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

[rdenney]

Even if RMS Watt is not an official measurement there is an on line calculator:
https://calculator.academy/rms-wattage-calculator/
It is just a mathematical calculation made with the wattage input.
RMS Volt is the same with a volt measurement as input.
If somebody want to use the RMS Watt unit, it is fine to me as it brings some margin.
Nobody will make me believe that an amplifier the size of my palm hand, without any heatsink is able to provide hundreds of watts during 5s or more.

It’s about efficiency. An amp making 250 watts that is 90% efficient is drawing 275 watts and dissipating 25 watts as heat. That’s not much for a short period. An AB amp that is maybe 55% efficient will be drawing 455 watts while producing 250 watts and dissipating 205 watts as heat. My AB amp draws and dissipates more while idling than my D amp.

But this I know for sure: the D amp makes music noticeably louder than the AB amp, which verifies for me in practical terms that the 3X power rating is approximately real. And it does so for a lot longer that five minutes.

Rick “measured as a ~5dB difference in SPL” Denney

 

[NTK]

Even if RMS Watt is not an official measurement there is an on line calculator:
https://calculator.academy/rms-wattage-calculator/
It is just a mathematical calculation made with the wattage input.
RMS Volt is the same with a volt measurement as input.
If somebody want to use the RMS Watt unit, it is fine to me as it brings some margin.
Nobody will make me believe that an amplifier the size of my palm hand, without any heatsink is able to provide hundreds of watts during 5s or more.

The website you've linked to in your post is so wrong

 

[mhardy6647]

But this I know for sure: the D amp makes music noticeably louder than the AB amp, which verifies for me in practical terms that the 3X power rating is approximately real. And it does so for a lot longer that five minutes.

3x power = an increase of 4.8 dB (all else being equal)... so... maybe.

 

[KSTR]

IMHO and IME, what people tend to mean with "watts rms" is the simple average over time... only that this is not a squareroot-of-sum-of squares type of average, rather it is standard arithmetic (straight sum of values) average.

If you apply 10Vrms on a 4R resistor, say, a pink noise signal, it will dissipate 25W average (not rms) in the resistor but peak powers are larger. This then gets confused and people write 25 watts rms "because the voltage spec also was rms" (copy&pase error, bascially).

If we replace the resistor with a pure reactive load (capacitor or inductor, placing sinusodial voltage and current 90 degrees apart) the same 10Vrms give net dissipation zero in that capactor because (simplified) half of all the instantaneous powers are negative and this fully cancels total dissipation. Using an rms algorithm to average power would produce a fundamentally wrong result and therefore the term watts rms should really be avoided... but when it is used we should give people some slack when it is clear they actually meant standard average.

 

[rwortman]

This reminds me of a sales call I went on long ago. It was not audio related, microelectronics manufacturing. I was there to represent the service side of the business. The customer and salesman were discussing a a corrosion inhibiting feature. The customer asked how long the product could stay in open air before corrosion began. Salesman asked, “What is your requirement”? Customer replies, “Forever”. Salesman says,” We can promise that, but the acceptance test will take an awfully long time”

Personally, I expect that an amplifier that is rated for a continuous output of XX watts to be able to put out that amount of power for days. I’m pretty sure professional audio amps will. If it’s really only 20ms burst power then say so on the spec sheet.

If you’re worried that your customers won’t buy your cheap amps if you rate them properly, get your marketing people to educate them, NAD sold a crapload of amps and receivers with low rated power back in the day by explaining their burst power ability to consumers. If you think that’s impossible, I can’t say I care that much. I don’t think the trend towards replacing finely made audio equipment with cheap throw-away modules and pretending they are equivalent is a good one. Neither am I worried about using a kilowatt-hour or so per day listening to music.

 

[amirm]

If you’re worried that your customers won’t buy your cheap amps if you rate them properly, get your marketing people to educate them, NAD sold a crapload of amps and receivers with low rated power back in the day by explaining their burst power ability to consumers. If you think that’s impossible, I can’t say I care that much.

