Power amplifier tests with respect to FTC: 16 CFR Part 432 (July 5, 2024) requirements on output power claims

[EJ3]

It worked for Rolls Royce in 1966 when they specified the Silver Shadow's horsepower as "adequate".

Just barely adequate, I'm afraid:

Rolls-Royce Silver Shadow (LHD) (aut. 3) in 1966, the model with 4-door sedan body and V-8 6231 cm3 / 380.2 cui, 128 kW / 172 hp (brake) engine for Europe worldwide LHD.
For a base curb weight: 2103 kg / 4636 lbs
According to the ProfessCars™ estimation this Rolls-Royce would accelerate 0-60 mph in 11.0 sec, 0-100 km/h in 11.7 sec and a quarter mile time is 18.1 sec​

The standard wheelbase Silver Shadow measured 203.5 inches (5,170 mm), 4,700 lb (2,100 kg) and had a book price of £6,557[6] in the first year of production.

The Shadow featured a 172 hp (128 kW) 6.2 L V8 from 1965 to 1969, and a 189 hp (141 kW) 6.75 L V8.No official power outputs were stated, but registration authorities in many markets required outputs be listed. Left-hand-drive models were coupled to the recently introduced Turbo-Hydramatic 400 automatic gearbox sourced from General Motors (GM). Pre-1970, right-hand-drive (RHD) models used a highly modified, aluminum-cased version of the original cast-iron 4-speed Hydra-Matic gearbox that had been built in Crewe under licence from GM since 1953. From 1968, export RHD cars gained the Turbo-Hydramatic 400, and by 1970, the 4-speed unit had been completely phased out even in the home market.[7]

 

[BlackTalon]

In the design and testing of pressure vessels, the test pressure is generally set above the design pressure to ensure safety and structural integrity. This enables the detection of potential weaknesses or failures in the vessel when subjected to conditions beyond typical operational limits, creating a safety margin. It ensures that the vessel can endure unexpected pressures throughout its ecpected lifetime. This also verifies that the vessel is sufficiently over-engineered to manage unforeseen stresses.

Sees like a completely inappropriate analogy. A pressure vessel is a structure, not an electrical device.

And what you call 'overengineered to manage unforeseen stresses' is usually called a Factor of Safety, and can vary depending on the material used. And it is typically arrived at by some standards group testing a lot of samples (ACI, etc. in the US). Checks and splits in wood can prevent a structural member from achieving it's theoretical structural capacity (and the duration of loads on wood affects the capacity). Steel can have some anomalies, and if the members are shop-fabricated like plate girders there can be some variations. And there is plenty of potential for reinforced concrete to be compromised (voids around/ between rebar, etc.). The FS helps ensure there is extra capacity. What is common between the codes/ standards for these materials is they are designed for load combinations based on expected/ code-required conditions wind loads, dead loads, earthquake loads, live loads, etc.), and not a theoretical "test all steel beams from 20 plf to 150 plf for a duration of 5 minutes."

 

[Old_School_Brad]

A pressure vessel is a structure, not an electrical device.

Yeah, that’s just how analogies are, I'm afraid. I’m not a fan of them either.

 

[Old_School_Brad]

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.

Engineer here as well, and while I agree that more concrete regulations are preferable, these are what they are. That said, the FTC regulation is far from being worse than many others I’ve worked with.

Manufacturers are allowed to choose whichever frequency they test at. For example, they can test at 1 kHz and base their rating on that, provided they’re confident the amplifier meets the regulations across the full frequency range. They then disclose the rating as follows:

• Manufacturer test result at 1 kHz: 100 W with 0.01% THD+N
• Manufacturer rating per FTC: 20-20,000 Hz, 100 W, <0.01% THD+N

The amplifier still has to deliver full power across the entire range, even if the test itself is done at a single frequency.

In practice, I’d think testing at three different frequencies (e.g., low, mid, and high range) would be sufficient to verify whether the amplifier meets the stated claims.

 

[amirm]

That said, the FTC regulation is far from being worse than many others I’ve worked with.

