Mackie CR1604 Owner's Manual download pdf (Page 48)

Do’s and Don’ts of Fixed Installations

If you install sound systems into fixed installa-

tions, there are a number of things that you can

do to make your life easier and that increase

the likelihood of the sound system operating in

a predictable manner. Even if you don’t do fixed

installations, these are good practices for any

sound system, installed.

1. Do use foil-shielded snake cable for long cable

runs. Carefully terminate each end, minimiz-

ing the amount of shielding removed. Protect

the exposed foil shield with shrink sleeving

or PVC sleeving. Prevent adjacent shields

from contacting each other (electrically).

Use insulating sleeving on the drain wire

(the one that connects to pin 1) to prevent

it from contacting the connector shell.

2. Don’t connect the XLR connector shell to

pin 1 of the XLR connector (unless necessary

for RFI shielding). Doing so is an invitation

for a ground loop to come visiting.

3. Do ensure that your speaker lines and AC

power lines are physically separated from

your microphone lines.

4. If you use floor pockets, use separate

pockets for inputs and speakers, or put the

connectors on opposite sides of the box so

that they may be shielded separately.

5. If your speaker lines run in the open, they

should be twisted pairs, at least 6 twists per

foot. Otherwise, run the speaker lines in their

own conduit. (Of course, conduit is not too

practical for portable systems, heh-heh.)

6. Minimize the distance between the power

amplifiers and the speakers.

7. Use heavy gauge, stranded wire for speaker

lines. Ideally, the wire resistance should be

less than 6% (0.5dB power loss) of the load

impedance. Remember that the actual run

is twice as long as the physical length of

the run. See below.

Maximum wire run for 0.5dB power loss in feet

wire res. per 2 4 8

gauge 1000 ft. ΩΩΩ

10 1.00 60 120 240

12 1.59 40 75 150

14 2.5 24 48 95

16 4.02 15 30 60

8. Ensure that the electrician uses the star-

ground system for the safety grounds in

your electrical system. All of the audio

system grounds should terminate at the

same physical point. No other grounds may

come in contact with this ground system.

9. Ensure that the AC power feeds are connected

to the same transformer, and ideally, the

same circuit breaker.

10.Walk outside – look at the horizon, see any

radio towers? Locate potential sources of RF

interference and plan for them before you begin

construction. Know the frequency, transmitter

power, etc. You can get this information by

calling the station. Remember that many

broadcast stations change antenna coverage

pattern and transmitter power at night.

11. Don’t use hardware-store light dimmers.

12. Don’t allow for anything other than micro-

phone inputs at stage/altar locations.

Supplying line inputs at these locations is

an invitation for misuse. Make all sources

look like microphones to the console.

13. Balance (or at least impedance balance)

all connections that are remote from the

console’s immediate location.

14. If you bridge an amplifier, don’t use

⁄

phone plugs for speaker connectors.

Grounding

Grounding exists in your audio system for

two reasons: product safety and noise reduc-

tion. The third wire on the power cord exists

for product safety. It provides a low-resistance

path back to the electrical service to protect

the users of the product from electrical shock.

Hopefully, the resistance to ground through

the safety ground (third wire) is lower than

that through the user/operator to ground. If

you remove this connection (by breaking or

cutting the pin off, or by using a ‘ground

cheater’), this alternate ground path ceases to

exist, which is a safety hazard.

The metal chassis of the product, the

ground connections provided by the various

connectors, and the shields within your con-

necting cables provide a low potential point for

noise signals. The goal is to provide a lower im-

pedance path to ground for noise signals than

through the signal wiring. Doing so helps mini-

mize hum, buzz, and other extraneous

non-audio signals.

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Mackie CR1604 Owner's Manual Page 48

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