reverse phase

[rreiser]

I have my cab wired so the speakers move forward when a 9volt is applied. I experimented with a standard speaker cable and one reversed. I noticed two amps had more sustain and feedback with the reversed cable. A third amp sounded better with the standard cable. Is there a technical reason for this? Thanks, Russ

[billyguitar]

Some amps, like a tweed bassman, invert the polarity from the input. I believe original Jensens were labeled with the plus and minus backwards also. So if you have an inverting amp (I don't know how to tell that though) you might have to wire the speakers backwards to get them to play forward. I believe Gerald Weber explains all of this in one of his books.

[hasserl]

And of course, if you use any pedals that invert the signal it screws the whole thing,

Guys, were talking about vibrations in the hundreds to thousands per second. You really think it makes a difference if the first vibration moves the speaker forward or backward? I say any differences you heard from your experiment above were due to other differences in the amp/speakers/placement/room etc.

And like I mentioned above, sending the signal thru a pedal will usually invert it. Or it will invert it when it is on, then revert it when it is off. And if you have more than one pedal this is going on for each one.

Then you have to consider your picking techniques. Upstrokes will start the string moving one direction, downstrokes start it the other. What about finger picking?

Forget it! The variables are way too numerous to try to control so that the speaker would always move forward at the start of any note.

In a blind test I do not believe you would hear any difference between the way the speakers are wired. And even if you could, how could you possibly control all the variables?

[scottl]

I'll bet every penny in my name that I will immediately hear the difference using my gear. I plug straight in btw. The difference is exactly what the poster described. A VERY noticeable softening of the leading edge of the note, followed by greatly improved sustain and bloom. The feel is even different. Of course, I play a Dumble style amp that does invert. It is very touch sensative and has loads of bass. A less sensative or less bassy amp may not yield the same results.



Please don't poopoo that which you have not experienced for yourself.

:D

Edit: Didn't mean to come off real aggressive.... Just certain it is 100% true. Also, are we all certain the absolute phase coming out of the guitar has anything to do with pick vs fingers vs pick direction?? I am not certain of this in context of this discussion.

Originally posted by hasserl
And of course, if you use any pedals that invert the signal it screws the whole thing,

Guys, were talking about vibrations in the hundreds to thousands per second. You really think it makes a difference if the first vibration moves the speaker forward or backward? I say any differences you heard from your experiment above were due to other differences in the amp/speakers/placement/room etc.

And like I mentioned above, sending the signal thru a pedal will usually invert it. Or it will invert it when it is on, then revert it when it is off. And if you have more than one pedal this is going on for each one.

Then you have to consider your picking techniques. Upstrokes will start the string moving one direction, downstrokes start it the other. What about finger picking?

Forget it! The variables are way too numerous to try to control so that the speaker would always move forward at the start of any note.

In a blind test I do not believe you would hear any difference between the way the speakers are wired. And even if you could, how could you possibly control all the variables?

[John Phillips]

Just try it.


I think it does make a difference which direction the speaker first moves in - have a look at a DAW waveform of a guitar signal and see how uneven it is over the first few cycles especially, which is the bit your ear really focuses on. String picking direction does not reverse the phase because pickups are far more sensitive to up/down motion of the string relative to the polepiece, and very little side-to-side - and all notes start basically with the string moving away from the magnet when the pick comes off it (this was discussed in another thread).

Amplifer distortion (especially preamp distortion, or single-ended output stages) is often quite asymetrical too, so whatever phase the input signal, the output tends to be asymetrical in the same way. So for distorted signals in particular, the final phase between the amp and speaker is likely to be more important than anything in front of the amp, either at the guitar or any pedals.

Some pedals do reverse the phase, some don't. There's no hard and fast rule.

The reason some amps (or pedals) are in opposite phase to others is because most gain stages are inverting, so the final phase depends on the number of stages. You can even have channel-switching amps where the channels are out of phase with each other - you might think that this would make it impossible to have both channels sounding good at the same time, but a clean sound doesn't necessarily need the same phase as a distorted one to sound good. There's no 'right' or 'wrong' phase, only one way or the other.

It's certainly true that you have very little control over most of the phasing in a system, but that doesn't mean you can't hear it.

The simplest thing to do is make a reversed speaker cable and just listen. If you don't hear any difference, fine. That doesn't prove that other people might not, especially with a different set-up.

[scottl]

Hey John! Thanks for the string explanation. I was fairly certain it did not matter in my case , by just listening.

Now to dig up that Mike Landau discography for ya..... LOL :eek:

[TheAmpNerd]

Keep in mind there is a 90-degree phase shift when
a signal moves through a cap.

