Wattage output of a receiver -- cumulative? - AVS Forum
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post #1 of 19 Old 12-01-2012, 06:46 PM - Thread Starter
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Hi, I have an absolutely naive question to ask. I have a Denon 1613 receiver. It is rated at 75W per channel (5.1). If I am only running two speakers, does it still push out 75W to those speakers, or does it push out more since the other channels are not being used?

Obviously the true output is going to be less than 75W as reported, but for arguments sake, lets just say it's a true 75W per channel receiver.
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post #2 of 19 Old 12-01-2012, 07:02 PM
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Receivers are usually rated for 2 channels when they advertise so if it says 75w it's probably for 2 channels. When it goes to 5 channel or 7 channel is when it's going to drop to less than that.
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post #3 of 19 Old 12-02-2012, 10:29 AM
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I don't know if its still true, but Denon always used to have the reputation for delivering the spec wattage no matter how many channels were run. Unlike a lot of other companies. There were some AVRs that dropped big time when they switched from stereo to M/C.

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post #4 of 19 Old 12-02-2012, 10:55 AM
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When only running 2CH the actual output will generally be more than the marketed rating, with a wattage reduction as more channels are added. For example the 1913 is rated at 90W and has been bench tested as shown below ...

1913 (90W) – 2CH @ 102W, 5CH @ 70W, 7CH @ 52W

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post #5 of 19 Old 12-02-2012, 11:44 AM
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Some folks seem confused by this so I'll throw it out there in case it is helpful. Each channel of differntn content has, and must have, it's own separate amplifier inside the receiver. If you've ever fiddled with a guitar amp, you know you might be able to plug two guitars in the input and two speakers into the output, but both guitars will go into both speakers - - a single smplifier cannot send different signals to different places.

So you've got 7 amp units that are rated (likely any two at once, likely only at 1000 Hz) at 75 watts. What happens with receivers is the power supply that feeds all 7 amps lacks the wherewithal to keep all 7 fully "fed" if they are outputting full blast all at once. Luckily for most of us, the content we use doesn't call for all the channels to be full blast at once, and we may never actually notice ths "missing power"
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post #6 of 19 Old 12-03-2012, 03:07 AM
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Just look at the stated average power draw provided in the manual.
Practically all AVRs incl. the above mentioned Denons do have diminishing power output per channel for driving all channels at the same time depending on the built in power supply and the heat sink capacity of the unit.
If the max capacity of the power supply is known, its rather easy to calculate for common units. Up to 2 channel its the manufacturers rated power per channel x 2 + some small amount for the remaining electronics.
If more channels are been driven to its full capacity its usual: max power supply rating / 2 / number of channels for each channel plus some small amount for the rest of the electronics. This comes out to about 1/2 to 1/3 of the manufacturers stated 2-channel wattage / per channel, meaning, that 145 Watt / channel rms (2-channel mode) will end up somewhere around 70 Watt / channel rms in 7-channel mode and about 60 Watt / channel rms in 9-channel mode. Some will do this only for a few seconds, before some sort of limiter or circuit breaker within the unit will interrupt the power amps signal output for safety or temperature reasons.
On the average i would say that (at normal comfortable listening levels, not reference) the average power draw is somewhere around 100 - 140 Watt, depending on the unit you use.
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post #7 of 19 Old 12-03-2012, 03:12 AM
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IIRC, a Denon 3311CI (125W) owner used a Kill-O-Watt and posted that with no load the draw was about 80W and at reference volume (0db) about 95W.

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post #8 of 19 Old 12-03-2012, 03:23 AM
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Quote:
Originally Posted by jdsmoothie View Post

IIRC, a Denon 3311CI (125W) owner used a Kill-O-Watt and posted that with no load the draw was about 80W and at reference volume (0db) about 95W.

How could it be just 95 watts at reference volume or was it being used as a pre-pro?
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post #9 of 19 Old 12-03-2012, 03:30 AM
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Nope ... on board amps. Even at reference volume, most speakers only draw < 5W on average.

