Two amps, splitters and phase inversion

[Rambazamba]

So, I can't really get my head around it and decided to get some insights from the talkbass community.
When I use a setup with two amps, why would I benefit from phase inversion? I know that I get more bass, more clarity and better sound with a splitter with phase inversion, but in theory it should be the other way round because the phase inverted wave of one amp would physically delete the wave of the other amp. So... what's going on?

 

[Redbrangus]

There is no advantage to phase (polarity) inversion -- it is, in fact, exactly as you understand it: disadvantageous for two speaker systems to be 'out of phase' with each other. The confusion might come from the POSSIBLE need to invert [correct] the polarity of one of the signals to the two amps because they are out-of-polarity with each other; the 'phase inversion' switch would allow you to return the amps back to the same relative polarity. Further confusion arises because some amps -- some Fenders, specifically -- have a relative polarity inversion between the two different input channels on the same amp. But yes, it is highly undesirable to have your two amps 'out of phase' with each other.

 

[Geri O]

I know that I get more bass, more clarity and better sound with a splitter with phase inversion, but in theory it should be the other way round because the phase inverted wave of one amp would physically delete the wave of the other amp. So... what's going on?

Where are you getting this information?

The only advantage I can think of would be if you wanted to spend most of your time in front of only one cab or the other. Then what’s the point of two rigs? As soon as you get in the path of both rigs, it will get very messy with almost complete cancellation at a certain spot.

There simply no reason to invert the signal going to one of the rigs.

Edit: as Andy said below, the only reason to invert the signal to one of two amps in use would be if the signal is already inverted for reasons listed below. Yeah, I read the answers below and edited my response accordingly….

 

[agedhorse]

The only reason to invert the polarity of one signal/amp is if the relative polarities of the two amps is inverted. Inverting one brings the relative polarities back to (~) zero.

Many amps will create a polarity/phase inversion, there isn't really any standard and some amps will invert on some switched functions and not on others. Therefore, when operating a pair of amps, splitting the signal with the ability to invert the polarity to one can be helpful IF there is a polarity inversion in one of the signal paths.

 

[Wasnex]

So, I can't really get my head around it and decided to get some insights from the talkbass community.
When I use a setup with two amps, why would I benefit from phase inversion? I know that I get more bass, more clarity and better sound with a splitter with phase inversion, but in theory it should be the other way round because the phase inverted wave of one amp would physically delete the wave of the other amp. So... what's going on?

Having the output of an amp or pedal in phase with its input is not standardized. Some amps and pedals put the output in phase, and some put the output out of phase. So you when you use to different types of amps there is no guarantee they will be in phase.

Also, some pedals pass an in phase signal when they are bypassed and an out of phase signal when the effect is engaged. Some amps with switching preamps have the same problem.

Even worse are digital pedals. The time it takes for sound to pass through a digital pedal depends on processing time and also how long it takes for Analog to Digital and Digital to Analog conversion. This bit of delay is typically called latency. When you are running parallel processing the latency can cause undesired phasing. In order to correct the problem you need a device capable of inserting a small amount of time delay, so the propagation time through the unprocessed channel matches the propagation time through the effected channel.

 

[Rambazamba]

Alright, thank you guys, this really sheds some light on it. Yeah, I noticed that my signal almost disappears in some situations/pedal combinations, so I rembered that I read somewhere I need to switch the phase. I did so in a recording of our set and it magically cleaned up everything and returned the tightness in the lows. Seems like some of my pedals switch phase.