THE ALL CHANNELS DRIVEN FALLACY

[gene]

why would a company like Krell or Parasound underate their amps? A review on the A-52 found that it could put out over 170 Watts continuously into 2 channels at 8 ohms. Why not rate their amp at 170W/Ch? Same with the Krell?

Most amp companies are conservative with their 2CH power ratings as their amps will usually deliver more power than speced in that instance with one of the few exceptions being the Emotiva MPS-1 as I explained in my review.

The reason they adhere to or exceed their published spec for up to two channels driven, is because of the FTC mandate that regulates how stereo amplifiers are rated. These rules don't apply to multi-channel and, if I am not mistaken, they are working on establishing more realistic ones for that scenario. In any event, we will be working on our own multi-channel power tests in the future, you can be sure of that

The only thing I am not sure if you are 100% right is the 40% efficiency you assume. I thought it varies between different designs. It could be lower than 40%, as you had hinted, but it could also be higher than 50% in some rare cases, no?

Efficiency depends on several factors:

1) Amplifier topology
2) Power Supply topology
3) Losses in #2

Traditional Class A amps are only 25% efficient
Class AB is around 50%
Variants of Class AB such as Class G can be as high as 60-70%
Class D can be greater than 90%

These are, of course, best case scenarios without factoring in power supply losses, power factor, etc.

I think 40% is a very realistic # for traditional linear amp designs which we are discussing here.

 

[malvado78]

Amen.

(Had to add something to make this post more than 10 characters)

 

[Dan Banquer]

75 amps Instantaneous Current

Let's take a look at what 75 amps peak current means mathematically when it comes to power: The following numbers are derived from the good old formula for power which is the square of the current times the resistance.
For 8 ohms that equals 45,000 peak watts. If we divide by 5 we get 9,000 peak watts per channel.
For 4 ohms that equals 22,500 peak watts. If we divide by 5 we get 4,500 peak watts per channel.
For 2 ohms that equals 11,250 peak watts. If we divide by 5 we get 2,250 peak watts per channel.
After looking at those numbers does anyone think their unit has the headroom in voltage to actually do that?
Does anyone here possibly think that the voice coils of their speakers can actually handle that?
After looking at these numbers does anyone here think that this is at all applicable to home theater especially when the impedance of Home Theater speakers drop only to 4 ohms?
After looking at these numbers does anyone still think that instantaneous peak current spec is at all relevant?

 

[MacManNM]

Let's take a look at what 75 amps peak current means mathematically when it comes to power: The following numbers are derived from the good old formula for power which is the square of the current times the resistance.
For 8 ohms that equals 45,000 peak watts. If we divide by 5 we get 9,000 peak watts per channel.
For 4 ohms that equals 22,500 peak watts. If we divide by 5 we get 4,500 peak watts per channel.
For 2 ohms that equals 11,250 peak watts. If we divide by 5 we get 2,250 peak watts per channel.
After looking at those numbers does anyone think their unit has the headroom in voltage to actually do that?
Does anyone here possibly think that the voice coils of their speakers can actually handle that?
After looking at these numbers does anyone here think that this is at all applicable to home theater especially when the impedance of Home Theater speakers drop only to 4 ohms?
After looking at these numbers does anyone still think that instantaneous peak current spec is at all relevant?

Speakers can handle that.

 

[thxgoon]

Let's take a look at what 75 amps peak current means mathematically when it comes to power: The following numbers are derived from the good old formula for power which is the square of the current times the resistance.
For 8 ohms that equals 45,000 peak watts. If we divide by 5 we get 9,000 peak watts per channel.
For 4 ohms that equals 22,500 peak watts. If we divide by 5 we get 4,500 peak watts per channel.
For 2 ohms that equals 11,250 peak watts. If we divide by 5 we get 2,250 peak watts per channel.
After looking at those numbers does anyone think their unit has the headroom in voltage to actually do that?
Does anyone here possibly think that the voice coils of their speakers can actually handle that?
After looking at these numbers does anyone here think that this is at all applicable to home theater especially when the impedance of Home Theater speakers drop only to 4 ohms?
After looking at these numbers does anyone still think that instantaneous peak current spec is at all relevant?

That's interesting. I never looked at that before. Certainly seems absurd doesn't it. Occasionaly you'll run into speakers with impedence below 4 ohms. In fact most 4ohm speakers will dip well below that at certain frequencies, but still. I wonder where amp manufacturers come up with that number. Is that the theoretical current draw before the output transistors just explode?

 

[Dan Banquer]

All Channels Driven Controversy

"In fact most 4 ohm speakers will dip well below that at certain frequencies, but still. I wonder where amp manufacturers come up with that number. Is that the theoretical current draw before the output transistors just explode?"

Actually most don't dip much below 4 ohms at all.
If you note the impedance plots most speaker companies furnish or impedance plots done by reviewers you might see 3.5 ohms min these days, and that is typically for stereo not Home Theater. So How do they get this instantnaeous current spec?, Input a pulse to an amplifier for less than a millisecond into a 0.1ohm load. Know any speakers with a 0.1 ohm load?
Thanks for the question: I was begining to give up all hope of sanity.
d.b.

