In the former report, it was described that the high-velocity air flow and the pneumoacoustic ultrasonic vibration were effective for atomization, and that the acoustic singular point was found on the compound injection nozzle with the loop convergent nozzle and the resonant chamber. A favorable size of the resonant chamber with the compound spray D-type injection nozzle (used in the former paper) is experimentally obtained. The effect on the acoustic characteristics with the change of geometrical configuration of the resonant chamber, the relation between the acoustic characteristics and the atomization, and the condition of favorable atomization are obtained. The correlations between the acoustics and the atomization characteristics are clarified on the D-type injection nozzle with the various geometrical configurations, and a favorable geometrical size of the resonant chamber is obtained.