[billyguitar]

If you put a DC battery on a speaker it goes either in or out. This would seem to be the most simplified demonstration. Speakers are made to play forward to sound best, aren't they? If so that would be why the amp would sound better if the speaker pushes instead of pulls in.

[VaughnC]

Originally posted by billyguitar
If you put a DC battery on a speaker it goes either in or out. This would seem to be the most simplified demonstration. Speakers are made to play forward to sound best, aren't they? If so that would be why the amp would sound better if the speaker pushes instead of pulls in.

Speakers aren't made to "play foreward". In most applications, it doesn't matter which way the speaker moves in response to the input waveform as long as multiple speakers are in phase with each other. However, a guitar amp is a special application....and if the speaker moves foreward with the initial string attack, more initial presence will be felt with the resulting foreward air pressure. After the initial string attack, the rest of the note won't sound any different no matter what the phase. It's only that little thump at the very beginning of a note that makes the difference.

[VaughnC]

Originally posted by TheAmpNerd
Keep in mind there is a 90-degree phase shift when
a signal moves through a cap.

When a signal moves through a cap, the voltage phase dosen't change....only the phase relationship between the voltage and current changes. If you put two caps in series, the signal voltage doesn't invert with 90 degress each from each cap, does it?

[908SSP]

I made a phase reversal foot switch for testing and I can put it between the amp and speaker. It even has an LED on it. Anyway you hit the switch if the LED is on the speaker is in phase if it is off it is out of phase and yes I can hear a difference. All my amps sounded best in normal phase.


Just don't hit the switch while playing it might not be safe for the amp.

[hasserl]

Originally posted by John Phillips
Just try it.


I think it does make a difference which direction the speaker first moves in - have a look at a DAW waveform of a guitar signal and see how uneven it is over the first few cycles especially, which is the bit your ear really focuses on. String picking direction does not reverse the phase because pickups are far more sensitive to up/down motion of the string relative to the polepiece, and very little side-to-side - and all notes start basically with the string moving away from the magnet when the pick comes off it (this was discussed in another thread).

Amplifer distortion (especially preamp distortion, or single-ended output stages) is often quite asymetrical too, so whatever phase the input signal, the output tends to be asymetrical in the same way. So for distorted signals in particular, the final phase between the amp and speaker is likely to be more important than anything in front of the amp, either at the guitar or any pedals.

Some pedals do reverse the phase, some don't. There's no hard and fast rule.

The reason some amps (or pedals) are in opposite phase to others is because most gain stages are inverting, so the final phase depends on the number of stages. You can even have channel-switching amps where the channels are out of phase with each other - you might think that this would make it impossible to have both channels sounding good at the same time, but a clean sound doesn't necessarily need the same phase as a distorted one to sound good. There's no 'right' or 'wrong' phase, only one way or the other.

It's certainly true that you have very little control over most of the phasing in a system, but that doesn't mean you can't hear it.

The simplest thing to do is make a reversed speaker cable and just listen. If you don't hear any difference, fine. That doesn't prove that other people might not, especially with a different set-up.

John I have tried it, there is no difference. I don't believe you or anyone else could accurately with repeatability and reproduceability identify in a blind test which phase was which.

It would be cool if someone here set up such a test so we could resolve this once and for all.

BTW, how do you know that all notes start with the string moving away from the pickup? Where did this come from? It seems reasonable that when plucking the strings with fingertips (with a pulling motion) the string moves toward the pickup first, not away from it. The same with an upswept pick using a flat pick. What about finger picks? Each of these would seem to have the string moving first toward the pickup, while picking down would likely have it moving the opposite way. And strumming would seem to have the string moving side to side.

But that is just how it would seem. Without some type of measurement it is only a guess. So what measurement has been done so you say it moves away from the pup?

[trdlasvegas]

I made a inline speaker phase reverse with a switch for a very skeptical customer with excellent ears. He took it home and came back very sheepishly a few days later saying he could not tell the difference.

If you got two amps the phase is obvious... but with a single amp there is NO WAY you can hear the difference.

-Tony

[hasserl]

Originally posted by billyguitar
If you put a DC battery on a speaker it goes either in or out. This would seem to be the most simplified demonstration. Speakers are made to play forward to sound best, aren't they? If so that would be why the amp would sound better if the speaker pushes instead of pulls in.

A battery is DC, the signal from an amp to the speaker is AC. When you put a battery to the leads of a speaker it moves one direction as far as it can and stops. With an amp the speaker will vibrate back and forth from ~80 to several thousand times per second. It really doesn't matter which direction the speaker moves first. And you couldn't control it if it did.

