How Much Amplifier Power Is Too Much Power?
Q How much amplifier power is too much power? My speakers have a 75-to-100-watt RMS power rating and are connected to an entry-level Yamaha receiver, so it’s safe to say they aren’t being pushed anywhere near their potential. I plan to upgrade to separates in the near future, however, and need to know how powerful an amp I should buy. Should I go with too much amp (200 watts RMS per channel), or just enough (125 watts RMS per channel)? —Audiophile Noob via e-mail
A Too much power generally isn’t an issue when pairing hi-fi /home theater speakers and amplifiers. It’s the opposite situation—too little power—that can create problems. When an amplifier is driven into clipping (distortion) by being asked to produce more power than it’s capable of delivering, the voice coil of the speaker it’s attached to can overheat and become damaged. That said, an RMS power rating on a speaker doesn’t even begin to tell the whole story. Two other specs, sensitivity and impedance, are much more important in determining how much power a particular speaker requires to deliver sufficient volume levels.
In the way of a brief overview, a sensitivity spec is meant to give an indication of a speaker’s ability to efficiently translate amplifier power into sound. To give you an idea of how important this is, consider that a 3-dB increase in SPL requires a doubling of amplifier power. So if we’re talking about a speaker spec’d as having 86-dB sensitivity, it should require twice as much power to match the output of a speaker rated at 89-dB sensitivity.
A speaker impedance spec describes its resistance to power coming from the amplifier. Most speakers are specified as having an 8-ohm nominal impedance, which ultimately doesn’t tell you much. But in general, those that boast a lower spec—either 6 or 4 ohms—will be able to pull more power from the amplifier, provided the amplifier can supply the necessary current.
So, to circle back to your original question, any answer as to how much amp power your speakers will require should take into account their sensitivity and nominal impedance specs, not just the RMS power rating. Also, RMS power rates only the system’s ability to deliver power on a continuous basis and doesn’t take into account peak power requirements—something that could be a factor when loudly cranking death metal or watching action movies. If you’re into that stuff, to ensure adequate headroom, it will be a good idea to go with too much amp rather than too little or even “just enough.”