User Guide

Sound System Design Reference Manual
The Importance of Flat Power Response
If a radiator exhibits flat power response, then
the power it radiates, integrated over all directions,
will be constant with frequency. Typical compression
drivers inherently have a rolled-off response when
measured on a plane wave tube (PWT), as shown in
Figure 3-7A. When such a driver is mounted on a
typical radial horn such as the JBL model 2350, the
on-axis response of the combination will be the sum
of the PWT response and the Dl of the horn. Observe
at B that the combination is fairly flat on axis and
does not need additional equalization. Off-axis
response falls off, both vertically and horizontally,
and the total power response of the combination will
be the same as observed on the PWT; that is, it rolls
off above about 3 kHz.
Now, let us mount the same driver on a Bi-
Radial uniform coverage horn, as shown at C . Note
that both on-and off-axis response curves are rolled
off but run parallel with each other. Since the Dl of
the horn is essentially flat, the on-axis response will
be virtually the same as the PWT response.
At D , we have inserted a HF boost to
compensate for the driver’s rolled off power
response, and the result is now flat response both on
and off axis. Listeners anywhere in the area covered
by the horn will appreciate the smooth and extended
response of the system.
Flat power response makes sense only with
components exhibiting constant angular coverage.
If we had equalized the 2350 horn for flat power
response, then the on-axis response would have
been too bright and edgy sounding.
3-6
Figure 3-7. Power response of HF systems