Why so much Power? - AVS Forum
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post #1 of 32 Old 01-14-2008, 12:25 PM - Thread Starter
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I Have a 1990's possibly early 2000's "130 watt" Kenwood 103AR 2-channel receiver and you have to crank it up to at eat volume 20 to get any of my speakers to even really "wake-up" while My vintage superscope receiver "wakes them up" wth less cranking than the kenwood! Could the wattage rating on the kenwood be fake?

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post #2 of 32 Old 01-14-2008, 12:40 PM
 
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I have run across similar discrepancies. For example a 50 watt/ch Onkyo that sounded way more powerful than a 100 watt/ch Sony.
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post #3 of 32 Old 01-14-2008, 02:34 PM
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Why in 2007 do we still have people who think the position of the volume indicator has anything to do with the amp power output?
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post #4 of 32 Old 01-14-2008, 03:01 PM
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Quote:
Originally Posted by Raymond Leggs View Post

I Have a 1990's possibly early 2000's "130 watt" Kenwood 103AR 2-channel receiver and you have to crank it up to at eat volume 20 to get any of my speakers to even really "wake-up" while My vintage superscope receiver "wakes them up" wth less cranking than the kenwood! Could the wattage rating on the kenwood be fake?


Designers can put the maximum volume at any point on the dial (or display).

You really can't compare two pieces of audio equipment by how much the volume contol is rotated. A better way would be to get a Radio Shack SPL meter and some test tones and determine where, for example, 85db is reached on each.
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post #5 of 32 Old 01-14-2008, 03:25 PM
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This is a subject that has been discussed here many times. It seems that only a few companies are completely objective when rating their receivers.

AFAIK the companies that have receivers in the market and follow the FCT power requirements are NAD, Rotel and H/K, but I'm not sure. The main FTC requirement states the amps or receivers should show the minimum RMS power output per channel when ALL chanels are being driven.

Denon, Sony, Marantz, Onkyo and Yamaha usually rate the receivers when only two speakers are driven at the same time.

The volume level display (in dB) is different for every brand, so there's no point in trying to compare different receivers based on this figure.
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post #6 of 32 Old 01-15-2008, 04:55 PM
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Yeah, there's quite a bit of "bad math" out there in the specs.

My Yamaha RX-V1800 says (in the specs):

Quote:


Minimum RMS Power Output for Front, Center, Surround, Surround Back... 130W

7 channels x 130 W = 910W, but they don't make the "all channels driven" claim.

Later on in the specs, it lists 500W as the power consumption for US models and 1100W as the maximum power consumption for the "General" model (whatever that is).

If we were to assume that the amplifiers are 60% efficient (and this might be overly generous), it would take over 1500 watts of input power to produce the 910 watts of output.

To the casual observer, it might seem that 500 watts of power from the AC mains can produce 910 watts of power to the speakers. If this were true, I'd buy a rack of them and power my house off the excess.

As far as I know, the receiver contains 7 identical amplifiers. The power that doesn't go into amplification is dissipated mostly as heat, and the receiver does get quite hot. I could probably assume pretty safely that any individual amplifier is capable of the 130 watt specification, but in tandem, the power supply cannot handle all 7 amps running 130 watts at the same time. And even if it could, the chassis isn't designed to handle the heat that would be generated.

So... inflated numbers and a compromise. The important thing is that it will drive the speakers without distortion and at a level that works with a bit of headroom to spare. I don't imagine commercial/pro amps are spec'd in the same way.
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post #7 of 32 Old 01-15-2008, 05:02 PM
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One thing is certain. The back panel ratings don't mean squat in comparing different models and brands of gear.

The service manual for one of my amps lists FOUR different power consumption specs for the same amp depending on the intended market region.

The back panel rating is generally NOT listed at maximum output for USA models.

To the point though, the position of the volume control means nothing with respect to output power when comparing different amps/receivers.

Just because there is a knob doesn't mean you should turn it.
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post #8 of 32 Old 01-15-2008, 06:25 PM - Thread Starter
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Quote:
Originally Posted by whoaru99 View Post

One thing is certain. The back panel ratings don't mean squat in comparing different models and brands of gear.

