All channels driven ratings

mtrycrafts

mtrycrafts

Audioholic Slumlord
...supposed to be wRMS ...
There is no RMS power, just continuous average power. Easy to see by numbers.
RMS voltage and RMS current, peak voltage current and P=IE.
When you get peak power, then also multiply RMS I and E, you will get 1/2 of peak power, not .707 as what the RMS I and E are of peak.
 
GrimSurfer

GrimSurfer

Senior Audioholic
Maybe some of you guys don't remember how we got here. There were so many shenanigans going on in the 1970s wrt power output claims that the Federal Trade Commission felt it necessary to clamp down and impose a defined standard and test procedure that people could use to compare products reliably.

The standard was called root mean square. It was based on measuring the average (or mean) continuous voltage times the average amperage (square) of an amp reproducing a broadband signal (typically white or pink noise), before applying the root to yield value.

RMS is a recognized abbreviation. Wattage ratings in RMS (which I will refer to as WRMS for brevity) continues to be a recognized CE standard. There is a great deal of semantic debate elsewhere whether this is an appropriate term. Regardless, it is an accurate description of the calculation method used.

The FTC procedure used to measure WRMS involved preconditioning an amp for 30 minutes so that it would be at its normal operating temperature.

This was a tough procedure that many amps could not pass to the satisfaction of manufacturers. So a number of companies got together to form the Institute for High Fidelity (IHF) and develop a competing standard. This standard was less strenuous because it was based on a 20 millisecond burst, the peak output of which was measured and expressed in watts.

I'm not aware of any specified preconditioning time associated with the IHF or peak standard. Since this can play both ways (depending on design),I suspect manufacturers use whatever preconditioning method yields the best figures. How this aligns with average use is anyone's guess.

With a continuous broadband signal, the resulting measurement is representative of the total power occurring under the curve. With a burst signal, it only reflects the power over a 20 millisecond duration. That's 1/50th of a second, folks.

To achieve a certain RMS rating, manufacturers must ensure that the power stage of the amp is continuously supplied. Large storage capacitors can be used, but they're unable of providing energy continuously.... they can discharge completely and this has an impact on their longevity. So a pretty robust transformer is needed. That's why manufacturers of such gear often list a current output rating. It's hard to achieve current delivery in the 30-60 amp range but well worth it because this is what allows amps to operate loudspeakers down to 4 ohms.

This is not the case with an amp rated using IHF or peak power. Manufacturers are, therefore, able to use smaller transformers and just enough capacitors to achieve a certain peak amplitude over 20/1000ths (or 1/50th) of a second.

Amps rated under the RMS system (and especially those rated in "all channels driven") are normally quite capable of driving difficult loads, such as occur when speaker capacitance drops to 4 ohms or below.

Amps rated under an IHF or peak power, even when rated "all channels driven", can't do this without clipping. Why? Because doing so would require outputs of up to 50 times longer than what they were designed for (20 ms --> 1000 ms).

To mitigate the risk of clipping, some manufacturers employ anti clipping circuitry to suppress power output. Others rate their amps for "two channels" driven, knowing full well that their transformers are incapable of delivering the rated power to all channels at the same time.

Now some may say that the 1970s were a long time ago. Let me assure you that cost/profit models haven't changed over 40 years. Good, robust transformers cost money to build and money to ship. AB amps capable of high continuous output need big heat sinks and cooling fins. These cost money to design, build, and ship.

The issues haven't changed either, despite what those selling cheap multichannel amps would like you to think. There are qualitative and quantitative differences between an amp capable of continuously providing "x" watts versus one that can deliver the same wattage for a fraction of that time.

If you want an independent way to check the truth, do the following:

1. Look up the manufacturer's figure for whatever power (in watts) your amp is rated to consume (I.e. Power from the wall socket);

2. For an AB amp, divide that figure by 2 (AB amps are slightly more efficient than 50%, but some power is required to drive the preamp, led/LCD displays, equalization circuits etc.)

