Connecting loudspeakers whatifs...

2019-01-23 19:03:15

Hello all.

I have a theoretical question. I have an amplifier, 2x50W, and two speakers, 2x70W - for example. Usual way of connecting them would be from amp plus to speaker plus, minus to minus, both speakers. If one speaker is connected in reverse order, amp plus to speaker minus, speakers would be in reverse phase, and sound would be very bad.
But, what happens if both speakers are connected reversed, from amp plus to speaker minus? My understanding is that speakers would still play as they should, because signal is alternating current. But my colleagues say that they won't play as good as they should, especially at higher loudness level, arguing that speakers would make stronger inward motion than outward which could be blocked by magnet and/or something in speaker construction. I find that hard to believe, but again, I don't know much about speaker construction, and how much the membrane is moving forward, outward, and how much back, inward. Also, that situation is supposedly worse for compression boxes vs bass-reflex boxes.
How much of that is true? Can somebody explain that, give examples, links...?
I've tried searching for that, but web searches gave various situations, and 99,99% are reverse phase situations.

Re: Connecting loudspeakers whatifs...

Reply #1 – 2019-01-24 08:47:10

Loudspeakers will play just fine if you flip the polarity on both. The polarity from recording studio to playback is essentially like flipping a coin - you will find all kinds of microphones, processing gear, recorders, loudspeakers etc that flip phase, and users are unaffected as long as they dont try to combine them (in parallell) with other gear that does not flip phase.

There is a minority of listeners who claim to be sensitive to absolute phase. I am not aware of controlled experiments that have supported this claim.

There is usually a slight asymmetry in loudspeakers. Sufficient that subwoofer designers will commonly try to mount two low frequency drivers "back to back" in order to suppress such differences.

-k

Re: Connecting loudspeakers whatifs...

Reply #2 – 2019-01-24 14:28:14

It's true to say that all speakers must have a small difference in the throw of the cone between "in" and "out" before they hit mechanical stops but if the speaker is competently designed and manufactured the difference should be tiny. Assuming you can find an assymetric signal of the exact amplitude required to cause the cone to hit one limit and not the other, the phase would matter. You'd also have to do this for an individual speaker - a stereo pair might not be absolutely identical due to maufacturing tolerances. However, that's a lot to ask and it's very contrived, artificial and not guaranteed to be audible anyway. I'd suggest that in the real world you can safely ignore such things.

As for absolute phase, the only reference you have is the original live recording, which does not exist any longer, by definition. Therefore there cannot be an absolute phase.

You might like to read this:
http://sound.whsites.net/ptd.htm#s4

Your friends are correct only under a specific set of circumstances that are highly unlikely to arise without contrived means and still may not be audible even then.

Re: Connecting loudspeakers whatifs...

Reply #3 – 2019-01-24 17:22:08

The tweeter (or midrange in a 3-way speaker) is often reverse-wired...

The high-pass & low pass crossover filters introduce ~90 degree phase-shifts in opposite directions putting the woofer & tweeter ~180 degrees out-of-phase at the crossover point where both are operating.   Flipping the polarity of one driver puts them back in-phase at the crossover point.  

Re: Connecting loudspeakers whatifs...

Reply #4 – 2019-02-01 10:45:36

Thank you all. If someone has some more info, please share.