Wattage question, amp and speakers help!?

Question

Okay, so I am looking at a 50w per channel amplifier, and the two speakers I want are @ 150w per speaker.

I don't really understand wattage, who is supplying who? And how can I avoid blowing a speaker? (I assume too much wattage through the speaker/amp). Can someone simplify this for me please?

Thank you!

Answer 1

Speakers need power (watts) to make them move. How loud the speaker is with 1 watt of power is called sensitivity. The higher the sensitivity the easier the speaker is to drive. Sensitivity is rated in dB @ 1 watt @ 1 meter. A low sensitivity speaker needs a more powerful amp to get it loud.

It takes roughly double the wattage to increase the speaker volume by 3dB, which is roughly double the sound level. For example a speaker with 86dB sensitivity would be 86dB at 1W, 89 @ 2W, 92dB @ 4 watts.....101dB 32,W 104dB @ 64W.

The amplifier's wattage output is usually rated at a certain level of distortion (THD) and at a certain frequency. The lower the THD the better. A amplifier rated at 50W @ .05% THD is fairly good and means that when the amp is outputting 50W it is fairly clean. An amp pumping out 50W @ 10% THD is probably unlistenable. That same amp might only output < 10W cleanly.

Some THD is considered desirable in the case of tube amplifiers. This coloration of the sound is considered warm and acceptable.

What can damage speakers is too much power, or using an under powered amp and overdriving the amp to cause clipping. Clipping is when the tops and bottoms of the reproduced sine waves gets cut off and is the worst form of distortion. This typically happens when you turn up an inferior amplifier too far. The result is a sine wave that has a very high wattage due to the distortion.

A speaker is rated at a certain wattage. This can be continuous or peak wattage. Better speakers will list both peak and continuous. Peak wattage is what the speaker can handle for a brief amount of time. When the wattage the amplifier is outputting to the receivers exceeds the speakers continuous wattage for long periods this can cause the motors (yes a speaker is like motor) in the speakers to get too hot and melt, deform and/or seize up. The woofers and tweeters can rupture also if the sustained or peak wattage is exceeded.

Bottom line: clean power (low THD), even if lower wattage is acceptable for speakers. Speakers with high sensitivity match well with low powered amps.