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Power amplifier tests with respect to FTC: 16 CFR Part 432 (July 5, 2024) requirements on output power claims
- Thread starter pma
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It's possible to interpret continues as "without breaks" in many settings .
"apply the continues test signal y for x minutes "
"apply the continues test signal y for x minutes "
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continuous
all
Oy, I am such a literalist.
all
Oy, I am such a literalist.
or a signal long enough to reach some kind of steady state or for example thermal equilibrium . meaning looking at the system now or in X minutes would look the same to you
That's a more real world interpretation opposed to "continuous power until the heat death of the universe".
Old_School_Brad
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That depends on the context. If we’re referring back to the FTC, the regulation states that the power must be obtainable at all frequencies between 20 and 20,000 Hz, not that the testing has to be conducted using every frequency within that range.
Any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input. Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self-powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250 mW to the rated power shall be obtainable at all frequencies within the subwoofer amplifier's intended operating bandwidth without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input.
MRC01
Major Contributor
To me, "continuous" can mean 2 different yet related things. (A) smoothly connected (as in a mathematically continuous function) and (B) uninterrupted. Neither of these necessarily implies forever, but over some defined interval in space or time.
somebodyelse
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Testing until steady state is reached for whatever measures may be applicable is usually enough to convince the lawyers. Beyond that you're looking at reliability. Here that probably means testing until the temperature stops rising, or some failure condition occurs (exposed heatsink exceeds safe touch temperature etc.)That would be the lawyer's interpretation, which is also absolutely impractical. It would take the manufacturer forever to test it during development, and another forever for a third party to verify it. So, it will take two times eternity for consumers to find out
which will not happens as the amp continues to shed excess heat
Can't believe this is still going. Some random thoughts:
In my work/world, "continuous" means "for the life of the product". Since I have worked on circuits for things like space applications and mission-critical components for the medical and military fields, if something was rated for continuous operation, it had to pass stringent design reviews and testing to prove it could handle that. Low-level circuits rarely had issues passing lifetime tests. For high-power RF amplifiers, not something I designed, it was common to have a maximum continuous ("unlimited" time of operation) power rating, and a peak rating with defined peak (pulse) power and duration specified -- including a "cool-down" period between max power peaks. Things like commercial/military radar systems and medical scanners typically had such ratings. Early ultrasound scanners had some serious heat problems, for example, when the handheld scanner got hot on a lady's tummy.
For audio, given typical crest factors in music and movies, similar derating makes since to me. A continuous power rating of 10 W with a peak rating of 100 W (using something like the IHF burst test or similar) provides a pretty good look at the amplifier's capabilities. An amplifier rated for 100 W continuous and only slightly more peak power implies an amplifier that is likely to be much larger, heavier, and more expensive than the 10 W continuous amplifier. Whether it sounds better in the real world is the issue for us (and marketing) to decide. Many years ago, dynamic headroom was a popular marketing term, and I suspect if the FTC rule is followed, we will see that again. It has become so easy to produce prodigious power numbers that IMO we are in danger of falling into the trap of unrealistic power ratings similar to the virtually meaningless "peak dynamic instantaneous music power" numbers seen in the past.
I find the FTC rule reasonable and think marketing should focus on consumer education. We've done it before, we can do it again. Meanwhile, the FTC and manufacturers need to hammer out a reasonable test methodology for everyone (I don't think it's in the spec but have not looked closely). Testing every frequency from 20 Hz to 20 kHz for 5 minutes is impractical except maybe as a final design (prototype) test and not production test (of every unit). Some sort of spot-check, maybe 20 Hz, 1 kHz, and 20 kHz, makes more sense to me, or one point per octave, or something, and again that would likely not happen during production testing. A single-point 1 kHz test in production seems more reasonable during final QA testing (e.g. part of the burn-in process before shipping products, though I doubt every manufacturer does that). You test a few sample units (number varies according to expected manufacturing quantity; for ICs I helped design, it was tens to tens of thousands of samples) and use that to qualify your design meets specs, then spot-check production runs.
