Receiver's power for just one speaker - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 22 Old 06-12-2018, 12:28 PM - Thread Starter
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Receiver's power for just one speaker

Will a receiver utilize/concentrate all its watts/power/resources to one channel, if one connects just one speaker to it? Will it use all it's power on the one channel or channels in use or will it still just use a certain limited amount like it would've if all channels were being in use? Any help will be appreciated.
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post #2 of 22 Old 06-12-2018, 12:33 PM
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Somewhat.

Receivers have lots of limits on their amp sections, even more than power amps (which still have multiple limitations).

They have voltage limits, based on the design voltage of the power supply. Most amps/receivers use a specified voltage. Some amps do use constant-current supplies rather than constant-voltage, but those aren't nearly as common. This won't change with number of channels driven,

They have current limits per channel, based on the transistors used and the cooling system. The number of driven channels won't change how the transistors work, but for amps that are poorly cooled, you might get a per-channel power boost in using fewer channels due to the same amount of cooling capabilities being spread out over few channels.

They have total power limits based on the power supply, and in receivers the power supply is often shared for all channels. And is often the weak link. If your receiver has a power supply that can do 500 continuous watts, then that is all you have to work with, and if your receiver's actual amps themselves are rated for more than their "even share" of the power supply, then using fewer channels would indeed leave more of the power supply capacity to give you more power on fewer channels.

Power amps work the same, except that they usually have larger power supplies and sometimes the power supplies are separate per channel. You wouldn't see any benefit from using fewer channels in these amps, unless you were hitting the thermal capacity with all channels driven.

For most receivers, the "Rated power" is only with 1 or 2 channels driven, by the way. So if anything, expect to see LESS power with all channels driven, rather than more-than-rated when only driving stereo. Power amps are more typically rated for all channels, though there are certainly power amps on the market with BS specs as well.

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post #3 of 22 Old 06-12-2018, 12:50 PM
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Quote:
Originally Posted by Jeffamy15 View Post
Will a receiver utilize/concentrate all its watts/power/resources to one channel, if one connects just one speaker to it? Will it use all it's power on the one channel or channels in use or will it still just use a certain limited amount like it would've if all channels were being in use? Any help will be appreciated.
As noted above, the power goes down to each speaker as you add more speakers.
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post #4 of 22 Old 06-12-2018, 12:55 PM - Thread Starter
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Thanks for the very informative and fast replies, guys. Is there a way of measuring it to see if it's actually getting a boost or not, regardless of how small it might be?
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post #5 of 22 Old 06-12-2018, 01:03 PM
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There is a limited benefit to reducing the number of speakers attached to an amplifier. For example, many receivers have a total power limitation associated with the common power supply. If you use a 5.1 speaker set with a 7.1 receiver, or a 5.1/7.1 speaker set with a 9.1/9.2 receiver, and set the missing speakers to "None" in the setup menu, you will free up some extra power supply capacity for the remaining speakers. This in turn will allow slightly higher peak volumes in a home theater setup, before the individual amplifiers start clipping.

The benefit can be measured, but is not large, however some people can distinguish it in double-blind listening tests.
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post #6 of 22 Old 06-12-2018, 01:04 PM - Thread Starter
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I had everything connected to one receiver, now I have changed it, and I'm using 4 receivers, 2 for 4 subs and 2 for loud speakers (which I haven't finish setting them up). I noticed the sound is more clear since I have changed it, the bass is not as rumbling as it used to, but is more precise and clear, and that might be because of now each pair being wired in series (separately), with each pair having their own receiver, and not all 4 in series/parallel into one receiver only.
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post #7 of 22 Old 06-12-2018, 01:06 PM
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Quote:
Originally Posted by Jeffamy15 View Post
Thanks for the very informative and fast replies, guys. Is there a way of measuring it to see if it's actually getting a boost or not, regardless of how small it might be?
You can use a SPL meter (cheap ones under $50 do exist), but they won't measure distortion or tell you that you are clipping, so you'll have a margin of error in that you must stay within acceptable distortion using your own ears.

You can use a multimeter to measure voltage and current and multiply them to get power - or if you're using the same speakers, you can try to only measure voltage OR current and go only on that. You must do this with a signal that is easy to measure - a simple sine wave is generally fine. Use a frequency that is within your multimeter's rated frequency range for the voltage and current. You might find your meter is rated up to 100Hz, 1000Hz, 10000Hz, etc. Use a test tone at or below the meter's bandwidth, but still within the speaker's passband (don't use a 10Hz test tone on a bookshelf speaker). You still want to avoid distortion/clipping for accurate and meaningful results.

You can also use an oscilloscope (also with a sine wave test tone), which is probably my favorite method but oscilloscopes are physically larger, more expensive, and take more knowledge to use than a multimeter. But it will actually show you the waveform and you will see when it clips.

