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

[EJ3]

Car and truck engines have mixed results when used in aviation and marine applications. Most were never designed to produce their max rated power continuously. The typical car engine uses only about 1/4 of its rated power continuously when cruising down the freeway and its full rated power only for brief moments. Most car engines don't last when installed in boats & airplanes that continuously demand 70% or more of rated power. Even when driven at SCCA and similar racing events, many of these engines get heat soaked and lose power or go into "limp mode" if operated at full power in low gears for more than a few minutes. A few car engines have worked well in marine & aviation applications; they are either modified or comprise the over-engineered exceptions that prove the contrary rule. For each one, there are many others that don't.

This analogy to engines is not ideal because of the term "continuous". Most car engines will produce their rated power (for example on a dyno) when properly maintained - yet are not certified or advertised to produce that max rated power continuously. Yet when it comes to audio amplifiers, the term "continuous power" is used, even if the amp shuts down or melts while producing that power. It's understandable if that is misleading.

5 minutes is the FCC's idea of continuous (which I think is a little long for an indoor application) but it is what it is.
On the other hand, I can't see owning anything less than a 100 watt (at 8 ohms) rated amp (in spite of the fact that I do own 2 NAD 2100's
[but they will put out much more than their rated 50 watts at 8 ohms]):
Specification
Stereo Mode
Continuous Average Power Output into
8 ohm (Min, RMS power per channel
20-20kHz both Channels Driven
with no more than rated distortion) .......: 50 W
Rated Distortion 20Hz-20kHz ...............: 0.03%
Clipping Power (Maximum continuous....: 70 W
power per channel)
IHF Dynamic Headroom at 8 ohm .........: +6dB
IHF Dynamic Power at 8 ohm ...............: 200 W
(Short term power) at 4 ohm ...............: 250 W
at 2 ohm ...............: 330 W
Damping Factor at 50 Hz (Ref. 8 ohm) ..: 100
THD 20Hz-20kHz from 250mW to rated : <0.03%
Frequency Response, Lab input ...........: 3Hz - 100kHz, +0db -3dB
Signal to Noise Ratio A-weighted .........: 100db ref 1W, 117dB at rated power

Bridged (Monophonic) Mode
Continuous Average Power Output into
8 ohm (Min, RMS power per channel
20-20kHz both Channels Driven
with no more than rated distortion) ......: 150 W
IHF Dynamic Headroom at 8 ohm .........: +6dB
IHF Dynamic Power at 8 ohm (max.......: 500 W
(Short term power) at 4 ohm ...............: 660 W
So they are great in a bridged mono setup for 1 per channel.

In my case, I tri-amp my NAD 2200's: 2 bridged mono at 4 ohms, 1 for each channel and one running at 4 ohms in stereo for my pair of subs.
When I go put in my yard, with my windows open, I am probably running 40-50 watts per amp, continuous.
So, at max power, even for 5 minutes, would be unreasonable.
If I was doing the same thing off of one amp...don't know???

 

[MRC01]

No car analogy is perfect, but I understand why it’s often used -it’s something almost everyone can relate to. And you’re absolutely right; I agree with you that “continuous” should mean exactly what the word implies and represents.

I think the term "continuous power" implies some kind of time window. But I don't think that window has to be forever. It should be appropriate to the application - whether cars or audio amps. I think most of the participants here agree on that in principle. The tricky part is quantifying it with a specific number.

5 minutes is the FCC's idea of continuous (which I think is a little long for an indoor application) but it is what it is.
...
In my case, I tri-amp my NAD 2200's: 2 bridged mono at 4 ohms, 1 for each channel and one running at 4 ohms in stereo for my pair of subs.
When I go put in my yard, with my windows open, I am probably running 40-50 watts per amp, continuous.
So, at max power, even for 5 minutes, would be unreasonable.
If I was doing the same thing off of one amp...don't know???

That's the argument for the "it should be less than 5 minutes" case. Even if you're blasting your stereo all day long, due to the power vs. frequency curve and dynamics of music, the amp is only producing its full rated "continuous" power for a few moments at a time.

We could look at this empirically: how short can the time window be, such that no more than 1% of consumers & audiophiles would encounter an amp that shuts off or melts while producing its rated power?
In this case, I think the time window could be shorter than 5 minutes, maybe as short as 30 seconds. But that is just my intuition. The question has too many unstated variables.

 

[Old_School_Brad]

I think the term "continuous power" implies some kind of time window. But I don't think that window has to be forever. It should be appropriate to the application - whether cars or audio amps. I think most of the participants here agree on that in principle. The tricky part is quantifying it with a specific number.


That's the argument for the "it should be less than 5 minutes" case. Even if you're blasting your stereo all day long, due to the power vs. frequency curve and dynamics of music, the amp is only producing its full rated "continuous" power for a few moments at a time.

We could look at this empirically: how short can the time window be, such that no more than 1% of consumers & audiophiles would encounter an amp that shuts off or melts while producing its rated power?
In this case, I think the time window could be shorter than 5 minutes, maybe as short as 30 seconds. But that is just my intuition. The question has too many unstated variables.

It’s also important to design the test in a way that properly evaluates the thermal performance, as the worst-case scenario can vary between amplifier classes.

There’s a solid argument for a 5-minute continuous power test. While music is dynamic, running such a test would eliminate any doubts by setting a sufficiently high benchmark, ensuring it’s unlikely that people would damage their amplifiers during regular music playback. At the same time, it would also test the thermal performance of Class D amplifiers under this load.

 

[EJ3]

I think the term "continuous power" implies some kind of time window. But I don't think that window has to be forever. It should be appropriate to the application - whether cars or audio amps. I think most of the participants here agree on that in principle. The tricky part is quantifying it with a specific number.


