Loud Speaker polarity ... again !

[j0k3335]

sorry to bother you on this subject so often discussed: I try to explain, on French forums where there are some manufacturers of amps,
this phenomenon of inversion of polarity of the HP:
and obviously, for lack of theoretical demonstration, they laugh in my face , retorting that in single Loud speaker mode, the phase does not matter.

I asked them to do the test themselves (some have Dumble clones... VHT D-50, ...) BUT, nothing to do. they don't believe me and HEAR no difference.
( I've made some experiments in both my Fuchs -ODS30 and Triple Drive- and a previous Ceriatone Bluesmaster: ... and hear EACH time a difference !!!)

Would someone be willing to waste a little time to give me the beginning of an OBVIOUS THEORETICAL explanation!

... which my level of knowledge does not allow me !!!

Thank you in advance

PS: I already read Two Rock's explanation and transcribed it to them... BUT they tell me there is no theory in it

[Charlie Wilson]

Wish I could explain it but I can definitely hear it. It is part of the reason the FET sounds different than the normal input.
CW

[j0k3335]

Wish I could explain it but I can definitely hear it. ...
CW

... I'm in the same situation ... BUT without your knowledge ...

[martin manning]

One difference is in the initial attack. When the guitar string moves from the treble side to the bass side it produces a voltage at the jack that is opposite in polarity to the voltage produced when the string moves from the bass side to the treble side. This is due to the change in in the magnetic flux passing through the coil being reversed. The initial voltage that appears when the string is released by the pick causes the speaker cone the move in one direction or the other, either pulling or pushing the air in front of the cone, depending upon the phase relationship of the output to the input of the amp. If you reverse the speaker connections, or add another inverting gain stage to the chain (like the FET booster), the initial movement of the speaker cone will be reversed. You should be able to cause the same thing to happen by picking from the treble side vs. the bass side of a string. Once the string is vibrating, it doesn't matter how it started.

Some people have suggested that the sound waves coming from the speaker will reinforce the vibration of the guitar strings if they are in phase. That is certainly true, but the distance from the speaker to the guitar is an important part of that. A 1kHz sound wave has wavelength of 0.34m. A change of half that much 0.17m (~6.7 in) would change the phase of the speaker sound wave with respect to the guitar by 180 degrees, so a relatively small movement of the player would reverse the effect.

[j0k3335]

One difference is in the initial attack. When the guitar string moves from the treble side to the bass side it produces a voltage at the jack that is opposite in polarity to the voltage produced when the string moves from the bass side to the treble side. This is due to the change in in the magnetic flux passing through the coil being reversed. The initial voltage that appears when the string is released by the pick causes the speaker cone the move in one direction or the other, either pulling or pushing the air in front of the cone, depending upon the phase relationship of the output to the input of the amp. If you reverse the speaker connections, or add another inverting gain stage to the chain (like the FET booster), the initial movement of the speaker cone will be reversed. You should be able to cause the same thing to happen by picking from the treble side vs. the bass side of a string. Once the string is vibrating, it doesn't matter how it started.

Some people have suggested that the sound waves coming from the speaker will reinforce the vibration of the guitar strings if they are in phase. That is certainly true, but the distance from the speaker to the guitar is an important part of that. A 1kHz sound wave has wavelength of 0.34m. A change of half that much 0.17m (~6.7 in) would change the phase of the speaker sound wave with respect to the guitar by 180 degrees, so a relatively small movement of the player would reverse the effect.

Thank you very much for these explanations, it is very interesting!

However, I can't tell if you're convinced of this phenomenon!

So there wouldn't be any other technical explanations I could give them?

Anyway, thank you for this attempt!

José

[Colossal]

However, I can't tell if you're convinced of this phenomenon!
So there wouldn't be any other technical explanations I could give them?

Anyway, thank you for this attempt!

José

Martin just gave you a very thorough and clear technical explanation explaining the phenomenon you asked about. This has been a subject that is hotly debated as to its audible existence, yet, as you said, you hear it and others here are very aware of its reality. So why are you asking Martin if he is convinced of its existence and poking around for another answer? If there was another explanation, Martin would have mentioned it. To label Martin's explanation "an attempt" is somewhat insulting and dismissive of what he just gave you. This is like asking Einstein if there is another explanation for relativity. The math is the math.

Very confused by your response...

[pdf64]

Another possibility is speaker non linearity, eg speaker does not respond equally when generating positive as negative pressure.

[romberg]

The human ear is a very remarkable sensor. But the first 1/2 wavelength (or maybe few wavelengths) is a very short period of time. I can see speaker non-linearity having an effect here. But again it is a very short period of time. I'd be surprised but not shocked if this can really be heard. Is anyone aware of a controlled test of this being done where someone could reliably identify this polarity switch in a controlled environment? My intuition tells me this sounds improbable but it has been wrong before .

