Sound Patern Equalizer

The circuit

In order to get well balanced sound pattern, both the lower frequencies and the upper audio frequencies have to be equalised. Higher audio frequencies are reproduced by calotte tweeters. Normally, the efficiency of these speakers id lowered by the inertia of the voice coils. Because of radiation beaming, frequency roll-off is smoothed only around the speaker axis. To get a uniform distribution of sound over a solid angle, higher frequencies have to be emphasised. This may be done with a modified Wien network as shown below.

The input file

sound pattern equalizer

.control
ac dec 50 10Hz 10kHz
* phase should be continuous
set units = degress
let phase = vp(3) + 360 * (vp(3) lt 0)
plot vdb(3) phase/10 xlabel f[Hz] ylabel output[dB][degree] title 'AC analysis'
unlet phase
.endc

v1 1 0 dc 0 ac 1

r1 1 2 33k
r2 2 3 470k
r3 5 4 39k
r4 5 2 1k
r5 5 6 330

c1 4 3 18nF
c2 5 0 68nF
c3 6 0 0.47uF

e1 3 0 0 2 1meg

.end

The results