Watts and dynamic power question


if speakers are 120watts and the sub is 200w, how many watts is required by the amp to power the 5.1 channel system. i heard underpowering the amp may damage the speakers. another question what is dynamic power? does it only kick in when the amp is in the stereo mode or when it is in 5.1 mode too. maybe a good list of amp with model type will be great. help me choose to a list to amp like HK, marantz, nad or anything else in the market. please specify the model so i could know how many watts is required. I will be using the amp for movies and music. thanks

Silver Member
Username: Gman

Post Number: 217
Registered: 12-2003
I presume if your speakers say 120 watts it means the maximum amount of power they will tolerate before trouble may set in and blow a speaker. The self-powered watts of a subwoofer has zero to do with the rest of the system. It only has an effect on the subwoofer with the design of the subwoofer.

Dynamic watts is the amount of wattage that can be used for very short-term peaks in music. It cannot be used on a continuous basis. On a typical loudspeaker playing at medium loudness with an 88db sensitivity, if you were sitting about 10 feet away from the speakers an had an SPL Meter you might see a reading of anywhere from 80-85 db's. For loud you might get from 90-95 or so db's. Believe it or not, for this typical speaker the watts needed to produce this sound might be from 1 watt to 5 watts (10 at most). Let's say while listening there is a sudden burst in sound (like in the 1812 Overture) that causes the speaker to pull enough wattage to momentarily play a 105-110 db sound. This would be the dynamic sound difference.

This is why a good receiver with lots of dynamic headroom (such as a NAD or many HK's)are very good performers at listed 50-80 watts per channel and often far superior than many receivers or amps with 100 watt listings.

Under powered amps can hurt the speakers if they clip---but on 120 watt speakers that are probably normally driven at 5-20 watts with up to 100 watts at peak points, you'd have to buy a very poor receiver to have that bad a power envelope.

You have to worry more about the crossover point between your speakers and your subwoofer. Just because your speakers say they may go down to 40 0r 50 Hz does not mean they perform well down there. Also it takes more power from the amp to drive the low ranges (woofer) in your speakers.

Not being familiar with your speakers, it is often very beneficial to have a bass crossover anywhere from 60-100 Hz. You can experiment and see how much better your system sounds at each crossover. The subwoofer is built for handling the low frequencies and is self-powered, so it takes a lot of stress of your receiver's amp.

No doubt, if you have good speakers and money is not a huge object, getting the most good clean power you can get is good, because you will never get speaker distortion caused by a clipping or distortion increasing amplifier.

But in the real world--money is usually an important object. And sadly, in the real world, different manufacturers measure their power envelopes differently. This makes life difficult for the consumer trying to make a decision based on power. Read reviews from reputable magazines, get opinions from reputable people without an axe to grind, and look at how much power the receiver or amplifier draws from the outlet (it has to be listed). This is a good clue on how accurate the power ratings are.

Thanks. if the dynamic power is 162w for the NAD t752 will that create any problem for a q3 KEF. I like watching war movies or movies that deliver alot of action with lots of peaks. also u say that it would be better to get a 80w amp than a 100w to power the speaker. so i should go for the t752 rather than the t762 to power these speaker. also any comments on the dipole KEF or the q1 would be better for the rears. would greatly appreciate your answer. thanks
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