(2 ea) 100 w/ch power amps - vs - (1ea) 200 w/ch power amp ? - AVS Forum
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post #1 of 15 Old 05-01-2012, 06:39 PM - Thread Starter
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I asked this same question on the Polk Forum (no answers yet), but I thought I might ask some of the experts here too this same question:
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I don't have a firm grasp on audio electronics, so I would like to present to you a comparison. Lets say we have 2 separate 2-channel audio systems here:

#1: One single 2-channel Power Amp rated at 200 w/ch @ 8 ohms .. driving a set of (4 ea) 8 ohm speakers. Were taking about driving a pair of fronts and a pair of rears.

#2: A pair of 2-channel Power Amps rated at 100 w/ch @ 8 ohms each .. with each amp driving a single set of 8 ohm speakers. ( 1 amp driving the pair of fronts, and the other amp driving the pair of rears).


Do I presume correctly that the (2 ea) 100 w/ch Power Amps, each driving 2 speakers will be same same as having single power amp rated at 200 w/ch driving all 4 speakers?

Anyone of these 2 systems better than the other? ... considering the specs on the amps are exactly the same.

In my very novice mind, these 2 systems would produce the same power through all 4 speakers (same db of sound within the room)

Just wondering ..

Ron,
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post #2 of 15 Old 05-01-2012, 06:54 PM
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If the amps perform the same, then by definition there won't be a difference. If they are not truly equivalent, then you could experience clipping much earlier in one or the other.

The transformers and power transistors are major questions in amp design. If the transformer can deliver the power required in either setup and the transistors can carry the current, then it shouldn't make a difference.

Depending on application, the rear channels don't require as much power as the fronts. When multi-channel audio was first introduced, they were run with 20 watt rated amps typically. They provided "ambiance" requiring much less power. But, that didn't sell well with the public and was hotly debated by philes of all sorts. Today, all channels have the same power. This is probably good for multi-channel music, less important with movie soundtracks where the sub is the heavy hitter and the center channel is next inline for power demands.
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post #3 of 15 Old 05-04-2012, 04:43 PM
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Quote:
Originally Posted by Flt Simulation View Post

I asked this same question on the Polk Forum (no answers yet), but I thought I might ask some of the experts here too this same question:
_______________________________

I don't have a firm grasp on audio electronics, so I would like to present to you a comparison. Lets say we have 2 separate 2-channel audio systems here:

#1: One single 2-channel Power Amp rated at 200 w/ch @ 8 ohms .. driving a set of (4 ea) 8 ohm speakers. Were taking about driving a pair of fronts and a pair of rears.

#2: A pair of 2-channel Power Amps rated at 100 w/ch @ 8 ohms each .. with each amp driving a single set of 8 ohm speakers. ( 1 amp driving the pair of fronts, and the other amp driving the pair of rears).


Do I presume correctly that the (2 ea) 100 w/ch Power Amps, each driving 2 speakers will be same same as having single power amp rated at 200 w/ch driving all 4 speakers?

Anyone of these 2 systems better than the other? ... considering the specs on the amps are exactly the same.

In my very novice mind, these 2 systems would produce the same power through all 4 speakers (same db of sound within the room)

Just wondering ..

Ron,

If this first amp is a 2 channel amp, you should only be driving two speakers off it and not 4. It may have a speaker A/B connection, but is meant for only driving one pair of speakers at a time. I hope I understand your question.

Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus Five 200 amp, Chase SS 18.2(2), VS 18.1(2), Samsung BDP F 7500, Asus/My Book Live HPC 4 TB

Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500
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post #4 of 15 Old 05-04-2012, 06:02 PM - Thread Starter
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derrick ... See, I have been a little misinformed in the past.

I thought that if you bought a 2-channel integrated amp that had a 3-way selectable A - B - A/B switch on the front panel, and 2 sets of speaker binding posts on the back (1 for a set of front speakers, and 1 for a set of rear speakers) that this amp was pretty much intended to drive 4 speakers to begin with.

Maybe I'm wrong?
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post #5 of 15 Old 05-04-2012, 06:48 PM
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Quote:


I thought that if you bought a 2-channel integrated amp that had a 3-way selectable A - B - A/B switch on the front panel, and 2 sets of speaker binding posts on the back (1 for a set of front speakers, and 1 for a set of rear speakers) that this amp was pretty much intended to drive 4 speakers to begin with.

Depends on what you mean by "rear speakers." If you are thinking of the standard home theater arrangement, with the front channels and rear channels being different, then, no. The amp you are describing can only carry two channels.

But if you want your "rear" speakers to be playing the same two channels as the front speakers, this amp would do that. Why you'd want to do that, I'm not sure. More typically, an amp like this is used to drive two pairs of speakers in different rooms, with both pairs playing the same program.

