Specifications

EAW Smaart 6 Operation Manual Applications
89
Stabilizing a System with EQ
Feedback is most commonly solved using EQ to remove or attenuate offending peaks.
Carefully run the system into feedback, identify problem frequencies, and set up filters
(i.e., EQ stages) to reduce gain at those frequencies. We strongly recommend using
parametric equalizers.
1. Connect the system as shown in Figure 4-10. This allows using the EQ without
switching the input signals to the computer.
2. Click the Spectrum button to set a two-pane display with Spectrograph on top
and RTA on the bottom.
3. Set the Spectrum’s Avg to 8 or less, click the Start button, and excite the sound
system at a low level with pink noise.
4. Slowly and carefully bring up the gain of an open microphone until the peaks
grow on the RTA display. At this point, the system starts sounding hollow as
the pink noise tries to excite feedback at a number of frequencies at once.
5. Slowly and carefully, bring up the gain of the mic’s input channel until the system
just starts to feed back. Watch for a vertical streak forming in the Spectrograph
display, corresponding to a higher-than-average peak in the RTA display.
6. Click the Stop button to freeze the analyzer, then reduce the sound system gain
to a level at which there is no feedback. Click the Capture tab on the RTA
display bar and store the trace.
7. Click on the spike in the RTA display and note its frequency in the cursor
readout above the plot area.
8. Click the Frequency Response button to display the equalizer response. The
goal is to set an attenuation (cut) filter centered on the feedback frequency to
dampen the resonances causing feedback.
9. Set a narrow bandwidth with 6-10 dB of cut with the center frequency of the
filter on the feedback frequency noted earlier.
10. Increase the filter’s bandwidth to about 1/3-octave, and reduce the cut to 3 dB.
Using wide, shallow filters minimizes phase distortions and allows the feed-
back frequency to drift as acoustics and other circumstances change during
the performance.
11. To determine the effectiveness of the filter, click the RTA display tab, bring
the system gain up with the same microphone open until it feeds back again,
and check the feedback frequency. If it is the same or very close, increase the
cut in the filter just set. If feedback occurs at a new frequency, apply another
filter using the same technique.
This procedure is simple, systematic, and much more accurate than playing it by ear.
Identifying each problem frequency precisely makes it easier to adjust the filters later
if necessary.