Diffuser (breathing set part)

A diffuser is a device fitted over an underwater breathing set's exhaust hole to break up the resulting bubbles small so they will not be seen from out of the water, and make less noise (see acoustic signature). They are used in:

• Combat diving (see frogman), to avoid detection by surface guards or by underwater hydrophones.
• Mostly, in underwater mine operations conducted by clearance divers, to make less noise,^[1] as acoustic mines are designed to explode when they detect particular sounds.
• In marine biology, to avoid disruption of fish behavior.^[2]

Designing an adequate diffuser on a rebreather is much easier than on open-circuit scuba.

A system was shown on a Discovery Channel documentary about diving with hammerhead sharks at Cocos Island, Costa Rica. Eddie Paul designed—and in the early 1990s underwater photographers John McKenney and Marty Snyderman tested—a system they called the "scuba muffler", for open-circuit scuba. This system had two large filter stones on the back of the tank with a hose connected to the exhaust ports of the second stage regulator. The two filter stones were mounted on a hinged arm to float 1 to 2 feet (30 to 60 cm) above the diver, to set up a depth-pressure-differential suction effect to counteract the extra exhalation pressure needed to breathe out through the diffuser. The scuba muffler cut the exhalation noise by 90%. Closed circuit rebreathers proved more useful in letting divers get near sharks.^[3][4]

References