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5.4 DELAY TIME
The speed of sound is affected by air temperature. You can cal-
culate the sound speed as following:
C = 4 * (45.4 + °F)
1/2
in feet per second.
C = 20.6 * (273 + °C)
1/2
in meter per second.
Where C is the speed of sound.
To compensate the offset between the speakers, the time will
equal to the distance divided by speed.
T = D/C
Where T is the delay time in second, and D as distance in meter
or feet between the speakers.
The maximum delay time is 4 msec, which equal to 1.42 meters
at 25°C or 4.52 feet at 72°F. This distance is sufficient for most
speaker installation except those separating the speaker cabinet
far apart. The very large long throw horns usually measure at 1.2
meters. If you have any huge horn to work with direct radiate bass
unit, it is a good idea to move the bass a little back than the horn
mouth. Keep the speaker driver distance within 1.4 meter will be
fine for PCR2213 Plus.
If you want to make a precise delay time adjustment, connect
the PCR2213 Plus with dual channel oscilloscope with PCR2213
Plus input signal measured by one oscilloscope channel and LF
output to the other channel. Send the sine wave into PCR2213
Plus and adjust the delay time until the horizontal time offset equal
to your design.
5.5 LIMITER SETTING
1.
To properly set the limiter threshold. You need to find out the
capacity of the speaker and associated amplifier. Because
the threshold is global setting, we shall make use of the level
control on the PCR2213 Plus as well as those on the power
amplifiers, so that it works with all bands.
2.
Disconnect one set of the speakers and hook up dummy loads
(same value as the speaker loading) to the amplifiers (You can
connect only one output of the amplifier if you have multiple
for the same band, and turn them off without removing the
speaker connection.
3.
Turn the threshold all the way up, and switch on limiters.
4.
Let's start from the HF output.
5.
Turn up the mixer master level until the HF power channel
reached the threshold power you want to limit.
6.
Turn down the threshold until the HF limiter indicator lighted.
Now you have done the first limiter point. There are 3 more
(or 2 more ) to go.
7.
If you keep all the output levels on PCR2213 Plus at 0 (12
o'clock), the LF output of the same channel probably reached
limitng at the same time. But the power amplifier level maybe
higher or lower than the power you wish to limit. If the limiting
point is not yet reached, increase the mixer output level until
the limiter indicator is lighted. If it was too high already, bring
down the mixer output level until the limiter indicator just start
to light.
PCR2213
All manuals and user guides at all-guides.com
8.
Mark the output level at this point by measuring with AC
voltmeter.
9.
Turn up the level control of the power amplifier channel until
it reached the level you wish to limit.
10. Turn down the output level of PCR2213 Plus until the power
amplifier output level reduced back to the level marked in
step 8. Now, this output limiter is done.
11. Repeat the same procedure for other output limiter.
12. After all limiter points are set, connect all the speaker loads
back and send in the pink noise via the mixer again at -20dB
(or -30dB) refer to previous level.
13. Measure the HF amplifier channel used for previous setup
and write down the value.
14. Measure the other HF amplifier channels and adjust them as
the same as the write down value.
15. Measure the LF amplifier channel used for previous setup
and write down the value.
16. Measure the other LF amplifier channels and adjust them as
the same as the write down value.
5.6 SUB Σ
In case the PCR2213 Plus Plus is used to work with sub-woofer
system, no matter mono or stereo, it is good idea to drive all the
sub-woofer boxes in the same phase with identical signal. Keep
those sub-woofers the identical design with identical boxes and
drivers at all possible. This practice is true regardless of whether
it is a big stage installation or small in studio monitoring.
5.7 HORN EQ
30 years ago, the horn designs could not reach constant dispersion
over the frequency range it covers. The higher the frequency, the
narrower the covering area. 20 years ago, the design of constant
directivity can be realized, so that the energy can be distributed
wider area especially in higher frequency. This expose a problem
not noticeable in the past, because the high frequency energy
output from the driver will drop gradually as the frequency goes
higher. It was not a problem on axis before these constant direc-
tivity horns invented, and compensated with the beaming char-
acteristic of older horn. But to take good care of the audience in
various venues, constant directivity design provides much better
performance between on axis versus off axis. To compensate
this roll-off tendency, PCR2213 Plus provides a HORN EQ switch
which will boost +12dB at 15KHz with a 6dB/oct slope. This is a
generic curve and work fine with most constant directivity horns,
however fine tune may be needed with 1/3 octave equalizer.
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