Bi-Amping Polk TSx550t - AVS Forum
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post #1 of 10 Old 08-27-2014, 08:51 AM - Thread Starter
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Bi-Amping Polk TSx550t

I'm a rookie here who needs some help. I have the Polk TSx550t as well as an Onkyo TX-NR818. Both have the capability to bi-amp but is there really any advantage? Onkyo says that the NR818 can drive all channels at 135W (8 ohms) while the 550t is supposed to be able to handle up to 300W. There is a "Bi-Amp" setting on the amp where it basically says to plug in the 'highs' into one output and the 'lows' into another. Would I be correct in assuming that means I don't have to set any active crossovers? Shouldn't the passive crossovers in the speaker still work as well? Can't bi-amping change the impedance of a speaker as well? Or should I be worried about that?

As well, does anyone have experience with bi-amping where there has been a difference in sound quality below reference levels? I'm not really interested in bi-amping for increased volume but more for sound quality.
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post #2 of 10 Old 08-27-2014, 09:40 AM
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Hello,

I will try and answer your question.

I am running an onkyo tx-nr709 and I have my Polk rt55 bi-amp. I have not really noticed any change in sound quality compared to not having them bi-amp.
If you do bi-amp them make sure you set your speaker settings on the onkyo to bi-amp and connect the speakers correctly. I would probably also just leave them normal, may be less strain on the internal amp not having to drive the extra two channels.
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post #3 of 10 Old 08-27-2014, 09:43 AM
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I bi-amped my Polk II 70s on my Onkyo TX-NR708 and noticed a pretty big difference. If you're not running 7.1, it's a no-brainer to bi-amp. All it takes is a little more speaker wire.
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post #4 of 10 Old 08-27-2014, 11:06 AM
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Quote:
Originally Posted by mwalton90 View Post
I'm a rookie here who needs some help. I have the Polk TSx550t as well as an Onkyo TX-NR818. Both have the capability to bi-amp but is there really any advantage? Onkyo says that the NR818 can drive all channels at 135W (8 ohms) while the 550t is supposed to be able to handle up to 300W. There is a "Bi-Amp" setting on the amp where it basically says to plug in the 'highs' into one output and the 'lows' into another. Would I be correct in assuming that means I don't have to set any active crossovers? Shouldn't the passive crossovers in the speaker still work as well? Can't bi-amping change the impedance of a speaker as well? Or should I be worried about that?

As well, does anyone have experience with bi-amping where there has been a difference in sound quality below reference levels? I'm not really interested in bi-amping for increased volume but more for sound quality.
actually what Onkyo says is that the receiver can do "135 W (8 ohms, 20 Hz-20 kHz, 0.08%, 2 channels driven, FTC)" two channels driven is not all channels driven. Good news is you may never need 135 watts from any single channel anyway, and normal material never hits all channels equally hard as loud as possible all at the same time. So all channels simultaneous output is really of only theoretical interest.

Likely the speakers biamp between the tweeter and the mids/woofers. As it happens, real material rarely contains anywhere near 25% of total power in the tweeter range. So you can never actually use full power from a separate amp channel into the tweeter (you'd probably kill the tweeter immediately, anyway since it's chosen on the assumption that it'll see about 25 perxent or less of total power . . . .

I had my Magnepans biamped once upon a time, though I don't think it meant much.

The added potential clean power is less than one decibel with normal speakers (crossing over at 2ish KHz). The best explanation of how biamping might be useful that I've seen is if you are clipping the amp anyway. When you biamp, the amp connected to the mids/woofers still clips. But the amp connected to the tweeters does not. That keeps the added harshness from the clipping out of the tweeters. But unless you just want to pursue better bad sound (ie, keep distorting, just less horribly) you'd be better off with outboard amps powerful enough to avoid clipping.

But if you listen below reference levels, chances are that you aren't even touching the 135 watt potential power level. I tend to run 10 to 20 dB below reference and likely never use even 20 watts per channel. My speakers cannot see or smell or intuit that my amps could theoretically deliver 120 watts. They just get the 20 watts. The 20 watts has to be the same onaccounta physical laws of the universe like Ohm's law.