That's the argument for the "it should be less than 5 minutes" case. Even if you're blasting your stereo all day long, due to the power vs. frequency curve and dynamics of music, the amp is only producing its full rated "continuous" power for a few moments at a time.

We could look at this empirically: how short can the time window be, such that no more than 1% of consumers & audiophiles would encounter an amp that shuts off or melts while producing its rated power?
In this case, I think the time window could be shorter than 5 minutes, maybe as short as 30 seconds. But that is just my intuition. The question has too many unstated variables.

Suppose someone's toddler (cat or dog) does something that causes the volume to be wide open and it runs at max power:
If it melts down & catches fire in 30 seconds, is that enough time for someone to fix the issue if they are outside or up stairs or something?
So maybe 5 minutes is good.

 

[Old_School_Brad]

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.

 

[EJ3]

I'm thinking that if someone's toddler is in there and something happens that causes the system to go to wide open, the first instinct would be to get the toddler to somewhere that won't damage the toddlers ears, then run back in & shut the system down, unplug it or whatever it takes to make it stop. Or maybe get to your breaker box.
But if the amp melts down & catches before you are able to do that...(That may take 5 minutes)
Now you may have a home fire on your hands.

 

[amirm]

Suppose someone's toddler (cat or dog) does something that causes the volume to be wide open and it runs at max power:
If it melts down & catches fire in 30 seconds, is that enough time for someone to fix the issue if they are outside or up stairs or something?
So maybe 5 minutes is good.

I would worry about your speakers before I would worry about the amp. The latter has protection circuits. The former does not.

 

[Old_School_Brad]

I would worry about your speakers before I would worry about the amp. The latter has protection circuits. The former does not.

Your statement makes a couple of assumptions. First, it assumes that the speakers cannot handle the continuous power output of the amplifier. Second, it presumes that we actually know the true continuous power rating of the amplifier.

 

[Mnyb]

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.

+1 it's like elevators where they also factored variations in material quality , so they are often designe 10 times stronger .

That kind of dimensioning is probably never seen in an amp not even FTC compatible ones

 

[amirm]

First, it assumes that the speakers cannot handle the continuous power output of the amplifier.

Well, if you are OK just guessing if the speakers can handle the power, why bother with having regulations for amplifiers?

That aside, I have blown good number of speakers/drivers with powerful amplifiers.

 

[Sokel]

That kind of dimensioning is probably never seen in an amp not even FTC compatible ones

Every amp can be FTC compatible.
It's only that some of them will have to state single digit rated power

 

[olieb]

+1 it's like elevators where they also factored variations in material quality , so they are often designe 10 times stronger .
That kind of dimensioning is probably never seen in an amp not even FTC compatible ones

I would think otherwise.
With pink noise the onset of clipping is at -9dB of max sine power. Considering that pink noise is a rather good proxy for music this means that in the loudest seconds of listening you will rarely reach 10% of peak power.
And clipping is "beyond typical operational limits" for me.

 

[Old_School_Brad]

Well, if you are OK just guessing if the speakers can handle the power, why bother with having regulations for amplifiers?

That aside, I have blown good number of speakers/drivers with powerful amplifiers.

Transparency.

Sure, in those instances, you've conducted destructive testing on the speakers..

 

[EJ3]

I would worry about your speakers before I would worry about the amp. The latter has protection circuits. The former does not.

Well, I'm not sure what might catch fire, as this is not something that I have every had happen (nor do I want to test it).
I have had smoke coming out of a Denon 5.1 receiver (a speaker wire under the carpet had separated after many years and the positive & negative shorted to each other).
Another time: the power pole transformer shorted out and blew up outside my house, causing one of my UPS's to never work again and one of the speaker relays in one of my NAD 2200's that was plugged into that UPS to weld itself together, something flashed inside the house (presumably the UPS which had the welded relay NAD 2200 plugged into it) like the power pole transformer did (creating an instantaneous quite large flash and shadow that I saw in the living room [I was about 40 feet away and down three steps in the den, watching TV with my mother] {the stereo was not even on at the time}, the smoke came out of something and the magic of one channel on one NAD 2200 went away. The other channel worked just fine.
My other 2 identical UPS's were fine, as was my APT/Holman Pre, my other 2 NAD 2200's & the rest of my stereo gear that was plugged into the UPS's there.
Peter (Quirk Audio) replaced the relay in the NAD 2200 & checked out everything else in the 2200 (only the one speaker relay was bad), everything was was fine.
Very odd.
Apparently one UPS absorbed the majority of the surge.

 

[EJ3]

I would worry about your speakers before I would worry about the amp. The latter has protection circuits. The former does not.

My Dahlquist M-905's have 2 fuses each, one for the mid-woofer & one for the tweeter. M905 Main Fuse AGC3 (Fast acting 3 AMP). M905 Tweeter Fuse AGC .75 (Fast Acting 3/4 AMP).
Not exactly a circuit...but something is better than nothing.

 

[mcdn]

I think the term "continuous power" implies some kind of time window.

“Continuous” implies a limit? What on earth would make you think that? It’s got a perfectly plain English meaning, roughly speaking “forever”.

 

[NTK]

“Continuous” implies a limit? What on earth would make you think that? It’s got a perfectly plain English meaning, roughly speaking “forever”.

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

 

[EJ3]

I was under the impression that it was "continuous for 5 minutes". I could be wrong. My wife tells me that has happened before.

 

[mhardy6647]

“Continuous” implies a limit? What on earth would make you think that? It’s got a perfectly plain English meaning, roughly speaking “forever”.

Yeah. Words, eh?

 

[Old_School_Brad]

I was under the impression that it was "continuous for 5 minutes". I could be wrong. My wife tells me that has happened before.

At least it’s not "continuous for 2 seconds," which is another common interpretation of the term.