speaker phase

[MWJB]

"MWJB, Could you be more specific about what to play and what to listen for? Maybe a guitar part from a well-known song where the effect would really be obvious? That would be really helpful. Thanks." Just a chord with reasonable sustain should do it, even a single note with enough drive...you're only comparing the phase one way to the other in the same amp, comparing to another amp on a well known song isn't going to help.

If you can't hear the difference don't worry about it. Plenty of amps are inadvertantly wired reverse phase and no one threw them on a skip because of that difference.

It's a way to subtly alter the voice of the amp, you might find itto your advantage you might not? But is usually tangible.

[hasserl]

Like I posted earlier, even different channels of one amp have odd numbers of gain stages, and thus have different phase of the signal. Which channel did you want to be "in phase"? Then there is the issue of using FX pedals, which will again invert the signal, now did you want the amp "in phase" when the effect is engaged, or when it is not? What about when you engage more than one effect? Now what? You think that by simply switching the wires at the output is going to make any practicle difference? It's crazy.

FWIW, I did try this with a Super Reverb. It was relatively easy to switch the leads at the first speaker. Since the others are fed from that they all stayed in phase together. Playing at medium volume, not pushing the amp into distortion, I detected no difference at all. But the theory that makes any traction at all only works when the amp is pushed into distortion, and only when the distortion creates an assymetrical signal.

[MWJB]

I have tried this with dozens of amps.

Forget "in phase"/"out of phase" neither forward or reverse phase is correct/wrong (as long as everything functions normally - I had a test cab loaded with Eminence Alpha 10"s, they hated being wired in reverse - it wasn't subtle either). In the history of some amps they were forward with some speakers and reverse with others.

Phase of channels is only an issue if you are cross patching.

Phase of cabs is important if running multi amp set ups.

Phase of individual speakers in a multi speaker array is important.

I can usually hear the difference in forwards vs backwards speakers in the same amp at moderate volume, it will just be easier if you have good harmonic content to start with.

Because you could not hear a difference does not necessarily mean that there is no difference. It's like the old Confutious riddle, "does a tree that falls in a forest make asound if there is no one there to hear it?"...just because no one can hear it doesn't mean it makes no sound. Even musicians with average hearing (and some with frankly quite damaged hearing) have demonstrated to me that they can hear a difference.

There's no need to waste time theorising or speculating, if you can't hear a difference don't worry about it...if you want to experiment and see whether you get a tonal benefit then try it. Don't be put off by someone telling you that it makes no difference, see for yourself.

[hasserl]

The phase of the channels has to be important, because the phase of the signal from the power amp depends on the phase of the signal into it. If you inject a signal into the front of a Fender amp into the normal channel, and then into the Vibe channel, the resulting output signal to the speakers will be opposite from each of the channels.

So which one do you want the cab to be in phase with?

Psychoacoustics will make you think you hear a difference, just because you want to, or because you think the difference is there. Try to identify the the difference when you don't know which way the speakers are wired, I'm skeptical you would be able to do it.

[Rick Erickson]

Who is putting phase switches on Acoustic guitars? If you move a couple feet relative to your speaker, (or if you turn around)
you will alter your overall "phase". The question of a phase switch on a single speaker amp is more one of matching it to other amps or cabinets. It was probably done for just such technical reasons and mis-interpreted by those who didn't understand the why- kind of like Dylan's song lyrics. (I was just trying to make it rhyme, man...) Professional mixing consoles, particularly recording desks have phase reversal switches on each channel. This can be useful for mixing various amps or mics for tonal purposes or just to make the amp "sit" properly in the mix. I have a friend who used to complain that he had to reverse the phase switch every time a guitarist changed channels on his rather expensive two channel amp or he would change it's position in the mix.

RE

[tbryanh]

FEEDBACK ISSUE

Since the speed of sound is about 1100 ft/sec, if you pluck about an 1100 cycles/sec note on your guitar (about the sixth fret on the G string), the wavelength of the note is about 1 ft.

This means that at about every 6 inches of incremented distance from the speaker, there will be a peak of sound energy in either the positive or negative direction (compressed or expanded air).

If your standing a long distance from the amp so that there is no feedback, and you start walking slowly towards the amp, you will get feedback when you hit the first peak of sound energy that is in phase with your guitar that has enough energy to cause feedback.

If you stop the note, and move six inches closer to the amp and pluck the same note, you will not get feedback.

If your still holding the note, you now have the option of moving either six inches closer to the amp to get feedback or moving six inches away from the amp to get feedback.

Each note on the guitar has its own set of distances where the peaks of sound energy occur.

When you get close enough to the speaker, these sets of distances can be blured.


ASYMMETRY ISSUE

Amplifiers can distort asymmetrically.

