Richard A

Fazed by phase

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Super Wammer

My Modwright LS36.5 pre-amp has a phase button on the remote. Although the changes are subtle i much prefer one phase setting to the other. It just sounds more “right”.

But I have no real idea what I am actually doing to the signal. Anyone care to explain what’s going on  - to someone who struggled with physics O level more than 50 years ago. 
 

Or is there a book Phase for Dummies?

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Without looking into it, I would assume it simply reverses the phase of the signal.  So that your speakers suck instead of blow!  The only time, in 50 years, that I have heard a difference was with one piece of music on one system where the bass drum was obviously different.

With higher frequencies, and mixed up recording phase, I am curious why one sounds better than the other for you.  It would be nice to have a good answer.

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Super Wammer

Its like swapping the +ve and -ve wires on both your speakers. One way around a kick drum will first compress the air in the room (the first movement of the bass driver is outwards). The other way around it will rarify the air in the room (the first movement of the bass driver will be inwards).

This is called absolute phase. Some people can hear it. Others, like me, are not sensitive to it.

On the other hand, some people are sensitive to phase errors in drivers and crossovers and can hear the benefit of Linn's Exakt in correcting this. Others don't seem to notice.

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My pre has a phase reverse button and although you can hear something change it’s hard to pinpoint exactly what it is, so I never bother with it, but correctness of absolute phase is a ‘thing’ in itself...

https://www.stereophile.com/content/absolute-phase-fact-or-fallacy

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24 minutes ago, sunbeamgls said:

On the other hand, some people are sensitive to phase errors in drivers and crossovers and can hear the benefit of Linn's Exakt in correcting this. Others don't seem to notice.

I think it's worth pointing out that this is very different to changing absolute phase, which as you and others have described is simply inverting the polarity of the electrical output of the pre-amp. Changing the relative phase of frequency components is a completely different ball-game.

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Super Wammer
33 minutes ago, MartinC said:

I think it's worth pointing out that this is very different to changing absolute phase, which as you and others have described is simply inverting the polarity of the electrical output of the pre-amp. Changing the relative phase of frequency components is a completely different ball-game.

That's why I mentioned it.

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Super Wammer

This can have a mild affect - I am led to believe some amplifiers are inverted (reverse phase).  I have heard a difference but cannot understand why - one is pushing then pulling the  drive unit and when the phase is reversed, is pulling then pushing the drive unit.   The same affect can be had by swapping the speaker leads on each loudspeaker (put the positive to the negative and the negative to the positive on each loudspeaker) 

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I've thought about this before. I'm 95% sure that any differences are psycho acoustic.

The 5% chance there's something in it would rely on the ear/brain system being sensitive to the initial transient in a signal.

Or to put it another way, a sine wave at 50Hz would sound the same in either phase as a continuous sound, but could the human ear pick up whether the first 1/4 cycle from quiet was a rise or a fall? I'm not sure.

Now think of a music signal as a complex combination of such sine waves (is that a Fourier transform or something, I should look it up). Within that they are constantly changing and there are lots of initial transients to pick up, so maybe it's more possible than with a single bass note. It may even be possible at higher frequencies.

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Super Wammer

I’m beginning to understand what is going on but I can hear a difference. I first hit the phase button on the remote by accident and had no idea what I’d done but could hear that one way it seemed easier to listen to. Hard to explain - not particularly better but more “correct/natural” - less fatiguing perhaps. 
 

Can I put my question another way. Why did Dan Wright design a phase switch into the pre-amp in the first place? What is it supposed to do? The manual does not give much of a clue.

Thanks chaps for taking the time to reply.

Richard

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14 hours ago, uzzy said:

This can have a mild affect - I am led to believe some amplifiers are inverted (reverse phase).  I have heard a difference but cannot understand why - one is pushing then pulling the  drive unit and when the phase is reversed, is pulling then pushing the drive unit.   The same affect can be had by swapping the speaker leads on each loudspeaker (put the positive to the negative and the negative to the positive on each loudspeaker) 

Some amplifiers have an odd number of gain stages (my Conrad Johnson power amp has only three) and therefore, unless you are using a preamp that also has an uneven number of gain stages, phase has to be reversed at the speaker end (red to black, black to red)!

In phase, music can be heard through a system as having a strong central image, with louder bass.

Not all music is recorded in phase (go figure), hence the incorporation of phase switches on some amps!

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Super Wammer
1 hour ago, Snoopdog said:

Some amplifiers have an odd number of gain stages (my Conrad Johnson power amp has only three) and therefore, unless you are using a preamp that also has an uneven number of gain stages, phase has to be reversed at the speaker end (red to black, black to red)!

In phase, music can be heard through a system as having a strong central image, with louder bass.

Not all music is recorded in phase (go figure), hence the incorporation of phase switches on some amps!

I think you're mixing up absolute phase with the phase between each speaker. The phase switch will swap absolute phase and not the phase for one speaker only.

One speaker out of phase would always be bad.

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Regardless of audibility, the term "absolute phase" is wrong. Doubly so, in fact. Phase is always relative to something, and this isn't even a phase issue in the first place. The correct term is polarity.

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Super Wammer
4 minutes ago, mansr said:

Regardless of audibility, the term "absolute phase" is wrong. Doubly so, in fact. Phase is always relative to something, and this isn't even a phase issue in the first place. The correct term is polarity.

You are not wrong .. the effect of reversing the polarity of both speakers will be to give a 180 degree shift in polarity  .. if you reverse the polarity of one loudspeaker (which is termed as being out of phase not out of polarity and I have not a clue which is incorrect) then certain frequencies will cancel each other out.    For those who wish to know more about phase and polarity this little article may help (or not)  http://totalproaudio.stevebunting.com/30/basics/phase-or-polarity/ and this one explains use of phase in recording  https://www.bhphotovideo.com/explora/pro-audio/tips-and-solutions/polarity-vs-phase-whats-the-difference

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I think you're mixing up absolute phase with the phase between each speaker. The phase switch will swap absolute phase and not the phase for one speaker only.
One speaker out of phase would always be bad.
Do you accept that some people believe they can hear the difference between correct absolute phase and the reverse?

Just wondering if you're making the point that this and having speakers out of phase are different issues, with one being much worse than the other, or that one of them is completely irrelevant?

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