The common denominator here is that you need to make sure you avoid distortion (at the very least, clipping, but beyond clipping you also have THD and other types of distortion that go up with output power).
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post #8 of 22 Old 06-12-2018, 01:42 PM - Thread Starter
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Ok, thank you. I really appreciate the help. One last question. Would it make a difference when it comes to that, if it's set to stereo or surround?
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post #9 of 22 Old 06-12-2018, 01:45 PM
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Quote:
Originally Posted by Jeffamy15 View Post
Ok, thank you. I really appreciate the help. One last question. Would it make a difference when it comes to that, if it's set to stereo or surround?
Its settings will control how it downmixes or upmixes content, and bad settings might cause issues like not hearing dialogue (if you set your system to surround mode and set the receiver as if you have a center channel, but you don't actually have a center channel, it will try to send most of the dialogue to the non-existent center and you just won't hear it).

But as far as power goes, any channel that doesn't have a speaker plugged in is only going to use a very small amount of power for its built-in preamp stages. No power will run through its power/output stage if no speaker is connected. The preamp stage would use a couple watts per channel at most (for modern amps/receivers, it would probably be well under 1 watt per channel). It will be insignificant.

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post #10 of 22 Old 06-12-2018, 02:00 PM - Thread Starter
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Therefore, there will still be no difference when it comes to distributing its power, (to those two channels) if it was set to stereo, only how it will reproduce or mix the sound, other than sending a smaller amount to those not in use?
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post #11 of 22 Old 06-12-2018, 02:44 PM
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Quote:
Originally Posted by Jeffamy15 View Post
Therefore, there will still be no difference when it comes to distributing its power, (to those two channels) if it was set to stereo, only how it will reproduce or mix the sound, other than sending a smaller amount to those not in use?
I would call your quoted statement generally accurate except this part is rather confusing "other than sending a smaller amount to those not in use?"

Only speakers that are BOTH A) plugged in and B) actively being driven by the receiver use any significant amount of power. If a speaker is not plugged in OR if a speaker is not having any content sent to it by the receiver, that channel will use negligible power, but still more than zero, because each channel inside the receiver has an amp that is multiple stages. Each channel will have transistors that raise the voltage, transistors that raise the current, and transistors that drive the output (I've just named 3 types of stages but some amps have over 5 stages and the design can get pretty complex). The vast majority of power of a channel is used in the output stage (could also be called the power stage), and that only happens when a speaker is plugged in. When a speaker is not plugged in, the output stage is not drawing any power, but the preamp stages (preamp stage includes any stage that is NOT the output stage) draw a very small (negligible) amount of power, of generally less than watt per channel with modern equipment.

So if a speaker isn't being used, no power is being sent to it, but the receiver may still be using a very small amount of power internally.

If you disable those channels in the receiver's config, it might be smart enough to completely turn off power to those amp channels, which would solve that. But it's not a problem you should worry too much about because the preamp stages draw VERY little power.

Anyway, I intend for this to be my last reply on the topic. So in summary, use as many speakers as you want, or as few as you want, and just be aware that you should tell your receiver which speakers you do or don't have to make sure that it downmixes properly so you hear all of the content in whatever movie (or music or whatever) you watch. But your receiver will use its power as efficiently as it is capable automatically as long as you disconnect any speakers you don't want it to use.
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post #12 of 22 Old 06-12-2018, 03:58 PM - Thread Starter
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Thank you for your time, and the good explanations, Donoman. I understand everything.
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post #13 of 22 Old 06-12-2018, 04:51 PM
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What @DonoMan said. Note the quiescent power in the unused power amps is usually pretty small for AVRs, much less than that a larger external power amp might draw.

Generally IME you won't see much if any more power than the "two-channel" rating when driving just a single channel. Two channels does not usually max out the power supply and the amps themselves have only so much margin. The voltage output is limited by the power supply and does not go up as you decrease channels; rather, it reduces ("sags") less with fewer channels. So 100 W for two channels might go to 105~110 W or so with a single channel, down to 60 - 80 W/ch for all channels driven at max volume at the same time.

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post #14 of 22 Old 06-12-2018, 09:29 PM - Thread Starter
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Don, so in your experience, there's a disadvantage when using less channels?
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post #15 of 22 Old 06-13-2018, 07:55 AM
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Quote:
Originally Posted by Jeffamy15 View Post
Don, so in your experience, there's a disadvantage when using less channels?
No, not sure how you got that from my post. You are paying for channels you are not using, and technically there will be some wasted energy, but in practice there's no significant disadvantage. You can get more maximum sustained power if you use fewer channels, an advantage, but in practice chances are you won't notice a difference in sound driving one channel or five (or whatever).

If your original question was if you can get 5x the power by using only one channel of a five-channel amp, then the answer is "no".

HTH - Don
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post #16 of 22 Old 06-13-2018, 09:30 AM
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Plus most AVRs wont let you power just a single channel. You need at least the front L& R connected.

