Disconnect the speaker from the amplifier.
Take a 9Volt battery - touch the wires briefly to the battery.
If the woofer jumps forward towards you, then the Positive wire is on the Positive battery terminal.
If the woofer jumps backwards into the speaker, then the Negative wire is on the Positive battery terminal.
Works for any speaker.
There are other ways, but this is the simplest.
Menahem
Learn from the mistakes of others - you'll not live long enough to make them all yourself!