Miles Technology Multisonic M44, Руководство по эксплуатации

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3 Installation
22
Setup Adjustment Procedure
This setup adjustment will produce correct level
balance of all of the loudspeakers so that Multisonic
Imaging operates perfectly. Typically the levels are
set using the amplifier gain controls, while the
Imager’s output controls are straight up.
Although the description here is quite detailed, this
procedure is really very simple, and often can be
done in just a few minutes.
Gain Structure
It is important to have correct system gain structure
for the particular equipment in use. If the operating
signal level is too low, the system noise level will be
higher. If the operating signal level is too high, then
distortion and inadequate power can result.
The M44 and M86 Imagers are designed to operate
at line level. Its outputs will clip at over 15 volts rms,
and the dynamic range is over 110 dB. In order to
make maximum use of its available dynamic range,
the M86 is operated with a nominal output level of
about 1 to 2 volts rms, yielding approximately 20 dB
of internal headroom. The necessary headroom is
dependent on the type of program material and may
need to be increased if compression or limiting is
used in the signal path after the Imager.
Most power amplifiers have a maximum gain which
is too high, causing the amplifier to clip with an input
signal of only 1 or 2 volts. In that case the level
controls need to be reduced to allow the optimum
input signal level to the amplifier.
A power-amplifier sensitivity (the level which
produces full output) in the range of +8 dBu (2 Volts
rms) to +18 dBu (6 Volts rms) is recommended. If
more system gain is needed, then increase the
drive level from the signal source, or for stereo
sources use the Source Gain control on the Imager.
If signal processing is used between the Imager and
the amplifier, such as crossovers, compressors, or
equalizers, then depending on their signal handling
capabilities it may be necessary to increase the
amplifier gain (and sensitivity) to lower the signal
level through these devices.
The exact gain of each power amplifier is adjusted
as described in the following section.
A. Setup Adjustment of Front Amplifier Gains
For optimum Multisonic Imaging performance, it is
important to have each power amplifier gain set for
audibly matched loudspeaker output. This is easily
accomplished using the Setup switch on the M44 or
M86. Here is the basic procedure:
1. Set the center amplifier gain at an appropriate
level. As mentioned above, a sensitivity in the range
of +8 dBu to +18 dBu is recommended. For most
amplifiers this means turning down the gain control.
Usually somewhere near the middle of the control
range is about right. Set the left, center, and right
amplifier gain controls at the same position.
2. Press in the LC Setup switch on the M44/M86.
3. Play some program material through the system.
Listen at a location slightly behind the center of the
listening area (where the long dashed lines intersect
in Figure 11). You should hear the sound coming
from a point exactly midway between the left and
center loudspeakers.
4. If the sound is closer to the center loudspeaker,
then turn up the left amplifier gain. If the sound is
closer to the left loudspeaker, then turn down the
left amplifier gain. Precisely adjust the left amplifier
gain so that the sound is exactly as described in
step 3.
5. Press out the LC Setup switch and press in the
CR Setup switch on the M44/M86.
6. With program material playing through the
system, listen again at the same location slightly
behind the center of the listening area. You should
hear the sound coming from a point exactly midway
between the center and right loudspeakers.
7. If the sound is closer to the center loudspeaker,
then turn up the right amplifier gain. If the sound is
closer to the right loudspeaker, then turn down the
right amplifier gain. Adjust the right amplifier gain so
that the sound is as described in step 6.
8. Press out the CR Setup switch to return to normal
operation. Adjustment is now complete.
B. Setting Amplifier Gains With Bridged Center
Loudspeaker
When the bridged-center-loudspeaker connection is
used, the two amplifier channel gains should match.
Here is one method to achieve precise matching:
1. Set the amplifier gains close to the desired level.
2. Press in both the LC and the CR Setup switches.
3. Disconnect the center loudspeaker.
4. Play some program material and listen from a
location on the centerline equidistant from the left
and right loudspekaers and near the center of the
audience or listening area.
5. Carefully adjust the left or right amplifier gain, if
necessary, so that the sound creates a phantom
image at the location of the center loudspeaker. It