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post #17 of 22 Old 06-13-2018, 09:39 AM - Thread Starter
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Oh ok, yeah I misunderstood that, and thought there could be a disadvantage to it. And no, I wasn't expecting 5x the power but perhaps an increase in energy diverted towards that one subwoofer channel, only in use.
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post #18 of 22 Old 06-13-2018, 09:45 AM
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Subwoofer output is a preamp channel. Receiver's power has nothing to do with sub out. The amp in the sub itself is what matters.

Unless you have some old HTiB receiver with a passive sub. Common AVRs have dedicated preamp level sub out

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post #19 of 22 Old 06-13-2018, 09:47 AM - Thread Starter
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Afrogt, my Samsung, Lennox ln 70, and RCA rt2870, do. I have a pair of Toa PA 15" subwoofers/passive to the RCA's subwoofer channel (only them), and a pair of 12" acoustic audio subwoofers (also passive) into the lennox ln 70 subwoofer channel (also by themselves with that receiver). That's the reason I asked the original question.
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post #20 of 22 Old 06-13-2018, 10:54 AM
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Yeah, I know the RCA is a HTiB system. Not familiar with the others. Like I said most standalone AVR's don't have passive sub outputs, only Home Theater in a Box packaged systems do to my knowledge.

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post #21 of 22 Old 06-13-2018, 01:25 PM - Thread Starter
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Yeah, the samsung is a 7.1 and goes with a active subwoofer, not a passive one. But he powers any channel even if only one is connected. I asked, because I wanted to know if my subwoofers would benefit or have a greater output from the receivers, if they were how they are, each pair connected to the receiver by itself.
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post #22 of 22 Old 06-19-2018, 08:21 AM
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There are SPECS...which are based on Bench Tests using Dummy Loads with Exactly 4, 6 and/or 8-ohm PURE RESISTORS....and then there is REALITY.

An Amplifier is a CONSTANT VOLTAGE source....which means that when a Signal Generator at a fixed Voltage Level (RMS, Average) performs a Frequency Sweep on the Input, then the VOLTAGE OUTPUT on an Output Channel (or Channels) will also be a constant Voltage Level, although at a different Voltage [Po = Vo^2 * Z].

However, when the same Frequency Sweep is applied to a Dynamic Speaker (i.e. S-W or Woofer), then the amount of CURRENT sucked out of the Amp depends on the Impedance at each Frequency. The Highest Current (and hence most Power = I^2 * Z) is drawn in the 300-500 Hz region for most small Woofers [look for or MEASURE the Voice Coil DC Resistance = Re in the Specs] and perhaps 60-250 Hz region for Sub-Woofers, although it varies quite a bit with S-W Drivers varying from 8-in to over 18-in Diameter. Speaker Impedance is actually MUCH HIGHER in the vicinity of the -3 dB Roll-Off Freq and hence draws considerably LESS Current (and Power) to reproduce the Lowest Freqs. Also note that Amp Tests typically use a sustained sinewave signal....so we don't usually learn that the PEAK Power the Amp provides [which is what we SHOULD be worried about to avoid Clipping] is typically 10 dB HIGHER than the "Spec" number:
http://audiojudgement.com/speaker-im...urve-explained
https://www.avsforum.com/forum/89-sp...l#post53999617 [Typical 12-in Woofer]

Fortunately in most Music, Peak Power is also "typically" 10 dB higher than Average....so we can justify talking about AVERAGE SPL provided by a given Amp AVERAGE Power Rating...and perhaps IGNORE that pesky 3 dB AMPLIFIER HEADROOM "Fudge Factor" in fol. Room SPL Calculator:
https://geoffthegreygeek.com/calculator-amp-speaker-spl

Also bear in mind that Mid-Range and Tweeter Speakers are only lightly driven compared to Woofers & Sub-Woofers....AND frequently have an L-Pad Attenuator to reduce their SPL vs the Woofer's more efficient SPL. So only a SMALL FRACTION of the Musical Spectrum actually requires significant Current to be sucked out of the Amp....and it does NOT include those very LOUD, sustained Low Frequencies....but WILL include Drum Transients and also even louder CRASH, BANG, BOOM!!! special effects....where you would be hard pressed to KNOW whether your Amp went into Clipping or NOT.

If you could attach a DVM to your speakers output while playing LOUD Music....or even better a Real Time Spectrum Analyzer running on a PC, such as FREE TrueRTA or FREE REW (Room Equalization Wizard), then you would experience an AH-HA MOMENT....the AMP is usually NOT providing a very high AVERAGE Voltage....and the PEAKS are NO WHERE NEAR the Max PEAK Voltage that the Amp can supply. Your EARS will usually Overload long before your Amp.

Fol. series of posts provides specific info re. how LOUD your ears can tolerate before they no longer provide any musical enjoyment, depending on how long they are exposed to excessive Sound Levels:
https://www.avsforum.com/forum/90-re...l#post56361756
Note that Sub-Woofers are a special case, since human ears can tolerate MUCH higher SPL Levels (Euro Max Specs are 130 dBC to 145 dBC, depending on country).]

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