do receivers distribute watts? also bi-amping 2 speaker system with 5.1 reciever

[ndlaham]

I have 2 questions that are related, sorry about the novel I just wrote-

I just bought a pair of 150 watt floor standing speakers for music. I also have a 5 year old 5.1 Yamaha receiver that I think advertised 75 watts per channel. Since it is 5.1 capable, I usually see the specs will also say like 375 watts total (75 x 5 channels).

Anyway, from what I have gathered, even if I'm only using 2 channels, my speakers are only getting 75 watts even though my receiver is capable of 375 watts. Am I correct in saying this? And does that mean that 225 Watts are not being used in the other 3 channels (375 - 75*2 = 225)?

Or am I wrong, and does the receiver distribute more power to the 2 used channels when the other 3 channels aren't being used (so then in theory I could get 187.5 watts per channel since 375/2 = 187.5), thus using all 375 watts total that the receiver can output and getting the most speaker power possible?

My second questions is-

If it is true that I only get 75 watts per channel no matter what, then if I bi-amp from the rear left and right speaker outputs that aren't being used (which also supposedly get 75 watts each), shouldn't I get 150 watts to each speaker then (300 watts total to my system) and get more power and thus quite a bit more sound?

Thanks

Also I realize this was pretty much asked in a thread very recently but I felt my case was different with a 2 speaker setup and could make a difference. I read that whole thread too but I'm still not totally clear.

 

[markw]

A receiver has one power supply which is divided between all the driven channels.

When only two channels are driven, it's split between two channels and they might develop a bit more than the advertised power, but nowhere near the total advertised power divided by two.

So, in your case, each channel is rated for 75 wpc and each will deliver that, if only one or two channels are driven at any given time. But, if all channels are called upon, the power they deliver is significantly less than the advertised power.

What benefits the advertising industry is that it's rare that movies demand full power from all channels at the same time so, for movies, it generally works quite well.

The probem comes when one tries to "fake" two channel music into all available channels with an "all channel stereo" mode and the power supply cannot meet the demands.

If you want a good visual, check out the magazine "Sound and Vision" where hey show just this relationship. They show a new Onkyo, rated at 100 wpc, which puts out about 120 wpc in one or two channels but when all channels are called upon, it's more like 30 watts per channel.

So, biamping with the receivers internal amps might not be the best way to go.

 

[ndlaham]

This is very interesting, thank you.

I'm curious as to why manufacturers would advertise the total power to be whatever the WPC is multiplied by the channels? So this receiver I'm looking at online says 140 WPC (980 watts total). That seems like false advertising if it cannot produce 980 watts. If it actually is closer to 30 Watts when all channels are used at the same time, then they should say its max power is 210 watts, right?

Is there a way to find out the actual power supply output the receiver can handle?

Also, on the receiver I mentioned in my first post (the 75 wpc Yamaha), what do you think I would get if just running the 2 front channels? Maybe 100 watts to each?

 

[markw]

This is very interesting, thank you.

I'm curious as to why manufacturers would advertise the total power to be whatever the WPC is multiplied by the channels? So this receiver I'm looking at online says 140 WPC (980 watts total). That seems like false advertising if it cannot produce 980 watts. If it actually is closer to 30 Watts when all channels are used at the same time, then they should say its max power is 210 watts, right?

Because thay can. Would you buy it if they told the unvarnished truth?

Is there a way to find out the actual power supply output the receiver can handle?

You would have to check with the engineers who designed it.

Also, on the receiver I mentioned in my first post (the 75 wpc Yamaha), what do you think I would get if just running the 2 front channels? Maybe 100 watts to each?

Dunno. Check your owners manual. It's buried somewhere in the specs section but nobody ever bothers to read this stuff. It's easier to ask others on line.

 

[TLS Guy]

This is very interesting, thank you.

I'm curious as to why manufacturers would advertise the total power to be whatever the WPC is multiplied by the channels? So this receiver I'm looking at online says 140 WPC (980 watts total). That seems like false advertising if it cannot produce 980 watts. If it actually is closer to 30 Watts when all channels are used at the same time, then they should say its max power is 210 watts, right?

Is there a way to find out the actual power supply output the receiver can handle?

Also, on the receiver I mentioned in my first post (the 75 wpc Yamaha), what do you think I would get if just running the 2 front channels? Maybe 100 watts to each?

The power into a given load is determined by the rail voltage. If you drop the impedance then more current and power can flow if the output stage and power supply are up to it. However for most receivers they can not increase power and the cheaper offerings will pass less power.

Now most speakers are four ohm, especially towers, no matter what the speaker manufacturer claims in the meaningless nominal impedance ratings. So there is a very good chance you are getting less than 75 watts per channel.

We get this confusion over biamping continuously, which for most speakers is a waste of time.

This is what you need to understand about passive biamping.