The regulation is written by lay people with external people feeding them buzzwords. It has zero technical meat behind it. As such, it is not practicable in any manner. I have been part of, and led many AV specifications. What we have here would not pass for the blank cover page, let alone compete in any manner with those.

In practice, I’d think testing at three different frequencies (e.g., low, mid, and high range) would be sufficient to verify whether the amplifier meets the stated claims.

Will you be available to hold every manufacturer harmless through indemnification if FTC comes after them? If not, I suggest not making such claims.

This regulation could have trivially been made specific and correct. That this was not done, will be cause to have the whole thing thrown out.

Further, the regulation claims it has no impact on the industry. This can be shown to be completely wrong as well which would be another reason to dismiss it.

 

[amirm]

• Manufacturer test result at 1 kHz: 100 W with 0.01% THD+N
• Manufacturer rating per FTC: 20-20,000 Hz, 100 W, <0.01% THD+N

This would be incorrect. The FTC needs to be first and foremost and specified with far larger font. You don't get to put the 1 kHz number up first. You also can't say it is 20 to 20kHz. No lawyer would let you run with FTC numbers if you have only tested a few frequencies.

 

[DonH56]

Engineer here as well, and while I agree that more concrete regulations are preferable, these are what they are. That said, the FTC regulation is far from being worse than many others I’ve worked with.

I've dealt with plenty of "loose" regulations but this one is pretty bad. Without specified (and practical) test conditions and methodology, manufacturers will attempt to satisfy the rule and hope they don't get called, or just try to avoid specifying per the rule altogether.

Manufacturers are allowed to choose whichever frequency they test at. For example, they can test at 1 kHz and base their rating on that, provided they’re confident the amplifier meets the regulations across the full frequency range. They then disclose the rating as follows:

• Manufacturer test result at 1 kHz: 100 W with 0.01% THD+N
• Manufacturer rating per FTC: 20-20,000 Hz, 100 W, <0.01% THD+N

I do not read it that way, since it is pretty clear about 20 Hz to 20 kHz at full rated power for five minutes. The manufacturer can test as they wish, and report accordingly, per your first bullet. However, that does not (IMO) give them a pass to claim they meet the FTC rule per your second bullet. This is where (to me) the rule is far too ambiguous and impractical as stated; no manufacturer can meet the rule as stated with any reasonable test approach. That is where a more concrete, explicit test methodology is needed. The rule reads like something written by someone who knows the words but does not fully understand their implications for actual product testing, perhaps due to a lack of sufficient engineering experience in the field.

The amplifier still has to deliver full power across the entire range, even if the test itself is done at a single frequency.

Yes, but normally to meet a specification like this, someone has to actually perform sufficient characterization (testing) to prove it meets the spec. I would not allow a manufacturer to get away with a single-frequency test of a device covering multiple decades. Dealing with similar spec issues in the past, we would do full characterization of the product, with sufficient samples to satisfy our QA and gov't or whatever inspectors are judging we meet spec. After that, we could define a production test to verify the performance is met with some assurance that any random product pulled from the line would pass. In some cases, certain parameters are not practical to test in a finished product, so are guaranteed by design, but the FTC rule as written does not allow for that.

In practice, I’d think testing at three different frequencies (e.g., low, mid, and high range) would be sufficient to verify whether the amplifier meets the stated claims.

Sufficient to whom? I tend to agree, but again that is not how the rule was written, so it would be good if they'd (FTC would) do another round of comments to converge to a practical test suite manufacturers can follow. I have done a lot of R&D and even full product development where we could work with the standards bodies (often including industry folk, even from our own company) to discern the intent of the spec and develop a workable result. It does not seem to me that has been done here.

All IMO and so forth and so on - Don

Edit: I see Amir @amirm has many of the same thoughts. Perhaps unlike Amir, I see real value in the spec, but to realize that value feel the spec needs to be better defined.

p.s. Having waded into this again, I still feel the need to shower afterwards... A spec too loose, and entrenched bias for and against the basic principle of the spec, leads to an unending debate unwinnable by anyone (unless someone here has sufficient pull with the FTC). The main reason I am writing is because I need a distraction whilst waiting for my telescope to process the galaxy I'm trying to see tonight.

