constant (i.e., constant sound pressure at all frequencies in the sound wave), a transducer must be chosen whose output voltage for a constant differential force acting on the diaphragm is inversely proportional to the quantity A defined in Eq. (5.23), i.e.,5.8. Acoustical combination of pressure and pressure-gradient microphones
One example of an acoustical design responding to both pressure and pressure gradient in a sound wave was described earlier in Section 5.3 (p. 206). The directional patterns for this type of design are the same as those shown for Fig. 5.30.
Because this type of microphone has a flat response as a function of frequency for
constant (i.e., constant sound pressure at all frequencies in the sound wave), a transducer must be chosen whose output voltage for a constant differential force acting on the diaphragm is inversely proportional to the quantity A defined in Eq. (5.23), i.e.,
constant (i.e., constant sound pressure at all frequencies in the sound wave), a transducer must be chosen whose output voltage for a constant differential force acting on the diaphragm is inversely proportional to the quantity A defined in Eq. (5.23), i.e.,
(5.67)
As an example, let us take the case of a microphone for which Z
AD
>>
R
A
and 1/ω C
A
R
A
>>
1. In this case the response of the transducer must be proportional to
(5.68)
where B is given by Eq. (5.21).
Restated, the transducer must have an output voltage for a constant net force acting on the diaphragm that is inversely proportional to frequency, if a flat frequency response is desired. This is the case for a moving-coil or ribbon transducer above the natural resonance frequency of the diaphragm.
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