If you listen loud enough to be bothered by distortion, biamping might reduce your pain. And of course biamping (specifically the passive biamping we are discussing) is unlikely to hurt anything, so if you want to, you can go for it . . .
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post #5 of 10 Old 08-27-2014, 11:35 AM - Thread Starter
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Originally Posted by jcab2000 View Post
I bi-amped my Polk II 70s on my Onkyo TX-NR708 and noticed a pretty big difference. If you're not running 7.1, it's a no-brainer to bi-amp. All it takes is a little more speaker wire.
Do you typically have the speakers running pretty loud?
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post #6 of 10 Old 08-27-2014, 11:40 AM
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Originally Posted by mwalton90 View Post
Do you typically have the speakers running pretty loud?
Once in awhile, but not normally. I turn them up when listening to 2.1 music. I can still tell the difference at lower volumes. It sounds better.
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post #7 of 10 Old 08-27-2014, 11:41 AM - Thread Starter
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Originally Posted by JHAz View Post
actually what Onkyo says is that the receiver can do "135 W (8 ohms, 20 Hz-20 kHz, 0.08%, 2 channels driven, FTC)" two channels driven is not all channels driven. Good news is you may never need 135 watts from any single channel anyway, and normal material never hits all channels equally hard as loud as possible all at the same time. So all channels simultaneous output is really of only theoretical interest.

Likely the speakers biamp between the tweeter and the mids/woofers. As it happens, real material rarely contains anywhere near 25% of total power in the tweeter range. So you can never actually use full power from a separate amp channel into the tweeter (you'd probably kill the tweeter immediately, anyway since it's chosen on the assumption that it'll see about 25 perxent or less of total power . . . .
I talked to Onkyo Tech Support and they claim it is indeed 135 W per channel. Their power supply is good for almost 975 W so it does seem to line up. Although I imagine that operating all channels at that level I am bound to get more than 0.08% THD. I was shocked that as soon as you move to a 6 ohm speaker at 125 W a channel the THD goes up to 0.7%. Pretty brutal.

You are right about the bi-amp being between the tweeter and the mids/woofers. I am somewhat concerned about blowing the tweeter. Honestly I am not to phased by it because the in store warranty guarantees to either fix the speaker or to give me a speaker of equal or greater value. Honestly, I'm not that impressed with the TSX550t and would like to move to something different. I've looked into changing drivers and crossovers and such but it seems like to much of a hassle within the current box. And, honestly, I don't know enough to get away with that either. Haha

Last edited by mwalton90; 08-27-2014 at 11:47 AM.
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post #8 of 10 Old 08-27-2014, 11:55 AM
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Originally Posted by mwalton90 View Post
I talked to Onkyo Tech Support and they claim it is indeed 135 W per channel. Their power supply is good for almost 975 W so it does seem to line up. Although I imagine that operating all channels at that level I am bound to get more than 0.08% THD. I was shocked that as soon as you move to a 6 ohm speaker at 125 W a channel the THD goes up to 0.7%. Pretty brutal.

You are right about the bi-amp being between the tweeter and the mids/woofers. I am somewhat concerned about blowing the tweeter. Honestly I am not to phased by it because the in store warranty guarantees to either fix the speaker or to give me a speaker of equal or greater value. Honestly, I'm not that impressed with the TSX550t and would like to move to something different. I've looked into changing drivers and crossovers and such but it seems like to much of a hassle within the current box.
I'd have to look at the specs but likely you're not comparing the same type of measurement. You're placing too much importance on the wattage numbers in both your avr and speakers, too. If you want a better speaker either build one from scratch (check out the DIY forum here) or buy one...changing drivers and crossovers isn't a good option. If you're worried about blowing the tweeter use the volume control judiciously and you'll be fine.

Your 818 has a unique feature among avr's for bi-amping in that it actually has the ability to actively bi-amp (if you wanted to remove the crossover network from your speaker and try your own, which might especially be handy if you want to build your own). Passive bi-amping is a waste of wire IMHO.

