[Michael Baldwin]

I've found the answer to my question

5.17 How do I determine a speaker's polarity? [IDB]
If you have a speaker and the terminals are no longer marked, you can do
a simple test to determine which terminal is positive (+) and which is
negative (-). This test is useful for midrange/midbass/subwoofers, but
not for tweeters.
Use a 1.5V battery (AA, C, D) and connect the (+) terminal on the
battery to one terminal of the speaker, and connect the (-) terminal to
the other terminal of the speaker.
If the cone moves OUT, then the battery is connected "properly," i. e.,
the (+) terminal of the battery is connected to the (+) terminal of the
speaker, and the (-) terminal of the battery is connected to the (-)
terminal of the speaker.
If, however, the cone moves IN, the battery has been connected
"backwards," i. e., the (+) terminal of the battery is connected to the
(-) terminal of the speaker, and the (-) terminal of the battery is
connected to the (+) terminal of the speaker.

Mike