Is it possible for an AVR to smartly re-allocate power to some channels?

[Snoopy8]

Lately, I have been advising people to ignore the marketing BS in the AVR power specifications and use the power consumption as a good proxy to compare the power of AVRs. Also, to calculate what it can really do when multiple channels are driven.

 

Some AVRs can re-allocate power to different channels. e.g.  not using surround back channels, use it for Atmos. But I am not aware of an AVR in home theatre market which can smartly allocate and boost power from unused channels e.g. for stereo music, boost front power using unused surround channel amps.

 

I assume it is done in pro audio. Can those ideas be incorporated in an AVR? Putting aside budget, what are the technical challenges?

[LHC]

I thought some earlier Arcam AVR can use their surround channels to combine with the main in two channel applications. Kind of like a bi-amp. 

[Snoopy8]

4 minutes ago, LHC said:

I thought some earlier Arcam AVR can use their surround channels to combine with the main in two channel applications. Kind of like a bi-amp. 

I remember reading about them but not sure current ones do it?  If anyone can smart re-allocate power, it will be Arcam.

[bmc]

I'm not sure what you mean by smart re-allocate power. 
 

The limiting factor is usually the amps power supply. Each channel draws what it needs from the power supply. If some channels are not operating that leaves more power supply capacity for those that are. 
 

All AVRs using a single power supply will produce significantly more power per channel into 2 channels than 5 or 7 or 9.

[Snoopy8]

6 minutes ago, bmc said:

All AVRs using a single power supply will produce significantly more power per channel into 2 channels than 5 or 7 or 9.

I don't think this is correct. 

 

Have a look at the power specs of any entry level AVR that claim that power is as good or better than Arcam's entry level AVR costing many times more. The power consumption is usually hidden in the manual and no multi channel power numbers are published (because it is small).

 

Arcam publishes their multi channel power numbers and 2 channel driven and power consumption which is very large.

 

More power delivered = more power consumption. Somehow, the entry level AVR can deliver as good or more power to the speakers and at same time consume less power?  And much cheapet to buy. Wow! A break through design? Or marketing BS?

 

I do not know how power amps are designed and how they allocate power techically. Hence this post.  If you know how they work technically, please correct my misconception.

 

P/s do not own Arcam gear

[bmc]

From Wikipedia:

 

"When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square-wave-type waveform.

Amplifiers have voltage, current and thermal limits. Clipping may occur due to limitations in the power supply or the output stage. Some amplifiers are able to deliver peak power without clipping for short durations before energy stored in the power supply is depleted or the amplifier begins to overheat."

 

With multichannel amps each channel draws what it needs form the power supply. When the total drawn by all the channels reaches the maximum capacity of the power supply you get clipping. There is no "allocation" of power.

 

Cheap AVRs will have an inexpensive power supply which may be able to run 2 channels to a decent level but will be unable to run all channels at that same level.

 

More expensive AVRs (Arcam) will have bigger power supply which will enable all channels to run at  a high power level simultaneously. They will produce even more power per channel if only running 2 channels (subject to output stage and thermal limitations).

 

Naturally cheap AVRs specs won't quote power with all channels driven as it will be a low figure. They might also quote power into 6 ohms instead of 8 ohms, at just 1kHz instead of 20-20kHz, and with high or unspecified distortion levels. Not exactly BS but not very informative.

 

You can use the max power consumption as a rough guide to the capacity of the AVR's power supply, keeping in mind that different amp classes have inherently different efficiencies (i.e class A/B 60-70% efficiency, class D over 90%) and hence different power supply requirements. 

 

 

 

 

Edited March 12, 2020 by bmc
typo

[cwt]

5 hours ago, Snoopy8 said:

Some AVRs can re-allocate power to different channels. e.g.  not using surround back channels, use it for Atmos. But I am not aware of an AVR in home theatre market which can smartly allocate and boost power from unused channels e.g. for stereo music, boost front power using unused surround channel amps.

