Remember that with a 20 dB headroom figure, a
power amplifier as powerful as 500 watts will operate at
an average 5 watts output power. In some systems such
as studio monitoring, where fidelity and full dynamic
range are of utmost importance, and where sensitive
loudspeakers are used in relatively small rooms, this
low average power may be adequate. In other situa-
tions, a 20 dB headroom figure is not necessary and too
costly due to the number of amplifiers required.
After choosing a headroom figure, adjust the incom-
ing and outgoing signal levels at the various devices in
the system to achieve that figure. For a typical system,
the adjustments for a 20 dB headroom figure would be
made as follows:
1.
2.
3.
4.
Initially, set the attenuators on the power amp at
maximum attenuation (usually maximum counter-
clockwise rotation). Feed a sine wave signal at
1000 Hz to the console input at an expected average
input level (approximately -50 dBu (2.45 mV) for a
microphone, +4 dBu (1.23 volts) for a line level
signal. The exact voltage is not critical, and 1000 Hz
is a standard reference frequency, but any fre-
quency from 400 Hz to about 4 kHz may be used.
Set the input channel fader on the console at its
marked “nominal” setting, and adjust the channel
Gain so that the channel’s LED meter read zero.
The meter should be set to the Post-Fader mode
(MTR PRE switch [20] disengaged. Be sure this
channel is assigned to an output bus (i.e., one of the
group busses or the stereo bus).
Set the master fader for the bus to which the
channel is assigned so that the output level is
20 dB below the rated maximum output level for
the console. Suppose, for example, the maximum
rated output level is +24 dBu (12.3 volts); in that
case, the output level should be adjusted to +4 dBu
(1.23 volts), as indicated by a “zero” reading on the
console’s VU meter (0 VU corresponds to
+4 dBu with a steady-state sine wave signal output
per factory calibration).
If the rated maximum input level for the graphic
equalizer to which the console output is connected is
+24 dBu (12.3 volts), then no adjustment or padding
of the input to the EQ is required. If the maximum
input level is lower, for example
+18 dBu, then there would be reduced headroom in
the EQ unless its input is attenuated. Subtracting
+4 dBu from +18 dBu leaves only 14 dB of head-
room, so in order to maintain the desired
20 dB of headroom, 6 dB of attenuation must be
dialed in at the EQ input, or a 6 dB resistive pad
should be inserted between the console output and
the equalizer input. The nominal signal level at the
input to the equalizer should now be -2 dBu
(616 mV), which can be checked with a voltmeter.
5. Assume that the maximum rated output level of the
equalizer in this example is +18 dBu (6.16 volts).
Adjust the master level control on the equalizer so
that its output level is 20 dB below the rated
maximum, or -2 dBu (616 mV). If the equalizer has
no built-in VU meter, use an external voltmeter to
confirm this level.
NOTE: If the graphic equalizer is placed in the console’s
group or stereo INSERT IN/OUT loop, the nominal
sensitivity of the input is +4 dBu, which may seem to be
6 dB less sensitive than required for the necessary
headroom. However, any boost applied with the EQ will
raise the nominal level of the signal at the EQ output, so
this may help preserve adequate headroom in the
console. Remember, though, that applying boost with an
equalizer can reduce headroom within the EQ itself, so
you may want to turn down the EQ’s output level to
preserve the headroom.
6. Finally, starting with the attenuator(s) on the
power amplifier at maximum attenuation (maxi-
mum counterclockwise rotation), slowly decrease
the attenuation (raise the level), observing the
amplifier’s output level. When the POWER output
is 1/100 of the maximum rated power (1/10 of the
maximum output voltage), the amplifier has 20 dB
headroom left before clipping. A 250 watt amplifier
would operate at nominal 2.5 watts, or a 100 watt
amplifier at 1 watt, on average level passages in
order to allow 20 dB for the loud peaks.
To operate this system, use only the controls on the
console, and avoid levels that consistently peak the
console’s VU meter above the “zero” mark on its scale,
or that drive the amplifier above a safe power level for
the speaker system. Any level adjustments in the other
devices in the system will upset this established gain
structure.
If, for a given amount of headroom, portions of the
program appear to be “lost in the noise,” the answer is
not to turn up the levels since that will merely lead to
clipping and distortion. Instead, it will be necessary to
use either a compressor, or to manually “ride the gain”
of those console faders that are required to raise the
level when the signals are weak. This effectively re-
duces the required headroom of the signal, allowing the
lower level portions of the program to be raised in level
without exceeding the maximum level capability of the
system. Compressors can be used in the INSERT IN/
OUT loops of individual channels (say for a vocalist
with widely varying levels), or at the group, aux or
stereo master INSERT IN/OUT points or after the
Matrix Outputs when the overall mix has too much
Page 5-5
Summary of Contents for PM4000
Page 1: ...PROFESSIONAL AUDIO MIXING CONSOLE PM4000 OPERATING MANUAL YAMAHA ...
Page 2: ...PM4000 OPERATING MANUAL ...
Page 7: ...Section 1 Introduction ...
Page 11: ...Section 2 Brief Operating Instruction ...
Page 47: ...Section 3 Specifications ...
Page 51: ...Dimensional Drawings PM4000 Console all versions Page 3 4 ...
Page 52: ...Page 3 5 ...
Page 53: ...Page 3 6 PM4000 Console Rear Profiles ...
Page 54: ...Module Block Diagrams See back of the manual for overall system block diagram Page 3 7 ...
Page 55: ...Page 3 8 ...
Page 56: ...Page 3 9 ...
Page 57: ...Page 3 10 ...
Page 58: ...Page 3 11 ...
Page 59: ...Page 3 12 ...
Page 60: ...Section 4 Installation Notes ...
Page 72: ...Figure 4 13 Cables For Use With Balanced Sources Page 4 12 ...
Page 79: ...SECTION 5 Gain Structure and Levels ...
Page 82: ...Figure 5 1 Dynamic Range and Headroom in Sound Systems Page 5 3 ...
Page 86: ...Section 6 Optional Functions ...
Page 106: ...Section 7 Operating Notes and Hints ...
Page 119: ...Section 8 Applications ...
Page 127: ...Section 9 Maintenance ...
Page 131: ......
Page 132: ...YAMAHA VN02300 ...
