The rotary subwoofer: A controllable infrasound source

Abstract

The rotary subwoofer is a novel acoustic transducer capable of projecting infrasonic signals at high sound pressure levels. The projector produces higher acoustic particle velocities than conventional transducers which translate into higher radiated sound pressure levels. This paper characterizes measured performance of a rotary subwoofer and presents a model to predict sound pressure levels.

Aeroacoustic model of a modulation fan with pitching blades as a sound generator

“…The fan geometry and maximum blade excursion Dh max are exactly the same as the parameters of Park and Garc es. 6 The comparative results are tabulated in Table III Hz, the present model gives prediction of SPLs in much closer agreement with the measured data than the simplified model of Park and Garc es. 6 Generally the present model captures the decreasing trend of the measured SPLs as the modulation frequency increases above 8 Hz, but the model of Park and Garc es 6 , which ignores flow separation, fails to track the trend.…”

“…6 Generally speaking, the plate blade has lower lift coefficient and is more sensitive to flow separation, compared with other aerodynamic blade airfoil shapes. However, little attention has been paid on optimizing the blade airfoil shape in the design of the rotary subwoofer.…”

“…This can be the optimum selection in the design of the rotary subwoofer, which has been adopted in the existing prototype model. 6 Evidently, the maximum blade excursion can have important effect on the sound radiation of the rotary subwoofer. In the ideal situation of no flow separation on the blades, it can be expected that the amplitude of the fluctuating velocity is linearly proportional to the maximum blade excursion, i. e., Q A / Dh max .…”

“…7,8 However, as for the rotary subwoofer with pitching blades, to our best knowledge, the only theoretical attempt was the model of Park and Garc es. 6 In their model, the sound generation is attributed to the time-varying velocity on the front surfaces of the pitching blades. This implies that the benefit of the rotary subwoofer lies in that a portion of the rotational speed is converted into the acoustic particle velocity.…”

Vortex-Lift Mechanism in Axial Turbomachinery with Periodically Pitched Stators

“…The same authors have used this method to simulate the unsteady flow of a modulation fan with pitching blades [45], which can generate low-frequency sound at high sound pressure levels. The numerical results agreed very well with the measurements reported by Park and Garcés [46]. Finally, the present method has also been used to investigate the effect of shedding vortices in the process of rotor/stator interaction in turbine engines when the axial gap between blade rows is reduced [23].…”