gene said:
Actually the flagship Rotel and NAD receivers (although quite powerful and excellent products) still don't have as potent an amp section as flagships from B&K, Yamaha, and Denon for example (nor should they since they are at lower price points). However, Rotel/Nad do tend to rate their amps more conservatively by stating "all channels driven". What is interesting however is that when independent reviewers such as S&V Magazine for example measure the power of the Rotels, they do meet the all channels driven test specified by Rotel, but at clipping which is where you never want to drive an amp too. Others have sited these examples and I don't wish to hash though this yet again.
And how sure are you that brands like Pioneer and Yamaha are not rated at clipping points despite using 1 khz and not rating with all channels driven. Just to cite an example, the Pioneer VSXD811s is rated 100watts at 1khz at
1%THD. That is the extracted power at 1%THD at only 1 Khz with only one channel. With such a spec, the consumer is not getting the real picture as such a receiver can have more THDs below and above 1khz. The power envelope besides.
And if it is true that the power claims of Rotel can only be realized only under clipping conditions, does that make it OK to over-hype power figures by not rating with all channels driven? That S&V tests shows quite clearly the disparities between what is claimed by manufacturers and what the real score is when ALL channels are driven. It is so obvious that in order to extract the most numerical power strength to impresss the unwary public, ALL channels driven is frowned at by these manufacturers. (Those tabulated results seems to inidcate to me that only HK have consistently shown a higher power rating when measured with ALL channels driven than as claimed.)
But really, that's beside the point in this discussion. FTC mandates that ALL the channels be driven under test and to disclose the MAXIMUM THD levels across a full spectrum. (At the time of this FTC stipulation, there were only stereo gears, but the spirit behind the sitpulation remains as valid today as it was in the 70s - to allow a level playing field for comparison.)
The point of this article was to show that many of the mid to low end receivers employ current limiting to save on cost to achieve UL/CSA approval, and that the nature of music is not continuous sinusoids at full power into resistive loads to all channels. Thus the typical all channels driven test is invalid in this instance and for real world applications for that matter. We will be developing more real world tests in the future and are working with many test equipment manufacturers to ensure this.
I have no illusions about the point of your article. But among other things, I have to question the assumptions you made. To say that you need only PEAK signal bursts to measure the CONTINUOUS power capability of an amp because real musical sinusoids behave that way flies in the face of accuracy in measuring the minimum continuous RMS voltage that an amp can deliver. You might as well say that PEAK power ratings are more important than continuous RMS ratings. Voltages and current do not care about the music they carry. But they comprise what must be measured.
I don't know if 3 seconds signal burst is all that is needed to measure a continuous RMS value. Never mind if the sustained trombone and trumpet calls in Mussorgsky's Night On Bald Mountain last more than 10 seconds. And you assume a lot when you say not all channels are driven in the real world. Never mind if some people like to listen to mono masters of Frank Sinatra, Dean Martin or Ella Fitzgerald with all 5 channels on line. Have you heard about 7.1 stereo mode?
(A colleague once asked why shifting from stereo to multi didn't yield any appreciable increase in volume with his receiver at the same volume setting when he is expecting an increase since all the channels would now be deliveirng the same power as compared to only 2 channels in stereo. He was surprised to listen to my system which doubled the apparent volume as the stereo volume strength was conserved and didn't diminish when activating the other channelsl. The source was a stereo Frank Sinatra CD. I told him he was taken for ride believing all that hype about his 100wpc receiver. That power claim might only be valid in stereo mode. When shfiting to multichannel, all the channels will now have to compete for the lone power supply that previously powered only 2 channels.)
But how we play music on oure gears is entirely beside the point. Those measurement standards stipulated by the FTC is hardly about realistic musical sinusoids. It is about what the amplifying device can continuously deliver in terms of voltages and current that know nothing about music. It is about a level playing field that allow consumers to compare specs of different products and prevent one manufacturer declaring a higher power figure because it was measured with only one channel, at 1khz or at 10% THD, and thus hug the market unfairly with dubious claims that easily attract the unknowing public. And unless the FTC revises its rules to suit the rationalziations of receiver pittfalls, I remain an ardent follower of conservative measurement.
Just curious though, what exactly do you have against conservatism in power measurement? I think the downfall of ENRON is presicely that - violating the conservative practices in accounting.
AV_PHile, while your comments are welcomed, we would appreciate you not hijacking this thread and allow for all viewpoints to be expressed here. We are fully aware of your position on this topic by now. Thank you.
I am curioous as to what you mean by hijacking. Is answering the questions raised in this thread hijacking? Providing counter responses, hijacking?
