Speaker Phase

[martin manning]

I disagree. This is no different from the speaker-instrument feedback that occurs when playing an amplified guitar, and the controlled or uncontrolled nature of any feedback depends upon the frequency, phase of the feedback, and the damping in the system.

By the way, note that the Expression pickup and preamp system installed in some Taylor acoustic electric giutars includes a phase switch, which is used to help control feedback.

[Structo]

Although this may not be a direct comparison, take a look at a self powered subwoofer made for a home theater system.

Most of the better ones have a polarity or phase switch.

This changes which way the cone moves.

The switch is almost always on the back so you have to reach behind to flip it.
But every time I have tried it, there is one position that sounds a bit louder and boomier, and one that sounds a bit tighter but a little quieter.

I would think the position that is louder is in phase with the other speakers in the system and is moving out.

I know some of you say, well yes, you are correcting a phase problem among the surround speakers.

How about a bass kick drum?
When you kick it, does the drum head move out or in?
If you have a drum skin on the front of the drum, does it move out or in when kicked?

Try this with your #1 amp and speakers.
Turn it up quite loud to where you palm mute the strings and give it a single downward strike with the pick while watching the speaker/ grill cloth.

Does it move out, or suck in?

Now if you are playing in a group and say the bass guitar's speaker moves out on attack and your speaker sucks in on attack, won't there be some sort of cancellation or reactance between speakers?

[Lynxtrap]

I disagree. This is no different from the speaker-instrument feedback that occurs when playing an amplified guitar, and the controlled or uncontrolled nature of any feedback depends upon the frequency, phase of the feedback, and the damping in the system.

By the way, note that the Expression pickup and preamp system installed in some Taylor acoustic electric giutars includes a phase switch, which is used to help control feedback.

Well, I still don't agree (that's why it's called a discussion, isn't it )

The physical effects that happen in a tube as you mentioned, I see as dependent on many variable factors such as distance, sound level, heat, reflections, cab construction, type of tube, etc.
The feedback between speaker and guitar mic/pickup is something else. But even that is a bit random, since the signal phase could have been inversed X times before it reaches the speaker.

[martin manning]

I disagree. This is no different from the speaker-instrument feedback that occurs when playing an amplified guitar, and the controlled or uncontrolled nature of any feedback depends upon the frequency, phase of the feedback, and the damping in the system.

By the way, note that the Expression pickup and preamp system installed in some Taylor acoustic electric giutars includes a phase switch, which is used to help control feedback.

Well, I still don't agree (that's why it's called a discussion, isn't it )

The physical effects that happen in a tube as you mentioned, I see as dependent on many variable factors such as distance, sound level, heat, reflections, cab construction, type of tube, etc.
The feedback between speaker and guitar mic/pickup is something else. But even that is a bit random, since the signal phase could have been inversed X times before it reaches the speaker.

Yes, all disagreements here are voiced with the utmost respect :^)

Re your first point I agree completely. No acoustic energy is going to be passed directly to the tube's internal structure. It is after all in a vacuum!

On the second point, in speaker-instrument feedback, energy is passed from the speaker through the air to the guitar which causes its entire structure to vibrate, subject to some of the same variable factors you mention above. As a consequence, some relative motion is created between the pickups and the strings, which causes an electrical signal to be returned to the input of the amplifier. How is this different from the speaker-tube feedback? This feedback does not necessarily result in an uncontrolled howl; the argument being advanced here is that it can enhance or degrade the overall sound of the system, and that the net result can be affected by switching the phase of the speaker.

[vibratoking]

I think we are getting a little off-track here. I think the OP was discussing a speaker system that contains either a single speaker or multiple speakers wired in identical phase. Also, I believe the OP was not discussing how this speaker system interacts with any other sound source. I think the OP was asking if anyone can, or has, positively identified any difference in sound quality of this speaker system when the phase of the complete system is reversed in isolation. I think it is well known and obvious to everyone that phase can affect the sound quality as soon as you introduce other sound sources. Again, I believe the OP is asking about this speaker system in isolation only.