 

[thxgoon]

"In fact most 4 ohm speakers will dip well below that at certain frequencies, but still. I wonder where amp manufacturers come up with that number. Is that the theoretical current draw before the output transistors just explode?"

Actually most don't dip much below 4 ohms at all.
If you note the impedance plots most speaker companies furnish or impedance plots done by reviewers you might see 3.5 ohms min these days, and that is typically for stereo not Home Theater. So How do they get this instantnaeous current spec?, Input a pulse to an amplifier for less than a millisecond into a 0.1ohm load. Know any speakers with a 0.1 ohm load?
Thanks for the question: I was begining to give up all hope of sanity.
d.b.

Cool, that answers my question. That's sort of what I figured. So in reality this instant current spec really has no bearing on an amplifiers capability in any real world senario. Why do these companies do this to us? The people on this forum are probably some of the most educated in the industry and we're still all confused by it. Thanks for straightening it out.

 

[Dan Banquer]

The All Channels Driven Spec

This test/spec is left over from the 1970's and maybe into the early 80's when some speaker designers were not careful about the impedance of their crossover. This pretty much stopped by 1990. Now that we have readily available instrumentation this is really no longer an issue.
Hope this helps; and yes this is a useless spec. I still consider the only meaningful power spec to be watts rms into a given load.
d.b.
Thanks for your post: Finally someone is asking the right questions!

 

[macersl]

I can't help but to disagree with some member's statements about manufactures being honest about their ratings. Why wouldn't a consumer assume that the power rating was with all channels active? They list stats like 120w X 7 and total wattage number that adds up to sum of each channel if powered on its own. I feel this is misleading. We know the truth because we discuss it, study it, and test it independently. But for the average consumer they would walk away misinformed and without a clear picture of the output of the receiver. When car manufactures post horsepower ratings of their engines, they don't just add up that each individual cylinder will produce. They give the HP of the engine as a whole.

On a side note...this is the reason I decided to purchase a HK receiver. If they are honest (and I feel they are where others are not) about their power ratings, then I have more confidence in the other elements of the receiver.

 

[MDS]

I can't help but to disagree with some member's statements about manufactures being honest about their ratings. Why wouldn't a consumer assume that the power rating was with all channels active?

Why would a consumer 'assume' it is an all channels rating when the exact opposite is stated on the spec sheet? This is the crux of this silly argument. Everyone says 'yeah, I know it isn't all channels driven, but it SHOULD be, therefore they are lying'. If you don't know much about audio equipment in general or power ratings in particular, why would it matter to you if the rating were all channels driven? You wouldn't feel cheated, because you wouldn't know any better.

When car manufactures post horsepower ratings of their engines, they don't just add up that each individual cylinder will produce. They give the HP of the engine as a whole.

No, they sure don't. But using the same logic as the all channels driven controversey they are LYING. Some of them rate the horsepower at the crankshaft while some rate at the rear wheel. If you expect the rating to be bhp, but it was actually rated at the crankshaft you could say they are lying. But is it the car manufacturers fault that you read into something that was not stated? Nope.

 

[Buckeyefan 1]

Why would a consumer 'assume' it is an all channels rating when the exact opposite is stated on the spec sheet? This is the crux of this silly argument. Everyone says 'yeah, I know it isn't all channels driven, but it SHOULD be, therefore they are lying'. If you don't know much about audio equipment in general or power ratings in particular, why would it matter to you if the rating were all channels driven? You wouldn't feel cheated, because you wouldn't know any better.

We know. What percentage are we of all the A/V purchases annually? Go to the Best Buy HTIB section and see how they distinguish these systems. What is highlighted? The average joe doesn't have much to go on other than what the big box retailers are telling them.

No way in hell should they (BB) add watts per channel times number of channels, then add total subwoofer peak power output to attain this inflated b.s. figure. It's the worst case of misadvertising there is.

We know. But who are we? I can't tell you how many times I've answered and pm'd newbies who've already bought these systems, asking why their units are crapping out when jamming to their favorite cdr's.

They trust BB, and are being lied to. The employees also have no clue how to separate what is real and what is factual. It's all in print, and print is wrong.

Until the FTC corrects this - and makes big box retailers as responsible as manufacturers for hyped specs, people will go on spending big bucks on HTIB systems, or entry level receivers thinking they are getting some great deal.

Meanwile, for a tad more, they could have made a much better, informed decision and had a system that sounded 5x better than the junk they just purchased.

 

[frankf]

food for thought!

my dedicated home theater room is 25'long and 12'wide.i have a infocus7205 projector,comcast,sony777dvd player,toshiba 5disc dvd cd player,pioneer elite multi disc cd player, powered by a 100 watt per channel yamaha 3300 receiver.it sounds great! however after hearing a friends' similar set up being driven by OUTLAWS' 775 200 watt per channel amp with there 990 processor.....wow what a differance. power in a amplifier is not only used for loundness but for clarity and imaging. you will be hearing things that you have'nt heard before.