I suppose it might be easier to tell this polarity switch if you were

• Playing at a volume level loud enough for acoustic feedback to be a thing going on.
• Did not move the guitar much at all so that you don't change the distance between the strings and speaker much.
• Then carefully switch the polarity without changing anything. Most importantly the guitar to speaker positions.

I can see that under these conditions, you might have the guitar producing more feedback for a certain notes (positive feedback) and less for the reverse polarity. But of course as Martin points out, you don't have to move the guitar much to throw this all off and you would seemingly not be able to tell the difference again.

Mike

[j0k3335]

However, I can't tell if you're convinced of this phenomenon!
So there wouldn't be any other technical explanations I could give them?

Anyway, thank you for this attempt!

José

Martin just gave you a very thorough and clear technical explanation explaining the phenomenon you asked about. This has been a subject that is hotly debated as to its audible existence, yet, as you said, you hear it and others here are very aware of its reality. So why are you asking Martin if he is convinced of its existence and poking around for another answer? If there was another explanation, Martin would have mentioned it. To label Martin's explanation "an attempt" is somewhat insulting and dismissive of what he just gave you. This is like asking Einstein if there is another explanation for relativity. The math is the math.

Very confused by your response...

No, it should not be taken in this sense: I always read Martin's posts with great attention and respect and I am aware of his skills!

But I also think (?) that he has a sense of humor and since he ended his post with "so a relatively small movement of the player would reverse the effect", I thought he was heckling me, that he wanted me to understand that it was very subtle and very difficult to explain.

that's all, I did not in any way want to disrespect him OR to neglect the effort of explanation that he wanted to bring me!

(sorry if I expressed myself badly ,but English is not my native language and is quite complex and subtle!)

[j0k3335]

The human ear is a very remarkable sensor. But the first 1/2 wavelength (or maybe few wavelengths) is a very short period of time. I can see speaker non-linearity having an effect here. But again it is a very short period of time. I'd be surprised but not shocked if this can really be heard. Is anyone aware of a controlled test of this being done where someone could reliably identify this polarity switch in a controlled environment? My intuition tells me this sounds improbable but it has been wrong before .

I suppose it might be easier to tell this polarity switch if you were

• Playing at a volume level loud enough for acoustic feedback to be a thing going on.
• Did not move the guitar much at all so that you don't change the distance between the strings and speaker much.
• Then carefully switch the polarity without changing anything. Most importantly the guitar to speaker positions.

I can see that under these conditions, you might have the guitar producing more feedback for a certain notes (positive feedback) and less for the reverse polarity. But of course as Martin points out, you don't have to move the guitar much to throw this all off and you would seemingly not be able to tell the difference again.

Mike

yes, it's coherent and that could explain the phenomenon: in my case I only play (my age!) in Home-Studio and THEREFORE always in the same place and the amp too. Under these conditions, this could explain why I "feel" this effect.

Thank you anyway Mike !

José

[pdf64]

If signal polarity made a noticeable difference, wouldn’t polarity flip pedals would be a thing?

[j0k3335]

Another possibility is speaker non linearity, eg speaker does not respond equally when generating positive as negative pressure.

yes, I had never consider this speaker "non linearity": so probably, it could produce a such different behavior under positive as negative pressure ?

Thanks for this idea

[martin manning]

However, I can't tell if you're convinced of this phenomenon!

I'm on the side that says it doesn't matter unless there are multiple drivers involved.

If signal polarity made a noticeable difference, wouldn’t polarity flip pedals would be a thing?

It is in signal splitting pedals where you might be driving two amps at the same time.

[mojotom]

It can be quite noticeable when you hit your string as it will change the onset of attack (push vs pull) imo.

If I remember correctly the 5F6 Bassman used Jensen Speaker for a push configuration and was copied by Marshall but he used a Celestion speaker with an inverser polarity so a pull configuration and that did change the overall sound (besides the components changes, speaker cab, etc). I think he didn't even think about it when he cloned the bassman with EU components).

Off course each gain stage invert the signal back so a Fet stage will invert and any effect pedal could have an effect on phase so it can be messy to find if it’s a push or pull at the end and it felt less revelant once you run stompboxes a lot because you'll mess with phase a lot.

Matchless did include a polarity switch on their amps btw and indeed it could be usefull if you run multiple amps at once as you’ll want to run them in phase. In that case with 2 amps for exemple this is even more noticeable as they will fight against each other.

[Colossal]

Very confused by your response...

No, it should not be taken in this sense: I always read Martin's posts with great attention and respect and I am aware of his skills!

But I also think (?) that he has a sense of humor and since he ended his post with "so a relatively small movement of the player would reverse the effect", I thought he was heckling me, that he wanted me to understand that it was very subtle and very difficult to explain.

that's all, I did not in any way want to disrespect him OR to neglect the effort of explanation that he wanted to bring me!

(sorry if I expressed myself badly ,but English is not my native language and is quite complex and subtle!)

I understand. My apologies then.