| What happened to standards for advertised power? [message #75749] |
Fri, 08 March 2013 18:00  |
FloydV
Messages: 124
Registered: November 2011
Location: Boise, ID
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I first noticed with the advent of surround receivers and amps, that watts stated were listed into a certain load (ohms), and that the previous standard WATTS RMS had disappeared.
From Wikipedia:
Power handling
Amplifiers are valued in part by their power output capacity. And in the interest of being able to advertise a higher power output number, manufacturers in the US (and elsewhere) began to take advantage of the highly variable nature of most audio signals (especially musical sources) and to cite the peak output (quite brief and rarely sustainable for long) as the amplifier power. There being no standards, imaginative approaches came to be so common that the US Federal Trade Commission intervened in the market and required all amplifier manufacturers to use an engineering based measure (root-mean square) in addition to any other value they might cite.
In its 1974 Amplifier Rule meant to combat the unrealistic power claims made by many hi-fi amplifier manufacturers, the Federal Trade Commission prescribed continuous power measurements performed with sine wave signals on advertising and specification citations for amplifiers sold in the US. Typically, an amplifier's power specifications are calculated by measuring its RMS output voltage, with a continuous sine wave signal, at the onset of clipping--defined arbitrarily as a stated percentage of total harmonic distortion (THD)--into specified load resistances. Typical loads used are 8 and 4 ohms per channel; many amplifiers used in professional audio are also specified at 2 ohms.
Now most manufacturers state an unqualified number of watts for a surround receiver for one channel driven singly, and a much lower one when all channels are driven at the same load. The RMS qualification seems to have vanished, leaving a lot of room for exaggeration, and I wonder why.
Floyd
He who joyfully marches to music rank and file, has already earned my contempt. -- Albert Einstein
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| Re: What happened to standards for advertised power? [message #75753 is a reply to message #75750] |
Sat, 09 March 2013 00:30  |
FloydV
Messages: 124
Registered: November 2011
Location: Boise, ID
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Master |
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I'm glad someone agrees. It must be a lack of enforcement as you say. It seems that the FTC has become like the rest. If the companies have enough power in lobbies and so forth, things that should be enforced never get a second look.
It seems like any regulatory agency will look the other way if enough money is put into the hands of the right politicians.
He who joyfully marches to music rank and file, has already earned my contempt. -- Albert Einstein
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| Re: What happened to standards for advertised power? [message #75755 is a reply to message #75754] |
Sat, 09 March 2013 13:30 |
FloydV
Messages: 124
Registered: November 2011
Location: Boise, ID
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Master |
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I guess there has always been a group of people who don't understand what they are buying and who are easily gulled.
I know some of the people here like vinyl, but I was watching a short clip on the news showing manufacturers making vinyl discs that were half red and half green. When they showed a record playing, the cartridge was undulating like a boat at heavy sea. That is how poorly the disc had been pressed.
At the same time they had some person who could have been straight from the sixties saying "Yeah, man, the music is trapped in the vinyl!" I thought "And this is the guy who is holding up 6.1 surround." He probably bought a 5,000 watt amp to go with it.
He who joyfully marches to music rank and file, has already earned my contempt. -- Albert Einstein
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| Re: What happened to standards for advertised power? [message #75805 is a reply to message #75804] |
Thu, 14 March 2013 19:02 |
FloydV
Messages: 124
Registered: November 2011
Location: Boise, ID
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I see that you have a lineup of tubes under your post.
I was wondering lately: is it easier to build a high power amp from tubes or transistors?
Another question I had was this. By the time you go from digital recording to digital media, isn't it late in the game to use a tube amp if you think that amp will improve the sound?
Floyd
He who joyfully marches to music rank and file, has already earned my contempt. -- Albert Einstein
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| Re: What happened to standards for advertised power? [message #75814 is a reply to message #75807] |
Fri, 15 March 2013 12:44 |
FloydV
Messages: 124
Registered: November 2011
Location: Boise, ID
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| gofar99 wrote on Thu, 14 March 2013 22:08 | Hi, Yes I design things with tubes. Without getting into which is better tubes or SS, I will just state that they are different and I personally prefer the sound of tube audio. That all said... It is far easier to build powerful SS amps than tube ones. Also from a diy perspective a lot cheaper. Personally I have never found a need for more than 30-40 watts to drive any reasonable speaker system. So massive amounts of power are a non issue to me. My usual amps (as a designer and co-owner of an audio company I have many choices) are rated at 25 watts per channel. They drive my Martin Logan electrostatics quite well.
If you add a tube stage anywhere in a system it will introduce some "flavor" to the sound reproduction. The opposite is generally true if you add a SS stage to a tube system it will generally flavor it as well. Some designs for preamps with FETs are relatively benign. As you might guess there are no SS stages in my system with the exception of the power amps in a pair of sub woofers I am presently auditioning. They are set for response below 50 HZ and fortunately any artifacts they produce are largely innocuous. Normally I have more efficient subs and use tube amps on them.
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I was thinking that what you are saying about amps is true. First, that you don't need huge amounts of power, and second that SS would be easier to generate huge amounts of power.
If I recall, it takes a doubling of power for every db of increase in sound. I have heard that repeated many times, but it seems kind of overstated. It is difficult for me to hear an increase of 1 db, it generally takes 2 db for me to notice a real change.
I agree about the subs too. I keep seeing expensive SS ab amps for them. In my opinion, when you get to 80 db, you don't really need to spend that much.
Are Martin Logins electrostatic speakers? I'll be they sound nice when paired with subs.
He who joyfully marches to music rank and file, has already earned my contempt. -- Albert Einstein
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| Re: What happened to standards for advertised power? [message #75815 is a reply to message #75814] |
Fri, 15 March 2013 13:53 |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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Doubling power increases SPL 3dB. That is an audible increase, but most would say it's "just a nudge". To make it sound twice as loud to your ears, you would need a 10dB increase, which is also ten times the power. Twenty decibels is 100x power, and 30dB is 1000x power. So it's easy to get moderately loud, but the transients are surprisingly hard to hit without clipping.
When I was in school, I had a mentor that gave me a gag-gift for one of my birthdays. He glued a TTL chip to a the anode cap on top of a tube the size of a 2A3 and made a little plaque that said "microprocessor controlled tube". It was just a joke to us. Now days, every time I see a DAC with a tube output stage, I think of that gift.
All that said, tubes actually aren't just an old-fashioned throwback. They do some things better than transistors, which kind of surprised me. I can remember a lot of guitar players over the years saying how they liked tube amps better than solid state, and that tube watts were louder than transistor watts. I wrote it off to the gentler clipping of the tubes, and the presumption that they probably smoked a lot of pot too.
But really, after I actually studied it, I found that tubes run single ended are pretty linear devices, and so while they are more delicate and consumed more power, they could be used to make great little high-quality low and medium power amplifiers.
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Equally the 5.1 to 9.1 home theater systems with 100's of watts per channel. Usually with only one driven at a time. Like I only listen to one channel at a time. A good way to get a severely still neck. 