[rreiser]

I sat in various positions and played the same note with full volume on the guitar with the same amp settings. The only thing I changed was the speaker cable. Each time there was a noticeable increase in the length of the sustain and the note went more easily into feedback. I did this numerous times to see if it was a fluke. Everyone has a right to their opinion. I just know what I heard.

[John Phillips]

Originally posted by hasserl
BTW, how do you know that all notes start with the string moving away from the pickup? Where did this come from? It seems reasonable that when plucking the strings with fingertips (with a pulling motion) the string moves toward the pickup first, not away from it. The same with an upswept pick using a flat pick. What about finger picks? Each of these would seem to have the string moving first toward the pickup, while picking down would likely have it moving the opposite way. And strumming would seem to have the string moving side to side.

But that is just how it would seem. Without some type of measurement it is only a guess. So what measurement has been done so you say it moves away from the pup?
Very simple....have a look at the waveform in a DAW/computer recording software. I've done this (for many purposes concerned with phasing, latency etc) and it's not a guess.

Certainly the initial peak can be made to be in the opposite direction if you deliberately pull the string up and let go... that wasn't the question, you asked about upstrokes and downstokes. In normal picking the pick (or fingertip) pushes the string sideways and downward, so when it slips off and forms the initial attack the string is always moving sideways and away from the pickup. Same with strumming, in either direction.

As I said, the effects of phase are also more noticeable (and also different - not necessarily a clear case of one particular phase always being better) on some types of tone than others. I don't doubt that there are some where the phase is virtually irrelevant. But there are some where it's very clearly audible.

If you don't want to believe it, don't. I'm a skeptic by nature too BTW.

[billyguitar]

I'm satified that phase doesn't matter except when multiple amps or speakers are involved. Probably not a subject worth this much discussion but since we're all apparently minutiae freaks there it is! ha ha

[scottl]

Originally posted by rreiser
I sat in various positions and played the same note with full volume on the guitar with the same amp settings. The only thing I changed was the speaker cable. Each time there was a noticeable increase in the length of the sustain and the note went more easily into feedback. I did this numerous times to see if it was a fluke. Everyone has a right to their opinion. I just know what I heard.

Thank you. I agree. With my particular amp, there is an immediate and big difference in tone. The sustain and bloom is better. The notes feedback easier as well.

Anyone who says otherwise and that I am mistaken is insulting me. I hear what I hear and I have the ears and experience to back up my claims. We are not talking minutia. At least with a Dumble style circuit, it is a noticeable phenomena. Maybe in a Marshall style amp with less output section bass, etc... The effect is less noticeable. But until you listen to my setup, A/B, please don't insinuate I am a moron who thinks he hears something that is not there.

It is real. End of story.

[fullerplast]

Ever use a phase reversal switch on a DI for an acoustic? They can be quite effective for reducing or eliminating feedback between a monitor and an acoustic guitar.

I really think that the same physics that account for that effect come into play with an electric.....with the exception that (unlike the acoustic) we always *like* the phase that results in guitar-amp interaction that results in easier feedback. It's a natural speaker to guitar body vibration interaction that is either resulting in more frequencies in phase (and additive), or out of phase (and subtractive).

I'm as skeptical as anyone when it comes to stuff like this, and for all the same reasons others have already given. The fact is, I tried it and heard a difference quite easily. More so with some amps than others, and most often at higher volumes, but I did hear it.

For my particular tests, I just used an inverting buffer at the input of the amp so I could easily go back and forth while playing. I'm not convinced that there is any difference with an inversion introduced before the amp vs after the amp, asymmetrical distortion or not. I heard the same difference reversing the speaker wires that I did invering the buffer. But I am convinced that there is a difference with phase between guitar and speaker.

[scottl]

Thank you Mark for so eloquently putting it!! Sorry if I pissed anybody off but I know it to be true.

Scott

Originally posted by fullerplast
Ever use a phase reversal switch on a DI for an acoustic? They can be quite effective for reducing or eliminating feedback between a monitor and an acoustic guitar.

I really think that the same physics that account for that effect come into play with an electric.....with the exception that (unlike the acoustic) we always *like* the phase that results in guitar-amp interaction that results in easier feedback. It's a natural speaker to guitar body vibration interaction that is either resulting in more frequencies in phase (and additive), or out of phase (and subtractive).

I'm as skeptical as anyone when it comes to stuff like this, and for all the same reasons others have already given. The fact is, I tried it and heard a difference quite easily. More so with some amps than others, and most often at higher volumes, but I did hear it.

For my particular tests, I just used an inverting buffer at the input of the amp so I could easily go back and forth while playing. I'm not convinced that there is any difference with an inversion introduced before the amp vs after the amp, asymmetrical distortion or not. I heard the same difference reversing the speaker wires that I did invering the buffer. But I am convinced that there is a difference with phase between guitar and speaker.

