If you think one of your speakers is bad, simply unplug it and try it on the other side if you have modular EdSets. If the same speaker is still bad, then it's the speaker. If you move the speaker to the other side and the same side is still bad, it's the helmet connector or coiled cable instead. Most likely, it's the helmet connector since 2-3 out of 1000 may fail at some point. We've only had 1 bad coiled cable since we began using the current ones. A new speaker can be mailed to you as a replacement.
If you have our older non-modular sets where the speakers are 'hardwired' to the helmet connector, you can check the pins on the helmet connector with a meter: If the center hole of the 5 holes in the connector is at the 12:00 position...then the 1:30 is one speaker and the 3:00 position hole is the other one. Check continuity across the 12:00 and each of the other two holes and you should read continuity. If one of the pins does not read continuity about 8-16 Ohms, then most likely that speaker is bad. A new one can be soldered in locally or you can return it.
NOTE: As you hold our speakers up looking at the back side with the terminals at the top, the Positive terminal is the one on the left. If you solder on a new one, use that terminal for the 1:30 or 3:00 wire to keep them in phase with each other.