I believe the interaction in this case is the speaker's magnetic field, as modulated by the guitar audio, and the output transformer.martin manning wrote:Excellent! I'd say this suggests that there is another real and physical effect to speaker phase (that I had discounted). I guess not only the proximity but also the orientation of tubes placed close to the speaker would be important, then.Firestorm wrote:The fixed field from the back of a P12R begins to deflect the needle of a compass when it is 15 inches away... When a 9V battery is connected to the speaker terminals, the amount of deflection increases or decreases depending on the battery's polarity. ... this suggests that there may something real and physical to claims that speaker phase is important to the tone of certain amps.
I also think this is the effect that Husky John reported.
Differing speaker voice coil gap geometry may cause some speakers to exhibit this behaviour more than others.
In other words this is leakage.
I wonder if rotating the OT 90 degrees might minimize this effect (at the expense of 60Hz from the PT).
Is one style of output transformer construction more susceptible to stray fields than others ? SE vs PP
rd