Audio Systems: impedence, watts rms, maximum power output

Question
can i use 8ohm speakers with a 6ohm amp?

Answer
Dear Ron,

There is no such thing as a "6-ohm amp".

Amplifiers are designed to output a certain wattage depending on the load (impedance) presented by the speakers. Most amplifiers' power ratings are into a nominal 8-ohm load, mostly because a substantial number of speakers present that load at a certain frequency.

When an amplifier's power rating is, say, "100 watts @ 8 ohms", that means that for a certain frequency (generally 1kHz) at which the speaker presents pretty much an 8-ohm load, the maximum power output for that amplifier is 100 watts RMS per channel. Typically, however, music programs don't call for maximum power. Rarely does any amplifier max out. Most of the time your speakers are using a small fraction of the available power, on the order of 10 watts or so. Why 100 watts per channel then? Because some passages will require that, if only for an instant. You want it there, right?

Now, my guess is that your amplifier's power rating is specified at so many watts into 6 ohms. Okay, but that doesn't mean that you can't use 4- or 8-ohm speakers with it. What an amplifer will put into an 8-ohm load will increase if it's presented with a greater load (impedance is an inverse ratio, so 4 ohms is a greater load than 8 ohms). So, 100 watts into 8 ohms becomes, say (this varies with amplifer design), 150 watts into 6 ohms, and 200 watts into 4 ohms.

Bottom line: don't worry about the rated power output. The amplifier will adjust for whatever load you throw at it.

Good luck. And thanks for choosing allexperts.com!

Kindest regards,

Kevin