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post #10 of 19 Old 12-03-2012, 03:36 AM
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I disagree about how much "peak" ("average" is irrelevant if the amp is still called on to deliver its full power on peaks) power is used with "most" speakers. Highly efficient one's yes. Of course the Kill-O-Watt might not register short bursts of power. I've noticed you giving these ridiculously low power figures in other responses. I was able to easily drive a 90 watt/channel Yamaha receiver (DSP-A1) into clipping at comfortable levels so I take your figures with a grain of salt.
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post #11 of 19 Old 12-03-2012, 04:08 AM
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Speaker efficiency is really the relevant factor here. This might easily double stated values, unless you got some really efficient speakers by today's standards.
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post #12 of 19 Old 12-03-2012, 04:19 AM
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True. But speaker efficiency is greatly exaggerated by some companies. I know my center's mid-woofer is 86db/watt/meter and my L/R are 89db/watt/meter not counting the baffle step compensation that lowers efficiency even further. If one had speakers with 95db/watt/meter efficiency (or even sensitivity, which is different) then far less amplifier power would be needed, but I don't believe even Klipsch's claims for sensitivity/efficiency. Besides, I love the sound of my inefficient speakers. Back when I used the Yamaha DSP-A1 I was using 93db sensitive speakers and it still clipped while watching movies at a comfortable volume. I think that their impedence, being 4 ohms, may have had an affect on the not very beefy power amps of the Yamaha.

Since I DIY with speakers, I may change the configuration of my mains to two midwoofers a piece. This would theoretically boost sensitivity by 6db. That may be my next upgrade although with the 200 watts per midwoofer (at 8 ohms, 300 watts per for 4 ohms) that I currently have I do not experience audible clipping.
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post #13 of 19 Old 12-04-2012, 02:11 AM
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The problem with inefficient drivers is, that the driver can handle only that much power.
If the driver / design is inefficient you lose - more ore less - dynamic headroom, because the difference between supplied power and resultant loudness increases unfavorably, as the driver will only be able to handle electrical power to its specified maximum, reaching the limit much earlier than compared to an efficient design in terms of absolute loudness. Dynamic compression is another resultant problem, because excursion and power fed are no longer proportional at the extremes, which are reached much earlier.
Additionally the drivers and its surroundings are heating up more for the same loudness thus stressing the drivers more.
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post #14 of 19 Old 12-04-2012, 02:21 AM
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Yes, I know. But both the room and preferred listening level figure in too. I live in a small condo, although it is mostly one large room with a bedroom attached. I'm not looking for reference level with movies, my comfortable level is much lower than that. I'm not driving into clipping and the drivers are within their linear range. My midwoofers are rated at 8 hours at 80 watts at 80Hz and peak limits are rated at several hundred watts. What I value the most is clean, low distortion sound at reasonable (although loud to some) levels. I've never liked the sound of horns and other high efficiency designs and prefer the traditional cone and dome speakers to horns. If I were to replace my current speakers, which I quite like, it would probably be with 88db/watt/meter planars/ribbons (BG 50").
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post #15 of 19 Old 12-04-2012, 02:51 AM
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OT:
There is one more (theoretical ?) difference, which might affect the acoustical "resolution" for the drivers involved.
Because you need more power to get the driver (mechanically) moving, it might result in losing some lowest level signals (like whispers in the audience, breathing of the musicians, chairs and clothes moving around and all those other "little" noises etc.) because you have to go past a certain threshold level to get the driver moving. The lower the efficiency, the higher this threshold. Some high efficiency speakers like i.e. horns, will therefore show (sometimes) somewhat more "liveliness" or "ambiance" because of this.
/OT
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post #16 of 19 Old 12-04-2012, 03:49 AM
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The ScanSpeak drivers I use are considered some of the highest resolution one's available. They are very low distortion and don't compress as much as most. There are real advantages to horns especially for high spl but I don't like their sound especially for music. If I had a dedicated HT I would be tempted to try some of the new DIY horns as discussed in the DIY speaker forum but for now my living room serves for both movies and music. We should probably move this discussion to Speakers or some other category.
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post #17 of 19 Old 12-04-2012, 05:00 AM
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Quote:
Originally Posted by Theresa View Post

Quote:
Originally Posted by jdsmoothie View Post

IIRC, a Denon 3311CI (125W) owner used a Kill-O-Watt and posted that with no load the draw was about 80W and at reference volume (0db) about 95W.

How could it be just 95 watts at reference volume or was it being used as a pre-pro?

The Kill-A-watt measures the power going into an amplifier, and that power has its peaks heavily smoothed by the large capacitors in the amp's power supply.

Music has what is known as a high crest factor or peak-to-average ratio. It can be as high as 20 dB or more. This means that the peak power delivered to the speakers may be 100 watts at the same time the average power is only 1 watt. Usually its less extreme than that but it is also easy to observe the extremes, especially with unprocessed music.

