Example 3.6. An ideal moving-coil loudspeaker produces 2
W of acoustic power into an acoustic load of 4
×
10^{4}
N
s/m^{5} when driven from an amplifier with a constant voltage output of 1.0
V rms. The area of the diaphragm is 100
cm^{2}. What open-circuit voltage will it produce when operated as a microphone with an rms diaphragm velocity of 10
cm/s?

Solution. From Fig. 3.35 we see that, always,

$\tilde{e}=Bl\tilde{u}.$

The power dissipated W gives us the rms volume velocity of the diaphragm U
_{rms}:

${U}_{\text{rms}}=\sqrt{\frac{W}{{R}_{A}}}=\sqrt{\frac{2}{4\times {10}^{4}}}=7.07\times {10}^{-3}$

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