 

[mtrycrafts]

my dedicated home theater room is 25'long and 12'wide.i have a infocus7205 projector,comcast,sony777dvd player,toshiba 5disc dvd cd player,pioneer elite multi disc cd player, powered by a 100 watt per channel yamaha 3300 receiver.it sounds great! however after hearing a friends' similar set up being driven by OUTLAWS' 775 200 watt per channel amp with there 990 processor.....wow what a differance. power in a amplifier is not only used for loundness but for clarity and imaging. you will be hearing things that you have'nt heard before.

Yours sound great you say.
Your friend's impress you more because of the Outlaw amps he uses. How is his system similar? Certainly his room most likely is way different. Certainly the time elapsed between comparisons is way long and memory fades.

Power cannot give more clarity if neither amps are distorting, over driven, are flat in frequency response and certainly imaging is not an issue for an amp but room acoustics, speakers and the recording.

So, I am at a loss what you think you heard there.

 

[mtrycrafts]

.....bravo, your logic and reasoning applied make perfect sense.....

http://pg.photos.yahoo.com/ph/mulester77/detail?.dir=/47f8&.dnm=7bd5.jpg&.src=ph

Finally, something that impresses you

 

[mike c]

Peng

where do you get ratings like this peng? i cant find any for my rx-v 640 and the rx-v 1500 ; cant find it at htmag btw

"By 2 channel output into 8 ohms at 0.1% THD:
Denon (132.2W), Pioneer (121.2W), Yammie (102.9W), HK (84.6W)"

im only interested in 2 channel output (not this ALL channel stuff)

 

[Buckeyefan 1]

where do you get ratings like this peng? i cant find any for my rx-v 640 and the rx-v 1500 ; cant find it at htmag btw

"By 2 channel output into 8 ohms at 0.1% THD:
Denon (132.2W), Pioneer (121.2W), Yammie (102.9W), HK (84.6W)"

im only interested in 2 channel output (not this ALL channel stuff)

He's talking about the RX-V 2400, which is the model year before the 2500.

 

[mike c]

buck, yeah, but id like to see tests like this on the yam1500 and 640 so i can see the actual wattage churned out

btw, whats a buckeye?

 

[dponeill]

Yours sound great you say.
Your friend's impress you more because of the Outlaw amps he uses. How is his system similar? Certainly his room most likely is way different. Certainly the time elapsed between comparisons is way long and memory fades.

Power cannot give more clarity if neither amps are distorting, over driven, are flat in frequency response and certainly imaging is not an issue for an amp but room acoustics, speakers and the recording.

So, I am at a loss what you think you heard there.

That's the problem with these kind of "testimonials". They usually start out: "I listened to my freinds system (which is, of course, in a different room with different speakers and different front end components) and wow that more powerfull amp sure made it sound better than my system!".

 

[Buckeyefan 1]

btw, whats a buckeye?

Ouch! I'll cut you some slack since you're not from the U.S.

Does this help?

It's actually a seed from a Buckeye tree. Here's an explanation:

Why is the Buckeye associated with Ohio and with OSU?

Ohio is known as the "Buckeye State," the Ohio Buckeye is the official state tree, and Ohioans in general, but especially those associated with Ohio State University, are known as "buckeyes." The origin of this nickname, which dates from early pioneer days, is not completely known. Ohio may have become known as the Buckeye State simply because many large, economically important buckeye trees grew in the Ohio region at that time.

Another possibility was proposed by the pioneer historian S. P. Hildreth of Marietta, Ohio, who told how Col. Ebenezer Sproat, who held the first court of justice in the Northwest Territory at Marietta in September, 1788, was given the name "Big Buckeye" by admiring Indians. According to the story, the nickname became known far and wide and was eventually associated with all the settlers of the region.

Still another theory, and perhaps the most credible, is that the name caught on in 1840, after Gen. William Henry Harrison began using the buckeye as a campaign symbol in his presidential quest. During the campaign, hundreds of buckeye walking sticks and canes were distributed, and buckeye log cabins built on wagons as floats appeared in parades in many towns and villages. These, together with an accompanying song calling Ohio the "Bonnie Buckeye State," firmly established a link in many people's minds between the state and the tree. The Ohio Buckeye was popularly accepted as the State's symbol during the late 1800s and the first half of the twentieth century, but it was not formally adopted by the Ohio legislature as the State Tree until 1953, on the occasion of Ohio's 150th anniversary of statehood.

Today the Ohio Buckeye especially symbolizes Ohio State University, particularly with regard to intercollegiate athletics. But even at OSU the buckeye is a relatively new symbol. During the 1920s the buckeye gradually assumed an unofficial role as a school symbol through references in the news media. In 1930, a recent OSU graduate, Milton Caniff, who later became popular as the creator of a popular comic strip (Steve Canyon), designed and began to promote a logo consisting of a buckeye leaf and several fruits. He continued doing this until September, 1950, when the University accepted the logo as its official symbol. Today, this stylized buckeye emblem assumes a prominent place at the base of the University's seal.

 

[mike c]

oh. i sort of had an idea with all the other users here using NFL team names/avatars.
but we dont get football here, nobody likes it here (on tv) not like all the other sports that are shown on the many sports channels