“I’ve searched through the TTOTD files and have gotten some great information, but there is a fundamental question that I still need answered. When you change the impedance of a speaker system by hooking up in parallel versus serial, what effect does that have on the output power of the amplifier? For example, if I have an amp that delivers 250 watts per channel at 8 ohms, what are the changes in power that will occur if I drive two 8 ohm speakers on a channel that are hooked in parallel versus serial?”
As per previous issues of TTOTD two 8 ohm speakers in series present a 16 ohm load to the amp, whereas two in parallel present a 4 ohm load. Much more detail about this can be found in the 8/24/99 TTOTD. Of course we know the general rule is that as impedance goes down more current will flow and thus the power amp will put out more power. So, if you switch an amp from an 8 ohm load to a 4 ohm load it will put out more power. Some amps put out right at twice as much power when the load is cut in half, but the increase usually ranges between a 40% to 80% increase.
In your case you would be changing between a 16 ohm (series wiring) and 4 ohm load (parallel wiring). In an ideal world this means your amp’s output power would double twice. At 16 ohms it probably puts out around 125 watts (half of its 8 ohm rated output), so at 4 ohms it could potentially put out as much as 500 watts. The exact power ratios depend on your specific amp. Some behave in radically different ways under different load conditions. Some amps may not even be able to handle a 4 ohm impedance at all. You definitely need to consult your operator’s manual before you start experimenting. It should tell you what results to expect under different loads.