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Microphones and Acoustics

Frequently Asked Questions

Get your most commonly asked acoustics questions answered.

Section I: Definitions and Terminology
Section II: Microphone Recommendations
Section III: Calibration and Testing
Section IV: Specification Clarifications
Section V: Specialty Microphone Applications
Section VI: Maintenance and Handling

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If I add two sound sources together, for example 2 Pa each, what is the net effect on the sound pressure level in decibels?

This depends upon if the sound source is coherent or incoherent. Coherent sound sources are summed and using a logarithmic decibel (dB) scale will increase the sound by approximately 6 dB. 20log (2 Pa/20 µPa) = 100 dB and 20log (4 Pa/20 µPa) = 106 dB. The two sources must be in phase for this to be true. If the sound source is incoherent the increase is summed using an rms value Pa=√(22 Pa+22 Pa) = 2.82 Pa and when converted to dB represents approximately a 3 dB increase. The relative phases between the two sources generally must be random for this to be true.