amps out of phase?

orsen

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hi
lately i've read numerous threads about peeps using multi amp setups driven by a single pre or amp used as a pre or even avr used as a pre.
and almost always some one will pipe in that its a phase nightmare to do this.
is there a way to test for this or a correct way and incorrect way?

thanks
 
Polarity concerns are typically only a big consideration if you are mixing different brands of amps.

The easiest way, I think, would be to play a mono signal on one speaker on each of the different amps (playing simultaneously). Check that the sound seems to be coming from between the speakers.

At least that's how I'd try to do it, somewhat simply.
 
hi
lately i've read numerous threads about peeps using multi amp setups driven by a single pre or amp used as a pre or even avr used as a pre.
and almost always some one will pipe in that its a phase nightmare to do this.
is there a way to test for this or a correct way and incorrect way?

thanks

Whenever we use multi power amps to create sound and those amps are NOT identical or high quality commercial units, there is a 50 - 50 chance the amps are out of phase with each other. Now if the amps are out of phase, all you have to do is reverse all speaker leads on one of the amps. (Move the leads connected to all red speaker posts to black posts and leads that were on the black posts to red posts.) This will bring the amps into phase.

So how can you tell if you have a problem. Well the best way is with a dual trace scope. You can see that the signals are out of phase.

Lacking such equipment you can use your ears. Usually when you have multiple power amps, you have multiple sets of speakers. In this case listen to a known CD for an entire track. Leave volume controls as they are, power off one amp and then reverse leads as above on just this one amp. Power back on and listen to the track again. If this change brought the amps into phase the resulting sound will be louder. If it caused the amps to go out of phase, the resulting sound will be lower.

If you are using multiple amps to bi-amp and you only have one set of speakers, it becomes more complicated. With only one set of speakers, you'll need a mono source. Use one amp to power the left woofer and the other amp on the right woofer. Listen as above, then reverse one amp and listen again. You should easily be able to tell when the sound is added vs subtracted.

Hope this helps...
Jerry
 
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great answer!
i suspected the simple fix, but didnt know how to check this.
but at the same time i was troubled by why one amp seemed louder, with both on.
i only run 2 when no one else is home and i feel like loud :)
the whole sound is better... i have read how bass would cancel out if out of phase, but the whole sound was affected
 
great answer!
i suspected the simple fix, but didnt know how to check this.
but at the same time i was troubled by why one amp seemed louder, with both on.
i only run 2 when no one else is home and i feel like loud :)
the whole sound is better... i have read how bass would cancel out if out of phase, but the whole sound was affected

Well, yeah, if you are running two sets of speakers, you want all of the speaker's to be producing sound in phase. Yes, everything will be impacted by an out of phase condition, but the lower frequencies are the easiest to notice.

It's these low frequencies that are responsible for the vast majority of the overall loudness that we perceive.

Regards,
Jerry
 
the speakers were in phase going by the markings on the amps and speakers.
the amps were out of phase with each other, which why i asked how to check this
i had no idea amps could be out of phase, but i have seen this brought up numerous times lately.

it made a big difference and hopefully will help someone else
 
Well, yeah, if you are running two sets of speakers, you want all of the speaker's to be producing sound in phase. Yes, everything will be impacted by an out of phase condition, but the lower frequencies are the easiest to notice.

It's these low frequencies that are responsible for the vast majority of the overall loudness that we perceive.

Regards,
Jerry

All you can really do is ensure the polarity is correct.

Actual phase relationships are all over the place due to different frequencies, different distances, etc., etc.
 
i had no idea amps could be out of phase, but i have seen this brought up numerous times

It's a matter of polarity, not phase.

Most amps and pre amps pass the signal in normal polarity. Some amps and pre amps invert the signal passing through them. Some manuals mention whether the unit inverts the signal or not.

So, if you are using multiple different amps there is some chance (I don't believe it's high as 50/50, but whatever) that one amp inverts the signal and one does not.
 
i have numerous power amps [dont we all] but no 2 the same
this is good info to have and hopefully help some others
in between i'm selling off some gear to hopefully fund a second matching power amp
 
It's a matter of polarity, not phase.

Most amps and pre amps pass the signal in normal polarity. Some amps and pre amps invert the signal passing through them. Some manuals mention whether the unit inverts the signal or not.

So, if you are using multiple different amps there is some chance (I don't believe it's high as 50/50, but whatever) that one amp inverts the signal and one does not.

whoaru99, the really high quality commercial amps maintain phase, but rarely do consumer amps. You'll even see situations where consumer amps will invert the signal by flipping a switch. Tone defeat switches are good examples of this. Yes, they by-pass the tone controls, but at the same time the signal gets inverted.

This is the reason that all sub manufacturers must include a phase switch. All that switch really does is invert the audio signal.

Regards,
Jerry
 
whoaru99, the really high quality commercial amps maintain phase, but rarely do consumer amps. You'll even see situations where consumer amps will invert the signal by flipping a switch. Tone defeat switches are good examples of this. Yes, they by-pass the tone controls, but at the same time the signal gets inverted.

This is the reason that all sub manufacturers must include a phase switch. All that switch really does is invert the audio signal.

Regards,
Jerry

For what you describe, polarity is the correct term.

Phase is a time offset between two signals. That is not what's happening here.

With regard to a sub, without an examination of the output relative to input, it's hard to say if the control is just simple polarity or an actual phase control. One of my subs has both a polarity switch and a phase control. The other two have neither.

Phase and polarity are not the same, but the term phase is often wrongly used re. polarity.
 
