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**To**:**quiet-list@xxxxxxx****Subject**:**Re: Measuring noise****From**:**"David Staudacher" <quiet@xxxxxxxxxxx>**- Date: Mon, 15 Dec 97 14:13:06 EDT
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On Mon, 15 Dec 1997 09:37:29 +0100, PENTIUM 133 <aspa.strasbourg@wanadoo.fr> wrote: >David Staudacher wrote: > >>It would be convenient to have a unit of measure in which distance >>was already factored in, like the "foot-candle"... unit for measuring >>light intensity. > >Sound is a variation of pressure. Thus it is defined (amplitude) as a force >on a surface like the velocity is defined in terms of distance and time... >About having a unit of measure in which distance is already factored in, I >don't see what you mean... As Peter pointed out, trying to say how loud something is using dB values alone is meaningless unless you know the distance at which the measurement was taken. 90dB at 1 meter is quite different from 90dB at 10 meters. Thus it is not unlike trying to make a statement about velocity in terms of time or distance alone, which is obviously absurd. To overcome this, it would be convenient if there were some unit for sound in which distance was already factored in. The "footcandle" (U.S.) [or"lux" (metric)] measure of illumination is such a unit. Being based on a standard distance, 90 footcandles is still 90 footcandles, whether the distance is 1, 10, or 100 meters. So I propose something like a "foot-bel" [or "meter-bel" (metric)] unit for sound intensity - also based on a standard distance. Not that it would actually be necessary to _make_ the measurement at that distance. Since intensity is inversely proportional to the square of the distance, simply knowing the distance to the source would do. Stating the quantity in terms of the standard distance would be a matter of calculation. David Staudacher - quiet@igc.org ============================================================================ QUIET-LIST: Internet Mail List and Forum for discussion of Noise Pollution, Soundscape Awareness, and the Right to Quiet. Email: "quiet-list@igc.org" To subscribe, email "majordomo@igc.org" with message "subscribe quiet-list". For info, send message "info quiet-list" to same. =============================================================================

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