Speakers probably can distort asymmetrically.

If you have a clean amp and a clean speaker, the phase of the speaker probably has no effect in either an open back or in a closed back cabinet. (Assuming the cabinet only has one speaker in it)

If you have a dirty amp with asymmetrical distortion and a clean speaker, in a closed back cabinet, the phase of the speaker probably has no effect. In an open back cabinet, the phase of the speaker might have an effect. It might be that one half of the wave sounds better when it exists as compressed air coming out of the front rather than if if it exists as compressed air coming out of the back and reflecting off the wall. . . .

If you have a dirty amp with asymmetrical distortion and a dirty speaker with asymmetrical distortion, the phase of the speaker might have an effect in either an open back or in a closed back cabinet. For example, it might be that the best sound is had when the two asymmetries work together. . . .

…

[MWJB]

"So which one do you want the cab to be in phase with?" Aaaaargh...if you can't hear a difference it doesn't matter....if you can, then they way that sounds best! Usually there are more perrtinent factors deciding which channel you use (Reverb, trem, lead gain, bright, etc, etc,), you're going to use the channel you like the sound of best, irrespective of whether your speakers move forwards or backwards. Lets face it, most folks don't actually know for sure which way their speakers move, it only becomes an issue when using multiple cabs/amps.

"Psychoacoustics will make you think you hear a difference, just because you want to, or because you think the difference is there. Try to identify the the difference when you don't know which way the speakers are wired, I'm skeptical you would be able to do it." I'm sorry, I find that quite insulting. I'm pretty objective. I don't want/not want there to be a difference, I am reporting to you the benefit of my experience...if you can't hear the difference, don't sweat it, but don't presume to tell me what I do & don't hear.

[MattT]

This is extremely easy to test for yourself and I encourage everyone to do it...I was a non-believer until I tried it and then was like...wow.

This has nothing to do with the phase of each speaker relative to the other speakers...it is assumed that all speakers are in phase with each other. This is just about the phase of the entire speaker array relative to the amp output.

Make a reversed-polarity speaker cable...trust me...you'll be keeping it. Set your amp up with a regular-polarity speaker cable and dial it in such that it is just on the edge of feedback (get some OD and volume going)...enough such that you can coax feedback out of the amp with some effort but not so much that it takes off/sings on every note. Now switch to a reversed-polarity speaker cable (don't touch any controls) and play again...you should hear a difference in the feedback...either the amp will now sing on virtually every note or it virtually won't sing at all.

FWIW, in my limited experience an amp that has an odd number of inverting gain stages before the PI needs a reversed-polarity speaker cable and ones with an even number need a regular cable. I recently built a Dumble ODS clone and put the Dumblator FX loop in the amp...but before I put the loop 'in circuit' I wanted to listen to it with no loop (just to make sure the loop was sufficiently transparent). No loop = 4 inverting gain stages and With loop = 5 inverting gain stages. Amp feedsback better with a regular cable and no loop and with a polarity-reversed cable with loop...very repeatable.

hasserl I would do that blind test and I think anyone who actually tries this test would too. But maybe it matters less on some amps (like...almost negligible) than others? I just know on my ODS clone it was VERY apparent.

[woodyc]

MattT, Thanks for relating your experience. Just for reference was the cab open or closed back and what size room?

[MattT]

Hi woody,
It was open-back...not as open as a Fender combo cab but still about 1/4 open (Stone Age OS 2x12 FWIW). Room was about 25'x25', cathedral ceiling (popcorn texture), textured sheet rock walls with non-glossy paint, carpeted, with cloth/fabric sofa and love seat in it as well as some other furniture (mostly wood). IOW, not a particularly live/reflective room...but not totally dead either. I walked around the room and faced different directions and it didn't seem to lessen/intensify the effect any more than it usually does.

Who knows...maybe it's just a Dumble thing. Many of the experienced Dumble builders and users were already very aware of this (of course if you're using a Dumble or D-inspired amp without the Dumbleator then you don't need the reverse-polarity anyway).

[hasserl]

"So which one do you want the cab to be in phase with?" Aaaaargh...if you can't hear a difference it doesn't matter....if you can, then they way that sounds best! Usually there are more perrtinent factors deciding which channel you use (Reverb, trem, lead gain, bright, etc, etc,), you're going to use the channel you like the sound of best, irrespective of whether your speakers move forwards or backwards. Lets face it, most folks don't actually know for sure which way their speakers move, it only becomes an issue when using multiple cabs/amps.

But you said

Phase of channels is only an issue if you are cross patching.

Which makes no sense. The two channels are out of phase with each other, so the resulting output signal will be out of phase with either channel. If you're going to set the phase of the cabinet to match the amp, which channel are you going to match it to? That's the question. For those that only use one channel, the answer is easy, for those that use both it's not.

