Low-cost audio power amplifiers often avoid direct coupling of the loudspeaker to the output stage because any resulting dc bias current in the speaker can use up (and thereby waste) its limited mechanical dynamic range. Unfortunately, the coupling capacitor needed can be large! But feedback helps. For example, for an 8ohm loud speaker and fL=100Hz, what size capacitor is needed?
Now, if feedback is arranged around the amplifier speaker so that a closed-loop gain Af=10V/V is obtained from an amplifier whose open-loop gain is 1000V/V, what value of fLf results? if the ultimate product-design specification requires a 50Hz cutoff, what capacitor can be used?