Speaker wire for in-ceiling speakers background music

If the wire must be Plenum, you should also check if the speaker needs a back-box for fire.

I'd only use 16 AWG or larger for ANY distance on an 8 Ohm system. If you are doing a 70V system, 18 AWG would probably be OK.

Carl

18 AWG wire has a resistance of about 1.3 ohms per 100 feet (2-wire, round trip) so it depends upon the run length. 1.3 ohms reduces the sound level of an 8 ohm speaker by about 1.3dB.

It also reduces the damping factor, which can affect the sound quality. At what point that becomes a problem, I'm not sure. I've heard that it should be 10:1 or greater (0.8 ohm wire resistance for an 8 ohm speaker) but that's just a rule of thumb for high fidelity speakers. Ceiling speakers for background music are likely less sensitive to this.

As fedders noted a 70V system, which operates at a higher voltage and lower current then a direct connection, can operate at higher wire resistance without a problem.

You might try Monoprice for the wire. They usually have good prices.

If the speaker is exactly 8 Ohms at all frequencies, then there is no problem with a 1.3dB drop (just turn up the volume). The problem is that every speaker varies its impedance depending on frequency. The range may be roughly 4 Ohm to 16 Ohm over the audible frequency range. This means that the signal drop varies between 2.6dB [using crutschow's number] and 0.65dB (a 2dB difference) over the frequency range. This 2 dB difference means that certain frequencies are almost 1/2 as loud as other frequencies. The problem gets worse as the distance gets longer.

So, I guess it depends on how much the quality of sound matters to you.


Mono will not likely have Plenum. Try a local electrical distributor in your area like Graybar or CED. I know we also sell to Lowe's who can special order this for you. You only need 16/2 wire. Don't ask for specific "speaker" wire - there really isn't a difference.

Hope this helps.

Carl