The world is different now. It is an international market. If Fosi says their amp is producing 30 watts whereas the rest of the market says 300 watts, it will impact their sales. And mislead the consumer that their amp is 10% as powerful as the other.

For these regulations to work, there needs to be overnight enforcement. If there isn't, the "good guys" are the ones to suffer.

Note that the regulation requires that the FTC power be the most noticeable spec for the product. So it is very difficult to counter the small number with some other with realistic power delivery for music.

 

[amirm]

Personally, I expect that an amplifier that is rated for a continuous output of XX watts to be able to put out that amount of power for days. I’m pretty sure professional audio amps will. If it’s really only 20ms burst power then say so on the spec sheet.

I assure you that my power ratings represent a stressful situation for the amplifier. If it doesn't fail and go into protection, then I think it has the required thermal design to satisfy vast majority of users. For others, then buy something more stout and pay more for it of course.

Those professional amps rely on large boxes and fans. The have little cooling inside to keep cost and weight low. I am confident most of us don't want to see these fans and larger enclosures forced on us because of this regulation.

Note that once an amp has a fan, they can choose to make the thermal design even crappier per above. That means the fan will come on during use and will make noise.

What you want today exists anyway. You just have to pay more for it. My amps are 120 pounds each and cost $25,000. They run a lot hotter but I suspect will survive the 5 minute test due to huger thermal mass of the heatsinks.

 

[Old_School_Brad]

This might read a bit fragmented, but I find point-by-point quoting and answering worse. So..

It seems like the suggestion is to simply accept the situation and move on, but this has happened before, as both I and rwortmann have pointed out. Brands like NAD, Yamaha, and Onkyo used similar opportunities to their advantage in the past, and it’s possible that it could happen again. The argument that “it’s a different world now” feels somewhat unconvincing.
Manufacturers could still include their alternative ratings if they wished, perhaps in smaller font beneath the FTC values. There’s nothing preventing them from doing so.

An immediate enforcement of changes doesn’t seem necessary; typically a transition period takes time, so the manufacturers are not treated unfair.

The idea of revising ASR testing procedure was discussed previously, but it seemed like a decision was deferred. Has the conclusion now been reached to maintain the current testing methods?

It’s worth noting that FTC regulations don’t impose major demands on manufacturers. The main requirement is to add and clearly emphasize the FTC rating on the datasheet -you can do this by simply bolding it. There’s no mandate for larger enclosures or the addition of fans. Could you clarify where this misunderstanding comes from?

As for fans, it’s certainly possible to design them to operate quietly. For example, my mid-level Yamaha professional amplifier uses temperature-regulated fans that only activate above 50 °C and adjust their speed based on temperature, remaining nearly silent. If this is achievable in a cost-conscious pro amplifier, it seems reasonable to expect manufacturers to adopt similar thermal solutions if they aim to advertise higher FTC power ratings.

 

[olieb]

It’s worth noting that FTC regulations don’t impose major demands on manufacturers. The main requirement is to add and clearly emphasize the FTC rating on the datasheet -you can do this by simply bolding it. There’s no mandate for larger enclosures or the addition of fans. Could you clarify where this misunderstanding comes from?

That seems about correct. All you have to do is add a misleading number in bold print.
We will see, whether that happens. I doubt it. It is not even exactly clear how to arrive at that misleading number.
Fans will not happen for me, that much is settled.

 

[Doodski]

As for fans, it’s certainly possible to design them to operate quietly. For example, my mid-level Yamaha professional amplifier uses temperature-regulated fans that only activate above 50 °C and adjust their speed based on temperature, remaining nearly silent. If this is achievable in a cost-conscious pro amplifier, it seems reasonable to expect manufacturers to adopt similar thermal solutions if they aim to advertise higher FTC power ratings.

I shudder at the thought of cooling fans. They make noise and more importantly they force dust into the device, it gets dirty inside and in extreme cases that poses a fire risk. I'm looking at my very dusty multi-fan water cooled gaming PC right now hating the thought of dusting it because I have asthma, the dusting procedure makes a mess and more importantly I hate working on it and disturbing the internals with static discharge and whatever else can happen. I am firmly in the bigger heatsinks is better belief. As per the wattage calculation/metering get rid of RMS and use real Watts or apparent Watts but make a decision and do it sooner than later. Persisting with RMS wattage metering entrenches the use of it more. I have always worked in RMS Watts but it is cumbersome at times and requires more calculator strokes etc.

