How does one measure single digit dB levels? - diyAudio
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Old 13th March 2012, 07:38 PM   #1
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Default How does one measure single digit dB levels?

Probably OT, but are there any microphones that have low enough noise to measure down in the 0-10 dB region (unweighted)? I'd think a dynamic mic would make almost no contribution, and be limited mostly by the preamp. Is that true? Can a condenser mic get there? Can anything get there?
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Old 14th March 2012, 01:10 PM   #2
PChi is offline PChi  United Kingdom
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I guess that the answer is no, no one knows how to measure single digit dB levels.

For the Dynamic microphone the sensitivity versus the thermal noise caused by the resistance set an absolute noise floor (unless the microphone is cooled). A quick look at the Shure web site gives a sensitivity but no resistance. Then the preamplifier is likely to degrade it some more.
I guess unweighted means 20 Hz to 20 kHz bandwidth.

I have checked the obvious (to me) supplier of condenser Microphones, Bruel and Kjaer, and the noise floor is 15 dBA.
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Old 3rd July 2012, 12:23 AM   #3
richiem is offline richiem  United States
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Hi Conrad -- I'm guessing a 4 or 5 inch dynamic speaker witha 4-ohm voice coil would make a great low-noise mic -- but one that has fairly lousy bandwidth. I haven't done the math, but resistor noise is going to be plenty low and a matching low-Z mic amp will maximize power transfer. I don't see why under 10dB SPL isn't doable up to a kilohertz or so.
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