 

I assume it is done in pro audio. Can those ideas be incorporated in an AVR? Putting aside budget, what are the technical challenges?

I think what your describing would be equivalent to paralleling the power amps as some [like Rotel] like to do Snoopy for certain needs like driving a passive subwoofer  . This in particular would be hard to manage in a confined area like an avr chassis and wouldn't be cheap[ as you say] as most avr's have single ended circuitry . Heres a description of the 3 methods of increasing output current vvv Push pull circuitry is hard to get right as the load is carried by the + part of the signal and- the other ; leads  must be close tolerance I believe -

Quote

 Unequal amplification of the two halves of the signal introduces more distortion.

 https://www.analog.com/en/technical-articles/paralleling-amplifiers-increases-output-drive.html

 

[surprisetech]

15 hours ago, Snoopy8 said:

I don't think this is correct. 

 

Have a look at the power specs of any entry level AVR that claim that power is as good or better than Arcam's entry level AVR costing many times more. The power consumption is usually hidden in the manual and no multi channel power numbers are published (because it is small).

 

Arcam publishes their multi channel power numbers and 2 channel driven and power consumption which is very large.

 

More power delivered = more power consumption. Somehow, the entry level AVR can deliver as good or more power to the speakers and at same time consume less power?  And much cheapet to buy. Wow! A break through design? Or marketing BS?

 

I do not know how power amps are designed and how they allocate power techically. Hence this post.  If you know how they work technically, please correct my misconception.

 

P/s do not own Arcam gear

It's marketing.

The more reputable folk give you Continuous RMS power ratings AND Dynamic power ratings for 2-Channel operation AND for all channels driven simultaneously AND for different speaker impedance values.

 

Other than using the product's overall power consumption figure, if you have all that info for two different products, then you can make a more meaningful comparison.

 

The others use various levels of omission &/or deception to make their specs look better &/or muddy the waters.

 

As bmc says, there is usually one power supply for the output stages that is capable of delivering a given amount of total power.

In many AVRs, that total power available from the PS is adequate to drive the front L/R amps to their limit (hopefully) and the rest of the amps to whatever the designer thinks is an adequate level for centre/surround duties.  If you try and drive those other channels harder, the extra current draw causes the rail voltages to drop, so the front L/R amps can no longer deliver their rated output either.

 

So in the absence of detailed specs, the product's overall power consumption will give a guide as to how much power the designer has actually allowed for in multi-channel duties.

If comparing Class A/B (50-70% efficiency) to Class D (~90% efficiency) you also need to allow for the significantly different efficiency.

https://www.audioholics.com/audio-amplifier/amplifier-classes    About 2/3 way down the page.

[Snoopy8]

11 hours ago, bmc said:

From Wikipedia:

 

"When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square-wave-type waveform.

Amplifiers have voltage, current and thermal limits. Clipping may occur due to limitations in the power supply or the output stage. Some amplifiers are able to deliver peak power without clipping for short durations before energy stored in the power supply is depleted or the amplifier begins to overheat."

 

With multichannel amps each channel draws what it needs form the power supply. When the total drawn by all the channels reaches the maximum capacity of the power supply you get clipping. There is no "allocation" of power.

 

Cheap AVRs will have an inexpensive power supply which may be able to run 2 channels to a decent level but will be unable to run all channels at that same level.

 

More expensive AVRs (Arcam) will have bigger power supply which will enable all channels to run at  a high power level simultaneously. They will produce even more power per channel if only running 2 channels (subject to output stage and thermal limitations).

 

Naturally cheap AVRs specs won't quote power with all channels driven as it will be a low figure. They might also quote power into 6 ohms instead of 8 ohms, at just 1kHz instead of 20-20kHz, and with high or unspecified distortion levels. Not exactly BS but not very informative.

 

You can use the max power consumption as a rough guide to the capacity of the AVR's power supply, keeping in mind that different amp classes have inherently different efficiencies (i.e class A/B 60-70% efficiency, class D over 90%) and hence different power supply requirements. 