 

[Old_School_Brad]

That seems about correct. All you have to do is add a misleading number in bold print.
We will see, whether that happens. I doubt it. It is not even exactly clear how to arrive at that misleading number.
Fans will not happen for me, that much is settled.

You can call it whatever you like. I agree it’s not a perfect rule, but it’s the one we currently have. (Cue Batman ref. )
Once again, fans are not mandated or required. They are only necessary if a manufacturer aims to:

1. Achieve a higher FTC power rating,
   and simultaneously
2. Avoid adding additional passive thermal mass.

To reiterate, manufacturers are only required to include the FTC power rating -nothing more.

I shudder at the thought of cooling fans. They make noise and more importantly they force dust into the device, it gets dirty inside and in extreme cases that poses a fire risk. I'm looking at my very dusty multi-fan water cooled gaming PC right now hating the thought of dusting it because I have asthma, the dusting procedure makes a mess and more importantly I hate working on it and disturbing the internals with static discharge and whatever else can happen. I am firmly in the bigger heatsinks is better belief. As per the wattage calculation/metering get rid of RMS and use real Watts or apparent Watts but make a decision and do it sooner than later. Persisting with RMS wattage metering entrenches the use of it more. I have always worked in RMS Watts but it is cumbersome at times and requires more calculator strokes etc.

It's a compromise.
Like you, I tend to prefer the "bigger is better" approach and would rather have a large, solid block of aluminum over fans. However, I can appreciate how effective fans can be. As a result, I enjoy having plenty of real, continuous power in a compact 2U enclosure that doesn’t passively collect hair and dust 24/7 through cooling slots in the top plate.
Dust-collecting only starts when the fans actually start running, which is not that often. -Once a week for 30 minutes perhaps.

 

[amirm]

The people posting here, are aware of my testing. My testing cuts through empty claims such as 300 watts in desktop amps. The tests are rigorous and standardized. If an amp produces 50 watts and another 150, you can be the latter will play louder. Further, any faults, protection, etc. is clearly noted in the review. So all the wishing for standardization is of no value if you read my reviews which I assume you all do before purchasing an amplifier.

For people who are not members currently, shame on them if they don't do a single search for an amplifier review and buy just on bullet lists. Because if they do search, you are almost guaranteed to see my review on first page of the search, if not the top search result shown by Google. So these people are covered too as they will quickly see the real power output vs claimed.

What is left is this wishful thinking that FTC tests somehow means more reliable/beefier amplification for free. Well, that is not going to happen. There is no science behind this, nor will improvements come for free.

Finally, with no enforcement action from FTC, none of this may be material anyway. In that sense, you are asking for something you are never going to get.

 

[Old_School_Brad]

What is left is this wishful thinking that FTC tests somehow means more reliable/beefier amplification for free.

I don't recall anyone making such a statement.

The primary argument I see repeated in this thread by those advocating for standardization is that it promotes greater transparency.

 

[rdenney]

I don't recall anyone making such a statement.

The primary argument I see repeated in this thread by those advocating for standardization is that it promotes greater transparency.

I’ve said this over and over. There will be less transparency and greater market confusion because the FTC measure does not describe what people buy a more powerful amplifier to do, which is to make music louder. An amp can have a higher FTC power rating but still a lower power envelope at the point of clipping. Another amp might be forced to report a lower FTC rating but have a higher power envelope at clipping when playing actual content and not a test signal. For playing realistic content, it will play louder. Thus, the FTC ruling can result in exactly the opposite of what it attempts to achieve. Thank you, Federal government.

Now, tell me how that promotes transparency compared to a distortion vs. power curve over a range of frequencies that tells me precisely at what output power an amp clips into various loads. That’s an easy test to standardize. Remember that what makes it clip is when the power supply can no longer supply the voltage or current (depending on load) to fill out the waveform.

