Speaker impedance calculator

A lower impedance draws more current, so the amplifier runs hotter and its distortion rises as it struggles to supply it. Solid-state designs typically go into protection, shut down or eventually fail; a valve amplifier is unhappy in the other direction too, since running it with no load at all can damage the output transformer. The manufacturer’s minimum load is the number that decides this, not the arithmetic here.

Electrically yes, and the calculator will combine them, but the power does not divide evenly. In parallel the lowest-impedance speaker draws the most current and so takes the largest share of the power, which is how one driver in a pair ends up cooked. Matching impedances and power ratings is the reliable route.

Because a meter measures DC resistance while the rating describes impedance to an AC signal. DC resistance normally lands around three quarters of the nominal figure, so 6 to 6.4 ohms on an 8-ohm driver is exactly what you should expect. Use the label for wiring arithmetic and the meter only to check that a driver and its cable are not open or shorted.

Whichever lands on a load your amplifier is rated for. Beyond that, parallel keeps the rest of the speakers running if one fails or one cable comes loose, while a series chain goes silent at the first break. Series wiring also means each driver sees the signal after the ones before it, which is one more thing to get wrong in a live rig.

Those taps exist so the output transformer can be matched to the cabinet. Work out the combined load here, then use the tap that matches it, and never leave a valve amplifier running with nothing connected. If your total falls between two taps, the manufacturer’s guidance decides which one to use, not a rule of thumb.