Your speakers are claimed to excel at handling music with a high crest factor. So you should be very interested in crest factor.

http://en.wikipedia.org/wiki/Crest_factor

Power amplifier efficiency is itself highly variable depending on power level, ranging from less than about 30 percent to closer to 90 percent for a class AB power amp. Therefore estimating power delivered to the speakers based on a wattmeter measuring the that power line delivers to the power amplifier can be confusing and even misleading.
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post #18 of 19 Old 12-04-2012, 05:18 AM
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Quote:
Originally Posted by gcoulson View Post

Hi, I have an absolutely naive question to ask. I have a Denon 1613 receiver. It is rated at 75W per channel (5.1). If I am only running two speakers, does it still push out 75W to those speakers, or does it push out more since the other channels are not being used?

Neither.

Here's what actually happens - I have measured this many times.

The unused channels draw minimal amounts of current - usually just the bias current which is less than a tenth of an amp with most amplifiers. In comparison an amplifier channel running full tilt may draw over 10 amps.

The current drain of channels that are actually being used is highly dynamic, varying over a wide range from millisecond to millisecond.

Music has what is known as a high crest factor or peak to average ratio. The peaks are high and the average is often far lower.

http://en.wikipedia.org/wiki/Crest_factor

IOW music's peak values can be very high while the average values are very low. Some of this happens because different notes are being played with different loudness all along, and some of this happens simply because music is not composed of pure tones. Most musical sounds have a characteristic envelope with an attack, a peak, and a decay. But musical sounds will have a high crest factor even if they are played steadily. For example if a musician plays a steady note, there is still a high crest factor because in general musical sounds are not pure tones. One reason might be that they are chords, composed of multiple notes played at the same time. Even if a single note is being played on a single instrument, the crest factor is still high because the note is composed of both a fundamental and harmonics, often along with some tones that are not exactly pure harmonics.

To summarize, music has a high crest factor because:

(1) Different notes are being played with different loudnesses at different times. if you look at a music waveforms they are sprinkled with peaks and even short periods of silence.
(2) Musical sounds have acharacteristic envelopes with an attack, a peak, and a decay. The peak is high but in particular the decay may have very low energy. Classic examples: A piano note or a drum beat.
(3) In general musical sounds are not pure tones and only pure tones have high average energy. The laws of physics assert themselves!
(4) Musical sounds may not be pure tones because they are chords which are multiple notes being played at the same time.
(5) Musical sounds may not be pure tones because musical instruments generally make single note sounds that all by themselves aren't pure tones, but usually have a lot of harmonics and even non-harmonic components.

One consequence of all this is the fact that bench tests with pure tones, which are used to characterize the amplifiers in receivers etc., are very misleading since we use them to amplify music. Pure tones such as are used in bench tests have a very low crest factor but music generally has a very high crest factor (100:1 is not unusual).

I have recently seem some papers by some very smart people that I generally respect that completely ignore the effects of the high crest factor of music. Yet I'm sure they know about the crest factor of music, they just haven't put it togoether.
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post #19 of 19 Old 12-04-2012, 05:22 AM
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Quote:
Originally Posted by arnyk View Post

The Kill-A-watt measures the power going into an amplifier, and that power has its peaks heavily smoothed by the large capacitors in the amp's power supply.
Music has what is known as a high crest factor or peak-to-average ratio. It can be as high as 20 dB or more. This means that the peak power delivered to the speakers may be 100 watts at the same time the average power is only 1 watt. Usually its less extreme than that but it is also easy to observe the extremes, especially with unprocessed music.
Your speakers are claimed to excel at handling music with a high crest factor. So you should be very interested in crest factor.
http://en.wikipedia.org/wiki/Crest_factor
Power amplifier efficiency is itself highly variable depending on power level, ranging from less than about 30 percent to closer to 90 percent for a class AB power amp. Therefore estimating power delivered to the speakers based on a wattmeter measuring the that power line delivers to the power amplifier can be confusing and even misleading.

Yes, I know a little about crest factor. Its one of the reasons I have so much amplifier power, so that the peaks are reproduced without clipping even though the average power is often one watt. Glad to hear from another source that my drivers handle it well. Movies demand much higher average power in my experience but the subs are using most of that power. I think I'll get a Kill-A-Watt to measure the power draw of my system's amps. My electrical bill is quite high.
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