My bifocals have an "H" and "L" imprinted on them, presumably corresponding to High and Low. Don't know whether there if a physical difference or not, haven't tried it the other way around. You might try swapping the "leg" of the cable you are using to see if you hear any difference. If you do, it might be worth getting some banana/spade adapters or something and hooking up both legs. I'm presuming that if you don't connect both speaker ends, you are being careful to avoid any possibility that the unused + and - short together...