Can you please provide the link to the wikipedia page.  I have not been able to find it.

 

I have bolded some of those statements. It says may be able to run 2 channels to a decent level/ but is not definitive.  The author was being kind saying not exactly BS.  If putting 1 channel numbers at 1 kHZ with high or no THD levels is not BS, what is?  It is designed to trick the uninformed.

 

I can imagine the best Class A/B amps can operate at 70% but I doubt that the cheap ones in AVRs can reach 60% efficiency.  There are not many AVRs with Class D amps.  I know the Anthem MRX 1120 uses Class D for surrounds.  The NAD 778 uses better Class D.

2 minutes ago, surprisetech said:

It's marketing.

The more reputable folk give you Continuous RMS power ratings AND Dynamic power ratings for 2-Channel operation AND for all channels driven simultaneously AND for different speaker impedance values.

 

Other than using the product's overall power consumption figure, if you have all that info for two different products, then you can make a more meaningful comparison.

 

The others use various levels of omission &/or deception to make their specs look better &/or muddy the waters.

 

As bmc says, there is usually one power supply for the output stages that is capable of delivering a given amount of total power.

In many AVRs, that total power available from the PS is adequate to drive the front L/R amps to their limit (hopefully) and the rest of the amps to whatever the designer thinks is an adequate level for centre/surround duties.  If you try and drive those other channels harder, the extra current draw causes the rail voltages to drop, so the front L/R amps can no longer deliver their rated output either.

 

So in the absence of detailed specs, the product's overall power consumption will give a guide as to how much power the designer has actually allowed for in multi-channel duties.

If comparing Class A/B (50-70% efficiency) to Class D (~90% efficiency) you also need to allow for the significantly different efficiency.

https://www.audioholics.com/audio-amplifier/amplifier-classes    About 2/3 way down the page.

Continuos RMS power and dynamic power are well known measures for stereo.  In the home theatre world, there are no standards, so individual companies come up with their own so-called power numbers.  Yes, Arcam is also marketing the numbers, but those are probably more honest than others. And feedback from owners suggest Arcam have heaps of power.

 

Are you and BMC certain that one power supply mean there is lots of power for 2 channels?  If so, why are these not used as power amps in the 2 channel world because they are cheap as for raw power?

----

Would be great if someone who understands the design of multi channel amps (I don't)  post their thoughts here.

[Lashes]

@Snoopy8 I’m enjoying tracking this thread.
 

After sharing your point of view in my other thread I’ve been doing some of my own research to try and find some more info on this topic.
 

Firstly I tried to find some independent bench tests of my own receiver but was unable to find my exact model in one of these tests. However I was able to find a bench test of something pretty close to mine. 
 

Here is the link to the power test https://www.soundandvision.com/content/test-report-yamaha-rx-a3000-av-receiver-page-4

This definitely seems to indicate that the more channels that are used the lower wattage outputs from the amplifiers. 
 

The article linked below was interesting, as well as the other suggested articles in the See Also section down the bottom. Kinda old but I doubt the science has changed. https://www.audioholics.com/audio-amplifier/product-managing-receiver-platforms-power-ratings
 

I’m definitely no avr designer but in my research it seems to suggest that the amp assigned for each channel might be capable of outputting the 150 watts (whatever the rating is). However, the channel amps can only output that amount if they can access the power needed from the power supply to do that.

 

In my personal situation my AVR power supply would not be able to provide enough power to see each channel amp operate at its maximum potential simultaneously. 
 

I hope I haven’t added white noise to this thread, I’m new at this.

Edited March 13, 2020 by Lashes

[LHC]

10 minutes ago, Lashes said:

I hope I haven’t added white noise to this thread, I’m new at this.

Not at all. You've done a good job researching the background and seeking evidence. Even if you managed to only confirm what others already know, IMO that is still well worth doing. 

[bmc]

Only the first paragraph in quotation marks is from Wikipedia.