3. Take the sum of #2 and divide it by the total number of channels of your amp. The result is the theoretical maximum continuous power output of your amp/channel. I say theoretical because the real continuous output is often less.

This is basic electrical theory. Amps don't generate power, they are net users of power as they convert electrical energy from one form into another. So continuous power going into the amp MUST be the same or greater than power leaving the amp.

All this means that a 2 channel AB amp rated to draw 1800W of power (15A, the max load of a standard socket in North America, @ 120V) cannot produce more than 450WRMS per channel.

A 5 channel AVR drawing the same power cannot produce more than 180WRMS/channel.

A 7 channel AVR drawing the same power cannot produce more than 128 WRMS/channel.

The actual ability of an AB amp to reach these levels is entirely dependent on its design. No heavy heat sinks or cooling fins/fans makes it impossible for the unit to shed the 215 calories of heat per second (which is what 900W of energy, or half the 1800W load equates to in heat) to prevent the amp's temperature from running out of control. In comparative terms, this is about the same heat generated as a hair dryer operating at a "medium" heat setting.

Now if your AB amp draws something more realistic like 1200W (or 10 amps @ 120V),then its theoretical maximum continuous power output and thermal load would be 1/3 less than the figures above (2 Ch: 300WRMS/channel, 5 Ch: 120WRMS/channel, 7 Ch: 85WRMS/channel).

This is a lot to take in... and I do apologise for the length of this post. Not everyone will agree with my conclusions. But it is basic electrical theory and simple math, along with historical references, which you can verify for yourselves.
 
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lovinthehd

lovinthehd

Seriously, I have no life.
That's true. :) I guess Gene's testing wasn't real world. :) His 97 wpc @ 8ohms...

Odd no one has done real world testing using a SPL meter. I have one. :)
SPL meter won't tell you a lot by itself.

ACD spec is only so useful. More indicative of power supply to the amps than a individual amp channel's capabilities.
 
M Code

M Code

Audioholic General
The FTC procedure used to measure WRMS involved preconditioning an amp for 30 minutes so that it would be at its normal operating temperature.

This was a tough procedure that many amps could not pass to the satisfaction of manufacturers. So a number of companies got together to form the Institute for High Fidelity (IHF) and develop a competing standard. This standard was less strenuous because it was based on a 20 millisecond burst, the peak output of which was measured and expressed in watts.

I'm not aware of any specified preconditioning time associated with the IHF or peak standard. Since this can play both ways (depending on design),I suspect manufacturers use whatever preconditioning method yields the best figures. How this aligns with average use is anyone's guess.

With a continuous broadband signal, the resulting measurement is representative of the total power occurring under the curve. With a burst signal, it only reflects the power over a 20 millisecond duration. That's 1/50th of a second, folks.

To achieve a certain RMS rating, manufacturers must ensure that the power stage of the amp is continuously supplied. Large storage capacitors can be used, but they're unable of providing energy continuously.... they can discharge completely and this has an impact on their longevity. So a pretty robust transformer is needed. That's why manufacturers of such gear often list a current output rating. It's hard to achieve current delivery in the 30-60 amp range but well worth it because this is what allows amps to operate loudspeakers down to 4 ohms.
Correction... The original FTC statute released in 73, required a 1 hour preconditioning not 30 minutes. This was a major stress issue for many receivers and amplifiers, so they went with some external cooling fan scheme. Later the FTC relaxed the 1 hour preconditioning term to be cumulative rather than continuous....

The preconditioning was run @ 35% of rated power output which severely stressed power supply loads and often this was the weaker circuit rather than the output stage... The later amplifier statue revised by the CEA did require some preconditioning but again it was greatly decreased from the original FTC 73 status.

Just my $0.02... ;)
 
highfigh

highfigh

Audioholic Overlord
I want these to be rated in Horsepower. The actual numbers won't be impressive unless the person who sees it knows what it means. :)

Oh, wait- people didn't know what any of the power ratings meant in the '70s, '80s, '90s,.......