[Firestorm]

On the purely electronic implications of phase, have a look at this post from elsewhere (near the bottom of the text portion):http://chambonino.com/work/miscguitar/misc6.html

It seems plausible that the speaker's field (in particular, its phase) can impact the dimensions of the tube's virtual cathode and cause anomalies in the tube's behavior. The expanding and collapsing field of the speaker as it is driven could well produce a form of electronic feedback that could serve to enhance or "neuter" the performance of the affected tube(s). Needs more investigation, but seems interesting.

[greiswig]

Re your first point I agree completely. No acoustic energy is going to be passed directly to the tube's internal structure. It is after all in a vacuum!

Doesn't this only hold true if we define "acoustic energy" as only being transmissible via air? In other words, there is definitely vibration that gets passed to the internal structure via conduction through the chassis, glass, etc. Otherwise how could a tube ever become microphonic to the point of being a concern?

And to me, this may be part of the issue: I've done an experiment with four conditions (not blind, mind you): 1) Head ON cab, polarity +, 2) Head ON cab, polarity -, 3) Head OFF cab, polarity +, 4) Head OFF cab, polarity -.

There was a noticeable change in feel and ability to initiate feedback on most notes in all these conditions. Head on the cab and with the polarity + seemed to result in the best feel and bloom. The difference between the #3 and #4 conditions was not as apparent to me, but it was there...but it was also hard to attribute one as being distinctly better than the other.

I'd love to do this in a more controlled way.

[martin manning]

On the purely electronic implications of phase, have a look at this post from elsewhere (near the bottom of the text portion):http://chambonino.com/work/miscguitar/misc6.html

It seems plausible that the speaker's field (in particular, its phase) can impact the dimensions of the tube's virtual cathode and cause anomalies in the tube's behavior. The expanding and collapsing field of the speaker as it is driven could well produce a form of electronic feedback that could serve to enhance or "neuter" the performance of the affected tube(s). Needs more investigation, but seems interesting.

He doesn't say, but I think the author of that article is talking about the static magnetic field around the speaker magnet and not the time-varying field produced when the voice coil is energized with an AC signal. The static field could certainly affect the performance of the tube by altering the path of the electrons from the cathode to the plate.

[martin manning]

Re your first point I agree completely. No acoustic energy is going to be passed directly to the tube's internal structure. It is after all in a vacuum!

Doesn't this only hold true if we define "acoustic energy" as only being transmissible via air?

Yes, that's exactly what I mean, energy contained within a sound wave. Your trials seem to have confirmed the importance of physical contact, and therefore improved transmission of feedback to the chassis, and that the speaker phase also affected it.

[husky]

As a piece of metal approaches the guitar pickup pole piece the polarity swings positive out of the guitar if the pickup is clockwise and North top. If Everything in your chain (and that is a BIG IF) were to ultimately maintain that polarity all the way to the speaker it makes sense to me that it is something you could hear on the initial punch or attack. Probably much more so on a bass if you slapped. However.... as the string goes away it will swing negative. I still think it could be possible to hear the initial attack. Don't know if I could do it in a blind test. I say much like guitar cord direction.... flip it and see which way sounds better or if possible put a phase switch on the amp, didn't Matchless have a speaker phase switch? I remember people swearing they could hear a difference... yeah I know, I'm all for double blind tests. I do think in a combo there could be an interaction though. Maybe in that article is the same thing that Jim Kelley experienced

[Dr-Joned]

My turn !
The phasing will have an impact on the sound, ONLY if the guitar is in proximity to the speaker. The negative impact of the sound waves would tend to cancel or slow the effect of sustain. On the other hand, if the guitar and speaker were in phase, the effect would be noticible. It would have a tendency to sustain more, because the sound waves are moving in unison with the strings.