The service manual for one of my amps lists FOUR different power consumption specs for the same amp depending on the intended market region.

The back panel rating is generally NOT listed at maximum output for USA models.

To the point though, the position of the volume control means nothing with respect to output power when comparing different amps/receivers.

Looks like my question has been answered.

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post #9 of 32 Old 01-16-2008, 06:47 AM
 
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Quote:
Originally Posted by petergaryr View Post

Designers can put the maximum volume at any point on the dial (or display).

That makes no sense at all. If the maximum volume is reached before the dial has been turned all the way clockwise, then turning it beyond that point would surely fry the amp!
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post #10 of 32 Old 01-16-2008, 07:11 AM
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Quote:
Originally Posted by PULLIAMM View Post

That makes no sense at all. If the maximum volume is reached before the dial has been turned all the way clockwise, then turning it beyond that point would surely fry the amp!

Back before digital displays with their ambiguous "-20" type readouts, some manufacturers would set the taper on the volume controls so that by the 10 O'Clock position the volume would be very loud.

This would give the illusion that you had a real "powerhouse". Therefore, if someone were comparing that unit to one whose taper was set higher, say the 12 O'Clock position, it would appear that the first unit was more capable.

Some people wouldn't venture beyond that 10 O'Clock point for fear of blowing the speakers. The daring ones, however, would and then discover that there really wasn't much reserve left after that. You can tell the practice continues to this day.

As an aside, I always found the units with the longer taper easier to use because there was more opportunity for fine adjustement. The "10 O'Clock" ones went from loud to very loud very quickly.
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post #11 of 32 Old 01-16-2008, 03:42 PM - Thread Starter
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Quote:
Originally Posted by PULLIAMM View Post

That makes no sense at all. If the maximum volume is reached before the dial has been turned all the way clockwise, then turning it beyond that point would surely fry the amp!

That's why the Numbers on the display stop at 75 even if you keep turning the knob.

And as for the other user who quoted PULLIAM's post I was comparing a modern receiver to a vintage receiver so your post would be somewhat relevent.

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post #12 of 32 Old 01-17-2008, 10:43 AM
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Quote:
Originally Posted by PULLIAMM View Post

That makes no sense at all. If the maximum volume is reached before the dial has been turned all the way clockwise, then turning it beyond that point would surely fry the amp!

The knob sets gain not output power.

Assume an amplifer capable of delivering 40 volts peak which is good for sine waves at 100W RMS into an 8 Ohm load (peak magnitude of a sine wave is 1.414 times its RMS value; so this allows for a 28.28V RMS value. Power = V^2/R, so you get 800/8 = 100W into an 8 Ohm load).

Assume a CD player which puts out 2V peak at the loudest possible digital signal. Multiplying the signal by 20 (26dB of gain which is 20 log 20) is enough to get full output at 40V peak when CDs are recorded as loud as possible.

Assume a CD which was recorded at -6dBFS so the peaks are only 1V. To get 100W out of the amplifier its signal must be multiplied by 40 (32dB of gain).

If the maximum position on the volume knob was for 26dB of gain, you could only get 25W out of the system if you used that CD so the receiver is made with more gain.

Obviously, applying 32dB of gain to a 2V peak signal would be trying for 80V peak or 400W RMS which is not possible. Any part of the signal with magnitude greater than 40V gets truncated and you have distortion. This doesn't hurt the amplifier, it just doesn't output a peak voltage higher than 40V.

Since the musical power spectrum favors low frequencies, they clip first. Turning the volume knob up furthur can't increase the bass power. Turning the volume knob up past clipping does increase the volume of the high frequencies. And since the speakers were only built to accomodate musical signals with less high frequency output this can be enough to melt tweeter voice coils.

