Deimos, Rime and Strut had sound cancellation devices built into their helmets which they were still wearing. They simply activated the devices at Dr. Zanasiu's command. Dr. Kerzach was wearing earplugs that he had with him in his labcoat. Mr. Bigmouth simply put his hands over his ears.
"...8, 7, 6, 5, 4, 3, 2, 1, 0. Detonation now!" Strut counted down. At "detonation now", he flipped up a clear cover on a red rocker switch, pushed the switch down and held it for 3 seconds.
After 3 seconds, a deafening explosion ripped through the air, as several pounds of explosive went off, leveling the cafe.