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post #9 of 10 Old 08-27-2014, 12:25 PM
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Quote:
Originally Posted by mwalton90 View Post
I talked to Onkyo Tech Support and they claim it is indeed 135 W per channel. Their power supply is good for almost 975 W so it does seem to line up. Although I imagine that operating all channels at that level I am bound to get more than 0.08% THD. I was shocked that as soon as you move to a 6 ohm speaker at 125 W a channel the THD goes up to 0.7%. Pretty brutal.

You are right about the bi-amp being between the tweeter and the mids/woofers. I am somewhat concerned about blowing the tweeter. Honestly I am not to phased by it because the in store warranty guarantees to either fix the speaker or to give me a speaker of equal or greater value. Honestly, I'm not that impressed with the TSX550t and would like to move to something different. I've looked into changing drivers and crossovers and such but it seems like to much of a hassle within the current box. And, honestly, I don't know enough to get away with that either. Haha
if you biamp you will put exactly zero more power into the tweeter. zero. Power is the result of the volume control setting more than of the amp's output limits. You just cannot make real content, with say 15% of its power in the tweeter, suddenly have 7 or eight times more power in the tweeter. If it only needs 20 watts, it'll only make 20 watts.

More power = louder. The converse has to mean that at less loud you have less power. During the silences between songs, power should be zero. During the average parts of a movie, which are kinda mazed around 85 dB at reference, you are using one percent (1/100) of the power that would be needed to hig peaks at 105 dB. It cannot be otherwise. Most of the time, the power sits there unused. If you need it, you need it, but only on the loudest parts. When people are just talking, it's a lot quieter than the explosions. If they were at full power the whispers would be explosion loud . . . .

Somewhere around 1% THD is where folks start being able to actually hear distortion (AIUI) with some real content. Truth is, depending on the content, etc., much higher THD can "sound" clean. I've read that guitar players will identify an amp at 10% distortion as "clean," i.e. undistorted . . . . I don't seriously doubt it. But that simply does not mean that a complete music or movie mix at 10% distortion will still sound clean, because a lot more stuff is happening, meaning a lot more distortion-generated harmonics are present . . . .

P.S. go to Stereophile.com and look at some amp measurements. Doesn't much matter which ones. Power versus distortion is a curve, or a line, depending on the amp, and an amp that does 135 watts at .08% distortion might well be at 175 at 1% distortion. It's kind of a marketing decision where to specify power (ie at what distortion) because distortion will just keep rising with power until you become very severely clipped . . . . So Onkyo publishes output power at lower impedance with a higher distortion in order to give a bigger number. BTW, that higher distortion level is almost certainly an indication that the power supply is running out of gas . . . .

I'd want to see third party measurements of multiple channel output power, although, as I said, it's not really relevant anyway. If you biamp, the amps connected to the tweeter will never ever put out more than 25% of the power being put out by the amps connected to the mids/woofers with any real content in the world. It's just not where any concern should go.

Last edited by JHAz; 08-27-2014 at 12:30 PM.
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post #10 of 10 Old 08-27-2014, 02:42 PM
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Quote:
Originally Posted by mwalton90 View Post
I'm a rookie here who needs some help. I have the Polk TSx550t as well as an Onkyo TX-NR818. Both have the capability to bi-amp but is there really any advantage? Onkyo says that the NR818 can drive all channels at 135W (8 ohms) while the 550t is supposed to be able to handle up to 300W. There is a "Bi-Amp" setting on the amp where it basically says to plug in the 'highs' into one output and the 'lows' into another. Would I be correct in assuming that means I don't have to set any active crossovers? Shouldn't the passive crossovers in the speaker still work as well? Can't bi-amping change the impedance of a speaker as well? Or should I be worried about that?

As well, does anyone have experience with bi-amping where there has been a difference in sound quality below reference levels? I'm not really interested in bi-amping for increased volume but more for sound quality.
I guess you haven't read the many, many threads asking the same question. The answer on all of those is: Passive bi-amping does nothing but use more wire. It has no effect whatsoever the way it's implemented in the AVR and on the speaker.

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