[TheAmpNerd]

Originally posted by VaughnC
When a signal moves through a cap, the voltage phase dosen't change....only the phase relationship between the voltage and current changes. If you put two caps in series, the signal voltage doesn't invert with 90 degress each from each cap, does it?

Thinking, you may be right. It has been awhile.

And I don't have anything to play with to check.
Which is always part of the fun.

[trdlasvegas]

You guys are getting off base on this. There is a difference between PHASE and POLARITY. All we are talking about is can you hear the POLARITY of the speakers.

If you get into PHASE, there are shifts in the phase of the signal as if goes through the signal path of a amplifier. This gets very complicated as you change the tone controls etc. and can even go over 360 degress such as group delay, etc. going through different values of caps.

Let stick to arguing the orginal point... Can you hear a difference if the Speakers move out with a positive signal on the positive terminal or move in with a positive signal on the negative terminal?

-Tony

[scottl]

Hi Tony. I was referring to the absolute phase. 1 X12 cabinet in fact. I absolutely can hear the difference. Not only can I hear it, but the insane blooming feedback that occurs when I use my reversing cable (puts output in phase) proves it. My amp does output an inverted signal. Forget cap charge times and hocus pocus like that. I have an odd number of gain stages and the signal is inverted at the jack. Pretty simple.

Anyone who wants a demo is welcome over my house anytime.

Scott

[fullerplast]

Originally posted by trdlasvegas
You guys are getting off base on this. There is a difference between PHASE and POLARITY. All we are talking about is can you hear the POLARITY of the speakers.


When you swap the polarity of the speakers, it's the same as introducing a 180 degree phase shift anywhere in the signal path (like at every gain stage). That's all we're talking about relative to phase shifts.

[hasserl]

I was looking thru the Speaker Q&A's at Ted Weber's bbs today for something else and found this interesting tidbit:

"From Ralph Nichols:

This may seem like a "non question" to one looking for good sound but, I am really curious to know if a standard has ever been established regarding the polarity of the magnet in a loudspeaker. In other words, does the "north pole" of the magnet always face the front or cone part of the speaker while the "south pole" always faces the rear of the speaker housing, or does this vary with manufacturers or, perhaps even models and sizes of speakers?

Ralph, that's a good question. I suspect at some point in the early years of speaker development there was a standard, but it has never stuck. Virtually all custom speaker manufactures conform to the customers wishes rather than their own, so for whatever reason, the customers have flipped and flopped over the years both in the polarity and the actual marking of the plus terminal. This could have something to do with the customers assembly line installation of the speaker harness, or just about any reason, really. Speakers that are/were intended to be used in a single speaker installation, such as in an elevator, etc., for background music may not be marked at all. In fact, I saw some identical speakers going down two separate lines at a speaker company once, and noticing the line equipment was slightly different, I checked out the magnetizers and final test stations. Sure enough, the two identical speakers were magnetized oppositely. I asked my host about it, and learned about the doesn't matter application. Of course, I already understood that in a single speaker application such as a guitar amp using a single 10 or 12" speaker, the polarity doesn't matter as far as hooking it up, but I always thought manufacturers would at least magnetize everything in one direction. I also asked, as you have, and looked in several books that I have found on the subject and have never been able to find a specific agreed-upon standard for polarity, either at the magnet N/S position, or at the terminals with the polarity indication. Out of curiousity, I have run a bunch of tests with different speakers and amps to determine if I could hear a difference, knowing that the real physics of it says there shouldn't be. I couldn't hear a difference in any of the setups, and I even had a person who I couldn't see flipping the switch so I couldn't know which way it was while I was listening. I must admit, though, I was biased by the fact that the physics of it says there should not be a difference. Some people say they can definitely hear a difference, though, particulary when they have their favorite guitar, effects, and amp in the equation. "

Scott, there is no reason to get offended. We need to be able to discuss these things rationally without getting our panties in a twist.

You cannot objectivly do a test like this yourself. If you are aware of which cable is being used your mind will interfere with your observation of the event and your perception will be subjective. Hell, it's subjective anyway, but to eliminate as much subjectivity as possible you would need to have another person do the switching for you without telling you which was which, and you would need to be able to consistently identify which was which.

I work with objective analysis and testing methods all the time as part of what I do for a living. I just do this amp stuff for fun. To support my family I am a Lubrication Engineer. I am a memeber of the Society of Tribologists and Lubrication Engineers, as well as the International Council on Machinery Lubrication. We perform many tests on new and used lubricants and well as developmental fluids. Most of the tests have the parameters set by the ASTM. In order for a test to be objective it must have good repeatiblity (where the same person performing the same test under the same conditions will consistently acieve teh same results) and reproducibility (where someone else in a different lab performing the same test under the same conditions will also consistently achieve the same results). Some of these tests though are subjective and they have very poor reproducibility, i.e. the Timken OK Load test.

