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FTC Power Amplifier Rule

Dennis Murphy

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The Federal Trade Commission will be publishing a Notice of Proposed Rulemaking in the Federal Register in a day or two. The Notice will seek comment on proposed amendments to the Rule that may affect how power ratings for multichannel receivers must be measured. Currently, such AVR's need only publish power and distortion specs for 2-channel operation. The new Rulemaking will revisit this issue. The press release concerning the upcoming Federal Register Notice is pretty foggy except for the recommendation that THD must be lower than .1% at the rated power. That will prove controversial to say the least. Currently there is no cap on distortion--you just have to disclose what it is. Here's the press release, which asks for comments on:
  • "whether the Commission should amend the Rule to simplify power output measures by standardizing the test parameters used by amplifier sellers as follows: a load impedance of 8 ohms, a power band of 20 Hz to 20 kHz, and a THD limit of less than 0.1%; and
  • the parameters of consumers’ normal use of multichannel home theater amplifiers."
I have no idea what they mean by "the parameters of ...normal use..." But we'll know shortly. I'll post a link to the Federal Register Notice when it's published.
 
The Federal Trade Commission will be publishing a Notice of Proposed Rulemaking in the Federal Register in a day or two. The Notice will seek comment on proposed amendments to the Rule that may affect how power ratings for multichannel receivers must be measured. Currently, such AVR's need only publish power and distortion specs for 2-channel operation. The new Rulemaking will revisit this issue. The press release concerning the upcoming Federal Register Notice is pretty foggy except for the recommendation that THD must be lower than .1% at the rated power. That will prove controversial to say the least. Currently there is no cap on distortion--you just have to disclose what it is. Here's the press release, which asks for comments on:
  • "whether the Commission should amend the Rule to simplify power output measures by standardizing the test parameters used by amplifier sellers as follows: a load impedance of 8 ohms, a power band of 20 Hz to 20 kHz, and a THD limit of less than 0.1%; and
  • the parameters of consumers’ normal use of multichannel home theater amplifiers."
I have no idea what they mean by "the parameters of ...normal use..." But we'll know shortly. I'll post a link to the Federal Register Notice when it's published.

It sounds like all the comments and submissions we/people made have had some impact.

Whatever makes the manufacturers partially honest again will be a good thing.


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It’d be nice if 4-ohm was mandated. As well as low power SNR.

And while you likely will never have content that maxes out all your channels, and all channels driven wattage would be nice.
On a 2-channel amplifier I think all-channels driven specs make sense. On an 11ch AVR... seriously?
 
On an 11ch AVR... seriously?

Absolutely. All channels driven continuously up to the rated power, bandwidth and THD. The entire reason for the 1974 rule was to make power output claims honest. It worked. If manufacturers want to jam 11 channels in a box, rate the channels appropriately. If when running 11 channels, there is only enough thermal disipation for 20wpc that's what it is.
 
FTC should considering adding a rule about no impedance switches (Physical and Digital). Those switches were made for numbers, not for the customers.
 
Absolutely. All channels driven continuously up to the rated power, bandwidth and THD. The entire reason for the 1974 rule was to make power output claims honest. It worked. If manufacturers want to jam 11 channels in a box, rate the channels appropriately. If when running 11 channels, there is only enough thermal disipation for 20wpc that's what it is.
I know you're a purist on this topic, but with an AVR the surround channels are never running at high power simultaneously. So if all channels have to rated identically we'd probably have 11ch AVRs needlessly rated for low power, like 20W/ch/4ohms, if that.
 
"...but with an AVR the surround channels are never running at high power simultaneously."
Unless your a business that loves multi-ch stereo.
 
I know you're a purist on this topic, but with an AVR the surround channels are never running at high power simultaneously. So if all channels have to rated identically we'd probably have 11ch AVRs needlessly rated for low power, like 20W/ch/4ohms, if that.
Right--all channels driven isn't going to happen. In fact, from the fuzzy wording of the press release, I'm not sure the proposal will do much of anything about testing multichannel amplifiers. But we'll see. BTW, I posted my alert on the wrong forum--it should have gone on the dedicated amplifier one. I'm going to post it there and ask that any further replies be posted be posted on the new thread.
 