"How many Amps does this put out?" was not an uncommon question.
 
highfigh

highfigh

Audioholic Overlord
The later amplifier statue revised by the CEA did require some preconditioning but again it was greatly decreased from the original FTC 73 status.

Just my $0.02... ;)
That would be 'statute', not 'statue'.
 
GrimSurfer

GrimSurfer

Senior Audioholic
The preconditioning was run @ 35% of rated power output which severely stressed power supply loads and often this was the weaker circuit rather than the output stage... The later amplifier statue revised by the CEA did require some preconditioning but again it was greatly decreased from the original FTC 73 status.

Just my $0.02... ;)
Preconditioning at a moderate power level helps keep an AB amp in Class A mode, which places greater thermal stress on the output stage.

I'd love to learn more about the relaxation of run-in procedures in the US and EU as part of RMS check preconditioning. Do you have any applicable links on this?
 
highfigh

highfigh

Audioholic Overlord
Preconditioning at a moderate power level helps keep an AB amp in Class A mode, which places greater thermal stress on the output stage.

I'd love to learn more about the relaxation of run-in procedures in the US and EU as part of RMS check preconditioning. Do you have any applicable links on this?
35% is not going to be ClassA- most amps hit ClassB far below that point. I think he was referring to 35% power, not bias level

Here you go- have at it.
https://www.crownaudio.com/listing-marks
 
GrimSurfer

GrimSurfer

Senior Audioholic
35% is not going to be ClassA- most amps hit ClassB far below that point. I think he was referring to 35% power, not bias level

Here you go- have at it.
https://www.crownaudio.com/listing-marks
Don't forget the FTC procedure was developed in the 70s. Amps put out a lot less power then, so they probably stayed in Class A longer... though your point is something I will look into further.
 
Swerd

Swerd

Audioholic Spartan
The OP's question shows his confusion over the different ways to rate amplifier power. I'm not surprised, he's not the only one confused by that.

When you are shopping for an amp or receiver it doesn't really matter just how the amplifier power ratings were performed, as long as all the models being compared were rated by the same method. The FTC method serves that purpose. All amps and receivers sold in the USA are required to publish those power ratings. That allows a consumer to compare apple-to-apples. It doesn't really matter if the amp or receiver has 2 channels or more, so long as the rating method is the same among all models.

I'm disappointed to see how many posts here avoided mentioning this obvious answer. Debating at great length over the merits of various different power rating methods doesn't address the OP's question. It may have driven him away. That disappoints me even more.
 
GrimSurfer

GrimSurfer

Senior Audioholic
The OP's question shows his confusion over the different ways to rate amplifier power. I'm not surprised, he's not the only one confused by that.

When you are shopping for an amp or receiver it doesn't really matter just how the amplifier power ratings were performed, as long as all the models being compared were rated by the same method. The FTC method serves that purpose. All amps and receivers sold in the USA are required to publish those power ratings. That allows a consumer to compare apple-to-apples. It doesn't really matter if the amp or receiver has 2 channels or more, so long as the rating method is the same among all models.

I'm disappointed to see how many posts here avoided mentioning this obvious answer. Debating at great length over the merits of various different power rating methods doesn't address the OP's question. It may have driven him away. That disappoints me even more.
It is important to note that FTC rules that came into effect in 2008 only require two channels to be rated. This is a problem in AVRs which, as you know, can have as many as nine (at last count).

You make a very good point about confusion, responsibility for which lies firmly at the feet of the audio industry (as outlined in the AH article below):

https://www.audioholics.com/audio-amplifier/ftc-consumer-audio

It's certainly a complex world. The answers to life's questions aren't always binary. In such cases, presenting more complete or nuanced info can be helpful. This is especially true when the audio industry appears to go out of its way to provide contradictory and often confusing info on product performance.