If you want to test thermal handling, test thermal handling. Use a signal like real music played where the peaks are at onset of clipping, and then test it for an extended period, at least until the temperatures stabilize. That may be longer than five minutes. See if those temps exceed component ratings. That’s an easy test to standardize, too.

But don’t expect a single number poorly traced to realistic use cases to tell people which amp will play music louder, because it often won’t.

Rick “where it clips is the loudest it will play” Denney

 

[JustJones]

To reiterate, manufacturers are only required to include the FTC power rating -nothing more

Manufacturers aren't required to include FTC power ratings.

 

[LSPhil]

The FTC Test seems to be more suited for PA amplifiers or a "party mode" scenario rather than for home use. Thermal durability is important, but it's difficult to determine the exact conditions under which passive cooling should operate effectively. Many users place the amplifier on the very bottom because of its weight, and in such a setup, achieving effective convection cooling becomes significantly more challenging.

 

[Old_School_Brad]

Manufacturers aren't required to include FTC power ratings.

True. If they withhold performance figures, they are not. If they disclose any, they are.

 

[LSPhil]

An amp can have a higher FTC power rating but still a lower power envelope at the point of clipping. Another amp might be forced to report a lower FTC rating but have a higher power envelope at clipping when playing actual content and not a test signal. For playing realistic content, it will play louder.

Your observation that the difference exists is due to the capacitors and is limited to 3 dB. While this difference may provide audible benefits in dynamic content, it is not a dealbreaker in terms of perceived loudness. The primary advantage lies in the ability to reproduce transients more cleanly, not in achieving higher SPL.

 

[NTK]

An amp can have a higher FTC power rating but still a lower power envelope at the point of clipping. Another amp might be forced to report a lower FTC rating but have a higher power envelope at clipping when playing actual content and not a test signal. For playing realistic content, it will play louder.

Your observation that the difference exists is due to the capacitors and is limited to 3 dB. While this difference may provide audible benefits in dynamic content, it is not a dealbreaker in terms of perceived loudness. The primary advantage lies in the ability to reproduce transients more cleanly, not in achieving higher SPL.

What @rdenney described can be easily demonstrated with an example.

If we build 2 amplifiers using the same Hypex (or Purifi) amp modules, except one is built with heat sinks sized to accommodate continuous full power (single frequency sine waves) and the other one sized for 1/5 continuous full power. The one with the larger heat sinks will have a higher FTC power rating than the one with the smaller heat sinks. But when reproducing normal music, they will produce the same max loudness. So very different FTC power ratings, identical loudness output capability in actual use.

 

[rdenney]

Your observation that the difference exists is due to the capacitors and is limited to 3 dB. While this difference may provide audible benefits in dynamic content, it is not a dealbreaker in terms of perceived loudness. The primary advantage lies in the ability to reproduce transients more cleanly, not in achieving higher SPL.

Maybe for you, but not for the average consumer.

“Why buy a more powerful amp?” Average consumer: “To play stuff louder.”

And I don’t know what you mean by the difference being only capacitors. The 125-watt continuous rated B&K amps have a traditional linear power supply with the typical large toroidal transformer and soda-can-size electrolytic filter caps. The output devices are MOSFET transistors known for not being fond of low impedance. They sound nice, but the Buckeye, despite its 100-watt continuous rating (in contrast to 350+ watts at the onset of clipping into my 6-ohm speakers), plays music about 5 dB louder measured as SPL (peaks at 110-112 dBA SPL from six feet in my real room). That’s with Revel tower speakers at the point of clipping (the clipping indicators were flashing). The clipping indicators are looking for distortion above a threshold, but I never got a clear idea of what that threshold was. I certainly couldn’t hear that it was clipping in the occasions when those lights flashed, but the strain of the B&K was a bit more detectable (perhaps) at the point where I was unwilling to turn it up further.

The only audible difference up to that level was the loudness.

Note that playing music at this loudness is uncommon for me. I play tuba and want to occasionally play along with an orchestra recording without having to hold back. I only do that when my wife isn’t home. But I want the ability.

Rick “measured difference but not measured distortion” Denney