As far as speaker movement goes, there is no cone pushing out or cone sucking in. If you hit an open A, the cone moves at 110 cycles per second. It may start by pushing out first, but will retract on the downsweep of the cycle.

The effect of phase cancellation is quite noticible on stage, after you do a comparison of an instrument with the phase reversed. I remember quite well playing with another guitarist where we were out of phase with each other. You would normally notice the effect when hitting a chord or when in the lower frequency registers.

So in summation, it is possible to hear the difference in phase.

[husky]

My turn !
The phasing will have an impact on the sound, ONLY if the guitar is in I remember quite well playing with another guitarist where we were out of phase with each other. You would normally notice the effect when hitting a chord or when in the lower frequency registers.

So in summation, it is possible to hear the difference in phase.

I don't know if that is possible. How could you make the strings sync up coming from different sources (players)? I don't think you can tell that two players are out of phase from each other they would have to be in perfect unison. Think of the nightmares! Fender pickups flipped phase every 5 years or so. Not many amps are in phase in to out and most flip the phase with effects loops or gain channels. How could you even diagnose you and he were out of phase? I would think you would need to pull metal away from the guitar pickup pole piece and see which way the cone moves.

[LeftyStrat]

To further what John said, speakers move in and out and have a definable phase, but guitar strings bounce around wildly in three dimensions. The distance from the amp also has an effect. Depending on the distance to the amp you might be dealing with a couple of milliseconds difference from the time you play a note until it hits the guitar.

Also the angle of the guitar to the source would affect the reinforcements and cancellations.

I can see that there might be interactions in a combo amp, but a head separated from the speaker cab, with the player at a distance, I can't find any scientific explanation of how anyone can determine phase of a single speaker simply by listening in a double blind test. Remember, double blind means both the testee and tester are unaware what A vs B actually is.

I'd need some definitive proof, otherwise it's just some guy name Geller with a bent spoon.

[Lynxtrap]

This is how I see it. For phase cancellation to occur there needs to be:
- One signal source
- One primary and one secondary path for the signal
- A point where the paths meet
- At that point, the signalwave on the secondary path has to be fully or partially reversed.

The perfect example would be the negative feedback loop in some amps. Two speakers out of phase with each other fed by the same signal source is another example.
A guitar pickup picking up the signal from the speaker could form a secondary path when it is fairly close to the speaker. After all, this is also how feedback occurs.
With the guitar totally isolated from the amp, you can't have feedback. So I can't see how there could be phase cancellation either.

[martin manning]

Okay, to sum up we have three possible interactions that might be affected by the electrical phase of the speaker connection, and there is anecdotal evidence that there can be an audible effect from reversing the speaker phase.

One of these interactions is the acoustic feedback to the guitar, which in turn results in electrical feedback to the amplifier. This is full of other variables that will change the phase of the sound waves reaching the guitar, including the highly variable position of the guitarist relative to the amp. I am inclined to believe that speaker phase is less important here.

A second is the mechanical feedback from the speaker to vacuum tubes and other non-ridgid components in the amplifier, resulting in electrical feedback. This is much more controlled, and very much so in the case of a combo amp configuration. IMO, it is not unreasonable to think that the speaker phase will affect this process and that the result would be audible.

The third is the direction (+ or -) of the initial pressure pulse in the sound wave produced by the speaker as determined by the initial direction of the guitar string movement upon release. Whether a human can detect this is questionable, but I could imagine a blind test where pairs of single pulses are sent to the amplifier and a listener is asked to identify any difference between the first and the second, each of these being of a random polarity.

Another thought: If the initial pulse direction is important, and the feedback from the speaker to the chassis is as well (meaning that for each of these one speaker phase relationship sounds better than the other), then it's possible that the "better" speaker phase for one could be the less desireable one for the other. The best combination might then require selecting the phase of the pickup signal and the speaker, or alternatively that some amp topologies (number of inverting stages) might be better in this regard than others for a given guitar.