Stereo Amplifier Power: How Many Watts Are Enough for Speakers?

Matching amplifier wattage to speaker wattage

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When you're ready to purchase your next stereo amplifier or receiver, make sure to factor in amplifier output power, which is measured in watts per channel. The decision as to how much power you need should be based on the types of speakers, the room size and acoustic characteristics, and the planned loudness and desired quality of your music.

A pair of stereo speakers

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Match the Power Requirements

Match the power requirements of the speakers with the output power of the amplifier or receiver. The power should equal the impedance rating for each of the speakers. Some speakers require more or less power than others.

Speaker sensitivity is expressed in decibels, which is a measure of how much sound output is produced with a specified amount of amplifier power. For example, a speaker with low sensitivity (88 to 93 dB) tends to require more amplifier power than a speaker with a higher sensitivity (94 to 100 dB or more) to play and sound optimally at the same volume level.

Power and Volume

Power output and speaker volume follow a logarithmic, not linear, relationship. For example, an amplifier with 100 watts per channel does not play twice as loud as an amplifier with 50 watts per channel using the same speakers. In such a situation, the difference in maximum loudness is slightly louder; the change is only 3 dB.

It takes an increase of 10 dB to make speakers play twice as loud as before. A 1 dB increase would barely be discernible. More amplifier power allows the system to handle musical peaks with greater ease and less strain, which results in better overall sound clarity.

Some speakers must work a little harder than others to achieve a specific volume output. Certain speaker designs are more effective than others in projecting sound evenly across open spaces. If your listening room is small or carries audio well, you may not necessarily need a super-powerful amplifier, especially with speakers that are more sensitive to power. Bigger rooms, greater listening distances, or less sensitive speakers demand more power from the source.

Measuring Power Output

The most common measure of power is root mean square, but manufacturers can also provide values for peak power. The former indicates continuous power output over periods of time, while the latter indicates output in short bursts. Speaker specifications can also list nominal power, which is what the speaker can handle over periods of time.

Overpowering a speaker by supplying more watts than it needs can cause distortion or clipping, but damage is unlikely.

Some manufacturers inflate specifications by measuring power at a single frequency, say 1 kHz, rather than an entire frequency range, such as 20 Hz to 20 kHz.

For the most part, you can't go wrong with having more power at your disposal than not, even if you don't plan on blasting music at concert-like levels in your listening spaces.

Amplifiers with higher power ratings can deliver without being pushed to maximum output limits, which keeps distortion down and audio quality up.

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