"Amp playing forward" comments from Gerald Weber book

[W5FH]

Hello-
    Probably opening a real can of worms here but after reading this it has got into my head (at least what is left of it) and I must ask others. I am speaking of the chapter on the 5F6A Fender Bassman in the book "A Desktop Reference to Hip Vintage Guitar Amplifiers" by Gerald Weber. A statement is made in regards to the phase relationship of the input signal (from guitar going into the amp) to amp output signal (going to speakers). I understand about the inversion of a sine wave signal as it passes through a triode gain stage. I never really pondered on the sum total of inversions passing through amplifier. But it is said by the author, in that 5F6A discussion, that an amp that "plays forward" sounds better. By this it is meant that the phase of the output signal to speakers is the same as the input signal to amp. This point is made during a discussion of determining speaker polarity (with battery test) and insuring all speaker cones (in the 4x10 version) are moving in same direction. I can understand the importance of all speakers being of correct polarity but I am pondering on the other point of "an amp playing forward". Would this point be important if the instrument signal is being fed into another sound system in addition to the amp? I have no knowledge or experience in sound systems so please excuse my ignorance.

[shooter]

it all falls apart the second the speaker "sound" hits, walls, doors, bars, other signals from other amps.....


phase is important inside the amp, when you "mix" 2 signals into 1 and they are out of phase, they tend to cancel.

[bmccowan]

In addition to what Shooter said, the speaker cones moving in the same direction is important. Very noticeable decline in bass in a Hi Fi stereo if the polarity of the two speakers is not in phase.
Prior to discovering this and other forums, Gerald's books were my main source of information and misinformation. If I go back and read them now, I keep a small bowl of salt at the ready. There is actually a lot of good info in them, but also a lot of junk science. 

[PRR]

Harp/harmonica, mike is often so close to speaker that it can make a  difference. Not predictable: the howling tones will shift but which is better depends on unknowable factors.

I have no idea what the "phase" of a wound pickup is. Yes if you stand in front of the speaker for feedback you'll get different tones and harmonics one way from the other.

Speakers are simple things, you can flip their phase with a DPDT "reversing" switch.

Conceptually you can use a DPDT stomp switch to flip your speaker at will. The usual 50mA (0.050A) stompbox part won't take a lot of 2A speaker hot-switching or minutes-long howl before the contacts go nova, but enough to prove the worth (or not).

[HotBluePlates]

... it is said by the author, in that 5F6A discussion, that an amp that "plays forward" sounds better. ...

If no one told you, and you play through only 1 amp at a time, you wouldn't know "plays forward" or not.

If your signal splits to play through >1 amp at a time, the relative phase of each amp matters for your low end.

Even if your amps are in-phase, if they are spaced FAR apart then weird things can happen with phase & comb-filtering.