Advertisement
satisfactory sound amplification and coverage. The SR107
Audio Equalizer provides the means for selective sup-
pression of those octave frequency bands in the audio
spectrum where feedback is likely to occur. These fre-
quency bands differ from one installation to another
depending upon the acoustics of the room, equipment
used, and speaker and microphone placement. The range
of control of both frequency and amplitude provided in
the SR107 is sufficient to accomplish significant feedback
suppression without noticeable loss of program material.
Proper adjustment of the Equalizer for feedback control
is a matter of some experimentation; a general procedure
is described here. These procedures for both house and
stage monitor live performance sound reinforcement sys-
tems assume that the system speakers have a consistent
phase relationship and that all microphones used are
also wired for consistent phase operation. If necessary,
the phase of any balanced microphone line equipped
with professional 3-pin connectors can be reversed using
a plug-in Shure Model Al5PR Phase Reverser.
House System
1. Refer to General Operating Instructions for initial
connections and setup.
2. Adjust individual mixer volume control for each per-
former's microphone to level slightly below feed-
back threshold. If console or mixer is equipped
with output phase reversal switch, set to position
giving highest gain without feedback. If necessary,
reduce setting of master volume control slightly and
return to feedback point for each switch position to
evaluate switch effect. Operation of this switch will
usually affect only low-frequency feedback.
3, Increase LEVEL setting until feedback squeal or
ringing is heard. If feedback appears to be high-
pitched, one of five mid-to high-frequency Filter
Controls (1 thru 16 kHz) will be most effective in
eliminating feedback. Each Filter Control should be
turned down (counterclockwise) and back to "0"
position slowly to determine which is most effective.
Control which stops feedback with the least rota-
tion should be turned down only so far as necessary
to eliminate feedback.
4. If feedback frequency happens to fall between
bands covered by two adjacent controls, it may be
necessary to turn down both controls slightly to
obtain desired feedback suppression.
5. If feedback sound first noted in step 3 was low-
pitched, adjustment procedure should be started
using low-frequency (31 to 500 Hz) Filter Controls.
6. Having eliminated first feedback condition, increase
gain by clockwise rotation of LEVEL Control until
feedback is again noted. Repeat steps 3, 4, and 5
to eliminate new feedback condition. This may re-
quire adjustment of different Filter Control or a
further decrease in control or controls previously
turned down.
7. Repeat step 6 until either: (a) volume level of sound
system before feedback is sufficient for perform-
ance involved, (b) feedback becomes a combination
of sounds of various frequencies, or (c) any one
Filter Control has been turned all the way down
(-15).
Adjust LEVEL Control to slightly below
point at which final feedback sound occurred.
8.
Conduct voice test using each live microphone in
sequence. As each microphone is used, listen for
ringing. If ringing is noted, attempt to eliminate it
by further decrease in appropriate Filter Control
or slight decrease in LEVEL Control setting.
9. Perform critical listening check in audience area
during talk test or live performance to determine if
additional equalization adjustments are necessary
to improve sound quality (boost of frequency bands
in the 1 kHz to 4 kHz region to improve presence
and intelligibility, etc.). Refer to Live Performance
Equalization for additional information.
Stage Monitor System
In a stage monitor system the SR107 is connected be-
tween the audio console monitor line output (line level)
or the line level output of a monitor mixer and the line
level input of the power amplifier used to drive the stage
monitor loudspeakers. With this exception the initial set-
up of the stage monitor system is the same as that given
in General Operating Instructions. The number, type and
arrangement of microphones and speakers should be the
same as used in the performance.
1. If more than one performer's microphone is in-
volved, select lead performer or center stage micro-
phone for use in feedback equalization procedure.
NOTE: During this procedure a person must stand
in front of or hold the microphone being equalized
in a manner similar to that of the performer.
2. Roll off low frequency response of system by ad-
justing 31 Hz Filter Control to
-
15, 63 Hz to
-
10,
125 Hz to -5. This will reduce low frequency noise
pickup without affecting intelligibility.
3. Equalize stage monitor system following House
System procedure, Steps 2 through 7.
4. Conduct voice test for each of remaining micro-
phone positions in sequence using same channel
gain setting as for first microphone. (This assumes
that all microphones used have essentially the same
sensitivity and response.) If feedback or ringing is
encountered at any microphone location, try elim-
inating it by adjustment of nearest speaker position
or microphone distance. While performing voice
test, check intelligibility of sound from monitor
speakers. Intelligibility can usually be improved by
boosting frequencies in 1 kHz to
4
kHz range, pro-
vided that the feedback threshold is not affected.
5. Check operation of stage monitor system with all
performer microphones on (preferably with some-
one standing in front of or holding each micro-
phone) to determine maximum gain settings before
feedback for individual channel and master volume
controls.
6. Operate stage monitor system and house system
simultaneously at desired volume levels to verify
satisfactory performance. If house system console
or mixer is equipped with output phase reversal
switch, operate switch and check for any improve-
ment in gain before feedback in either house or
stage monitor system.
Playback Equalization
The SR107 Equalizer may be used to adjust the overall
frequency response, octave by octave, of an audio play-
back system to compensate for any electrical or acousti-
cal response deficiencies of the system and to provide
more natural sound reproduction.
Assuming that good engineering practice has been
followed in selecting and installing the loudspeakers for
uniform sound coverage, it is necessary to subjectively
evaluate the sound quality and to equalize for reasonable
audio spectral balance. While no specific procedure can
be offered for this type of equalization, the following
recommendations should be helpful:
Advertisement
