An air pulse generator for providing high frequency chest wall oscillation therapy to a patient is provided. The air pulse generator has a housing and first and second diaphragms supported in the housing. The air pulse generator further has a crankshaft assembly coupled to the first and second diaphragms to reciprocally move the diaphragms back and forth to produce oscillating pressure pulses. The crank shaft assembly includes a motor with an output shaft that rotates about a first axis, a flywheel mounted on the shaft to rotate therewith, a first member coupled to the first diaphragm and pinned to the flywheel by a first stub shaft that is offset from the first axis, a second member coupled to the second diaphragm, and a cam interposed between the first member and the second member. The first member is pinned to the cam by the first stub shaft and the second member is pinned to the cam by a second stub shaft.