Function 4     : On / Off Speaker.

Entry          : BX = 4.
               : AL = 0, OFF.
                    = Non-zero, ON.
Exit           : None.

This function turns on/off the speaker's connection to the DAC.
The value in the AL register determines whether the speaker is
to be turned ON or OFF.

The speaker's connection is turned on after the "Initialize Driver"
function is called. The application program has to turn OFF the
speaker before exit.

This "Speaker" has to be turned off dureing the voice input.
Otherwise, the recording is output direct to the speaker.