The likely culprit is the amount of simulated cycles used by DOSBox (the DOS emulator that ACK runs within). By default, DOSBox runs ACK at 15000 cycles, a speed which handily deals with heavier processes like the ‘limited visibility at night’ option. But on some older machines, this high cycle rate can cause all of ACK to slow down. This will most obviously be noticable in choppy sound playback.
You can decrease the cycles used by pressing CTRL + F11 while playing an adventure. Keep doing this until sound plays normally. You can also increase cycles with CTRL + F12. If you want to change ACK’s default cycle rate, you can edit the ‘cycles=’ line in the files dosbox.conf and (PC only) ackmod.conf.
If you’re using ACK on a newer Mac laptop, see the tip about function keys below.