Abstract: This invention is a manually tunable underwater breathing apparatus (UBA) which the resonant frequency of the UBA may be adjusted to meet the diver's breathing frequency by controlling the inertance component of the UBA impedance. The principles of the present invention may be adapted to existing UBA by adding a tuning apparatus comprising a valve, a tee and a tuned length of hose. Water displaced by volume change in the breathing bag due to exhalation/inhalation is partly diverted through the valve. Depending on the valve opening set by the diver the inertance and resonant frequency of the UBA can be altered to reduce breathing load.

Abstract: This invention comprises a tunable underwater breathing apparatus (UBA) in hich the resonant frequency of the UBA may be adjusted to meet the diver's breathing frequency by controlling the inertance component of the UBA impedance. The principles of the present invention may be adapted to existing UBA with minor redesign and some additions.

Abstract: This invention comprises a minimal elastance underwater breathing apparatus UBA) in which the elastance component of UBA impedance is substantially eliminated by forcing the breathing bag to expand and contract in a horizontal plane with small vertical displacements and hence minimal elastance. The invention further includes a servo-mechanism operating with a microprocessor, 3-axis position sensor and rotatable joints which act to keep the breathing bag oriented horizontally no matter what the diver's position. The principles of the present invention may be adapted to existing UBA with redesign and additions.