Audio arguments about power often say that underpowering is worse than overpowering. Too much power is too much no matter how you get there. Clipping (see old article here on Clipping 101) boosts HF energy and can damage tweeters, true, but these days lots of power is cheap, and people playing too loud and thus applying too much power to the speakers will damage them no matter how low the distortion. Unclipped clean power has no "distress signals" like harsh sound from clipping so it is easy to play a system louder and for longer than the speakers can handle. Short of physical cues like voices coils hitting their stops or severe distortion (more likely with panels than conventional drivers IME), we become desensitized to distortion at very high SPL (hearing damage, anyone?) and the first clue we are overpowering the drivers may be when they go silent.
FWIWFM/IME/IMO/etc. - Don
In my work/world, "continuous" means "for the life of the product". Since I have worked on circuits for things like space applications and mission-critical components for the medical and military fields, if something was rated for continuous operation, it had to pass stringent design reviews and testing to prove it could handle that. Low-level circuits rarely had issues passing lifetime tests. For high-power RF amplifiers, not something I designed, it was common to have a maximum continuous ("unlimited" time of operation) power rating, and a peak rating with defined peak (pulse) power and duration specified -- including a "cool-down" period between max power peaks. Things like commercial/military radar systems and medical scanners typically had such ratings. Early ultrasound scanners had some serious heat problems, for example, when the handheld scanner got hot on a lady's tummy.
For audio, given typical crest factors in music and movies, similar derating makes since to me. A continuous power rating of 10 W with a peak rating of 100 W (using something like the IHF burst test or similar) provides a pretty good look at the amplifier's capabilities. An amplifier rated for 100 W continuous and only slightly more peak power implies an amplifier that is likely to be much larger, heavier, and more expensive than the 10 W continuous amplifier. Whether it sounds better in the real world is the issue for us (and marketing) to decide. Many years ago, dynamic headroom was a popular marketing term, and I suspect if the FTC rule is followed, we will see that again. It has become so easy to produce prodigious power numbers that IMO we are in danger of falling into the trap of unrealistic power ratings similar to the virtually meaningless "peak dynamic instantaneous music power" numbers seen in the past.
I find the FTC rule reasonable and think marketing should focus on consumer education. We've done it before, we can do it again. Meanwhile, the FTC and manufacturers need to hammer out a reasonable test methodology for everyone (I don't think it's in the spec but have not looked closely). Testing every frequency from 20 Hz to 20 kHz for 5 minutes is impractical except maybe as a final design (prototype) test and not production test (of every unit). Some sort of spot-check, maybe 20 Hz, 1 kHz, and 20 kHz, makes more sense to me, or one point per octave, or something, and again that would likely not happen during production testing. A single-point 1 kHz test in production seems more reasonable during final QA testing (e.g. part of the burn-in process before shipping products, though I doubt every manufacturer does that). You test a few sample units (number varies according to expected manufacturing quantity; for ICs I helped design, it was tens to tens of thousands of samples) and use that to qualify your design meets specs, then spot-check production runs.
Audio arguments about power often say that underpowering is worse than overpowering. Too much power is too much no matter how you get there. Clipping (see old article here on Clipping 101) boosts HF energy and can damage tweeters, true, but these days lots of power is cheap, and people playing too loud and thus applying too much power to the speakers will damage them no matter how low the distortion. Unclipped clean power has no "distress signals" like harsh sound from clipping so it is easy to play a system louder and for longer than the speakers can handle. Short of physical cues like voices coils hitting their stops or severe distortion (more likely with panels than conventional drivers IME), we become desensitized to distortion at very high SPL (hearing damage, anyone?) and the first clue we are overpowering the drivers may be when they go silent.
FWIWFM/IME/IMO/etc. - Don
Last edited:
Audio Science Pal
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Thank you for sharing your knowledge and wisdom.
FEDERAL TRADE COMMISSION16 CFR Part 432RIN 3084-AB62TRADE REGULATION RULE RELATING TO POWER OUTPUT CLAIMS FORAMPLIFIERS UTILIZED IN HOME ENTERTAINMENT PRODUCTSAGENCY: Federal Trade Commission. ACTION: Final rule.
§ 432.2 Required disclosures.
Whenever any direct or indirect representation is made of the power output, power band or power frequency response, or distortion characteristics of sound power amplification equipment, the manufacturer’s rated power output shall be disclosed subject to the following conditions
a) The rated power output is measured in compliance with the standard test conditions in§ 432.3;(b) The rated power output is disclosed clearly, conspicuously, and more prominently than any other representations or disclosures permitted under this part;(c) The disclosure of the rated power output is clearly and conspicuously labeled “FTC Power Output Rating”; and(d) The disclosures or representations required under this section shall not be made by a footnote, asterisk, or similar notation.3.
§ 432.3 Standard test conditions.* * * * *(e) Any power level from 250 mw to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input.
Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self-powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250 mw to the rated power shall be obtainable at all frequencies within the subwoofer amplifier’s intended operating bandwidth without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input. * * * * *(g) Rated power shall be minimum sine wave continuous average power output, in watts per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.
(h) Associated channels for multichannel amplifiers shall include, at a minimum, the left front and right front channels used for reproducing stereo programming. Provided, however, when measuring the maximum per channel output of self-powered combination speaker systems that employ two or more amplifiers dedicated to different portions of the audio frequency spectrum, such as those incorporated into combination subwoofer-satellite speaker systems, only those channels dedicated to the same audio frequency spectrum should be considered associated channels.
I hope that this helps:
I did not copy the whole (complete) text but that which I thought was likely to be applicable to us here and what we do.
EJ3
Thanks, I remembered that, was hoping they had gone a little further since the rule came out, but probably not. Technically there are an infinite number of frequencies and power levels from 20 to 20,000 Hz and from 250 mW to full power, making for a rather long test... If the amp can provide full power at 20 kHz with <1% distortion for five minutes, then it will pass the test at any other frequency and power level, unless something is seriously wrong. As an engineer, I prefer to define (or see defined) specific, practical test criteria and methodologies to qualify a product. "Qualified by design and characterization" is adequate for most of us, without having to run a full set of tests on everything. Then the challenge is to define a set of tests that prove shipping product will meet all specs without fully characterizing each and every product rolling out the door. Lots of ways to do that, but the wording of the FTC's rule is... interesting.FEDERAL TRADE COMMISSION16 CFR Part 432RIN 3084-AB62TRADE REGULATION RULE RELATING TO POWER OUTPUT CLAIMS FORAMPLIFIERS UTILIZED IN HOME ENTERTAINMENT PRODUCTSAGENCY: Federal Trade Commission. ACTION: Final rule.
§ 432.2 Required disclosures.
Whenever any direct or indirect representation is made of the power output, power band or power frequency response, or distortion characteristics of sound power amplification equipment, the manufacturer’s rated power output shall be disclosed subject to the following conditions
(b) The rated power output is disclosed clearly, conspicuously, and more prominently than any other representations or disclosures permitted under this part;(c) The disclosure of the rated power output is clearly and conspicuously labeled “FTC Power Output Rating”; and(d) The disclosures or representations required under this section shall not be made by a footnote, asterisk, or similar notation.3.
§ 432.3 Standard test conditions.* * * * *(e) Any power level from 250 mw to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input.
Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self-powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250 mw to the rated power shall be obtainable at all frequencies within the subwoofer amplifier’s intended operating bandwidth without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input. * * * * *(g) Rated power shall be minimum sine wave continuous average power output, in watts per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.
(h) Associated channels for multichannel amplifiers shall include, at a minimum, the left front and right front channels used for reproducing stereo programming. Provided, however, when measuring the maximum per channel output of self-powered combination speaker systems that employ two or more amplifiers dedicated to different portions of the audio frequency spectrum, such as those incorporated into combination subwoofer-satellite speaker systems, only those channels dedicated to the same audio frequency spectrum should be considered associated channels.
I hope that this helps:
I did not copy the whole (complete) text but that which I thought was likely to be applicable to us here and what we do.
EJ3
Thank you, but whilst I have some knowledge, and experience, wisdom, meh.
So given there are an infinity of frequencies between 20Hz and 20kHz, you are proposing an infinitely long test?
No I'm not , the FTC is. I didn't write this ambiguous mess.
Understood.
The only manufacturers I've seen in compliance with the new rule are Sonos and SVS. They are by not posting any power ratings. There are probably others but I've not come across them in the 6 months this has been in effect.
restorer-john
Grand Contributor
It worked for Rolls Royce in 1966 when they specified the Silver Shadow's horsepower as "adequate".
Sonos could say the amplifiers are "powerful" and not run afoul of the FTC.
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