Edit 2: Since I'm fanning the flames, I give to you the Flame Nebula, taken using my telescope. Gotta' say it's more interesting than FTC rules at the moment.

 

[SIY]

I've dealt with plenty of "loose" regulations but this one is pretty bad. Without specified (and practical) test conditions and methodology, manufacturers will attempt to satisfy the rule and hope they don't get called, or just try to avoid specifying per the rule altogether.


I do not read it that way, since it is pretty clear about 20 Hz to 20 kHz at full rated power for five minutes. The manufacturer can test as they wish, and report accordingly, per your first bullet. However, that does not (IMO) give them a pass to claim they meet the FTC rule per your second bullet. This is where (to me) the rule is far too ambiguous and impractical as stated; no manufacturer can meet the rule as stated with any reasonable test approach. That is where a more concrete, explicit test methodology is needed. The rule reads like something written by someone who knows the words but does not fully understand their implications for actual product testing, perhaps due to a lack of sufficient engineering experience in the field.


Yes, but normally to meet a specification like this, someone has to actually perform sufficient characterization (testing) to prove it meets the spec. I would not allow a manufacturer to get away with a single-frequency test of a device covering multiple decades. Dealing with similar spec issues in the past, we would do full characterization of the product, with sufficient samples to satisfy our QA and gov't or whatever inspectors are judging we meet spec. After that, we could define a production test to verify the performance is met with some assurance that any random product pulled from the line would pass. In some cases, certain parameters are not practical to test in a finished product, so are guaranteed by design, but the FTC rule as written does not allow for that.


Sufficient to whom? I tend to agree, but again that is not how the rule was written, so it would be good if they'd (FTC would) do another round of comments to converge to a practical test suite manufacturers can follow. I have done a lot of R&D and even full product development where we could work with the standards bodies (often including industry folk, even from our own company) to discern the intent of the spec and develop a workable result. It does not seem to me that has been done here.

All IMO and so forth and so on - Don

Edit: I see Amir @amirm has many of the same thoughts. Perhaps unlike Amir, I see real value in the spec, but to realize that value feel the spec needs to be better defined.

p.s. Having waded into this again, I still feel the need to shower afterwards... A spec too loose, and entrenched bias for and against the basic principle of the spec, leads to an unending debate unwinnable by anyone (unless someone here has sufficient pull with the FTC). The main reason I am writing is because I need a distraction whilst waiting for my telescope to process the galaxy I'm trying to see tonight.

Edit 2: Since I'm fanning the flames, I give to you the Flame Nebula, taken using my telescope. Gotta' say it's more interesting than FTC rules at the moment.
View attachment 424357

First, tell me about your telescope/camera setup!

Again, the reg was clearly written by lawyers and bureaucrats. If you compare it to something like an ASTM test protocol, it's pitiful. Difference is that ASTM can't forcibly go after my bank account or me.

 

[restorer-john]

Engineer here as well, and while I agree that more concrete regulations are preferable, these are what they are. That said, the FTC regulation is far from being worse than many others I’ve worked with.

Manufacturers are allowed to choose whichever frequency they test at. For example, they can test at 1 kHz and base their rating on that, provided they’re confident the amplifier meets the regulations across the full frequency range. They then disclose the rating as follows:

• Manufacturer test result at 1 kHz: 100 W with 0.01% THD+N
• Manufacturer rating per FTC: 20-20,000 Hz, 100 W, <0.01% THD+N

The amplifier still has to deliver full power across the entire range, even if the test itself is done at a single frequency.

In practice, I’d think testing at three different frequencies (e.g., low, mid, and high range) would be sufficient to verify whether the amplifier meets the stated claims.

My advice?

Don't try to convince individuals with logic, facts, or even laws, when they have a deep-seated inability to consider anything other than their own sense of infallibility. You are just wasting your time.

Way bigger fish to fry.

 

[MaxwellsEq]

"...Any power level from 250 mw to the rated power shall be obtainable at any frequency within the rated power band of 20 Hz to 20 kHz.."

