Mtd System Operation; Recommended Maintenance Procedures - L-Acoustics MTD Series Operator's Manual

7. MTD SYSTEM OPERATION

Please refer to Section 4 for cabling and configuration details for typical MTD system configurations.
Once the system is cabled (LLC controllers, amplifiers and loudspeakers), connect program signal
lines (L/R outputs from a mixing console, for example) to the appropriate input channels of the LLC
Controller(s). Recall that LLC Controllers are calibrated for use with power amplifiers having 32 dB
gain (i.e., 40 x voltage gain or 1 volt input = 40 volts output).
Power on the LLC controller(s) and select the appropriate setting for 2-way operation (FRONT or
MONITOR) or 3-way operation (X-OVER mode) for MTD108a, MTD112b or MTD115b plus SB115,
SB118 or SB218 subwoofers.
Perform the following steps as a system check:
1) turn down the level of all amplifier channels before turning the amplifiers on
2) send a pink noise signal to the LLC controller
3) turn up the level of each HIGH amplifier channel individually (MTD115b in active mode) or
each MTD (passive mode) amplifier channel and check that this provides the expected
frequency band in the expected loudspeaker component. Test each HIGH or MTD (passive)
amplifier channel individually until all amplifier channels have been tested.
4) repeat steps 2-3 for LOW (MTD115b in active mode) and SUB amplifier channels
5) turn off the pink noise
6) use a polarity testing device to confirm that all SUB, LOW and HIGH components are
operating with positive polarity
7) set all amplifier output levels to 0 dB gain and the system is ready for use.
NOTE: Remember the old saying: "amps on last, amps off first" in order to avoid component damage due to
power on/off transients.

7.1 RECOMMENDED MAINTENANCE PROCEDURES

a) HF diaphragm replacement
To access the HF compression driver diaphragm, the front grille of the MTD enclosure should be
removed and the entire 8", 12" or 15" coaxial assembly de-mounted.
To remove the front grille, lift the edges of the acoustic foam and remove the screws. Screws can be
found where the edges of the foam are not glued onto the grille (there is no need to completely
remove the acoustic foam in order to remove the loudspeaker grille).
Once the coaxial assembly has been de-mounted, unscrew the back cover of the rear-mounted
compression driver assembly to obtain access to the compression driver diaphragm.
Remove the damaged diaphragm and before installing the replacement diaphragm ensure that the
voice coil gap is free from any metallic particles, dirt or other debris by using 2-sided tape and
acetone, if necessary, to thoroughly clean out the gap.
After installing the replacement diaphragm, apply a low level, low frequency sine wave sweep (for
example: 4 volts from 100 Hz - 1 kHz) to ensure that the diaphragm is properly centered in the gap
before reinstalling the compression driver back cover. Make sure all compression driver diaphragm
and back cover mount screws are securely fastened (loctite is optional but recommended).
As a final check apply a high level sine sweep over the HF compression driver's operating bandwidth
(for example: 13 volts from 1 kHz to 18 kHz). Re-mount the entire MTD coaxial assembly in its
enclosure and perform a system polarity check.
Following service, the damaged compression driver diaphragm should be returned to your distributor
or directly to L-ACOUSTICS for warranty examination.
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