Also, from your initial post:

Quote:


Do I presume correctly that the (2 ea) 100 w/ch Power Amps, each driving 2 speakers will be same same as having single power amp rated at 200 w/ch driving all 4 speakers?

No. You cannot make that assumption, for a whole host of reasons.

Perhaps you would do better to start by describing what it is you want to do.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #6 of 15 Old 05-05-2012, 01:37 AM
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Quote:
Originally Posted by Flt Simulation View Post

I asked this same question on the Polk Forum (no answers yet), but I thought I might ask some of the experts here too this same question:
_______________________________

I don't have a firm grasp on audio electronics, so I would like to present to you a comparison. Lets say we have 2 separate 2-channel audio systems here:

#1: One single 2-channel Power Amp rated at 200 w/ch @ 8 ohms .. driving a set of (4 ea) 8 ohm speakers. Were taking about driving a pair of fronts and a pair of rears.

#2: A pair of 2-channel Power Amps rated at 100 w/ch @ 8 ohms each .. with each amp driving a single set of 8 ohm speakers. ( 1 amp driving the pair of fronts, and the other amp driving the pair of rears).


Do I presume correctly that the (2 ea) 100 w/ch Power Amps, each driving 2 speakers will be same same as having single power amp rated at 200 w/ch driving all 4 speakers?

Anyone of these 2 systems better than the other? ... considering the specs on the amps are exactly the same.

In my very novice mind, these 2 systems would produce the same power through all 4 speakers (same db of sound within the room)

Just wondering ..

Ron,

You will have more power delivery potential with #2.

In #1, if you are powering 2 speakers of 8Ω in parallel, this represents a 4Ω load on each channel on the amp.

In theory, a good SS amplifier will 'double down' into double the load (half the impedance), that it, your 100W/ch/8Ω amp should deliver 200W into 4Ω.

P=V²/R
With either amp condition #1 or #2, the output voltage will be the same, the only difference is the load. Halve the impedance and the power should double.

Almost none do - because of commercial requirements, there usually aren't enough output devices (transistors or MOSFETs), or a large enough power supply to do it. Somewhere around 40-60% is what most will do, so 100W/8Ω will mean 140-160W/4Ω which is about 1-1.5dB difference from what a theoretically perfect amp would do.

So with #2, 2 x 2ch amps at 100W/ch/8Ω, each will then be able to potentially deliver it's rated power into each 8Ω speaker.

In reality, it will likely make 2/10th of SFA difference which ever one you use.

Note: as others have mentioned, you would not ordinarily connect fronts and surrounds to the same channel, they would be connected to discrete amplifiers such as your #2 or inside an AVR. However, if you were to connect 2 identical speakers to each channel of a single 2ch amp, what I wrote applies. The discussion also assumes the amp will be happy with the loads.
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post #7 of 15 Old 05-05-2012, 07:25 AM - Thread Starter
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mcnarus / A9X ....

Let me say what I plan to do when I get this modest system of mine hooked up.

This is to be a 2-channel audio system only. No TV, no surround sound, no movies. It is to be used just for listening to CDs and streaming music from the internet.

I understand that most people would just use 2 speakers for this application .. a left and a right front.

In my case, I am just adding a set of rear speakers to the mix. The Rt rear speaker gets the same audio signal as the Rt front. And the Lft rear gets the same audio signal as the Lft front.

Why am I doing it this way? ... Well, on my other audio system I have in my house in the Philippines, I added that 2nd set of rear speakers just because it sounded better than hearing the music just from pair of front speakers. I would do an A - A/B test, and listen to the music coming from front speakers alone, and then switch to A/B so the music would come from both the fronts and the rears ... This sounded better to me (more "spacious") than just listening to the fronts by themselves.

So, since I am now installing a new system in my house here in Florida, I thought I would go the same route as the system in the Philippines.

I bought an Onkyo TX-8050 Network Stereo Reciever. This is a 2-channel unit. There is no 5.1 or 7.1, or anything you would buy for home theater. I bought this instead of just a regular 2-channel integrated amp because of it's ability to play music streamed from the internet and play music wirelessly from my home computer's hard drive. No need to purchase a separate item like a Squeezebox to do that when using this reciever.

I also like the fact that this reciever has a USB port on it's front panel. I can have music stored on a 'memory stick', and just plug it into the front of the reciever (my integrated 2-channel amp in the Philippines never had a USB port).

But, when looking at the specs on this Onkyo reviever, I realized that it only put out 80 w/ch @ 8 ohms (2 speakers driven) ... Well, I thought that might be a little low on power, so I purchased a pair of Onkyo M-282 power amps. These power amps are both rated at 100 w/ch @ 8 ohms (2 speakers driven). I would drive the front speakers with one of these power amps, and drive the rear speakers with the other Onkyo M-282 power amp.

