Speech Reinforcement: Wiring and Cables

This article is part of a series; see Speech Reinforcement.

Microphone/line level

Use a 2 conductor cable with a shield for any of the following:

microphone level (eg. 0.002 Vrms)
-10 dBV consumer line level (0.316 Vrms)
0 dBu professional reference level (0.775 Vrms)
0 dBV consumer reference level (1 Vrms)
+4 dBu professional line level (1.228 Vrms)

Use something like Belden 9145 for installed wiring (in a building or rack cabinet).

8 ohm speaker wire

As speaker wire, use 2 conductor wire.
Shielding is not necessary and increases the risk of a short.

70V speaker wire

For 70V, use 2 conductor wire.
Shielding is not necessary and increases the risk of a short.
18 AWG wire will yield less than 5% power loss up to about 100 m (330 ft).
For installed 70V audio, use 18 AWG or larger wire. Solid and stranded wire are both acceptable, up to 12 AWG. Stranded may be easier to work with when soldering connectors, especially with large gauge wire.
For portable 70V audio, use stranded 18 AWG wire or larger. Stranded wire is more durable for handling.

Attenuators and isolators

AudioTechnica AT8202
Shure A15AS
Whirlwind ISOXL

Compatible wiring scheme

Amplifier output is 70V, 2 channels, with male twist connector.

Supported outputs:

2x 70V bare wire
2x 70V phone male (for female jack)
2x 70V female twist speaker connector (for male jack)
2x 8-ohm bare wire
2x 8-ohm phone male (for female jack)
2x 8-ohm female twist speaker connector (for male jack)
2x 600-ohm (line/mic level) phone/XLR male (for male jack)

Standard cables/adapters required:

3x XLR-F to XLR-M standard microphone/line cable, 50 ft (15 m), 16-24 AWG, stranded: TecNec XLM-XLF-50, Audio-Technica AT8314, Monoprice 4756
3x speakON-F to speakON-F standard speaker cable, 50 ft (15 m), 12-18 AWG, stranded: Technical Pro CSS1650, Monoprice 8771
2x XLR-F to 1/4 inch male TRS microphone/line cable, short, 16-22 AWG, stranded: Monoprice 4767
2x speakON-F to speakON-F standard speaker cable, 6 ft (2 m), 12-18 AWG, stranded: Monoprice 8768
1x speakON-M to speakON-M splicing adapter (Neutrik NL4MMX): Markertek NL4MMX

Special cables/adapters required:

2x 30W 70V transformer/splitter box with 3 parallel speakON-M chassis inputs and 1 speakON-M chassis output: Atlas Sound T20, OSD Audio, Polycase DC-34PMBYR, 9/64 inch bit, 7/8 inch bit, (add template)
2x speakON-F to bare speaker wire cable, short, 12-16 AWG, stranded
2x speakON-F to 1/4 inch male TS cable, short, 12-18 AWG, stranded

Suggested connectors:

speakON-F cable connector: Neutrik NL2FX (Markertek), Monoprice 601500
speakON-M panel mount: Neutrik NL4MP-ST (Markertek)
speakON-M cable connector: Neutrik NLT4MX (Markertek)

More speaker wiring

There are two options for speaker wiring: low impedance and high impedance. Low impedance is typical for basic systems with few speakers and short cable runs. High impedance or constant voltage wiring (typically 70V in the United States) requires a transformer at each speaker but offers numerous advantages over low impedance:

All speaker transformers are wired in parallel.
Higher gauge (smaller) wire can be used.
Each speaker can use whatever wattage is necessary for its location. The transformers generally have taps ranging from 0.25 W to 30 W, depending on the transformer, to facilitate this.
The level of a speaker or group of speakers can be adjusted after installation by using a switch-selected transformer and/or attenuator.
If one or more speakers fail, if the wattage tap/level for a speaker is changed, or if speakers are added or removed, the other speakers continue to operate as before.

Sources: