What Are Speaker Watts?

By Steve McDonnell

An amplifier sends sound out to your speakers in the form of electrical power, which is measured in watts. The root mean squared, or RMS, power rating of an amplifier identifies the maximum wattage output under normal listening conditions. The peak power rating indicates the amplifier's maximum output for short bursts of sound. Speakers have corresponding ratings for the maximum wattage they can safely receive without being damaged. Nominal wattage is for normal listening and peak wattage is for short bursts. For best results, match an amplifier's RMS rating to a speaker's nominal rating.

Volume and Wattage

There is no direct relationship between the number of watts you send to a speaker and the volume of the resulting sound, which is measured in decibels. For example, the sound from a vacuum cleaner is about 80 decibels, a rock concert is about 120 decibels and a jet engine is about 140 decibels at an altitude of three meters. When you double the wattage from an amplifier, you add about three decibels to the volume, which is barely noticeable. For a sound that's twice as loud, you must add 10 times the power. For example, to double the maximum volume of a 50-watt amplifier, you must upgrade to a 500-watt amplifier.

Speaker Sensitivity

Volume is also determined by a speaker's sensitivity rating, which is also measured in decibels. An extremely sensitive speaker has a sensitivity near 110 decibels; a low-sensitivity speaker is about 85 decibels. Similar to the relationship with wattage, if you upgrade to a speaker that's 3 decibelsv more sensitive, you can reach the same volume with 10 times fewer watts. If you upgrade to a speaker that's 10 times more sensitive, you can reach the same volume with 100 times less power. Speakers that are more sensitive require less power, generate less heat and typically last longer than inefficient speakers. While technically incorrect, speaker sensitivity is commonly referred to as speaker efficiency.

Distortion and Clipping

If you use an amplifier that produces higher wattage than a speaker is rated to receive, you can avoid damaging the speaker by turning the amplifier down, especially if you hear the sound becoming distorted. Although distorted sound is louder, the noise from the distortion makes it louder, not an increase in the sound you intend to hear. Clipping happens when a speaker receives excess wattage, produces its maximum capacity and drops the remaining signal. This sometimes causes people to turn the volume up even louder because of the loss of the clipped sound.

Speaker Damage

You can damage your speakers by sending too many watts from an amplifier. Sending too much power to a speaker causes the speaker parts to overheat. When the parts overheat, they can warp, melt or catch on fire. This usually affects the woofers because the bass sound is so strong. However, if your amplifier isn't powerful enough to send the number of watts required to meet the volume demanded, it can also cause distortion and clipping, and you can burn out the voice coil in the tweeters.