Sound cannons are actually pretty weird, in that they don’t work like you’d imagine them to work. They produce sound when multiple beams of ultrasound collide with an object, so if they’re pointed at you, you’re the one producing the sound that hurts you. That’s why they’re so effective.

Some people online have done some tests, and thin cardboard appears to be the best way to stop them. Put the thin cardboard before you, and it stops most of the sound. It can be the cardboard from a poster, if you have one.

Ear protection headphones (for workshops) also help, and their effectiveness is enhanced further by wearing small earplugs inside. Active noise cancelling headphones don’t help and can even be counter productive, so don’t use those.