Audio Power Output Measurement Feedback

[WA2SQQ]

Though this is not AM radio related, I know that some of you are into high end audio systems so I though this might be a good place to obtain some feedback. I’ve been tasked with submitting comments on some proposed FTC rule changes that would specify how consumer electronic companies measure and advertise the maximum audio power output of a device, and whether THD and bandwidth should or should not be included.

These guidelines were last updated in 2000. Historically the primary power output specification disclosed in any advertising distributed through the media be the manufacturer’s rated minimum sine wave continuous average power output, per channel, at an impedance of 8 ohms. I’ve attached two documents.  Changes were later made that used an alternate testing method measuring “peak” power often into lower impedance s. This allowed the manufacturer to advertise much higher power output ratings but at the expense of much higher THD. This can be seen in PC speakers, powered by small “wall warts” claiming 75W output. The “power bandwidth’’ associated with the rated THD disclosure be the single frequency 1000 Hz, rather than the customary 20Hz–20kHz. It was recommended that the Commission adopt 1000 Hz as the basis for primary power output claims, and allow advertisers to make secondary qualitative claims, such as ‘‘Ultra-wide Bandwidth’’ or ‘‘20–20 kHz’’.

Some of the comments that led to the current standards suggested that today’s younger generation listened to audio on portable (battery powered) devices. Since fidelity was not as important as it once was, digital designs could provide more “peak” power with less power consumption, though noticeably higher THD.

Do you feel the current testing and specification reporting should be changed or is it adequate for the average consumer?

[KD6VXI]

I'd say, first, get rid of the "RMS Power" line.  Seriously, what is RMS power?

Second, maybe take a look at the youtube channel for "Williston Audio Labs".  He does comprehensive testing of car audio amplifiers on an amp dyno.  The tests run show total power output clipped, avg and dynamic burst.  Those are the three I would think are needed for people to qualify what they are looking at / for.  His tests he lists the frequency of the tones used to enable you to understand what is being tested.

--Shane
KD6VXI

[Opcom]

I want things tightened up, and for every amplifier product.

RMS power measured with a sine is very cheap, easy, and accurate way to describe the minimum capabilities of an amplifier.
To illustrate a proper disclosure for a random amplifier:
"100 Watts RMS continuous sine wave power output per channel into 4 Ohms, with all channels driven to rated output, from 20Hz to 20KHz at 1% THD".
(not mine, see any of hundreds of old documents)

100 Watts  -A standard measurement of power, easily measured, to be delivered to a load.

RMS -an industry-wide  standard way of measuring the area (and thereby power) contained in a waveform or physical movement.

continuous -A statement that the operating condition is continuous, or at least for a few minutes. In the past, this meant a 24x7 operation and was an indicator of quality. However, if the amplifier survives for 15 minutes, it may be enough for consumer use since average music levels are 20-30% of peak. The statement could be (and in my opinion, should be) qualified by a time endurance unless it is truly 'continuous'.

sine wave -A type of waveform composed of a single frequency, making it easiest to measure amplifier error.

power output -Combines the above items into a single claim.

per channel -Says that each channel (or a specified channel) will provide the above performance.

into 4 Ohms -Defines the physical load to which the power is to be delivered. Assumed to be non-reactive.*

with all channels driven to rated output -This brings the quality of the power supply into the statement. It must be able to support all of the channels under the conditions stated above, or
the test is not scientific due to incorrect procedure for scientific experiment -that is, leaving some very basic data out.

from 20Hz to 20KHz -The above conditions must be met over this frequency range.

at 1% THD - the above conditions must be met without the total harmonic distortion exceeding this level.**

and 1% IMD - the above conditions must be met without the intermodulation distortion exceeding this level. -yes that should be added. This is 2021, not 1965. Amplifiers are capable of very fine performance, as is modern test equipment. So they should be required to state this as well.**

 
* non-inductive loads are used for test because no speaker load is perfect -all have reactance, and we must have a common ground for factual statements when they are used to compare one product to another.
**I make no demand for more or less than 1% distortion. Only the truth, be it lower or higher. Some times, running the amp at lower power causes it to produce lower percentage of distortion. But of course that power level must be stated.


No objection to factual statements of total power output clipped, avg and dynamic burst, as long as they are qualified. in addition to the standard time-honored method previously applied to protect consumers (Section 432.2 of the Rule).

Dynamic burst -at what program level is it tested and what is the total distortion during the burst? I hate listening to crappy sounding drums and live cannon recordings.

Behringer claims 4KW peak power on the Europower EP4000. That peak output would likely fall short of the duration required for the the live cannon shot in Dorati's recording of Tchaikovsky's 1812 Overture. The newer Telarc digital recording of same is impossible. Unqualified peak power claims (ratings?) are worthless, except when taking money from a consumer.

[W3SLK]

Patrick said:

I want things tightened up, and for every amplifier product.

