L-Acoustics MTD Series, Operator'S Manual, Page: 17 / 69

L-ACOUSTICS MTD Manual V1.2 11/30/2004
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2. POWERING MTD
It is important that power amplifiers with sufficient power are used to power MTD108a, MTD112b or
MTD115b loudspeakers since headroom is less likely to damage loudspeaker components than
clipping. Apart from normal standards regarding construction, protection, cooling and damping factor
that are expected of any professional sound reinforcement amplifier, MTD loudspeakers and LLC
controllers are intended to be used with amplifiers with the following specifications:
GAIN STRUCTURE
Protection circuitry employed in all LLC Controllers is calibrated and optimized for 32 dB amplifier gain.
LLC controllers can be safely used with amplifiers having less than 32 dB gain, however, the maximum
SPL output obtainable from your loudspeaker system will be less than optimum. In addition, due to
the higher input sensitivity of lower gain amplifiers (i.e., less input signal level is required in order to
drive the amplifier to clip) it is also possible that LLC controller limiting circuitry will not operate
correctly. This could allow amplifiers to be operated under continuous clipping conditions and may
result in damage to your loudspeaker.
For amplifiers with more than 32 dB gain, in extreme cases, oscillation of LLC controller sense return
circuitry can occur, resulting in potential damage to the MTD loudspeaker and/or amplifier. For
amplifiers with greater than 32 dB gain, please contact your amplifier supplier for technical support
regarding how to calibrate the amplifier for 32 dB gain.
LIMITERS
Peak limiters on all amplifier outputs with soft clipping characteristics; attack time less than 3msec
COOLING
Temperature speed-controlled fan recommended
In practice, L-ACOUSTICS specifies power amplifiers with output power equivalent to twice the RMS
power handling for the low section and equivalent to the peak power handling for the high section.
These requirements typically allow the same amplifier to be used for both sections since the drive
level for the HF section is attenuated relative to the LF section to account for efficiency differences
(i.e., full continuous power will never be delivered to the HF section due to this attenuation). When
the same amplifier is used for the HF section, the extra available power then translates into headroom
for improved high frequency transient response.
Sections 2.1, 2.2, 2.3 and 2.4 give a summary of rms and peak power handling along with
recommended power amplifier output specifications for operation of single or multiple MTD108a,
MTD112b or MTD115b (active or passive mode) enclosures.
As standard, L-ACOUSTICS LA power amplifiers are 32 dB gain and there are four models available:
LA15a, LA17a, LA24a and LA48a (please see Table 11 for a specification summary). L-ACOUSTICS LA
amplifiers can be configured to provide power matching into different loads (for example, Figure 6
shows the location of MLS switches on the LA24a and LA48a rear panel).
Figure 6: MLS switches on the rear panel of L-ACOUSTICS LA24a, LA48a amplifiers