Well we ain't leaving the 9V battery connected to the driver! :khan:

Just a touch will do. Yes, it jumps a lot farther with 9 volts, but it's no big deal. No matter the current in the battery, you'll only get a current flow of I = V/R. The DCR of the voice coil sets the current that can flow from the 9V battery. About 1.4A in this case, or ~13 watts (if DCR= 6.3 ohms).