 

https://en.wikipedia.org/wiki/Clipping_(audio)

 

I wrote the rest.

 

6 hours ago, Snoopy8 said:

It says may be able to run 2 channels to a decent level/ but is not definitive. 

I chose not to make a sweeping statement about an entire class of audio product.

 

6 hours ago, Snoopy8 said:

The author was being kind saying not exactly BS.  If putting 1 channel numbers at 1 kHZ with high or no THD levels is not BS, what is?  It is designed to trick the uninformed

To me BS is an outright lie. Figures quoted in this manner are not lies, but I agree they are designed to portray the product in a favourable light to influence the uninformed.

 

6 hours ago, Snoopy8 said:

I can imagine the best Class A/B amps can operate at 70% but I doubt that the cheap ones in AVRs can reach 60% efficiency.  There are not many AVRs with Class D amps.  I know the Anthem MRX 1120 uses Class D for surrounds.  The NAD 778 uses better Class D.

I'm not sure what your point is here.
 

Edited March 13, 2020 by bmc
Typo

[LHC]

12 minutes ago, bmc said:

To me BS is an outright lie. Figures quoted in this manner are not lies, but I agree they are designed to portray the product in a favourable light to influence the uninformed.

Granted what you said is correct. But if every company use the same practice, does it matter? By using the same approach the consumer can still compare AVR relative to each other, even though one can't know their true level of performance. 

[Snoopy8]

1 hour ago, bmc said:

Only the first paragraph in quotation marks is from Wikipedia.

 

https://en.wikipedia.org/wiki/Clipping_(audio)

 

I wrote the rest.

 

I chose not to make sweeping statement about any entire class of audio product.

 

To me BS is an outright lie. Figures quoted in this manner are not lies, but I agree they are designed to portray the product in a favourable light to influence the uninformed.

 

I'm not sure what your point is here.
 

Sorry, it looked like you were quoting everything from Wikipedia and I would have loved to learn from it.  On one hand, you say you are not making a sweeping statement but then proceed to give sweeping advice.  

 

We agree to disagree on the meaning of BS.  

 

I often get asked why I use a 50/60% efficiency figure for AVR amps and why can't AVRs be more efficient using Class D amps.  Then perhaps there is a less mismatch between claimed power for speakers and power consumption.  Very few AVRs use Class D amps and mentioning Class D amps in the context of AVRs can mislead.

 

As I said earlier, I welcome all contributions.  I do not claim I know everything,  If you have technical knowledge on how the AVRs distributes power or even provide examples when an AVR has driven a particularly inefficient speaker, please post. 

 

p/s I have nothing against AVRs (I have owned 3).  I have no vested interest in (nor grudge with) any audio company.  You can see what I currently own in my About Me.   

1 hour ago, Lashes said:

The article linked below was interesting, as well as the other suggested articles in the See Also section down the bottom. Kinda old but I doubt the science has changed. https://www.audioholics.com/audio-amplifier/product-managing-receiver-platforms-power-ratings

Thank you @Lashes . Yes, the audioholics article is still relevant. It is excellent at explaining how and why the companies are manipulating power numbers.  And yes, it is not clear what the power is for 2 channels driven, ** is when driving stereo, hence I am looking for someone with more technical knowledge to help us interpret it.

Edited March 13, 2020 by Snoopy8
Added **

[bmc]

24 minutes ago, Snoopy8 said:

As I said earlier, I welcome all contributions.

Personally, I don't feel that my contribution has been welcomed at all and I will not be revisiting this thread.

[Steffen]

On the topic of repurposing unused surround channels for bi-amping the fronts, I believe this is a common feature among AVRs. My last two (mid-tier) Sony AVRs both did that, and I believe the Pioneer I had before that did too.

[cwt]

2 hours ago, Steffen said:

On the topic of repurposing unused surround channels for bi-amping the fronts, I believe this is a common feature among AVRs. My last two (mid-tier) Sony AVRs both did that, and I believe the Pioneer I had before that did too.

