How to make sure that the speakers are connected in the same polarity?

Question

Do it yourself

Converting active speakers to passive. How, without opening the “former passive” speaker (it can only be opened by removing the loudspeaker), make sure that both speakers are connected in the same polarity - that is, when the current of the same name is applied, both membrane goes forward or backward, and not randomly?

If by indirect evidence - the remains of the amplifier in the "former active" have been preserved.

Answer 1

Take 1 AAA battery and briefly connect to the speaker. The speaker will either move the cone towards you or away from you.
It shifts on you - plus the batteries are connected to the conditional “plus” of the speaker.
Well, then mark the wires and connect as you need.

Answer 2

And you can also google special audio recordings for checking phase and antiphase.
This is for example when already collected, but there are doubts.