,
>without removing any of the 'desired' material
>from the recording at the same time?
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