Stop turning the volume up after you hear distortion and you won't have problems. Not drinking too much makes that unlikely to happen accidentally.
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post #13 of 32 Old 01-23-2008, 10:04 AM
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Quote:
Originally Posted by PULLIAMM View Post

That makes no sense at all. If the maximum volume is reached before the dial has been turned all the way clockwise, then turning it beyond that point would surely fry the amp!

All the volume control does is attenuate (cut) the input signal. At zero, it is fully attenuating the input signal. As you turn the volume control up, its attenuating effect becomes less and less. At some point in its range of rotation its attenuating effect will be nil and it will be letting all of the signal through. If you have a source that has a low output level that's where you need the range of the volume control where its attenuating effect is less, and you find yourself turning it beyond the 12 o'clock position for example. The degree of attenuation throughout its range of rotation varies from one volume control potentiometer to the next and is called the TAPER. Think of a water faucet. When water pressure is very high, a slight turn of the faucet handle causes a lot of water to flow. When water pressure is low, you need to turn the handle more to get the same amount of flow. The volume control on the amp works just like that faucet.

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post #14 of 32 Old 03-03-2008, 03:03 PM
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Hi

One has to remember that music is really the sum of many sine wave functions which results in large peaks and valleys of output voltage vs time. The average power consumed with a typical music signal without clipping is something less than 1/5 of the power consumed by a single pure sine wave, for full range audio. Of course this differs a bit with the type of music, say highly compressed heavy rock vs classical, but generally with a music signal, one doesn't get much more than 20W of real continuous power from a 100W labeled amp before the large transients are clipped. A singe sine or square wave is a different story. For this reason, IMO, a little extra headroom is a good thing.
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post #15 of 32 Old 03-04-2008, 06:57 AM
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Quote:
Originally Posted by Proto-amp View Post

Hi

One has to remember that music is really the sum of many sine wave functions which results in large peaks and valleys of output voltage vs time. The average power consumed with a typical music signal without clipping is something less than 1/5 of the power consumed by a single pure sine wave, for full range audio. Of course this differs a bit with the type of music, say highly compressed heavy rock vs classical, but generally with a music signal, one doesn't get much more than 20W of real continuous power from a 100W labeled amp before the large transients are clipped. A singe sine or square wave is a different story. For this reason, IMO, a little extra headroom is a good thing.

Agreed. During a local "DIY Audio" get together a couple years ago, some members had a multimeter hooked up to the amplifier output while we were listening to music. We were listening at a moderate level that was easy to talk over without shouting. This was a listening level that many would exceed during normal listening. We were seeing peaks of 28 volts at the output, which is right around 100 watts with an 8 ohm load. This powerful amp was right at the edge of clipping during a very normal listening session. I don't remember what speakers we were using at the time, but they weren't anything with a ridiculously low sensitivity. Having an amp that's got a sufficiently high rail voltage and a power supply that's capable of maintaining that voltage during high demand can have a significant impact on sound quality... certainly much more than anything that would impact the sound of amplifiers that are being driven below clipping.
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post #16 of 32 Old 03-04-2008, 08:01 AM
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Quote:
Originally Posted by PULLIAMM View Post

I have run across similar discrepancies. For example a 50 watt/ch Onkyo that sounded way more powerful than a 100 watt/ch Sony.

What is the sound of "more powerful?"
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post #17 of 32 Old 03-04-2008, 11:05 AM
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Quote:
Originally Posted by FMW View Post

What is the sound of "more powerful?"

The sound of not clipping.
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post #18 of 32 Old 03-04-2008, 04:19 PM
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Quote:
Originally Posted by Jim85IROC View Post

The sound of not clipping.

The sound of which, IMO, isn't obvious to many until it gets to a fairly high amount.

Just because there is a knob doesn't mean you should turn it.
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post #19 of 32 Old 03-04-2008, 06:10 PM
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Quote:
Originally Posted by whoaru99 View Post

The sound of which, IMO, isn't obvious to many until it gets to a fairly high amount.

This too depends on SS or Tubes...sorry FMW, I couldn't resist !!
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post #20 of 32 Old 03-04-2008, 06:18 PM
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I agree there is a difference, but even with SS, many cannot readily ID low levels of clipping.

