The frequency response of a complete horn loudspeaker, in the range where the throat impedance of the horn is a resistance as given by
Eq. (9.1), is determined by solution of the circuit of
Fig. 9.3. A horn-loaded drive unit behaves very differently from a direct radiator. The diaphragm of a direct-radiator loudspeaker is
mass controlled because a flat on-axis response is given at frequencies where the acceleration of the diaphragm is constant. Because the velocity decreases with frequency, so does the radiated power for
ω
>
c/
a, but this is compensated for by an increasingly narrow directivity pattern, which is how the flat on-axis response is maintained. By contrast, a horn has a fairly constant directivity pattern ...