Whats the SPL at source (@0 m) when SPL is 90dB@1M?
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David McBean
diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by JMFahey In theory, SPL should be infinite, and you should have an infinitesimal source, thatīs why itīs called a "point" source.
"A point source is a small source which alternately injects fluid into a medium and withdraws it." ~ Harry F. Olson - "Acoustical Engineering"

In the example considered earlier the source was assumed to have a surface area of 5 cm2, equivalent to a spherical "point source" of radius 6.3mm (less than 0.37 wavelengths at 20000 hertz). The SPL of 134 dB was calculated at the surface of this source.
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Last edited by David McBean; 17th July 2019 at 09:12 AM.

David McBean
diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by wonderfulaudio The question occurred to me while trying to find the SPL as I move closer to the driver.
SPL2 = SPL1 + 10 * Log10(S1 / S2)

Given:

SPL1 = 90 dB
S1 = 4 * Pi * 1 ^ 2 m2 (surface area of sphere of radius 1 metre)
S2 = 5 cm2 = 5 * 10 ^ -4 m2

Then:

SPL2 = 90 + 10 * Log10((4 * Pi) / (5 * 10 ^ -4)) = 134.00 dB
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 17th July 2019, 07:03 PM #13 steveu   diyAudio Member   Join Date: May 2005 Location: Colorado Springs Sound Fields - acoustic glossary - article "Near Sound Field, that part of a sound field, usually within about two wavelengths of a noise source, where there is no simple relationship between sound level and distance, where the sound pressure does not obey the inverse square law and the particle velocity is not in phase with the sound pressure. Near Sound Field Definition IEC 801-23-29, sound field near a sound source where instantaneous sound pressure and particle velocity are substantially out of phase" Web search for "near field effect" and you will find you tube videos and more. Last edited by steveu; 17th July 2019 at 07:06 PM.

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