Power ratings
thecoolguy11 said:
As suggested, I visited the Yamaha site. I understood all the cosmetic differences mentioned on the site. But I really could not understand the following lines
"The amplifiers in the HTR and RX-V units are identical but rated differently to comply with the accepted measurement standards of their respective channels of distribution. Both ratings are FTC approved and are designed to handle the dynamics of today's audio and video sources. The RX-V line has the power amplifiers rated from 20-20000 Hz. The HTR line has the power amplifiers rated at 1000 Hz. Both lines can reproduce the full frequency response of 20-20000 Hz."
Does this mean that one is better than the other? Does this mean that 95W per channel in RXV is same as 110W in HTR? Please help
The short answer is that the power of the amp is the same, but the method the power is rated is different. The lower power rating (95W) is an RMS rating (RMS stands for root-mean squared, a fancy kind of averaging) for the entire range of frequency output, 20Hz - 20,000Hz, roughly equal to what we can hear. The higher number (110W) you referred to is for a single frequency, 1,000Hz which is a midrange. The second method usually results in a 15-25% higher rating as the amp is only driving a single frequency, and one that is very much in the sweet spot of signals that an amp handles. The comparison chart for the HTR line shows both power rating measures.
A couple other things (in case this is new for you) for you to look out for:
- Peak power output ratings: Specs on lower end amps often publish power ratings using a peak rating. Instead a sustainable power output like the RMS methods produce, the amp is measured with shorter burst of say 20 milliseconds at a time. (If the specs don't specify, you can assume it is a peak power rating.)
- THD (total harmonic distortion) - The power rating has a corresponding THD rating. Basically this is just a measure of the noise and interference that the amp is adding / clipping to the signal at a given power output. Acceptable levels are less than 1%, and you'll find most decent receivers below 0.1% THD at their power ratings. I made the mistake of buying a home theater in a box system and only focused on the power output of 65W per channel. Turns out when I learned how to read the specs, that the amp was rated 65W per channel with 10% THD. Yikes! It's safe to say that this power rating was VERY misleading, and in reality would probably be more like 50W (or lower) if it were measured using a tolerance of 0.1% THD.
- Speaker resistance (measured in ohms) - another item to look for is the resistance of the speakers you are driving using your receiver. Power output is inversely proportional to the resistance of the speaker. So, back to my HTIB system with 65W, 10%THD...it was rated for 4 ohm speakers. If I ever wanted to drive 8 ohm speakers (most common), I would now have a 32.5W, 10% THD receiver. Needless to say I bought a more powerful receiver to help my problem.
Good luck! Aaron
