Notches. Note: Very sharp bandwidth lowers the, Block Diagram

Operating Manual - PQX 571 and PQX 572 Parametric Equalizer

With the entire PA hooked up and turned on,

6.5

Large Room Equalization

slowly increase the sound level at the mixer un-

til feedback is heard, then lower the level by about

Large rooms tend to suffer from multiple reflec-

3 dB so that feedback does not continue.

tions with long time delays, long reverberation times, and

“ring-modes”, all of which lead to reduced intelligibility

Start with one of the PQX filters by setting

and a generally “muddy” sound. As sound travels long

the level at 0, bandwidth set fairly sharp (about

distances through the air, high frequencies are attenuated

.3 oct.), and adjust the frequency control to where

more than low frequencies. In general, large rooms ben-

you estimate the predominate feedback frequency

efit from some low frequency shelf roll-off, high frequency

to occur.

shelf boost, and attenuation of ring mode frequencies by

the parametric filters.

4. Push in the filter’s EQ switch and increase its

level control by about +6 dB. Now “sweep” the

6.6

Small Room Equalization

frequency around where you have estimated the

feedback frequency until feedback occurs. Once

Small rooms need less equalization than large

you have induced the feedback by boosting its

ones. However, with reflective surfaces so close together

frequency, quickly turn down the filter’s level

it is more likely to encounter high frequency feedback

control to about -6 dB to suppress or “notch out”

problems.

Finding and critically notching out these of-

the feedback frequency.

fending “hot spots” is precisely what the PQX equalizer

does best. Use the narrowest possible bandwidth, and as

Again slowly increase the master level at the

always, avoid over-equalization.

mixer until feedback is heard. If a new feedback

frequency is heard, then repeat step 3 to find and

THEORY

suppress the new frequency. If the original feed-

back frequency is still heard, then adjust the first

The heart of the PQX equalizers is a unique

filter’s level even lower. The bandwidth control

bandpass filter circuit. Basically a “state-variable” type, this

may be adjusted full clockwise to produce a very

filter is trimmed and optimized to provide excellent transient

sharp notch so that a severe feedback frequency

response and a wide range of frequency and bandwidth ad-

can be attenuated by as much as 15 dB without

justment.

Each filter can be tuned over a 100:1 frequency

degrading the frequency response with noticeable

range (about 6.6 octaves) and a 70:1 bandwidth range with

notches. Note: Very sharp bandwidth lowers the

no more than a 2 dB amplitude error at center frequency. At

maximum equalizer input level because of the

its sharpest setting, the filter has a “Q” of about 35 and gen-

high filter gain necessary to obtain such a nar-

erates a response curve with 3 dB points only 1/20 octave

row bandwidth. Only use bandwidth control full

apart, making feedback control possible with no audible side

CW (.05 Octave) in severe cases.

effects. Each filter is placed in the feedback loop of a sum-

ming amplifier to produce the desired frequency response.

Continue this iterative process of increasing

Since a separate summing amplifier is used for each band,

the mixer’s master level and finding, then sup-

no interaction between bands occurs.

pressing feedback frequencies until a de-

sired sound system gain-before-feedback

level has been achieved.

OUT

OUTPUT

6.4

Console Channel Equalization

BALANCED

INPUT

GAIN

CLIP

PEAK

Many mixing consoles provide only

DETECTOR

simple equalization for individual channels. If

your console has channel inserts, you can patch

your equalizer into a channel that is used for some-

thing important, and use it to tailor the

sound of

this channel exactly the way you want.

LOW

PAR.

HIGH

SHELF

FILTER

SHELF

FILTER

20-20K

+/-

PQX

Ashly PQX-571 manual notches. Note: Very sharp bandwidth lowers the, CW .05 Octave in severe cases

Models: PQX-571 PQX-572

notches. Note: Very sharp bandwidth lowers the

maximum equalizer input level because of the

high filter gain necessary to obtain such a nar-

row bandwidth. Only use bandwidth control full

CW (.05 Octave) in severe cases.

Block Diagram