Fixed it for you.

 

[tmtomh]

Don't try to convince individuals with logic, facts, or even laws, when they have a deep-seated inability to consider anything other than their own sense of infallibility. You are just wasting your time.

It's like you were looking straight into a mirror when you wrote that.

 

[Old_School_Brad]

I do not read it that way, since it is pretty clear about 20 Hz to 20 kHz at full rated power for five minutes. The manufacturer can test as they wish, and report accordingly, per your first bullet. However, that does not (IMO) give them a pass to claim they meet the FTC rule per your second bullet.

I don’t see why not. If they’re confident that the design will pass a third-party test (after all, they designed it and should know), they can test at any frequency and still claim compliance.

Yes, but normally to meet a specification like this, someone has to actually perform sufficient characterization (testing) to prove it meets the spec. I would not allow a manufacturer to get away with a single-frequency test of a device covering multiple decades.

If it passes the test, all is good. Manufacturers can choose to rely more or less on simulations and calculations if they find them accurate and trustworthy, and then proceed with a 1 kHz test. Ultimately, it comes down to confidence in their design and engineering.

 

[IPunchCholla]

My advice?

Don't try to convince individuals with logic, facts, or even laws, when they have a deep-seated inability to consider anything other than their own sense of infallibility. You are just wasting your time.

Way bigger fish to fry.

This is great advice, as long as one remembers we all are those people with a sense of infallibility about which we are wrong and we are blind to ourselves about it.

 

[DonH56]

I don’t see why not. If they’re confident that the design will pass a third-party test (after all, they designed it and should know), they can test at any frequency and still claim compliance.

Confidence is one thing; proving it another. The FTC does not provide that leeway as I read it, bearing in mind I am not the FTC nor a manufacturer, so don't get a vote. If they have a third party test the amp to the spec and it passes, and have data to show (to themselves if nobody else) that a spot test is enough to support the claim that the amp will pass at all other frequencies, then that sort of thing happens all the time. But at some point I feel they need to actually run a compliance test.

If it passes the test, all is good. Manufacturers can choose to rely more or less on simulations and calculations if they find them accurate and trustworthy, and then proceed with a 1 kHz test. Ultimately, it comes down to confidence in their design and engineering.

No argument. The only caveat is what the customer and/or standards body will accept. I have done plenty of designs that I am confident will meet spec, but the customer usually demands proof. As does my management... Production test is usually negotiated among design, test, manufacturing, and customers to trade confidence in meeting all specifications against test cost in time and money (tightly coupled, natch).

I know you know this, just putting it out there for everyone to follow the debate. A big disclaimer is that, while I have done commercial and other (medical, military, space, etc.) designs, virtually everything I have done in my career has required stringent testing to satisfy internal and external standards compliance. Something like this FTC rule would go through a period of working with FTC and other industry personnel to nail down a "proper" spec and appropriate compliance tests. Again IME, but I suspect most audio manufacturers will wing it with their own plans and wait to see if they are challenged.

To follow your example, I could see them doing a five-minute test at 1 kHz, then doing a distortion sweep from 20 Hz to 20 kHz as proof of compliance. Technically they have not run every frequency for five minutes, but the amp has run for five minutes, and doing the sweep without pausing may be sufficient. But I do not think that is the way the spec is currently written.

 

[DonH56]

First, tell me about your telescope/camera setup!

Unistellar eQuinox 2, a "smart" telescope. It has me staying up far too late on far too many nights. Instead of digging through Norton's Star Atlas and trying to find where interesting objects lie, select from a catalog and tell it to go. Many telescopes do that now, but this one is imager-based so it stacks images, processes and colorizes them, then spits out an impressive picture, all from an app on your phone (or tablet). No need for a separate camera and image-processing SW and all that jazz, and no need to spend hours outside in the CO winter! It won't match my ancient 8" Newtonian reflector for raw light capture, but the processing makes up for it, and it is so much easier to set up and use that I'm having a blast.

I posted in the pictures thread; start here and there are a few more following plus more info on the telescope.

Post pictures of anything, with comment...couple words.

