Meyer Sound MPS-488HP Manual Do Utilizador

24

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Pin 3 — Signal (–)

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Case — Earth (AC) ground and chassis

Pins 2 and 3 carry the input as a differential signal. Pin 1 is 
connected to earth through a 220 kOhm, 1000 pF, 15 V 
clamped network. This circuitry provides virtual ground lift 
for audio frequencies while allowing unwanted signals to 
bleed to ground. Make sure to use standard, balanced XLR 
audio cables with all three pins connected on both ends. 
Telescopic grounding is not recommended, and shorting an 
input connector pin to the case may cause a ground loop, 
resulting in hum.

If unwanted noise or hiss is produced by 

the subwoofer, disconnect its input cable. If the 

noise stops, there is most likely nothing wrong with 
the subwoofer. To locate the source of the noise, 
check the audio cable, source audio, and AC power.

The XLR male Audio Loop Out connector allows multiple 
MM-10AC subwoofers to be looped from a single audio 
source. For applications that require multiple MM-10ACs, 
connect the Audio Loop Out of the first unit to the Audio In 
of the second, and so forth. 

The order in which subwoofers are con-

nected when looping audio signals is unim-

portant. The Audio Loop Out connector is wired in 
parallel to the Audio In connector and transmits the 
unbuffered source signal even when the MM-10AC is 
powered off.

To avoid distortion when looping multiple MM-10ACs, make 
sure the source device can drive the total load impedance of 
the looped subwoofers. In addition, the source device must 
be capable of delivering approximately 20 dBV (10 V rms 
into 600 ohms) to yield the maximum peak SPL over the 
entire operating bandwidth of the subwoofers. Most profes-
sional audio equipment can transmit these source levels.

To calculate the load impedance for the looped subwoofers, 
divide 10 kOhms (the input impedance for a single 
MM-10AC) by the number of looped subwoofers. For exam-
ple, the load impedance for 10 MM-10AC subwoofers is 
1000 ohms (10 kOhms / 10). To drive this number of looped 
subwoofers, the source device should have an output 
impedance of 100 ohms or less. This same rule applies 
when looping MM-10AC subwoofers with other self-pow-
ered Meyer Sound loudspeakers.

Most source devices are capable of 

driving loads no smaller than 10 times their 

output impedance.

Make sure that all cabling for 

looped subwoofers is wired correctly (Pin 1 to 

Pin 1, Pin 2 to Pin 2, and so forth) to prevent the 
polarity from being reversed. If one or more subwoof-
ers in a system have reversed polarity, frequency 
response and coverage will be significantly 
degraded.

The Input Polarity switch swaps the polarity of the audio 
source signal, which is sometimes necessary to acoustically 
align the subwoofer with other loudspeakers in the system. 
When the switch is in the up (+), non-inverting position, pin 2 
is hot relative to pin 3, resulting in a positive pressure wave 
when a positive signal is applied to pin 2. When the switch is 
in the down (–), inverting position, pin 3 is hot relative to 
pin 2, resulting in a positive pressure wave when a positive 
signal is applied to pin 3.

The Input Polarity switch only affects 

the subwoofer signal. It has no effect on the 

Audio Loop Out signal.

The MM-10AC has a three-color Limit LED on its rear panel 
that changes color to indicate the subwoofer’s status.