The mouth would then act as a resonating chamber. In males, the abdomen is largely hollow and used as a resonating chamber. This forms the hand into a resonating chamber for the clave. Additionally, the swim bladder functions as a resonating chamber, to produce or receive sound. A Helmholtz resonating chamber is unusually selective in amplifying a single frequency. A resonating chamber made of palm leaves is housed in the mouthguard. The resonating chamber, a cylinder, is made of hardwood or ivory. Unlike most acoustic-electrics, the SST had no resonating chamber or soundhole.