Hi.
When the positive signal is applied to a speaker terminal marked (+) and the negative to its terminal marked (-) ; the cone is supposed to retract towards the magnet or extend way from the magnet ? What is the standard motion ?
If it does not matter nor alters the sound; what is preferred mechanically ? The coil to be repelled or attracted by the magnet when polarities are as above ? (like applying small direct current to the speaker)

 

I don’t believe the polarity makes any difference on a single speaker to the sound perception, but it is very important on stereo or other multi-speaker systems because there will be a tendency to cancel sound waves if the speakers are wired in differing polarities.

 

I've never seen a standard that says "the cone shall always move outwards for positive voltage applied to the terminals".

I've always used the 9V battery test to check.

 

It makes a difference in 2-way and 3-way speakers systems. If I remember correctly, even order crossovers have the signals in phase at the crossover frequency and odd order have them anti-phase. So you wire the tweeter and woofer with opposite polarity with an odd order crossover so the two do not cancel each other. This assumes they will move the same way if the - terminal is common.

 

Don't do the 9v battery test on tweeters. I would say for any mid-range speaker size smaller than about 3 inches or a tweeter the speaker polarity is much less important because of small cone displacement, the number of acoustic wavelengths between the tweeter and the listener plus room reflections that muddy high frequency phase relationships. At 3 kHz it's only 11.44 cm or 4.5 inches so turning your head to a slight offset from the speakers can completely change the ears phase relationship.

 

For your information, positive current moves the cone outwards. (Ref: Philips Speaker Systems)
For single speaker systems, polarity does not matter.

 

For your information, positive current moves the cone outwards. (Ref: Philips Speaker Systems)
...

Sure, per Philips but that's only if you use conventional instead of electron current. Really there is a convention but no actual standard I've ever seen about the direction of speaker cone displacement. I seriously wonder if there is an offical industry standard today.
https://reconingspeakers.com/faq/how-to-understand-jbl-reverse-polarity/