@DonH56 -- do you live in a dark sky location, or are you using an interference filter (or both, or neither)? :) These images are pretty incredible from my extremely amateur sky-gazer perspective! We're not dark sky, but we're not that far from good dark sky sites (30 or 40 miles). If it...

www.audiosciencereview.com

This is the post about the 'scope:

Post pictures of anything, with comment...couple words.

@DonH56 -- do you live in a dark sky location, or are you using an interference filter (or both, or neither)? :) These images are pretty incredible from my extremely amateur sky-gazer perspective! We're not dark sky, but we're not that far from good dark sky sites (30 or 40 miles). If it...

www.audiosciencereview.com

Again, the reg was clearly written by lawyers and bureaucrats. If you compare it to something like an ASTM test protocol, it's pitiful. Difference is that ASTM can't forcibly go after my bank account or me.

No argument, and I should note clearly that I have not been keeping up with this thread, mainly because it was clear (to me anyway) in the beginning that it was not a topic Amir felt worth debating and I did not want to cross a line tilting at windmills. Which I am admittedly doing anyway...

 

[Old_School_Brad]

Confidence is one thing; proving it another. The FTC does not provide that leeway as I read it,

I see that leeway in their use of the phrase "shall be obtainable," which implies that while certain information should be accessible to consumers, it does not mean manufacturers are obligated to disclose every detail. The ratings provided can be accurate or misleading, depending on whether the manufacturer chooses to take that risk. Ultimately, it is the manufacturer's decision.

I apologize for truncating your comment. I generally agree with the rest of your points. Let me know if you feel it has been taken out of context.

 

[DonH56]

I see that leeway in their use of the phrase "shall be obtainable," which implies that while certain information should be accessible to consumers, it does not mean manufacturers are obligated to disclose every detail. The ratings provided can be accurate or misleading, depending on whether the manufacturer chooses to take that risk. Ultimately, it is the manufacturer's decision.

Therein lies the rub, eh? "Shall be obtainable" is subject to interpretation... Legally "shall" is a very strong word that must be fully supported. In specs with which I have worked, "shall" means something that must be met (tested, whatever). That is a separate argument from what manufacturers disclose to customers, to me anyway, as I expect any manufacturer has a wealth of data that is not routinely (if ever) provided to end customers. Most consumers are not going to question a line in a brochure, nor have the knowledge to do so. But, again IME/IMO, if the manufacturer states "100 W FTC rated power" then they must have data to back up (support) that claim.

I apologize for truncating your comment. I generally agree with the rest of your points. Let me know if you feel it has been taken out of context.

Yeah, I would never, ever, even accidentally, take someone out of context... No worries. The 'net is often a lousy means of communication.

 

[IPunchCholla]

I see that leeway in their use of the phrase "shall be obtainable," which implies that while certain information should be accessible to consumers, it does not mean manufacturers are obligated to disclose every detail. The ratings provided can be accurate or misleading, depending on whether the manufacturer chooses to take that risk. Ultimately, it is the manufacturer's decision.

I apologize for truncating your comment. I generally agree with the rest of your points. Let me know if you feel it has been taken out of context.

In my experience of legalese “shall” and “must” are equivalent. So I’m not reading that phrase the way you suggest.

 

[DonH56]

Off topic: Re. @restorer-john's comment and mirrors, my experience has been that the world is filled with one-way mirrors we all (most especially me) look into (through) all the time....

 

[Old_School_Brad]

In my experience of legalese “shall” and “must” are equivalent. So I’m not reading that phrase the way you suggest.

Yes, when considering the words "shall" and "must" in isolation, that is accurate.

In the context of the phrase "shall be obtainable," it has a different implication: it suggests that the amplifier must be capable of delivering its full power across the entire frequency range. However, it does not explicitly require manufacturers to conduct tests across that range or to provide documentation of such tests. In practice, a manufacturer could potentially avoid testing their amplifier altogether, opting instead to rely on simulations and calculations if they choose. However, if the amplifier is tested by third-party reviewers or the like or selected for examination by the FTC, it must meet the performance claims made by the manufacturer.