Speaker polarity

[Fischerman]

I recently saw a thread on TGP regarding speaker polarity and Dumble-type amps...dogears participated in it. It was mentioned that if you are using an ODS without a loop then the signal at the speaker is in phase with the input...but if you have a built-in Dumbleator then the signal at the speaker is out-of-phase with the input. It was suggested that those using a built-in Dumbleator use a reverse-polarity speaker cable and that the difference was significant and noticeable. Of course there was a doubter or two...I wasn't one but I wasn't convinced either...until now. This past weekend I made one of my speaker cables 'reversed' and tried with my HRM w/loop and it definitely makes a difference. With a regular speaker cable the amp was a bit hesitant to 'sing' until you got the volume up a good bit. So I set the amp such that it would sing sometimes but was still a bit hesitant and sometimes would fade out and not feedback. Then I switched to the reversed speaker cable and the amp just wanted to sing no matter what note I hit or how I hit it...it just wanted to sing.

I hadn't seen this mentioned here so I thought I'd mention it...it's not subtle. The amp also seemed to have a warmer, more balanced tone but this part of it was more subtle.

It also seems that this would apply to the Trainwrecks too (i.e. an odd number of phase-inverting gain stages before the LTPI means the signal at the speaker is out-of-phase with the input...so an Express should benefit from a reversed-polarity speaker cable).

[Bob-I]

I'm still a doubter, but I'll have to give this a try.

[Fischerman]

The 'improved' tone may be my imagination Bob...I don't consider myself any more immune to 'hearing what I want to hear' than anybody else...except that I'm aware that I might do it. I'm typically not very easily convinced but I always try to keep an open mind...so I should say that I wasn't convinced either way prior to testing it.

But the sustain/feedback thing is pretty unmistakeable...although I must admit I didn't stand in a bunch of different locations (some claim it's all dependant where you stand in the room and relative to the speakers). I just stood in the same general area but I did face different directions and took a step here and there. That didn't seem to matter...the amp just wanted to sing.

[Fischerman]

One last thing...it seems that if people are doing an A/B test of an ODS with loop and without loop (like with a loop bypass switch)...that they aren't giving the 'loop' a fair shot. I remember when I was doing A/B testing of the amp with/without the loop; I thought I got the loop sounding pretty transparent but the amp always wanted to sing more without the loop than with it. Now I know that this at least contributed to that.

[tele_player]

As I mentioned on TGP, I wonder if there's an even sweeter spot than a simple 180 degree phase switch.

To a first approximation, an amp might have a 180 degree phase shift, but at deeper levels of analysis, various parts of the circuit introduce smaller phase shifts of their own. The result - I expect the end-to-end phase shift on most amps to be something other than exactly 0 or 180 degrees.

[Bob-I]

I have a loop bypass switch on my 4x6V6 amp. I have not noticed that the amp sings more without or with the loop.

Also, don't forget that these amps tend to sing better when they're fully warmed up. My amps tend to take about 20-30 minutes to really come alive.

[Pete]

If I'm not mistaken, the same would apply to an external loop (i.e. same circuit in a stand alone 'umblator). Also, this may or may not apply when actually having an effect patched in of course. Just stating the fairly obvious.

...but if you have a built-in Dumbleator then the signal at the speaker is out-of-phase with the input.

[Stanz]

It would seem the only thing that would be different would be where the wave resolves (relevant to feedback and harmonics).

If you move half the distance of the freq in question, you should now have a similar setup. Of course if this is closer, it will feedback easier. I can see where having the output phase lined up with the phase of the strings will induce better feedback and harmonics.

[JimiB]

get a speaker cable and a pair of banana plugs that way you can make a 2 part speaker cable that is easy to switch. You definetly can hear the difference between the phases.

[BobW]

get a speaker cable and a pair of banana plugs that way you can make a 2 part speaker cable that is easy to switch. You definetly can hear the difference between the phases.

Jimi, As you may know, you should NEVER open circuit the OT. Put the amp in standby before swapping the polarity.

[JimiB]

true make sure there is no signal going thru the amp - better yet put it on standby before you swap the plugs.

[Tonegeek]

I was a non-believer till I tried it (thanks to Scott ). I get more sing/feedback with the cable wired one way vs the other. Read Fischeman's first post and set your test up like he did (right on the edge of feedback). One more thing: Use whatever effects you normally use because your FX unit could also flip the phase (like mine does). My HRM with built in loop actually sounds better with the speaker cable wired normally because my fx unit flips the phase. With so many possibilities when it comes to loops, FX, etc. I am considering putting a phase reverse switch on my next build (or on the speaker cab).

[Stanz]

All of this is good, and I have no reason to doubt that those who have tried this have heard something different between the two output phase options.

As an audio engineer I understand that reversing an audio output 180 can have dramatic differences. This of course is more so if there are multiple versions of the same signal, or in the context of a mix. I am assuming these test have been conducted with only the amp playing, thus reducing the audio to a single source. And in that scenario, reversing output phase shouldn't matter one bit. The only factor that I can see coming into play is interaction between speaker output and the strings, which as I stated before, can be replicated by moving to a new location as the nodes will have moved.

So can someone explain why it matters other than "I tried it and it sounds better"?

[Bob-I]

So can someone explain why it matters other than "I tried it and it sounds better"?

If that's all that mattered, we wouldn't be here trying to improve our amps .

It's just a matter of understanding.

[tele_player]

So can someone explain why it matters other than "I tried it and it sounds better"?

'scottl' on TGP (he's dogears here) says wrote:
"Big feedback with reverse cable and just ok feedback with regular cable."

and

"Notes bloom into INFINITE sustain one way and fade out weakly the other way. There is also a slightly softer initial attack when the speaker moves forward first. Without enough gain to get that singing feedback, you may not notice."

Others confirm his observations. Personally, I don't believe it's got anything to do with the speaker moving 'forward first' - my interpretation is that the total loop gain (strings, pickups, amp, speaker, air, guitar body, back to strings) depends on which way you wire the speaker. Of the two ways, one will have less attenuation, and produce a livelier interaction with the guitar.