Quite correct Steffen ; I took Snoopy's question a bit differently when he said ''smartly allocate and boost power" to mean just 2 channels and not bi amping through removal of a speakers bridges . If you do biamping specifically ; its a question of doing it properly with active crossovers or the faux way passively . And even then you have to rid your speakers of their hi pass/low pass filters to properly isolate the drivers ; a lot of work

[Snoopy8]

I have started a new thread.

My title in this thread was rather clumsy, but the various posts here have inspired me to dig further and find out for myself.  There is no such thing as "smartly re-allocate power from unused channels. It can draw more power from the power supply when driving stereo but not as much as some have speculated.  The answer is in the other thread...

 

Also thank you for pointing out bi-amping. Yes it is possible with some AVRs but that belongs to another discussion.

Edited March 15, 2020 by Snoopy8
Typo

[Neilsy]

Good topic to open up, Snoopy. 

 

As I think you've concluded, no, AVRs and amps cannot smartly allocate power to dorment channels. 

However I would draw attention to the idea that what amplification power can be hard comes not from the channels, or on a per channel basis, but back to the source of the power supply. 

It's like the pool of which each lane (channel) draws its water from. 

So, if you have an amp that claims say 100w per channel, all channels driven, yes; you probably can score a good 120 or 130w out of it as a single channel or just listening to two channel stereo. 

 

In a way, it is reallocating the power, if you want to view it that way. 

 

However, each channel will have electrical limitations that prohibit a single channel at a time being able to extract all of the power supply. E.g a 7 channel 100w x 7 RMS capable amp will not lend you 700w down just a single channel. As the circuity itself will hold limitation to be able to cope will the level of amps and voltage. 

 

And one should take some time to assess the measurements manufacturers claim about their output. I mean, some phones now claim to have Atmos.... Really... Sure, maybe it supports the format itself but that is primarily a marketing initiative to get you on board. 

Same with AVRs and amps... 

 

Also ALWAYS, ALWAYS find out the THD % of the rated RMS value under 20hz-20khz load, all channels driven. 

THD is often overlooked, particularly by AVRs, which can be claiming power with multiple digit distortion values - which can break speaker drivers 

[Snoopy8]

5 minutes ago, Neilsy said:

Good topic to open up, Snoopy. 

 

As I think you've concluded, no, AVRs and amps cannot smartly allocate power to dorment channels. 

However I would draw attention to the idea that what amplification power can be hard comes not from the channels, or on a per channel basis, but back to the source of the power supply. 

It's like the pool of which each lane (channel) draws its water from. 

So, if you have an amp that claims say 100w per channel, all channels driven, yes; you probably can score a good 120 or 130w out of it as a single channel or just listening to two channel stereo. 

 

In a way, it is reallocating the power, if you want to view it that way. 

 

However, each channel will have electrical limitations that prohibit a single channel at a time being able to extract all of the power supply. E.g a 7 channel 100w x 7 RMS capable amp will not lend you 700w down just a single channel. As the circuity itself will hold limitation to be able to cope will the level of amps and voltage. 

I am still shaking my head about my thread title.   

 

Do you know technically, what those electrical limitations are?  I assume they will burn up if drawing too much?

8 minutes ago, Neilsy said:

And one should take some time to assess the measurements manufacturers claim about their output. I mean, some phones now claim to have Atmos.... Really... Sure, maybe it supports the format itself but that is primarily a marketing initiative to get you on board. 

Same with AVRs and amps... 

 

Also ALWAYS, ALWAYS find out the THD % of the rated RMS value under 20hz-20khz load, all channels driven. 

THD is often overlooked, particularly by AVRs, which can be claiming power with multiple digit distortion values - which can break speaker drivers 

That is broadly the same recommendations I make in the other thread.     

 

While the likes of Yamaha and Marantnz publish crap power specs for their AVRs,  I was shocked that they use them for their multi channel amps!!!  They probably fear no AVR owner, who have their AVR, will upgrade to the multi-channel amps.  What!  My AVR does 110W and you want me to upgrade to a multi-channel amp which produces (real) 100W only???     I'll write up something about this in the other thread with supporting evidence.