Don't get offended, prove the point. Have someone else swap cables without you knowing which is which and see if you can consistently identify which is which. You would want to do this multiple times per test session to account for statistical coincidences. And you would want to do multiple sessions to prove repeatibility. If you can consistently determine which cable has the straight polarity and which has the reversed polarity you'll have proved your point. Without that all we have is your subjective perception that you can hear a difference. People say that Eric Johnson can hear the difference between brands of 9 volt batteries in his effects. I don't believe that. People say that they can hear the diference between types of speaker cables, I don't believe that. People say they can hear the difference between different types of power cords, I don't believe that either. I believe they all think they can hear a difference, I just don't think that in a blind test they actually could. Prove me wrong. It is okay, I don't have an emotional investment here. If I'm wrong then I'm worng. No biggie. But as Ted says, physics are against it.

And please, take no offense okay?

[scottl]

I like Ted, but I don't give any credence to his opinion on the matter. I respect his speaker building abilities but none of us know what kind of ear he has or if he can even play....

I don't need anyone flicking a switch. What is so hard to understand with me getting big feedback one way and noticeably less another way. That is not an opinion but a measureable result. I absolutely guarantee I will hear the ddifference. My panties are not in a twist (not wearing any...lol)! haha

Fwiw, I have demoed the cable change many many times for people and everyone always notices the difference. I don't tell them what I am changing btw.


Have a nice holiday...

Scott

[scottl]

Those same engineer types still argue till they are blue in the face that type of cap makes no difference in tone..... I have seen the arguments.

;)

[scottl]

This all has me thinking since a good number of people have convinced themselves that there is NO effect from having the speaker push out first.

Maybe, it is the speaker cabinet design that is the issue. If the speaker sends the initial attack into the box first, it could very well be the source of the tonal difference. I would have a tough time believing otherwise from a purely scientific point of view.

Makes perfect sense to me and I would be shocked to hear any engineeer explain why the tone would be the same if the sound first goes backwards into an enclosure as opposed to the strong leading edge of the wave being pushed out direct to you.

To take it a step further, maybe cabinet design makes no difference at all since the sound comes from the speaker. LOL ;)

Scott

[VacuumVoodoo]

I am one of the "nonmusician engineer types" but consider myself to be an experienced and seasoned guitar listener so I had to conduct an experiment today. I connected a polarity reversal switch on the speaker cable and had one of my guitarist friends play my amp.

After about 1 hour of playing the guitarist commented:
"I felt a distinct difference in the amp's playability, the reverse polarity configuration required more effort while nonreversed felt like direct physical connection between the speaker and my fingers. I also could move around more freely without losing that connection"

My own qualitative impression: Like the difference in the sound you make speaking while exhaling vs.inhaling. ok. maybe i exaggerated a little here.

For a quick, rough "engineer's view": The sound character is to a very high degree defined by the initial transient and shape of the wavefront. The speaker has to move air to create a pressurewave resembling the transient and wavefront as closely as possible. In correct polarity the speaker membrane will move foreward pushing the air in front of it thus making the wavefront propagate directly (exhaling). In reverse polarity the membrane will move backwards on initial transient creating underpressure in front of itself (inhaling). The transient pressurewave is directed into the speaker cabinet instead of open space in front.

I think a lot of misundertanding comes from the fact that as engineers we are used to precise physically correct definitions and descriptions of various phenomena. While to an engineer phase shift is something completely different from passive polarity reversal which is almost the same as active phase invertion - these terms are often used interchangeably by "nonengineer musician types" ;) - therefore the confusion.

Hope the above explains a little of the subject under discussion.

[scottl]

Thank you Alex!

Another real world example of correct speaker polarity, or absolute phase if you will, making a noticeable difference.


:dude

[fullerplast]

I really don't think the intial transient has much to do with it. For a 1Khz signal, the *entire waveform* is only 1 millisecond. I think it has much more to do with the speaker and guitar string/body vibrating sympathetically with each other. Again, refer to my acoustic guitar and DI inversion example earlier. Notes blooming with one polarity and not blooming with the opposite polarity happens well outside the intial transient.

I think that some of the differences of opinion result from non-similar testing. For this 180 degree phase (same as inverted polarity) effect to be apparent, you need to be playing at a reasonably high volume. I personally cannot hear a difference at very low volumes and I think that is because the coupling between speaker and guitar is not really that strong. Likewise, I would not expect to hear a significant difference if the guitar and amp were isolated from one another (like playing in a control booth with the amp in the studio). It's the same reason it's all but imposible to get feedback without the amp and guitar in the same room. I've not actually tried the isolation however, so that's just a theory.

