Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubesornothing on April 24, 2010, 03:16:18 pm
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So a buddy says to me that dumble and fuchs single 1x12 speakers are wired out of phase. That when the guitar signal moves positive, the speaker sucks in, and it should push out. This is a single, solo speaker - I am not talking about more than one speaker.
To me this sounds like just a bunch more mojo hype stuff. With the number of times inverting stage flips the signal, combined with the phase shift of RC networks and other circuits I think designers get lucky if the guitar signal matches the speaker signal phase.
So... is there any fact behind this?
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Sounds like mojo.
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It shouldn't matter unless you use it in a multi-amp setup, where it matters a lot! That said, many hi-fi guys swear that reversing the speaker polarity while playing some recorded music will "enhance the sound stage."
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I figured as much. Perhaps I'll take the time to figure it out and add it as a selling feature.
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You're too late. Matchless already did it. Check out page 3.
http://www.schematicheaven.com/newamps/matchless_dc30_old.pdf (http://www.schematicheaven.com/newamps/matchless_dc30_old.pdf)
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You're too late. Matchless already did it. Check out page 3.
http://www.schematicheaven.com/newamps/matchless_dc30_old.pdf (http://www.schematicheaven.com/newamps/matchless_dc30_old.pdf)
:laugh:
I can actually see that being useful. You want all the guitar players and bass player speakers to be in phase. If not the band can sound like crap.
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You want all the guitar players and bass player speakers to be in phase.
Can you explain this?
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You want all the guitar players and bass player speakers to be in phase.
Can you explain this?
It's just the same thing as having a speaker out of phase in a 2x12 cabinet. It's noticeable to me when two guitars playing the same note. It's a weird phasing effect. All I can say is try it sometime.
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From what I have read even some effects put the signal out of phase.
Is it true that is an amp has an odd number of stages that the signal will be out of phase?
That every stage inverts the signal so if it is out of phase going into the phase inverter that it is out of phase at the speaker?
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Not every stage inverts the signal - for instance, cathode followers do not.
I just put a scope on the PI and speaker output of an AB763 (ish). They are out of phase with each other. I could probably re-jig this by swapping OT leads or grid leads. So "it all depends".
If phasing is something to worry about, then you would want to get the input signal in phase with the speaker output.
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At the risk of sounding pedantic, there will be more effect on phase between a guitar and bass or two guitar cabinets with the physical distance involved. plus there is a geometrical function: think of the triangle between the two speakers and your ear, as you move around the angles and the distances change. A lot. Much more than flipping the phase one way or another. Also the distances to and from the walls and ceilings have other effects as the distances and frequencies change. There is a lot more room for actual acoustical physics than the (mojo) effect of flipping the phase of the amp. Have someone pick up your speaker box and slowly rotate or tilt it as you play, you'll hear what I mean. A guy named Leslie sold a lot of speakers that did the phase shift thing mechanically for organs- and guitars... till someone invented a little stomp box that sounds kinda like it but weighs less...
Just had a 'Neil Young' moment: considering the logistics of hookin' up some actuators to a footswich to move the cabinet around... kinda like his 'wizzer' setup- (tilt up, down twist left...) that gymbal setup might not be practical for anything larger than a champ or pignose... but it's a fun mental excercise.
Addendum: I seem to remember a section in Weber's "Hip Guitar Amp" book where he waxed eloquent on the subject... Much as I respect most of his knowlege... that section was a bunch of hooey. (my .02c)
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I seem to remember a section in Weber's "Hip Guitar Amp" book where he waxed eloquent on the subject...
He did at least mention that it was "absolute phase" and say that it was more important in multi-amp/multi-speaker setups.
By yourself, he claimed that it could have an effect on acoustic feedback. But if that's true, so could moving closer/farther away from your speaker, due to the wavelength of the sound.
I wouldn't worry about all this too much; it's a bigger issue if you send a single signal through 2 amps which result in opposing phases at the speaker, because (presumably) you're dealing with 2 signals that are otherwise identical.
Time-based effects like phasing, chorus and reverb do crazy things to the phase of a signal as well, and most people are typically pleased with the result.
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As someone said, the physical distance involved will affect the phasing and probably negate any effect of the different instruments speaker phasing. Same thing with the acoustics of the room. I've wondered if speaker phasing (or the relationship between the speaker and pickup phasing) affects the feedback you get from holding your guitar in front of your amp.
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If you do get into a complex, multi-miked, multi-speaker set-up it is something to consider, you (or your sound tech) will have to come to grips with this issue. If it is only two cabinets, not miked (or only one miked), I don't think you will have a problem, there are so many phase cancellations going on at different frequencies that the relative polarity shouldn't matter. When I used to do sound, I would always have a phase reverser for the mics, just in case.