But the point of the question, while based on practical application, is really to point out the futility of trying to match the phase of the cab with the phase of the amp, because the phase of the amp is constantly changing, depending on which channel is used, what effects are used, and I still say it all starts with the signal from the guitar. How the pickups are wired, and even how you pick or strum the strings. If you pick a single note with a down stroke, then you pick the same note with an upstroke, is the phase of the signal the same or opposite? I think they will be opposite. So which one did you want the cab to be in phase with, your upstroke picks or your downstroke picks? Or you upstroke picks on which channel? Or your downstroke picks on which channel with which effect pedal (or combination) turned on? Go ahead, you're going to decide under which circumstance you want the cab to be in phase with the amp. Go for it.

"Psychoacoustics will make you think you hear a difference, just because you want to, or because you think the difference is there. Try to identify the the difference when you don't know which way the speakers are wired, I'm skeptical you would be able to do it." I'm sorry, I find that quite insulting. I'm pretty objective. I don't want/not want there to be a difference, I am reporting to you the benefit of my experience...if you can't hear the difference, don't sweat it, but don't presume to tell me what I do & don't hear.

And the usual response is indignation at being challenged. That's not my intent. You, as well as I and everybody else here, are influenced by things that we really cannot control. The science, at least to my understanding of it (and I'm more than willing to be swayed with a logical explanation), says this should not be an issue, that you couldn't possibly control the phase of the signal, and that there should be no difference which way the speaker cable is wired. You say there is. Fine, prove it. Don't be insulted, just take the challenge and set up the experiment that will lay to rest whether the phenomenon is genuine or not.

[hasserl]

hasserl I would do that blind test and I think anyone who actually tries this test would too. But maybe it matters less on some amps (like...almost negligible) than others? I just know on my ODS clone it was VERY apparent.

At this point I'd settle for just some sound clips. Stick an SM57 in front of that bad boy, let someone else switch the cable, without you knowing when/if they changed it, while you play. Then post the clip here so we can all hear it for ourselves.

[MWJB]

"Which makes no sense. The two channels are out of phase with each other, so the resulting output signal will be out of phase with either channel. If you're going to set the phase of the cabinet to match the amp, which channel are you going to match it to? That's the question. For those that only use one channel, the answer is easy, for those that use both it's not." If you are using one amp, what does it matter which channel plays forward or backwards...there is no "matching" unless you are using multiple amps/cabs...I don't understand what you mean by "matching", the amp either plays forwards or backwards...that's it. Both work, both will sound OK, just a little different.

Yes, the phase changes with channels, gain stages & other factors...but the cab is always "in phase" with the amp, just out of phase with specific stages. It is only out of phase when other influences dictate (multiple amps, cabs wired differently to each other). This seems to be the apart that you are overlooking.

"Don't be insulted, just take the challenge and set up the experiment that will lay to rest whether the phenomenon is genuine or not." How can I not be insulted? People pay me to work on their amps because they trust my ears & judgement, I have worked hard & long, spending many many hours performing critical hearing tests, devloping my hearing skills (the more you do the better you get) and you are sitting thousands of miles away, with no first hand experience of my work, or having sat in on many of the polarity tests that I have performed for customers in their "final fittings" for an amp service/mod", telling me I can't hear what I hear? Indignant...ya think?

What exactly does "the science" say on the specific subject of a given speaker in a given amp sounding different, when the cone fires forwards when a positive signal is applied, compared to backwards when a positive signal is applied? Why do you need an explanation, what's wrong with a practical test?

Prove it? How do you intend to prove what I can and can't hear? Why do I need to waste my time proving that there's a difference...I don't need to prove that the wind blows, the rain falls, or the sun rises either.

Why do you describe it as a "phenomenon"?

You have tried it once and not found a marked difference, fine, that's your experience...you could just say that, rather than questioning my integrity and proclaiming in a rather grandiose manner that you have "science" on your side.

If you said that you preferred a specific brand of tube or speaker...I'd have to believe you, even if I didn't share that opinion...I wouldn't suggest that you prove it.

[MWJB]

If you can't hear the effect in the room, why do you think that you will hear it better after being amplified, recorded, compressed, played back through the typical PC speakers?

YOU prove it doesn't make any difference.

[MattT]

hasserl,
Can I just make a clip (or two) that compares them? It would be apparent enough in a clip.

Of course, now I'll have submit to the ridicule of my playing and my crappy sounding build.

hasserl, you and I were typing at the same time but I wanted to add that I don't have an explanation for it...I never believed until I tried it. I just know that when I tried it that it wasn't subtle...it was very noticeable.

And as far as the imperfections of humans, our biases, and how we can be influenced by so many factors and none of us are immune...that's my line!