[aleclee]

I think it's a bit over the top to think in terms of phase/polarity being "correct" or "absolute". I don't see how those words have meaningful definitions in this context.

We've already established that speakers' + and - terminals don't always predict the direction of cone travel for a given signal. It seems to me that, at best, we can discuss polarity in terms of an amp's inverting characteristics (which can vary from channel to channel) and a speaker's behavior relative to what most other speakers do.

So much for absolute. Who's to say what's "correct"? :confused:

That said, you can count me in as one who believes that polarity matters. Having rigged up a crossover speaker cable, I could definitely tell the difference in the cab's transient response. Could I tell you which one was in absolute phase? Hell, no! ...but as I state above, I don't think absolute phase is very meaningful. Back to my A/B experience, I could definitely tell the difference on a note's initial attack and found one preferable to the other.

I'll stick with the one I like better and leave the discussion of which one is right to the engineers and academics. I'll just enjoy the fruits of my research. :)

[aleclee]

Originally posted by fullerplast
I really don't think the intial transient has much to do with it. For a 1Khz signal, the *entire waveform* is only 1 millisecond.True, but I think that the waveform needs to be fairly symmetrical for that logic to hold. We've all seen speakers "jump" with a transient, where the cone tends to have a fairly long excursion either towards or away from the back of the cab. I'd think that it would be preferable to have it be away from the back of the cab so the listener gets a palpable low-frequency "thump" with the transient.

Polarity is probably a more academic issue at bedroom volume but IMO tone is academic at very low SPLs as well. :eek:

[fullerplast]

Originally posted by aleclee
True, but I think that the waveform needs to be fairly symmetrical for that logic to hold. We've all seen speakers "jump" with a transient, where the cone tends to have a fairly long excursion either towards or away from the back of the cab. I'd think that it would be preferable to have it be away from the back of the cab so the listener gets a palpable low-frequency "thump" with the transient.

Polarity is probably a more academic issue at bedroom volume but IMO tone is academic at very low SPLs as well. :eek:

Symmetrical or not, frequency and wavelength are still primarily determined by the fundamental tone. The initial "thump" is still an extremely short duration. The effect I hear with polarity changes occurs *much* later in the form of feedback and a more lively feel. The initial transient is over in a matter of milliseconds.

Here's a waveform (courtesy Seymour Duncan) of the initial thump (in green). See how quickly the transient is gone? There is basically one large jump in a positive directive and another of almost equal amplitude in the negative direction about 2ms later. After that, the signal approximates a sawtooth more than anything else.

The red signal is the output of a *very* overdriven gain stage. The first 30ms response to the signal is due to the coupling cap. After that, there is a very noticeably asymmetry, almost like series of pulses. The "positive" excursions for the speaker in this case are of much longer duration than the negative excursions.

I have no way of proving it, but I suspect that for an overdriven preamp stage, one of these polarities will couple with the guitar better than the other as the speaker spends more time at one excursion than the other. In one direction, the cone moves and "stays" there for a millisecond, in the other direction, the cone has to reverse direction as soon as it gets there, effectively pushing more air one direction than the other.....

Again, this would occur mostly with an overdriven signal, which would agree with my real-life observations. At lower volumes the speaker basically spends equal time in both directions. Anyway, that's my theory FWIW...:cool:

http://img.photobucket.com/albums/v83/fullerplast/guitar-signal.gif

[VacuumVoodoo]

Just for the sake of technical correctness: the red waveform in the illustration above is your typical blocking distortion. Notice that after initial pulse there is a period of 20ms of silence. This amp is in dire need of fixing.:eek:

Jackie:

I think that had you been playing amplified trumpet live and listened back through stage monitors you would probably notice difference between the two phase configurations.

It's all about total system response and interactions between it's various parts that produce desired effects. Amp-Speaker-Air-Guitar is a resonant system and phase relationships will determine whether the system is underdamped, critically damped or unstable/oscillating.

It's when amp's gain (volume) is high enough to put the system in the (desireable) critically damped condition that the in-phase vs. inverted phase difference is most clearly noticable.

[scottl]

Originally posted by VacuumVoodoo
Just for the sake of technical correctness: the red waveform in the illustration above is your typical blocking distortion. Notice that after initial pulse there is a period of 20ms of silence. This amp is in dire need of fixing.:eek:

Well Alex, if this is Mark's SLX Fuchs, hand tuned by me, I would suggest otherwise....

