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Boosting acoustic efficiency

05 Jan 2016  | John Dunn

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You may have seen a simple science experiment in middle school class that is actually quite instructive about an important topic: The transmission of sound.

We take a tuning fork, hold it in one hand and strike it. We can hear the fork's tone at its resonant frequency, but the sound is not all that loud. You might actually have to get a little bit close to hear it.

Next, we strike the fork and then hold the bottom of the tuning fork on a hollow wooden box. The tone comes out much louder than before.

The efficiency with which the tuning fork's vibrational energy can get from the metal of the tuning fork into the surrounding air is enhanced by making the acoustic connection to the wooden box. In doing that, we enhance what might be called the "acoustic efficiency" which is a turn of phrase that may sound like a good thing, but it is NOT.

It is an effect that can do significant harm in the design of real world products.

Imagine that you have some whoop-de-doo wonderful thing-a-mabob in which you happen to have included a cooling fan. Then imagine that you have used some kind of open enclosure that acts like the wooden box in our little experiment. The noise coming from that fan can propagate out into the real world at enhanced and sometimes quite objectionable decibel levels.

You don't want to make a product that tries to imitate the sound of a vacuum cleaner, yet I have seen some products made that way and they were not nice having to sit close to, especially when placed in a 19-inch relay rack.

Where are my earplugs?

About the author
John Dunn contributed this article.

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