ADL files are used in the PC-DOS version of EOB1&2 to play sound through an adlib compatible sound card.

For EOB2:
#x0000: 120 bytes which are indices for the following pointer array
#x0078: 250*16bit pointers for sound/music tracks
#x026C: start of configuration data for adlib instruments
#x????: tracks

EOB1 ADL files are adlib.dat and sound.dat. The difference to EOB2 is the size of the pointer array for tracks which is here 300 bytes instead of 500.

For more details see adlplay.