:D

[fullerplast]

Originally posted by VacuumVoodoo
Just for the sake of technical correctness: the red waveform in the illustration above is your typical blocking distortion. Notice that after initial pulse there is a period of 20ms of silence. This amp is in dire need of fixing.:eek:

It's an example of extremely overdriven stage, as I mentioned. Seymour Duncan provided the photo to illustrate a point, but I think it also serves well for our discussion. I was really just trying to visually show what we have been talking about relative to intial attack and symmetry. Sorry if I made it more confusing. You can ignore the blocking distortion for purposes of the polarity discussion IMHO.

[VacuumVoodoo]

Originally posted by scottl
Well Alex, if this is Mark's SLX Fuchs, hand tuned by me, I would suggest otherwise....

:D

Well Scott, if it is.....send to me and I'll fix it :cool: :p

[fullerplast]

Originally posted by Jackie Treehorn
After the last thread on this topic, I listened to a variety of recorded material through my stereo (one channel only), and flipped the phase. I listened to some trumpet music, since that's an instrument that is supposed to make absolute phase more obvious. Honestly, I could not hear any difference. Listening to phase in this way removes the variables of phase relationships with the guitar/pickup as well as those of cabinet resonances etc. since hifi speakers are generally more damped.

There's no doubt in my mind that the phase of the speaker impacts tone, however not because of "absolute phase." I don't think the guitar produces low enough notes for the initial cycle of the transient to be affected by the direction of the cone's first movement. I'm curious for those who hear the difference to try the test with a synth or tone generator, removing the guitar pickup from the equation.

Jackie- I think the guitar pickup *is* part of the equation, along with the guitar body and strings vibrations. It's a coupling anomoly, just like feedback. I do agree with you that the initial transient is not the primary component of the difference we hear.

[scottl]

Hey Jackie,

While I appreciate a good technical discussion as much as the next guy, why can't people just accept that there is an irrefutable difference in tone when you reverse the phase? Sometimes it is quite extreme and I guess for some it is not very evident.

It just bugs me that some people can't accept that it is real and in many cases obvious.

I think the speaker/cab/pickup relationship hypothesis has merit......

Happy holidays btw!

Scott

[TheAmpNerd]

Originally posted by VacuumVoodoo
I am one of the "nonmusician engineer types" but consider myself to be an experienced and seasoned guitar listener so I had to conduct an experiment today. I connected a polarity reversal switch on the speaker cable and had one of my guitarist friends play my amp.

After about 1 hour of playing the guitarist commented:
"I felt a distinct difference in the amp's playability, the reverse polarity configuration required more effort while nonreversed felt like direct physical connection between the speaker and my fingers. I also could move around more freely without losing that connection".

It would be interesting to re-do that cable
with the phase reversal switch that does absolutely nothing.

Then let the guy play it again and after and hour see which
side he prefers or if it plays differently.

We'ev all read about the placebo effect, it is real, it does
exist. That is why there are "double-blind" studies becasue
the person observing, if known, can influence the result by
sublte cues and non verbal communication.

[scottl]

Originally posted by TheAmpNerd
It would be interesting to re-do that cable
with the phase reversal switch that does absolutely nothing.

Then let the guy play it again and after and hour see which
side he prefers or if it plays differently.

We'ev all read about the placebo effect, it is real, it does
exist. That is why there are "double-blind" studies becasue
the person observing, if known, can influence the result by
sublte cues and non verbal communication.

I agree. The really obvious singing feedback when I use the cable might be different in a double blind study.... Feedback is quite gullible and is easily influenced by innuendo.

;)

[TheAmpNerd]

Originally posted by fullerplast
I really don't think the intial transient has much to do with it. For a 1Khz signal, the *entire waveform* is only 1 millisecond. I do know in the stuff I've read with conversations
with professionals have taught me that we get most of the information in the initial transient (if I recall correctly).

There is a very interesting book "Music, the Brain, and Ecstacy"
which discusses how we hear and its affect on the brain.

[TheAmpNerd]

Originally posted by TheAmpNerd
EDIT:

What I meant to say is this..."there are "double-blind" studies becasue the person listening, if known, can influence the result by listening to singing sustain, over driven tones, and pick attack!
This is further enhanced by the inhalation of certain
controlled substances. Roll a Rex anyone? Rawk on.... :dude :dude :dude :dude :dude :dude :dude :dude :dude :dude

[fullerplast]

Originally posted by TheAmpNerd
I do know in the stuff I've read with conversations
with professionals have taught me that we get most of the information in the initial transient (if I recall correctly).


There is much information in the initial transient and it is very important to the sound of a guitar. But it has little to do with notes blooming into feedback with one polarity and not blooming with the opposite polarity. This happens well outside the initial transient. Attack vs decay vs positive feedback due to constructive vibration.

