Sonic is considered energy in DND, and in NWN, elemental protection resists it. Would it be possible to create a potion similar to crimson brews that protect against negative energy but instead protecting against sonic damage, and remove its resistance from insulation and such?
Silence grants 100% immunity to sonic. Would be an amusing potion to exist. Not that I think removing sonic damage from elemental protection is a good idea given we have quests where you may enduring a barrage of 10+ sound bursts in a round if you are unfortunate.