If the OP gets frightened by this, they can skip the techie bits and read them whenever they become more comfortable with (or receptive to) the concepts. But they did ask...
 
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highfigh

highfigh

Audioholic Overlord
Don't forget the FTC procedure was developed in the 70s. Amps put out a lot less power then, so they probably stayed in Class A longer... though your point is something I will look into further.
Some did- Phase Linear, Crown, Altec, Peavey, Mark Levinson, SAE, Soundcraftsman and lots of others made amps of various output power and they were often pretty darned good. The Peavey CS-800 amps we got at the music store where I worked came with a spec sheet from being tested, individually- it was a 400W/ch rated amp that usually did better than 460W/channel and they were pretty bulletproof. A lot of them from that vintage are still out there, too.
 
highfigh

highfigh

Audioholic Overlord
The OP's question shows his confusion over the different ways to rate amplifier power. I'm not surprised, he's not the only one confused by that.

When you are shopping for an amp or receiver it doesn't really matter just how the amplifier power ratings were performed, as long as all the models being compared were rated by the same method. The FTC method serves that purpose. All amps and receivers sold in the USA are required to publish those power ratings. That allows a consumer to compare apple-to-apples. It doesn't really matter if the amp or receiver has 2 channels or more, so long as the rating method is the same among all models.

I'm disappointed to see how many posts here avoided mentioning this obvious answer. Debating at great length over the merits of various different power rating methods doesn't address the OP's question. It may have driven him away. That disappoints me even more.
OK, but are the methods used now actually meaningful? Power @1KHz vs full bandwidth for a 2 channel amp that won't use a crossover- I'll go with the full bandwidth test.
 
GrimSurfer

GrimSurfer

Senior Audioholic
Some did- Phase Linear, Crown, Altec, Peavey, Mark Levinson, SAE, Soundcraftsman and lots of others made amps of various output power and they were often pretty darned good. The Peavey CS-800 amps we got at the music store where I worked came with a spec sheet from being tested, individually- it was a 400W/ch rated amp that usually did better than 460W/channel and they were pretty bulletproof. A lot of them from that vintage are still out there, too.
They were good!
 
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highfigh

highfigh

Audioholic Overlord
I don'
They were good!
I don't remember any of them that didn't beat spec by a wide margin. I had some Sony amps that did the same- one was spec'd at 30W/ch and they also had a 50W version- the 30W did 46W/ch and the 50W did 76W/ch, both channels driven to rated THD, 20Hz-20KHz. They had larger amps that performed similarly- I had an integrated amp that was rated for 100W/ch and when I had it tested, it did 176W/ch- it was one of the first amps with PWM power supply.
 
GrimSurfer

GrimSurfer

Senior Audioholic
I don'


I don't remember any of them that didn't beat spec by a wide margin. I had some Sony amps that did the same- one was spec'd at 30W/ch and they also had a 50W version- the 30W did 46W/ch and the 50W did 76W/ch, both channels driven to rated THD, 20Hz-20KHz. They had larger amps that performed similarly- I had an integrated amp that was rated for 100W/ch and when I had it tested, it did 176W/ch- it was one of the first amps with PWM power supply.
There are some amps that measure this way today, but none of them AFAIK come from a big box store. More often, their specs contain so many loopholes and qualifiers that it's impossible to feel cheated when they don't measure up.
 
highfigh

highfigh

Audioholic Overlord
There are some amps that measure this way today, but none of them AFAIK come from a big box store. More often, their specs contain so many loopholes and qualifiers that it's impossible to feel cheated when they don't measure up.
I really don't like the way Beast Buy states power output- they add all of the channels together, so a 9 channel AVR @ 130W/channel is shown as 1170W.
 
GrimSurfer

GrimSurfer

Senior Audioholic
I really don't like the way Beast Buy states power output- they add all of the channels together, so a 9 channel AVR @ 130W/channel is shown as 1170W.
It's misleading, particularly when very few people understand the difference between peak music power and Watts RMS.
 

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