Meyer Sound MSL-4

Power Connector Wiring

Use the following AC cable wiring diagram to create interna-

tional or special-purpose power connectors:

brown = hot

blue =

neutral

yellow/green =

earth ground

(chassis)

AC cable color code

If the colors referred to in the diagram don't correspond to the

terminals in your plug, use the following guidelines:

• Connect the blue wire to the terminal marked with an

N or colored black.

• Connect the brown wire to the terminal marked with an

L or colored red.

• Connect the green and yellow wire to the terminal marked

with an E (or ) or colored green (or green and yel-

low).

Audio Input

The MSL-4 presents a 10 kΩ balanced input impedance to a three-

pin XLR connector wired with the following convention:

Pin 1 — 220 kΩ to chassis and earth ground (ESD clamped)

Pin 2 — Signal

Pin 3 — Signal

Case — Earth (AC) ground and chassis

Shorting an input connector pin to the case can form a ground

loop and cause hum.

Pins 2 and 3 carry the input as a differential signal; their polar-

ity can be reversed with the input polarity switch on the user

panel. If the switch is in the up position, pin 2 is hot relative

to pin 3, resulting in a positive pressure wave when a positive

signal is applied to pin 2. Use standard audio cables with XLR

connectors for balanced signal sources.

TROUBLESHOOTING NOTE: If abnormal noise (hum,

hiss, popping) is produced from the loudspeaker, disconnect

the audio source from the speaker. If the noise stops, then the

problem is not within the loudspeaker; check the audio input

and AC power.

A single source can drive multiple MSL-4s with a paralleled

input loop, creating an unbuffered hardwired loop connection.

The input impedance fo a single MSL-4 is 10kΩ; cascading

n MSL-4s will produce a balanced input impedance of 10kΩ

divided by n. To avoid distortion from the source, make sure

that the source equipment can drive the total load impedance

presented by the paralleled input circuit. For most source

equipment it is safe to drive circuits whose input impedance

is no smaller than 10 times its output impedance. For example,

cascading 10 MSL-4s produces an input impedance of 1000

Ohms (10kΩ divided by 10). The source equipment should

have an output impedance of 100 ohms or less.

This is also true when connecting in parallel (loop out) MSL-

4s to 650-Ps, DS-4Ps, or any other Meyer Sound self-powered

loudspeaker system.

The LD-1A is highly recommended when driving systems

using multiple speakers. (See Measurement and Integration

Tools, page 9.)

Ampliﬁcation and Protection Cir-

cuitry

Each driver in the MSL-4 is powered by one channel of the

Meyer Sound MP-2, a 1240W RMS ampliﬁer (620W RMS/ch)

utilizing complementary power MOSFET output stages (class

AB/H). The following sections discuss the MP-2’s limiting

circuitry and the two-fan cooling system.

TruPower™ Limiting System

Conventional limiters assume that the resistance of a loudspeaker

remains constant and set the limiting threshold by measuring

voltage only. This method is inaccurate because the loudspeaker’s

resistance changes in response to the frequency content of the

source material and thermal variations in the loudspeaker’s

voice coil and magnet. Conventional limiters begin limiting

prematurely, which under-utilizes system headroom and deprives

the loudspeaker of its full dynamic range.

The TruPower limiting (TPL) system accounts for varying

loudpeaker impedance by measuring current, in addition

to voltage, to compute the power dissipation and voice coil

temperature. TPL improves performance during limiting by al-

lowing the loudspeaker to produce its maximum SPL across its

entire frequency range and extends the lifetime of the drivers

by controlling the temperature of the voice coil.

HI Limit and LO Limit LEDs on the user panel indicate TPL

activity for the high and low frequency ampliﬁer channels. When

either channel exceeds the safe continuous power level, its limiter

engages, ceasing operation when the power level returns to normal.

The limiters for each channel function independently and do

not affect the signal when the LEDs are inactive.

The MSL-4 performs within its acoustical speciﬁcations and

operates at a normal temperature if the limit LEDs are on for no

Differential Inputs