Microphone Technology
Don Davis and Eugene Patronis22.1 Microphone Sensitivity .........................................................................................
In order to determine the electrical input level to a sound system, we need to measure the
electrical output generated by the system microphone when it is subjected to a known
sound pressure ( SP ). In making such measurements an LP of 94 dB (1 Pa) is recommended
as this value is well above the normally encountered ambient noise levels.
Everyone seriously interested in the fi eld of professional sound should own or have easy
access to a precision sound level meter (SLM). Among other uses, an SLM is required to
measure ambient noise, to calibrate sources, and, on occasion, to serve as input for frequency
response, reverberation time, signal delay, distortion, and acoustic gain measurements.
Setting up the microphone measurement system shown in Figure 22.1 requires a pink
noise generator, a micro-voltmeter, a high-pass and low-pass fi lter set such as the one
illustrated in Figure 22.2 , a power amplifi er, and a well-constructed test loudspeaker, in
addition to the SLM.
Select a measuring point (about 5 to 6 ft) in front of the loudspeaker and place the SLM
there. Adjust the system until the SLM reads anLP of 94 dB (a band of pink noise from
250 to 5000 Hz is excellent for this purpose). Now substitute the microphone to be tested
for the SLM. Take the microphone open circuit voltage reading on the micro-voltmeter.
The voltage sensitivity of the microphone can then be defi ned as
SEVo20 dB log( ) (22.1)where SV is the voltage sensitivity expressed in decibels referenced to 1 V for a 1-Pa acoustic
input to the microphone andEo is the open circuit output of the microphone in volts.
CHAPTER 22