ABSTRACT
The necessity for amplification becomes apparent from an analysis of the unlikely arrangement depicted in Fig. 20-1 wherein a dynamic microphone is connected directly to a loudspeaker.
The microphone typically, with moderate excitation, would generate an open circuit voltage of 10 mV and possess an internal impedance of 200 . The loudspeaker typically would have an impedance of 8 and an efficiency of 10%. The electrical power delivered to the loudspeaker assuming that the microphone and loudspeaker impedances are predominantly resistive would be 1.8 × 108 W while the acoustical output of the loudspeaker would only be 1.8 × 109 W. Even if a matching transformer is interposed between the microphone and the loudspeaker, the improvement is hardly significant. The acoustical output in this event becomes only 1.25 × 108 W which is several orders of magnitude below the acoustical power requirements of most applications.
