A knife cut to the speaker diaphragm probably would just make the audio harsh and possibly (perceptually) louder. I've repaired speakers in similar conditions b

A knife cut to the speaker diaphragm probably would just make the audio harsh and possibly (perceptually) louder. I've repaired speakers in similar conditions before. A complete girdling of the diaphragm is probably tricky to do through the speaker grille. My suggestion would be to spray expanding polyurethane foam (e.g. Great Stuff) into the grille. Immobilize the diaphragm, and muffle anything that's left. But, vandalism is bad. Even when it is justified retaliation. :-/