JBL MPC Series Owner's Manual page 9

Computing channel loading
LOW IMPEDANCE
Due to frequency-dependent impedance variations, "constant voltage" loudspeakers can sometimes draw
more power from the distributed line than their transformer tap labels indicate. Although driving too low an
impedance will not harm your MPC amplifier, it might activate its protection circuitry or cause less-than-
optimal performance. When in doubt about actual loudspeaker characteristics, we recommend you use a
slightly higher nominal load impedance on the LOW IMPEDANCE output and/or a slightly lower total power
demand (i.e., sum of all the power taps) on the AUDIO TRANSFORMER outputs than what the following
formulas suggest.
1) Computing maximum allowable distributed line loading with a known low-impedance load
MaxATP
MaxATP
Rated LZP
Impedance
Example:
MaxATP
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Loading an amp channel—
Internal output signal flow—
IMPEDANCE
Minimum impedance considerations—
Ω
Ω
RatedLZP RatedLZP Impedance
112 watts
and
UDIO TRANSFORMER
LOW IMPEDANCE
AUDIO TRANSFORMER
minimum
AUDIO TRANSFORMER
Ω
LOW IMPEDANCE
Ω
AUDIO TRANSFORMER
no
maximum
LOW IMPEDANCE
LOW