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# Microphones and Acoustics

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

If you don’t see the answer to your question, call our 24/7 SensorLineSM 716-684-0001 to speak with an application engineer or visit Ask the Acoustics Experts.

How do I estimate what my output voltage will be so that I can set my resolution on my DAQ?

The output voltage that is delivered by a microphone and preamplifier combination is dependent upon the system sensitivity of the microphone and preamplifier pair, along with the amount of sound pressure that the diaphragm is exposed to. The output voltage can be calculated by using the following formula, where Sound Pressure is Pascals (P), and Sensitivity is Volts per Pascal (S).

V = Pressure x Sensitivity

Pressure can be expressed in PSI (pounds per Square Inch) or more commonly in Decibels (dB) for acoustics. So we first need to convert the pressure into Pascals to use the formula above.The relationship of PSI to Pascals is linear and can be calculated using the following formula: 1 PSI = 6895 Pascals. The relationship of dB to Pascals is logarithmic and can be calculated using the following formula:

Where Po is the reference Pascal = 0.00002

100 Decibels is roughly the equivalent of 2 Pascals. For reference, this is approximately the sound of loud truck going down the street. If we were to use our most common condenser microphone 378B02 which has a sensitivity of 50 mV/Pa and is a Free-field mic designed to measure truck noise in a pass by test, we could calculate the output voltage that would be sent to our DAQ (Data Acquisition) using the first formula above.

V = Pressure x Sensitivity
V = 100 dB x 50 mV/Pa

But we need to convert the decibels to Pascals and with wanting our output to be voltage instead of mV, we need to correct the units from mV to Volts. Doing this, we get:

V = 2 Pa x 0.05 V/Pa
V = 0.10V

So a 100 dB sound with a 50 mV/Pa microphone will output 0.10 Volts.

How do I estimate what my output voltage will be so that I can set my resolution on my DAQ?

The output voltage that is delivered by a microphone and preamplifier combination is dependent upon the system sensitivity of the microphone and preamplifier pair, along with the amount of sound pressure that the diaphragm is exposed to. The output voltage can be calculated by using the following formula, where Sound Pressure is Pascals (P), and Sensitivity is Volts per Pascal (S).

V = Pressure x Sensitivity

Pressure can be expressed in PSI (pounds per Square Inch) or more commonly in Decibels (dB) for acoustics. So we first need to convert the pressure into Pascals to use the formula above.The relationship of PSI to Pascals is linear and can be calculated using the following formula: 1 PSI = 6895 Pascals. The relationship of dB to Pascals is logarithmic and can be calculated using the following formula:

Where Po is the reference Pascal = 0.00002

100 Decibels is roughly the equivalent of 2 Pascals. For reference, this is approximately the sound of loud truck going down the street. If we were to use our most common condenser microphone 378B02 which has a sensitivity of 50 mV/Pa and is a Free-field mic designed to measure truck noise in a pass by test, we could calculate the output voltage that would be sent to our DAQ (Data Acquisition) using the first formula above.

V = Pressure x Sensitivity
V = 100 dB x 50 mV/Pa

But we need to convert the decibels to Pascals and with wanting our output to be voltage instead of mV, we need to correct the units from mV to Volts. Doing this, we get:

V = 2 Pa x 0.05 V/Pa
V = 0.10V

So a 100 dB sound with a 50 mV/Pa microphone will output 0.10 Volts.