RMS power measured with a sine is very cheap, easy, and accurate way to describe the minimum capabilities of an amplifier.
To illustrate a proper disclosure for a random amplifier:
"100 Watts RMS continuous sine wave power output per channel into 4 Ohms, with all channels driven to rated output, from 20Hz to 20KHz at 1% THD".
(not mine, see any of hundreds of old documents)

100 Watts  -A standard measurement of power, easily measured, to be delivered to a load.

RMS -an industry-wide  standard way of measuring the area (and thereby power) contained in a waveform or physical movement.

continuous -A statement that the operating condition is continuous, or at least for a few minutes. In the past, this meant a 24x7 operation and was an indicator of quality. However, if the amplifier survives for 15 minutes, it may be enough for consumer use since average music levels are 20-30% of peak. The statement could be (and in my opinion, should be) qualified by a time endurance unless it is truly 'continuous'.

sine wave -A type of waveform composed of a single frequency, making it easiest to measure amplifier error.

power output -Combines the above items into a single claim.

per channel -Says that each channel (or a specified channel) will provide the above performance.

into 4 Ohms -Defines the physical load to which the power is to be delivered. Assumed to be non-reactive.*

with all channels driven to rated output -This brings the quality of the power supply into the statement. It must be able to support all of the channels under the conditions stated above, or
the test is not scientific due to incorrect procedure for scientific experiment -that is, leaving some very basic data out.

from 20Hz to 20KHz -The above conditions must be met over this frequency range.

at 1% THD - the above conditions must be met without the total harmonic distortion exceeding this level.**

and 1% IMD - the above conditions must be met without the intermodulation distortion exceeding this level. -yes that should be added. This is 2021, not 1965. Amplifiers are capable of very fine performance, as is modern test equipment. So they should be required to state this as well.**

 
* non-inductive loads are used for test because no speaker load is perfect -all have reactance, and we must have a common ground for factual statements when they are used to compare one product to another.
**I make no demand for more or less than 1% distortion. Only the truth, be it lower or higher. Some times, running the amp at lower power causes it to produce lower percentage of distortion. But of course that power level must be stated.


No objection to factual statements of total power output clipped, avg and dynamic burst, as long as they are qualified. in addition to the standard time-honored method previously applied to protect consumers (Section 432.2 of the Rule).

Dynamic burst -at what program level is it tested and what is the total distortion during the burst? I hate listening to crappy sounding drums and live cannon recordings.

Behringer claims 4KW peak power on the Europower EP4000. That peak output would likely fall short of the duration required for the the live cannon shot in Dorati's recording of Tchaikovsky's 1812 Overture. The newer Telarc digital recording of same is impossible. Unqualified peak power claims (ratings?) are worthless, except when taking money from a consumer.

Right you are Patrick! To quote Don, K4KYV: "An audio phool and his money are soon pharted!"

[WA2SQQ]

Appreciate the feedback, never expected to get so much, so quickly .... attending 1st meeting on this today

[WBear2GCR]

This is a very complex issue.

I did not read all the comments in the second document.
Having been a manufacturer of audio equipment, I can say that some of the comments, especially
CEMA's are b***s***t intended to make it easier for manufacturers of cheap gear to slide by
with cheap crap. PERIOD.

This should not be permitted.

YES, a THD measurement IS a measure of QUALITY - albeit a limited one.

IM distortion being more better.

Bandwidth? POWER BANDWIDTH matters.
Specifying 20-20khz? Dumb.
That tends to force mfrs to meet a meaningless spec.

High end gear, solid state will go DC to light... consumer crap, no.
So, what one wants to see is what the individual product can do.

The 1000Hz. measurement point for THD? Better than nothing IF it pertains to
maximum power that it is reached? Or, perhaps a 1watt measurement AND a -3dB measurement.
Yes, better. (actually just publish the damn curve, right up to clipping)

The assertion that sub audible levels of THD are routinely present today in consumer
equipment is false.

What is true is that THD is a poor predictor of audible distortion.

8 ohms?? WTF?
Car audio is ALL 4 ohms or 2 ohms or ONE OHM!

Many amps have limited CURRENT capabilities and an INSUFFICIENTLY LOW output Z
to provide DOUBLING OF POWER INTO HALVED IMPEDANCE LOADS!!
Does the consumer need or want to KNOW this??

The average consumer either will HAVE specifications that will permit the products to be
compared and a discrimination made, OR they will not.

We can just go back to "IHF" power??

Today publishing a WIDE ARRAY of information and data - THAT is trivial due to modern
computer based FFT analyzers that virtually all mfrs have - OUGHT TO BE STANDARD.

That the average consumer is not equipped to analyze this information is not the primary criterion.
Providing real information should be the goal.
Giving the consumer the ABILITY to find information and data that CAN be used to make reasonable
determinations as to the performance of any given piece of equipment OUGHT to be the aim.
NOT making everything opaque and unknowable.

There are a lot of more details... but this is a crude start.
Email me, if you wish.

                              _-_-bear

[KD6VXI]

Bear,

I'm at .5 ohms in my car stereo on the sub channel.

2 x dual voice coil 2 ohms per coil.  2 speakers.

There are car audio amps rated to a quarter ohm now.


--Shane
KD6VXI

[WBear2GCR]

Etc...

More fool to the fi-yah...