Connecting 70/ 100 volt constant voltage speakers

In this short post you’ll learn how to make the connections for a constant voltage speaker system.

Around the 1920’s or 30’s the constant voltage speaker system started to be used and it remains the best way to distribute sound over long cable runs with multiple speakers.

Switchable output

Switchable output

If you don’t have speakers with switchable output levels, setting up ceiling speakers with all these leads can be a bit of a nightmare.

Now this is where some get confused.  There are so many connections or leads you might say “I’m not sure where they all go”.  To make it simple, there are only two leads or connections that you need.

On this speaker the coloured leads or connections vary the output from 2.5, 5, 10 and 15 watts.  If I wanted only 10 watts I would select the common black wire plus the red wire.  Rcoloured wiresemember that other speakers may not have these colored leads, they may have a terminal block you configure to select the needed output.


A word of warning at this point.

Calculate power

Calculate power

You will need to take note of how much power each speaker is consuming and total these up making sure not to exceed the output of the amplifier so you don’t overload it and cause clipping or distortion.

For example if you selected 10 watts for each speaker and there were 10 of them you would be loading the amp with 100 watts so a 120 watt amplifier would be quite happy.

phase checkAll you need to do now is connect the main feed line to the speaker ensuring that the polarity remains the same relative to the speakers so they are in phase with each other.

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