 

[Swerd]

I'm curious as to why manufacturers would advertise the total power to be whatever the WPC is multiplied by the channels? So this receiver I'm looking at online says 140 WPC (980 watts total). That seems like false advertising if it cannot produce 980 watts. If it actually is closer to 30 Watts when all channels are used at the same time, then they should say its max power is 210 watts, right?

Is there a way to find out the actual power supply output the receiver can handle?

markw has it right.

You're not the first to ask about this. The short answer is that the Federal Trade Commission (FTC) requires that amp makers rate multi-channel amps when 2 channels are driven with an 8 ohms impedance load, over the range of 20 Hz–20 kHz, and that they state the % total harmonic distortion. You can compare power ratings of different amps if they say they say they were done under those conditions, or if they say "FTC". For any other conditions, like all channels driven, all bets are off.

I remembered an older thread that may answer your question in a bit more detail. Read the whole thread - it eventually answers your question.

 

[ndlaham]

Yeah it doesn't make that much sense to me yet but I'm new to this stuff.

So if I wanted to take full advantage of just my 2 speakers at full volume(150 watts each) and blow my house up how big of a receiver would I need?? (That they advertise )

Also I found the "Power Consumption" in a random Yamaha manual. The model claims 140 wpc (980 total) and the power consumption in the manual states only 490 Watts. So is that the limiting factor then? Meaning if divided between 2 speakers I should get 245 watts? Or between 7 channels, 70 watts?

Hopefully I'm on the right page here.

Thanks for the info on bi-amping too.

 

[TLS Guy]

Yeah it doesn't make that much sense to me yet but I'm new to this stuff.

So if I wanted to take full advantage of just my 2 speakers at full volume(150 watts each) and blow my house up how big of a receiver would I need?? (That they advertise )

Also I found the "Power Consumption" in a random Yamaha manual. The model claims 140 wpc (980 total) and the power consumption in the manual states only 490 Watts. So is that the limiting factor then? Meaning if divided between 2 speakers I should get 245 watts? Or between 7 channels, 70 watts?

Hopefully I'm on the right page here.

Thanks for the info on bi-amping too.

At best only 70% of the power will go to the speakers, the rest as heat.

The actual power delivered will depend on the impedance curve of your speakers and the phase angle between current and power with frequency. That information is impossible to get for most speakers.

Remember receivers are rated into a resistive load, speaker loads are highly reactive and all over the place. So the power you will get is all over the map. Bargain on it being less than you think under real world conditions.

 

[ndlaham]

Wow thanks for all this info. It's good to know these things.

I read on another forum too something similar to the 70% rule, just stated differently

The guy says that is takes 150% more input power to produce the rated output power. So that is consistent with 70% since the reciprocal of 150% is about 66%, which is saying the same thing but inversed.

It also makes sense too, because if you look at the power consumption of the reciever I looked at (490 watts) and divide it by 1.5 (150%) you get 327 watts, which as I understand is all that can go to the speakers, generally speaking. So across 2 channels your getting about 163 watts, and across 7 you are getting 47 watts.

This seems pretty consistent with what markw said about the Onkyo reciever

If you want a good visual, check out the magazine "Sound and Vision" where hey show just this relationship. They show a new Onkyo, rated at 100 wpc, which puts out about 120 wpc in one or two channels but when all channels are called upon, it's more like 30 watts per channel.

But that receiver is rated at 700 watts total (100x7) so the input power is less, therefore the numbers seem to come out pretty close to what he said.

Do you happen to know the model of that Onkyo receiver mark?

 

[markw]

Don't get too hung up on the math.

What's being bandied about here are approximations for examples sake. If you expect exact answers, you're in the wrong place.

From your mention of that 163 watts per channel in stereo, I see you're still not getting it, even the main, basic concept laid out in my first response in this thread. Re-read this thread (and the linked ones as well), this time to learn rather than trying to justify what you want to believe.

As for the receiver in the magazine, I don't remember. Take a hike to your local Barnes and Noble and check it out. They don't charge, unless you wanna get a cuppa joe.

Sometimes, a little research on ones own can be rewarding, too.

 

[ndlaham]

I'm not looking for exact answers, but math does help me understand things, even if just approximations.

I now realize even doubling the power to a channel is not even a huge change in volume for that speaker. I just want to understand how receivers are rated and marketed for that matter and how that might affect what I buy and how I set things up.

I'll read through the threads again though.

 

[markw]

Doubling the power is the least of what you've got to learn here.

I'm not looking for exact answers, but math does help me understand things, even if just approximations.

I now realize even doubling the power to a channel is not even a huge change in volume for that speaker. I just want to understand how receivers are rated and marketed for that matter and how that might affect what I buy and how I set things up.

I'll read through the threads again though.

Post 11 in this thread offers three links that should answer your questions.

FWIW, this thread was linked to in a previous post in this thread. We are glad to help, but sometimes one must take advantge of what's offered to them and read a little.

Or, short of boning up on some quasi-serious electrical theory, you might just want to know that specs lie and learn how to read them. You've already had a crash course in simple english here in this thread. Just read the spec sheets carefully.