One of the best articles written here at Audioholics
bmac said:
When I read home theater mag. they give a 5 channels driven spec.I had no Idea that was unrealistic.
The bigger issue here is how and why most receivers are rated at 100 or more watts per channel, when back in the 70's and 80's, more powerful and more expensive units were rated at 30-75 watts per channel. This article is what sold me on this site's realistic views of home theater. It's priceless.
Here's some notes taken from this article:
http://www.audioholics.com/techtips/audioprinciples/amplifiers/receiverpower.php
Now, jump forward to the current paradigm asked of the leading mid-fi receiver manufacturers. That all receivers, no matter how inexpensive (for the larger Japanese manufacturers), must be rated at 100 watts/channel. How is this possible?
One answer to this seemingly incongruous specification is that some 100 watt amplifiers are more capable than others when taking on lower impedance speaker systems. But amplifiers are never rated when driving speaker systems, they’re rated when driving fixed-load 8 ohm or 6 ohm resistors (which can be a much easier load to drive from an overheating standpoint than a 4 ohm load). This fact gives the manufacturers a little wiggle room with their power spec and the amount of costly heat sinking they must use to obtain agency approvals.
This “wiggle room” is more real than you might expect because many loudspeaker manufacturers’ supposed 8 ohm impedance loudspeakers are closer to a 6 ohm rating than being a true eight ohms. The loudspeaker guys design this way, using woofers with a 5.5 ohm DCR (direct current resistance).
Imagine what your 6 ohm speakers are truely rated! You 4 ohm guys might as well just hang it up.
For consistency’s sake, manufacturers like to quote distortion figures as an important feature. So, for instance, the bottom four receiver’s in a line may have 0.06% THD and the top two receivers may have 0.04%. This number is really nothing more than “graph manipulation”. Of note though is that in the “old days” of stereo receivers the engineers didn’t have to deal so much with pinching pennies in the power supply to achieve THD figures that were one third of what they are now. As quantities of receivers sold have increased so have has the competition in shooting for that illusive 100 watts/channel figure. But larger quantities buy lower parts prices. (Think less $ for the same VA rated transformer.)
A second, also fairly well understood way to be able to quote “more power” is by quoting the power at only 1kHz instead of the more traditional 20Hz to 20kHz figure. In some cases the difference can be 15% to 25% more power at 1kHz.
Think of your HTIB's, compacts, and shelf systems.
Your “conservative rating” manufacturers like Harman-Kardon, for instance, will quote only power ratings for their receivers which always stay about 20% under the area in which the curve is fairly horizontal.
(They are talking about where distortion skyrockets quickly, and rate these units right under this point) In this case HK might rate this as an 80 watt RMS/channel receiver. Power for HK (and to an extent Rotel, NAD and Marantz) are rated in this “old fashioned” manner. This is part of these company’s “better performance” marketing strategies and it is an entirely legitimate one.
In dealing with Yamaha's receivers: Another item to look at is the weight of the 550 and 450. No difference. You’re probably looking at identical power supplies and identical power amps. And once again possibly, just possibly the 550’s voltage rails are a volt or two higher than the 450 to claim the extra 5 watts. Going up in the line to the RX-V750 and RX-V650 you’ve got an even more similar story. With identical weights you can be pretty certain that you’ve got identical power supplies with just the voltage rails bumped to make a couple more watts of power.
(Ah, the weight issue)
The 80-watt, 1996 Yamaha DSP-A3090 was one of the best sounding units Yamaha had built in years. And I believe part of the reason is that the engineers weren’t forced to hit what was an unrealistic 100 watt figure given the great sounding, easy clipping, 80-watt topology they had at the time. The only other true avenue of freedom most receiver engineers have nowadays can be found in their top-of-the-line $4000+ receiver offerings.