[fullerplast]

Originally posted by Jackie Treehorn
Well, I'm kind of arguing cause instead of effect. If you play trumpet amplified, you're in a feedback loop essentially caused by a microphone or some other transducer picking up the amplified sound. There is obviously a big difference between negative and positive feedback loops. I suppose I'm challenging those who hear and claim an "absolute" phase relationship to test those claims in the absence of a "loop."


I don't really care or know how to define "absolute" phase or polarity between a guitar and amp. All I know is that when I get the speaker polarity that gives me a more lively sounding guitar-amp interaction and lets me get controlled feedback more often and sooner than the other polarity- that's absolutely the polarity I want to use!;)

The (feedback) "loop" is the tool to find it, although you could probably come up with a consistent means to predict it with enough measurements. The ear is by far the easiest method.

[philster]

Just spotted this thread, and it has been an intersting read since I have been playing around with reversed speaker cables for the past 3 months.

I have no idea whether all amps will show a difference but in the ones I have tried (homebrew TW style amps), the difference has been incredibly easy to hear. Keeping the same guitar, volume etc, and just muting the amp and switching the speaker cable from a normal to reverse wired and just hitting the G string on the 14th fret showed 100% of the time that the reversed arrangement would just sustain on and on and feedback easily. With, the normal cable, the note would just die off and decay without fedding back. There is no need to listen to some subtle changes, this was a night and day difference.

I also notice that the attack is a bit softer with the reversed cable, as if the amp has more sag.

Playing live however that softness did not turn out to be an advantage as the tone seemed to get slightly muddy and I actually preferred the tone using the standard cable.

[scottl]

Originally posted by philster
Just spotted this thread, and it has been an intersting read since I have been playing around with reversed speaker cables for the past 3 months.

I have no idea whether all amps will show a difference but in the ones I have tried (homebrew TW style amps), the difference has been incredibly easy to hear. Keeping the same guitar, volume etc, and just muting the amp and switching the speaker cable from a normal to reverse wired and just hitting the G string on the 14th fret showed 100% of the time that the reversed arrangement would just sustain on and on and feedback easily. With, the normal cable, the note would just die off and decay without fedding back. There is no need to listen to some subtle changes, this was a night and day difference.

I also notice that the attack is a bit softer with the reversed cable, as if the amp has more sag.

Playing live however that softness did not turn out to be an advantage as the tone seemed to get slightly muddy and I actually preferred the tone using the standard cable.

Big ups.... Exactly my observation. Slightly softer attack, and big difference in bloom and sustain. Notes die quickly one way and not the other.

Easy to hear.

:dude

[malabarmusic]

Originally posted by philster
... switching the speaker cable from a normal to reverse wired ... Is there an easy way for a hamfisted solder monkey to purchase a reverse wired speaker cable?

- DB

[philster]

Originally posted by malabarmusic
Is there an easy way for a hamfisted solder monkey to purchase a reverse wired speaker cable?

- DB

Yeah sure.
I just had Butch from Bayou cables make me a reversed cable. Just make sure you have him label the reversed end and connect that end to the speaker cabinet.

It is worth having one of these cables around.

[scottl]

Originally posted by philster
Yeah sure.
I just had Butch from Bayou cables make me a reversed cable. Just make sure you have him label the reversed end and connect that end to the speaker cabinet.

It is worth having one of these cables around.

Why do you need to know which end is reversed?? Same difference.... :confused:

[VacuumVoodoo]

Originally posted by scottl
Why do you need to know which end is reversed?? Same difference.... :confused:

Directionally determined speaker cables ?......don't let this thread go in THAT direction:p

[philster]

Originally posted by scottl
Why do you need to know which end is reversed?? Same difference.... :confused:

As I understand it, you can generate some voltage at the output jacks of your amp head that could get you in trouble especially if you have a pacemaker. I heard it could be up to 40 volts. There would be no sonic difference.

[trdlasvegas]

Originally posted by VacuumVoodoo
Directionally determined speaker cables ?......don't let this thread go in THAT direction:p

Hey why not??? Some cables have arrows on them to tell you what direction the electrons should flow. If you guys can hear the difference of speaker polarity in a guitar amp you should be able to hear those electrons swiming upstream the wrong way in the cable. :rolleyes:

-Tony

[hasserl]

Originally posted by trdlasvegas
Hey why not??? Some cables have arrows on them to tell you what direction the electrons should flow. If you guys can hear the difference of speaker polarity in a guitar amp you should be able to hear those electrons swiming upstream the wrong way in the cable. :rolleyes:

-Tony

Doh!!! :D