speaker phase

[woodyc]

I'd be interested to hear from anyone who has found that reversing speaker phase matters in a single-speaker amp.

It isn't necessary to read this part... but if you're wondering why I'm asking its because I just started reading Gerald Webers Desktop Reference book and its an idea that he pushes. In particular, he claims that amps in which the speaker moves forward with a positive signal have a better apparent low end. I'm not sure who originated this idea but it may have been Ken Fisher because it was mentioned in a Vintage Guitar column he wrote about JTM45s and that was a couple years before Weber's book. But Weber has a more elaborate description of the whole thing. He says on p.53-54 that what matters is the phase of the speaker relative to the input signal to the amp. I've run into several people who read about this ask to have the phase of their speakers checked or reversed and I've always politely declined.

[tbryanh]

I've read that too in the places you mentioned.

It doesn't seem that it should matter.

Ken Fisher also said that because an aluminum chassis is a better conductor than a steel chassis, aluminum chassis are faster that steel chassis and that you can hear the difference in pick attack or something to that effect.
I really wonder about this one too.

Ken Fisher and Gerald Weber were both great amp builders and techs, but I think this stuff here is probably snake oil.

[dai h.]

some interesting threads on the gear page if you search their archives like this one:

http://www.thegearpage.net/board/arc.../t-189948.html

[tbryanh]

some interesting threads on the gear page if you search their archives like this one:

http://www.thegearpage.net/board/arc.../t-189948.html

Thats a long thread.

I scanned through it, and there is something that might be true.

Since one half cycle in a distorted amp is different than the other half cycle, it might be that in an open back cabinet, the sound coming out of the front of the cabinet might sound better for one of the half cycles, and the reflected signal coming out of the back of the cabinet might sound better for the other half cycle.

[tbryanh]

It probably wouldn't hurt to have a speaker phase switch.

If nothing else, it could be used to match the phase of a second amp in a bi-amp situation.

[Alex R]

I can see how it might affect acoustic feedback.

[hasserl]

I've been involved in several of these threads at The Gear Page. I've always been very skeptical about it, and have argued my POV quite a bit. But ultimatley the guys there that believe this have provided a decent enough argument that I may not buy it all, but I'll let it go.

The issue is NOT whether a positive signal causes the speaker to move forward or not. The theory that works, for me, is: a distorted output signal is rarely symmetrical, it is often very asymmetrical. And, a speaker's efficiency is rarely symmetrical, most often a speaker will be more efficient when moving in one direction vs the other. So, if you can match the speaker to the amp so that the asymmetry of the output signal matches up with the asymmetry of the speaker efficiency, you may have a result where the amp responds better when driven into distortion, with increased sustain that rolls into feedback better. That's the theory in a very abbreviated account.

I've not experienced it myself, but lots of guys have and they swear they can hear a difference. I'd love to have one of them pick it out in a blind test, but none of them seem willing to put themselves up for such a test.

I'm still not convinced you can even control the positive / negative signal swings. It seems to me that, besides the signal being inverted at every gain stage, so different amp channels will have a different number of gain stages, and will invert the signal a different number of times. But every time you engage or disengage a pedal you'll change the phase of the signal. And I'm not convinced that even the way we pick the strings won't change the phase of the signal. As in, if you pluck the string with an up motion the beginning of the note will be opposite what it will be with a down stroke, right? With all of these variables, how in the world can you control how the speaker moves in relation to plucking or strumming the guitar? I remain skeptical. Until one of these guys that swear it makes a difference shows they can identify this difference in a blind test.

[Sweetfinger]

Ken Fisher and Gerald Weber were both great amp builders and techs...

Um, IMO, one of those is much better than the other or should I say, ..was better..

[dai h.]

yup GW doesn't really have much of a technical background. More of a hobbyist portrayed as "guru". Not that everything is wrong but, be careful with his info (co-planar traces, putting alu electros under a lightbulb to reform them, etc.).

[Joe Bee]

Even if the distorted signal were symmetrical I see a mechanism how the speaker phase could affect the sound: Feedback.
Even if the deliberate, squealing type of feedback does only come up in certain genres, there surely is _some_ effect even if the loop gain is less than unity. So switching between negative and positive "acoustical feedback" really ought to have a difference on the sound.

[woodyc]

daih, thanks for the link. I finally read the whole thread at gearpage.

About feedback... with a guitar I don't think the phase of the acoustical feedback has to match the phase of the original vibration since the string is a resonator. It will always resonate when it receives energy at the right freq and the phase can adjust itself to the driving force.

About the Weber/Fisher low end claim... I ordered some parts yesterday to make a footswitch and check it out. The business about phase making a difference when there is asymmetrical distortion seems totally valid, but its not clear to me that it would be audible in any normal situation.

[David Schwab]

I can see how it might affect acoustic feedback.

They put phase switches on electric/acoustic guitars to help control feedback, so it does have an effect.

I suppose if the sound from the amp is in phase to the guitar, you will have enhanced the feedback.

In the case of the acoustic guitars, they put the guitar out of phase from the amp to eliminate feedback.

[Alex R]

Yeah I can see that the string resonates all ways but the body of the guitar will response in phase to a degree I guess. Hence particularly important for acoustic guitar, but I believe a solid body would act that way to a degree also. In fact I should think it does more picking-up of sound that does the string, until it sets off the string to resonating.

[MWJB]

Weber/Fischer's claim is not snake oil, phase is obviously most important when dealing with multi speaker arrays, but is perfectly detectable in single speaker amps. It slightly changes the harmonic character...some speakers really don't like it, most are happy enough either way.

Does it matter? So long as the amp functions as it should it's not going to change your life.

In fact, in less time than it takes to read/write this thread you could have switched speaker leads and tried it. If you don't hear a difference don't worry about it any more, on the other hand you may find that you have a preference.

Yeah, a switch is a good idea for imediate A/B'ing, by the time alot of guys have rewired their speakers they can't really remember what original polarity sounded like (especially if having to solder) & then the "new" sound just "overwrites" the old one.

You might need a fair degree of sustain to really bring the effect to the fore, but I find it's usually quite perceptible.

[woodyc]

David, re: feedback. What you're saying is true about acoustic guitars but I think its a special case that isn't relevant. The phase switch only works at one frequency (I think its for damping a particular mid-bass cavity resonance), only at relatively low volume, and only if you don't move. With electrics you get some level of sustain/feeeback at all frequencies wherever you are. I think the electric scenario is more like the effect of plugging into a Marshall in a guitar shop and hitting a B, and every acoustic in the whole store has its B string ringing. That kind of ringing just takes on the phase of the driving force?

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.