13
INSTALLATION & OPERATION
switches are three position, with center position
being off, the top position giving an in-phase sig-
nal and the bottom position giving an out-of-
phase signal. There is a built-in high quality pink
noise source which feeds these switches.
If a Pink Noise Card is not available for the
MODIIC calibration, then an external pink noise
source may be used instead. Feed the external
pink noise source into the DIGITAL INPUTS on
the rear DB25 input connector of the MODIIC for
the following checks. Set the pink noise source
level for .55 volts RMS. You must use an analog
meter to measure this voltage level.
Special Note: If you will be installing an external digi-
tal decoder, do so AFTER setting house levels. See the
DIGITAL LEVEL SETTINGS at the end of the B
CHAIN CALIBRATION section for more information.
For the following procedures, select STEREO A by
pushing the appropriate button on the Format Card.
Also, set the STEREO MASTER FADER to the one
o’clock position.
EQUALIZATION
AND HOUSE
LEVELS:
The equalizers are
normally shipped
with the individual
trimpots set for a
flat frequency
response. The
optional 1/3 octave
equalizers used for
the stage channels
are capable of cut-
ting and boosting
each frequency
band ± 10 dB. The individual trimpots are single turn
types, with the mid position of each pot being flat
(unity gain).
On the standard one octave equalizer cards, all fre-
quencies are cut and boost ± 10 dB with single turn
trimpots also.
Remove the MATRIX CARD from its slot and set it
aside. Plug the PINK NOISE CARD into the MATRIX
CARD slot. Make sure the NORMAL/CHOO-CHOO
switch is in the NORMAL position. Turn on the
appropriate switch on the PINK NOISE CARD for the
channel you wish to equalize. Perform the equaliza-
tion (see diagram 3) and then adjust the output trim-
pot on the OUTPUT/MUSIC CARD so that 79 dBC spl
is measured in the auditorium. Do this for the five
main channels (Left, Center, Right, Left Surround &
Right Surround). If more gain is needed, then the gain
pot on the stage EQs can be used which gives an addi-
tional 6 dB of gain. However, do not boost the gain on
the EQ cards unless it is absolutely necessary.
The optional 1/3 octave stage channel equalizers in
the MODIIC allow the same tuning results obtained in
professional room tuning filter sets used in high-end
sound playback applications. Sound contractors
learned, a long time ago, that boosting frequency
bands adjacent to bands that are cut introduce a phase
shift that the ear is very sensitive to. Although the test
instruments show a nice curve, the sound has a col-
oration that is not natural. For this reason, we encour-
age you to apply the minimum amount of boost and
cut whenever needed. Never over-equalize the sys-
tem. All frequencies may be cut and boosted by as
much as 7 dB in each of the 1/3 octave bands without
creating the above problems. The use of bass and tre-
ble controls on the equalizer has also been avoided to
further minimize phase shift. Each filter section uses a
single turn trimpot for adjustment. The equalizers are
factory set for a flat response during final QC test.
Before attempting to equalize be sure the stage speak-
er connections are properly polarized, the polarity of
the components in each speaker system is correct, and
the speaker devices are mechanically aligned accord-
ing to the manufacturer’s recommendations.
Remember that equalizers are used to tune the room,
NOT to correct poor speaker installation and align-
ment.
SUB-BASS LEVELS:
With the Pink Noise Generator Card plugged into the
Matrix Card slot, turn on the LEFT and RIGHT pink
noise switches. Turn off the Left and Right channel
amplifiers to prevent sound from the Left and Right
stage speakers from affecting this adjustment. Adjust
the SUB LEVEL trimpot on the Output Card for 90
ISO Cinema playback standard states that 1/3 octave bands
should be tuned for flat response to 2 kHz, with a 3
dB/octave rolloff above 2K.
10
5
0
-5
-10
-15
31.5
63
125
250
500
1K
2K
4K
8K
16K
Diagram 3
dB
The optional 1/3 octave EQ card
