You are checking the sound level of a noisy \"Cooch\" roll in a pulp and paper p

Question

You are checking the sound level of a noisy "Cooch" roll in a pulp and paper plant. This sound, which is one of the most dangerous in such a plant, is an ear-splitting pure tone, like that of a nearby siren. For this particular Cooch roll the frequency is 1231 Hz. Using a calibrated microphone in a place where a worker might happen to be you observe a signal on your oscilloscope that shows the pressure oscillation at the microphone to have an amplitude of 14.500 Pa. What is the sound level in decibels? (Use 28.0 microPascals as the pressure amplitude at zero decibels.)

Explanation / Answer

(Use 28.0 microPascals as the pressure amplitude at zero decibels.) ??? Why should I do that? And we don't use the pressure amplitude. We use the RMS value of the sound pressure. The threshold of hearing in air is po = 2 µPa = 0.00002 Pa and that has the level 0 dB. The sound pressure level Lp = 20 × log (p / po) = 20 × log (5500 / 0.00002) = 168.8 dB for a sound pressure of p = 5500 Pa.

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