 

Agree adding amps to an AVR, as you have, is ideal.  That is not something most people consider at the beginning. And even for someone like me, need to consider WAF and space.  My NAD is powerful enough for my purpose and I have a separate stereo setup.  

[betty boop]

as been mentioned earlier arcam did have a diva range that could re allocate eg use rear channels in a 5.1 setup to bi-amp mains ... that was the thinking behind it...

 

but no as per above its ALL down to power supply... that is its capability. Cant beat the...

Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another

 

max power consumption is a great guide... you cant produce more than can consume...

 

Some makes make some fanciful claims baed more on marketing than real specs. and yes some brands will cheat... 1khz... or 10% distortion or 2ch driven... or at 2ohm

 

other brands will be more conservative reminds me first AVR i bought a HK that was rated at only 60w per channel and bigger power supply than those claiming much higher power outputs and more puny supplies that could never sustain.

 

some might makes some claims and even show test to report.. yet wont admit it wass for a very split second...ie relying on capacitors ... so basically as soon as capacitors drained which will only be tiny split second then yep you are looking at clipping which is not very good !

 

the main problem is really its hard to squeeze in large power sections let alone any serious heat sinks in most AVRS... look at most humble multichannel amps and they'd never fit in any AVR. yes go up in price and there are better power sections and even brands quoting honestly and with decent power sections. likes of nad, rotel, arcam and no longer cambridge audio that went via wayside sadly. 

 

the line of shame  is inhabited by denon, marantz, anthem, yamaha, onyo, pioneer all make outrageous claims that dont stack up with what their power supplies can deliver. and when quoting ... quote to deceive...

 

 they'd argue otherwise and so they will as there is no similarlity in quoting spec for power output... why varies so much. yet same brands are far more honest when comes to 2ch amps(anthem excepted) with usually a power supply far more able to supply needs of 2ch vs multiple.

 

yes for AVRs look for spec 8ohm all channels driven and 20-20hz. and at low distortion ie under single digit... if all thats missing look at power supply and power consumption... usually pretty good guide....

 

[Neilsy]

In terms of what the actual electrical limitations are it's basically all circuitry based. Without getting specific to any one brand or model refer instead to any electrical appliance and therefore it's intended purpose. The manufacturers have no need to design every electrical thing to consume the absolute power that can be sucked from a 240v outlet as your household will just sag and fail to meet the demand, as would the nation. 

And to store power takes larger power supplies which imply more weight which = more materials and more import/export costs. 

So a lot of 'general' companies make a product to meet a success criteria - only.      E.g. I'm a big brand home theatre company part owned by xx multi national mega company and I see the ability for market share in the home theatre realm

. Now, what do my market potentials need? 

Features.. Ah yes, lots of those! Atmos? Of course.. But I don't know how to make that. I know! I'll buy the rights via an OEM to make it.. Room correction? Ah yeah, they all want that these days, pointless having manual EQ only as then everyone things it's not intuitive enough and newbies will get stuck.. 

Video? Oh no...we don't touch that.. That's OK let's just pay another OEM to handle that. 

Oh - but we also need tonnes of power output!!!  How much money is left. 

And then there's the choice - do I put in a massive, well engineered power supply and have great amp output but take up 4 or 6RU of space just for an AVR, and have to charge way above the typical client I'm trying to reach..? 

Maybe, so let's take this idea to the board of my mega business.

No, they want number of sales and market cap, not a few people buying them. 

OK smaller power supply and capability it is. 

 

This is why companies, like Elektra, etc specialise in amps and the quality that goes into it because that is their go to market - only 

[Snoopy8]

On 14/03/2020 at 12:30 AM, bmc said:

Personally, I don't feel that my contribution has been welcomed at all and I will not be revisiting this thread.

My apologies.  Have new thread with backing data.