• Check the connections on each speaker. Make sure they are solid and the polarity is correct.
• Examine the drivers of all speakers. Make sure they are in proper condition. For regular drivers, lightly push them to make sure they spring freely and don't rub.
• Neutralize any tone settings or EQ. Some speakers have these.
• This test shows the sine wave signal generator. Turn on the generator and and scroll through a range of frequencies listening for any problematic buzzing. This may indicate a faulty driver.
• Be aware that all speakers will be playing the tone, so listen closely to each speaker.
• Look for any external EQs or crossovers. These should be neutralized or bypassed for now as well.
• It's a good idea to have a clean cloth available to wipe off any fingerprints.