I know you're a purist on this topic, but with an AVR the surround channels are never running at high power simultaneously. So if all channels have to rated identically we'd probably have 11ch AVRs needlessly rated for low power, like 20W/ch/4ohms, if that.
Let them give two specs, one of which is all channels driven at the same time. Then some version of the other spec, like front channels max and the rest on burst or however makes sense. Not that hard to give them a pair of specs for different situations. One that would make sense to me is all channels driven with a max rating for each channel that need not be the same for all channels. Maybe 20 wpc for rears and 100 wpc for fronts.
 
Let them give two specs, one of which is all channels driven at the same time. Then some version of the other spec, like front channels max and the rest on burst or however makes sense. Not that hard to give them a pair of specs for different situations. One that would make sense to me is all channels driven with a max rating for each channel that need not be the same for all channels. Maybe 20 wpc for rears and 100 wpc for fronts.
This is what I had in mind.
 
I like the idea of different specs. If you have a multichannel AVR advertised as 100 W/ch but when all channels are driven it can only make ~30 W/ch I feel that I as a consumer deserve to know that. (I have an AVR that has those specs and measured output, BTW.) Most manufacturers seem to put out a two-channel spec and leave it open to interpretation as to whether the other channels could hit that power at the same time. They play (prey) on "everybody knows" not all channels peak at the same time (not true, when that big explosion goes off all around, all speakers are active), most users have smaller surrounds and rears with less bass so need less power, and so forth. Some of us actually have full-range speakers all around, and the assumption that small speakers need less power is blatantly false -- they tend to be less sensitive than towers, mainly to get a little more bass out by padding the tweeter, so tend to need more power (even though they usually handle less maximum power).

Two-channel spec at some reasonable load and distortion (e.g. 100 W/2-ch driven at 0.1% THD)
All-channels driven spec with continuous and IHF burst or headroom specified (e.g. 30 W/ch, all channels driven at 0.1% THD; 3 dB (60 W/ch) headroom for dynamic peaks)
 
I know you're a purist on this topic, but with an AVR the surround channels are never running at high power simultaneously. So if all channels have to rated identically we'd probably have 11ch AVRs needlessly rated for low power, like 20W/ch/4ohms, if that.
It’s a fact that centre channel has more signal than LR on almost all soundtrack, hence stereo is not relevant in movies. If I was FTC I would say LCR driven at 100% and all other surround and spatial channels at 50%.
 
It’s a fact that centre channel has more signal than LR on almost all soundtrack, hence stereo is not relevant in movies. If I was FTC I would say LCR driven at 100% and all other surround and spatial channels at 50%.
I can't dispute this "fact", as I have no data. But given that I've never met a purpose-designed center channel speaker that I liked, even expensive ones, I'm glad my HT system runs in 2.1 mode.
 
I can't dispute this "fact", as I have no data. But given that I've never met a purpose-designed center channel speaker that I liked, even expensive ones, I'm glad my HT system runs in 2.1 mode.
The cinema spec requires the use of same speakers used for LR to be used as the centre speaker. A purpose designed centre speaker is a TV creation due to the lack of transparent screen. In a movie theatre all three LCR speakers are located behind a screen.
 
I like the idea of different specs. If you have a multichannel AVR advertised as 100 W/ch but when all channels are driven it can only make ~30 W/ch I feel that I as a consumer deserve to know that. (I have an AVR that has those specs and measured output, BTW.) Most manufacturers seem to put out a two-channel spec and leave it open to interpretation as to whether the other channels could hit that power at the same time. They play (prey) on "everybody knows" not all channels peak at the same time (not true, when that big explosion goes off all around, all speakers are active), most users have smaller surrounds and rears with less bass so need less power, and so forth. Some of us actually have full-range speakers all around, and the assumption that small speakers need less power is blatantly false -- they tend to be less sensitive than towers, mainly to get a little more bass out by padding the tweeter, so tend to need more power (even though they usually handle less maximum power).

