Meyer Sound 1100-LFC Operations Instructions download pdf (Page 16)

CHAPTER 3: AMPLIFICATION AND AUDIO

To avoid distortion when looping multiple 1100-LFCs, make

sure the source device can drive the total load impedance of

the looped loudspeakers. 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 loudspeakers.

Most professional audio equipment can transmit these

source levels.

To calculate the load impedance for the looped loudspeak-

ers, divide 10 kOhms (the input impedance for a single

1100-LFC) by the number of looped loudspeakers. For

example, the load impedance for 10 1100-LFC loudspeak-

ers is 1000 ohms (10 kOhms / 10). To drive this number of

looped loudspeakers, the source device should have an out-

put impedance of 100 ohms or less. This same rule applies

when looping 1100-LFC loudspeakers with other self-pow-

ered Meyer Sound loudspeakers.

NOTE: Most source devices are capable of

driving loads no smaller than 10 times their

output impedance.

CAUTION: Make sure that all cabling for

looped loudspeakers 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 loud-

speakers in a system have reversed polarity, fre-

quency response and coverage will be significantly

degraded.

OPTIONAL XLR 3-PIN AUDIO CONNECTORS

The 1100-LFC is optionally available with XLR 3-pin connec-

tors for audio Input and audio Loop output. The connectors

accept balanced audio signals with an input impedance of

10 kOhm and use the following wiring:

■ Pin 1 — 220 kOhm to chassis and earth ground (ESD

clamped)

■ Pin 2 — Signal (+)

■ Pin 3 — Signal (–)

■ 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.

CABLE RINGS

Two cable rings are provided on the rear of the 1100-LFC

loudspeaker. The power and audio cables should be tied off

to the rings to reduce strain on the cables and prevent dam-

age to them during installation. The cable rings should not

be used for any other purpose.

CAUTION: the 1100-LFC cable rings should

only be used to reduce strain on cables. The

cable rings should not be used for any other purpose.

TRUPOWER LIMITING

The 1100-LFC employs Meyer Sound’s advanced TruPower

limiting. Conventional limiters assume a constant loud-

speaker impedance and set the limiting threshold by measur-

ing voltage alone. This method is inaccurate because

loudspeaker impedances change as frequency content in the

source material changes, and as thermal values for the loud-

speaker’s voice coil and magnet vary. Consequently, conven-

tional limiters often begin limiting prematurely, which reduces

system headroom and dynamic range.

In contrast, TruPower limiting anticipates varying loud-

speaker impedances by measuring both current and voltage

to compute the actual power dissipation in the voice coil.

This improves performance, both before and during limiting,

1100-LFC Cables Tied Off to Cable Ring

1100-LFC Limit LEDs

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 39 40

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Meyer Sound 1100-LFC Operations Instructions Page 16

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