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For what you describe, polarity is the correct term.

Phase is a time offset between two signals. That is not what's happening here.

With regard to a sub, without an examination of the output relative to input, it's hard to say if the control is just simple polarity or an actual phase control. One of my subs has both a polarity switch and a phase control. The other two have neither.

Phase and polarity are not the same, but the term phase is often wrongly used re. polarity.


Whoaru99, when I talk about phase here, I'm referring to an audio signal that is 180 degrees out of phase with another signal from the same source.

When I think of polarity I think of poles on a magnet or the plus and minus poles on a battery. I have a difficult time thinking of polarity when referencing an asymmetrical , ac signal like the typical audio signal.

Jerry
 
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Whoaru99, when I talk about phase here, I'm referring to an audio signal that is 180 degrees out of phase with another signal from the same source.

When I think of polarity I think of poles on a magnet or the plus and minus poles on a battery. I have a difficult time thinking of polarity when referencing an asynchronous, ac signal like the typical audio signal.

Jerry

It is indeed polarity in these cases because it is simply inverted polarity, not a phase shift. Phase is relative to time, there is no time element involved here.

This post clearly highlights the difference between inverted/reverse polarity and a 180-deg phase shift.

http://audiokarma.org/forums/index....-pos-which-is-neg.754043/page-2#post-10247262
 
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I use XLO Test & Burn-in CD to help speaker setup.
Track 2: Voice in-Phase
Track 3: Voice Out-of-Phase
"Out-of-phase. My voice should have no apparent source, no apparent focus. Should Sound like it's coming at you from all around your room. Move your speakers incrementally a little bit a time to enhance this effect. The less focus you have in out-of-phase mode, the more focus you have in-phase."
 
It is indeed polarity in these cases because it is simply inverted polarity, not a phase shift. Phase is relative to time, there is no time element involved here.

This post clearly highlights the difference between inverted/reverse polarity and a 180-deg phase shift.

http://audiokarma.org/forums/index....-pos-which-is-neg.754043/page-2#post-10247262

Whoaru99, I'm familiar with that thread - I contributed, but lost all interest when it degenerated into a semantics argument. When my AR sub, Velodyne subs, JBL subs, etc refer to that little switch as phase, I think that means more to the people reading and posting here.

Indeed, those SVS subs that don't come with a switch, have a control that varies phase from 0 to 180 degrees.

Maybe polarity is the "perfect" term for audio engineers, I don't know and don't care. Because of those ubiquitous phase switches, I believe "phase", in this sense, means more to folks on this board.

Further confusing consumers is the use of polarity when referring to the Red and Black posts on speakers and amps and the need to keep polarity consistent between left and right channels.

Regards,
Jerry
 
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Whoaru99, I'm familiar with that thread - I contributed, but lost all interest when it degenerated into a semantics argument. When my AR sub, Velodyne subs, JBL subs, etc refer to that little switch as phase, I think that means more to the people reading and posting here.

Indeed, those SVS subs that don't come with a switch, have a control that varies phase from 0 to 180 degrees.

Without examination of the actual output one isn't sure if a two-position switch is shifting the phase by 180 degrees or simply inverting the polarity. They are not the same thing so it's hardly a matter of semantics. I'd like to think the big companies always get it right but I work for a big company (not audio, BTW). ;) The term phase is so pervasively used when polarity is actually the point it's hard to say what it's doing for sure without actually checking function.

An adjustable knob is pretty clear cut, no question that's a phase control.


Maybe polarity is the "perfect" term for audio engineers, I don't know and don't care. Because of those ubiquitous phase switches, I believe "phase", in this sense, means more to folks on this board.

Perfect? It's not about perfect, it's about correct.

Polarity is different than phase. Use polarity where polarity is the correct term, use phase where phase is the correct term.

Isn't everyone better off to learn something more correct than they might currently know?



Further confusing consumers is the use of polarity when referring to the Red and Black posts on speakers and amps and the need to keep polarity consistent between left and right channels.

That's a perfect example where polarity is unquestionably the correct term, yet old habits die hard and people still incorrectly refer to it as phase.
 
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I have 3 amps running speakers in different rooms all from same music source (PC-DAC). Works fine. Different amps and speakers, they each have their own sound but no issues with timing or polarity.
 
whoaru99 wrote: "One of my subs has both a polarity switch and a phase control."
Ok, so I can guess what the polarity switch does. What does the phase control do? (Assuming these are on the same sub.)

Chip
 
I have 3 amps running speakers in different rooms all from same music source (PC-DAC). Works fine. Different amps and speakers, they each have their own sound but no issues with timing or polarity.

In different rooms where there isn't direct interaction of the sound from the three different setups it's not a factor. All you have to be concerned about there is that the two speakers of each system are connected in the same polarity.
 
whoaru99 wrote: "One of my subs has both a polarity switch and a phase control."
Ok, so I can guess what the polarity switch does. What does the phase control do? (Assuming these are on the same sub.)

Chip

I refer you back to this post: http://audiokarma.org/forums/index....-pos-which-is-neg.754043/page-2#post-10247262

The first image in that post shows the effect of phase. The two signals are offset in time.

The second image shows the effect of polarity. There is no time offset, the signal is simply inverted.

The phase control of the sub creates the time offset of the sound coming out of the sub relative to the signal going in. Why is this useful? It's for fine tuning the sound of the sub to be "in phase" with the sound of the main speakers typically at the crossover point. Simple polarity inversion can't necessarily do that, particularly if the sub and the mains aren't the same distance from the listening position.
 
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