Two-channel spec at some reasonable load and distortion (e.g. 100 W/2-ch driven at 0.1% THD)
All-channels driven spec with continuous and IHF burst or headroom specified (e.g. 30 W/ch, all channels driven at 0.1% THD; 3 dB (60 W/ch) headroom for dynamic peaks)
I know of only three HT systems with full-range speakers all around (two are Salon2 systems, and one of those is yours), and none of these people use AVRs for amplification on those systems. It is reasonable to expect an FTC rule to have a spec everyone has to measure against for less than (I'm guessing here) 2% of all users? As for explosions, well, it is difficult to imagine that a stringent THD spec is important to their reproduction. ;)
 
The cinema spec requires the use of same speakers used for LR to be used as the centre speaker. A purpose designed centre speaker is a TV creation due to the lack of transparent screen. In a movie theatre all three LCR speakers are located behind a screen.
Okay, but only a small fraction of the video market is projection. I'd prefer projection myself. Six years ago when we were house-hunting we found an awesome home with a dedicated theater room that was designed for a projection system. But my wife nixed that house because it only had a two-car garage. Go figure.

I'm still having trouble with pushing for an FTC spec that is unlikely to be technically understood by the large majority of buyers, would be likely to increase product cost if manufacturers thought they had to make a good showing anyway, and most of you high-end HT guys wouldn't use an AVR in your primary systems.
 
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On the multi-channel power amps we make, all channels are usually identical and the power is generally 200-300 watts. The biggest challenge is heat buildup. Running 8 channels in a 19" wide chassis at anywhere near full power (or 1/3rd power) very quickly runs up to thermal limitations. Getting 300 watts at 0.1% distortion is dead easy; getting it with all channels putting out significant power for any length of time is not so easy before the amp channels reach the absolute limit of 85 degrees C. With 8 or more channels reaching 85 degrees C, you have a seriously hot brick.

Heat sinks can only be so big in a realistic chassis. The bigger they are, the more the amplifier costs to ship and build, but we use big ones anyway.

In the near future, especially if this new rule takes effect, expect to see more fans and more class D. Neither of these are a bad thing; class D can equal class A/B on specs and fans can be operated by microcontroller to only run as fast as necessary to keep heat down with low or no fan noise at normal temperatures.

I wonder though about some tube amps, and even some solid state ones, where the distortion is more than 0.1% right out of the gate. Does this mean that they have to be rated for zero power? :facepalm:
 
I know of only three HT systems with full-range speakers all around (two are Salon2 systems, and one of those is yours), and none of these people use AVRs for amplification on those systems. It is reasonable to expect an FTC rule to have a spec everyone has to measure against for less than (I'm guessing here) 2% of all users? As for explosions, well, it is difficult to imagine that a stringent THD spec is important to their reproduction. ;)
I think it is reasonable to have a valid spec vs. nothing at all. I agree that few users need all the power all the time and that distortion on explosions is probably a don't-care. But when I ran into problems with that AVR I was using 90~95 dB/W/m speakers, tower fronts and small satellites for surrounds, that were fairly benign in impedance in a modestly-sized room (same as now) and the AVR couldn't handle it. A different AVR, two different ones in fact, worked fine, despite being rated essentially the same in power. I would have loved to have known that before buying the "bad" AVR; it was highlighted in a review some months after I bought it (natch).

If there are two AVRs with similar features and two-channel power ratings I'd like to know if one handles 60 W/ch with all driven and the other drops to 20 W/ch. So many feature sets are similar that differentiation may happen on "smaller" matters. In any event I believe in publishing reasonable and reasonably complete specs.
 
Okay, but only a small fraction of the video market is projection. I'd prefer projection myself. Six years ago when we were house-hunting we found an awesome home with a dedicated theater room that was designed for a projection system. But my wife nixed that house because it only had a two-car garage. Go figure.
I believe vast majority of home theatre installations are projection.
 
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