When connecting multiple speakers to an amplifier, it’s important to stay above the amp’s minimum load requirements. Going below an impedance rating can overheat or even damage the amplifier. Fortunately, stereo volume controls with selectable impedance matching provide this means for protection.
Models like ELAN Home Systems’ VS and VSO stereo volume controls feature 1x, 2x, 4x and 8x configurable jumpers to select the optimum impedance match setting. What jumper settings to use depends on three numbers:
the minimum impedance rating of the amplifier
the total speakers being connected to the amplifier channel
the impedence of the speakers being connected to the amplifier channel.
After you know these three numbers, it’s a simple matter of elementary school math. It takes two simple equations to determine impedance match settings:
impedance rating of speakers / # of speakers connected to channel = load impedance
amplifier’s minimum impedance rating / load impedance = impedance match jumper setting
For example, if an amplifier’s minimum load impedance rating is 8 ohms, and you will connect four 8 ohm speakers to an amplifier channel, you’d make two calculations:
8 ohm speakers / 4 speakers = 2 ohm load impedance (8/4=2)
8 ohm amplifier / 2 ohm load impedance = 4x jumper setting (8/2=4)
Remember: Most speakers are rated at 4, 6 or 8 ohms. If your speakers aren’t those ratings, you’ll need to determine the average impedance. One pair of 4 ohm speakers is the equivalent of two pairs of 8 ohm speakers. Round up any fractional jumper setting to the next highest setting available on the volume control.
Also, all volume controls connected to the amplifier should have the same impedance match setting.