Just because there is a knob doesn't mean you should turn it.
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post #21 of 32 Old 03-05-2008, 04:43 AM
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Quote:
Originally Posted by twitch54 View Post

This too depends on SS or Tubes...sorry FMW, I couldn't resist !!

I agree with you, actually. Tubes tend to go into clipping more "elegantly" than solid state which goes into clipping more "digitally." Tubes seem to work their way into it while SS seems to fall into it. I'm sure there is a scientific term for that but I don't know what it is. Personally, I love the warm glow of power tubes across the room from me. I don't use them any more for practical reasons but I do like them. My audio days go back to the pre solid state era.

I'm surprised by some of the responses. Clipping isn't the least bit hard to recognize. It is obvious and awful. Anyone who has heard a guitar amplifer in "distortion" mode knows what it sounds like. They used to produce that sound in the old days by clipping the amplifier. These days it is just another form of digital signal processing.
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post #22 of 32 Old 03-05-2008, 04:45 AM
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Quote:
Originally Posted by whoaru99 View Post

I agree there is a difference, but even with SS, many cannot readily ID low levels of clipping.

Like anything, some things are measurable that aren't audible. I don't know at what level I hear clipping but it is certainly easy to hear when it is audible.
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post #23 of 32 Old 03-05-2008, 07:07 AM
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Quote:
Originally Posted by whoaru99 View Post

I agree there is a difference, but even with SS, many cannot readily ID low levels of clipping.

I agree, unless you A-B it. With mild clipping it just gets a tad harsh, or "bright". It's a sound that most people would just describe as "loud". If you listen at the same level with an unclipped signal, it doesn't sound as loud, but you're not likely to notice the difference otherwise. However, with an A/B, it becomes pretty easy to point out the difference in sound. Unfortunately, when I've done this type of A/B testing, I didn't have the luxury of being able to hook up a scope just to be able to see how badly the signals were clipped.
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post #24 of 32 Old 03-05-2008, 09:20 AM
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Quote:
Originally Posted by Jim85IROC View Post

Agreed. During a local "DIY Audio" get together a couple years ago, some members had a multimeter hooked up to the amplifier output while we were listening to music. We were listening at a moderate level that was easy to talk over without shouting. This was a listening level that many would exceed during normal listening. We were seeing peaks of 28 volts at the output, which is right around 100 watts with an 8 ohm load. This powerful amp was right at the edge of clipping during a very normal listening session. I don't remember what speakers we were using at the time, but they weren't anything with a ridiculously low sensitivity. Having an amp that's got a sufficiently high rail voltage and a power supply that's capable of maintaining that voltage during high demand can have a significant impact on sound quality... certainly much more than anything that would impact the sound of amplifiers that are being driven below clipping.

Were you listening using a sub or not?

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post #25 of 32 Old 03-05-2008, 12:29 PM
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Quote:


I don't know at what level I hear clipping but it is certainly easy to hear when it is audible.

Can't argue with that...

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post #26 of 32 Old 03-05-2008, 07:50 PM
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Originally Posted by Jack Gilvey View Post

Can't argue with that...

Took the words right out of my mouth.

Just because there is a knob doesn't mean you should turn it.
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post #27 of 32 Old 03-06-2008, 07:12 AM
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Quote:
Originally Posted by Chu Gai View Post

Were you listening using a sub or not?

No. That obviously would have freed up a lot of power. But since plenty of music listeners use full range 2-way main speakers for their playback, this remains a very relevant example.
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post #28 of 32 Old 03-06-2008, 01:12 PM
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Perhaps all the more reason to consider 2.1 don't you think?

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post #29 of 32 Old 03-10-2008, 07:53 AM
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Perhaps, but a 2.1 setup can result in a whole new set of problems.
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post #30 of 32 Old 03-10-2008, 09:49 AM
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anyone know why manuf'rs got away from using 'rms' for wattage ratings?
i always had confidence in that rating, 'specially if '20hz-20khz or even @1khz was used.
it seems like anything else can be b.s.
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