BTW ... I will be using a pair of Polk RTi A7 floorstanders for the fronts, and a set of Polk RTi A3 bookshelf speakers for the rears. These speakers are all 8 ohm. They will not be bi-wired or nothing like that ... just wired normaly.

Obviously with this setup, I would not be using the power amp section of the Onkyo reciever.

The wiring diagram for this system looks like this:

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post #8 of 15 Old 05-05-2012, 07:37 AM
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If you can still return the power amps, I would return one of them, and just drive one set of speakers off the receiver. That second amp isn't really getting you anything.

Just out of curiosity, how are you planning to control the volume between fronts and rears?

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #9 of 15 Old 05-05-2012, 07:54 AM
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The 2-channel amplifier is only a 2-channel amplifier.

You CAN drive 4 speakers with it, but you will be sending the SAME SOUND to both the front and rear speakers! Who would want to do that?

That doesn't make any sense. You need four separate amplifier channels to drive them with four separate inputs and outputs.



Quote:
Originally Posted by Flt Simulation View Post

derrick ... See, I have been a little misinformed in the past.

I thought that if you bought a 2-channel integrated amp that had a 3-way selectable A - B - A/B switch on the front panel, and 2 sets of speaker binding posts on the back (1 for a set of front speakers, and 1 for a set of rear speakers) that this amp was pretty much intended to drive 4 speakers to begin with.

Maybe I'm wrong?

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post #10 of 15 Old 05-05-2012, 07:57 AM - Thread Starter
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Quote:
Originally Posted by mcnarus View Post


Just out of curiosity, how are you planning to control the volume between fronts and rears?

There is an "Input Level" knob on the back of the power amps (see photo above). I would set the Input Level to "max" on the #1 amp driving the front speakers, and then initially set the Input Level to "max" on that 2nd power amp which drives the rear speakers ... If the rear speakers are a littke too loud, I can turn down that Input level knob on the #2 amp a little untill I am happy with the volume of the front and rear speakers working together ...... then just leave it at that ... set and forget.

The master volume control is of course on the front panel of the Reciever, along with the Lft / Rt balance knob:

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post #11 of 15 Old 05-05-2012, 08:05 AM - Thread Starter
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Originally Posted by commsysman View Post

The 2-channel amplifier is only a 2-channel amplifier.

You CAN drive 4 speakers with it, but you will be sending the SAME SOUND to both the front and rear speakers! Who would want to do that?

That doesn't make any sense. You need four separate amplifier channels to drive them with four separate inputs and outputs.

That's what my ears like. I like the sound of 2-channel music, but listening with front and rear speakers all running vs just 2 speakers in front of you.

You still get the same Left and Right channel separation ... just in this case, your hearing it from not only in front of you, but also from the rear sides too.

Again, music coming from 4 speakers just sounds more "spacious" and "open" than music just coming from 2 speakers to your front only.

Hey ... go into one of those Dance Clubs ... They have speakers all over the place. Even in different places on the ceiling. Sounds good to me!
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post #12 of 15 Old 05-05-2012, 08:17 AM
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There is an "Input Level" knob on the back of the power amps (see photo above).

Of course. Didn't notice that. You still only need one external amp, not two (although there's nothing wrong with having the second).

Quote:


That's what my ears like. I like the sound of 2-channel music, but listening with front and rear speakers all running vs just 2 speakers in front of you.

This is the part of audio that's about personal preference. I know others who do this as well.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #13 of 15 Old 05-05-2012, 08:17 AM - Thread Starter
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Here is my house in the Philippines. Not the best photo for seeing the 2-channel audio system, but you can see the front tower speakers, and one of the two rear speakers mounted on 30" stands.

Sounded really nice .. And again, flipping between A and A/B, it just sounded better in "A/B" with all 4 speakers running, than in just "A" with only the fronts running.

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post #14 of 15 Old 05-05-2012, 08:21 AM - Thread Starter
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Originally Posted by mcnarus View Post


You still only need one external amp, not two (although there's nothing wrong with having the second).

Well, those Onkyo M-282 power amps only cost $200 bucks each, so they were cheap.

They look pretty good too:

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post #15 of 15 Old 05-05-2012, 08:25 AM - Thread Starter
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Here is the setup I used to have here in the US along time ago.

It was a Pioneer Spec 1 pre-amp and a Pioneer Spec 4 power amp.

I also used 4 speakers in this 2-channel audio system too. Had a set of Pioneer HPM 1500 front floorstanders, and a set of JBL rears. Sounded good.

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