Animal flight noise can serve as an inspiration to engineering solutions to wind-noise problems in planes or wind turbines. Here we investigate the acoustics of wingbeats in birds and bats by co-registering wing-movement in natural flight with acoustic noise. To understand the relationships between wing movement and acoustics we conducted additional acoustic measurements of single moving wings and other moving surfaces with accurately tracked motion paths. We found a correlation between wing-surface area and the sound pressure level of wingbeats; with bats tending to produce lower levels than birds. Measuring moving wings in isolation showed that a downstroke toward a microphone causes negative sound pressure that flips back into positive pressure at the reversal to the upstroke. The flip back to positive pressure is unrelated to the action of the upstroke, but occurs when the downward motion is halted. If the microphone is positioned above the downward wingbeat, sound pressure instead quickly rises during the downward motion of the wing. The phase pattern of the impulse created by the wingbeat varies systematically with recording-angle. The curvature of the wing appears to be a determinant of the average frequency of the acoustic impulse. Our findings can be used to predict the acoustics of smaller flying animals where repetition pitch of similar underlying impulses, repeated at much higher wingbeat-rates become dominant.

中文翻译：

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鸟类和蝙蝠的翼拍频率及其声学

动物飞行噪声可以作为飞机或风力涡轮机风噪声问题的工程解决方案的灵感。在这里，我们通过将自然飞行中的翅膀运动与声学噪声共同记录来研究鸟类和蝙蝠翅膀拍动的声学。为了了解机翼运动和声学之间的关系，我们对单个运动的机翼和其他运动表面进行了额外的声学测量，并准确跟踪了运动路径。我们发现了翼表面积与翼拍声压级之间的相关性；蝙蝠产生的水平往往低于鸟类。单独测量移动的机翼表明，对着麦克风的下冲程会导致负声压，在与上冲程相反时又会翻转回正压。翻转回正压与向上行程的动作无关，而是在向下运动停止时发生。如果麦克风位于向下的翼拍上方，则在机翼向下运动期间声压反而会迅速升高。由翼拍产生的脉冲的相位模式随记录角度系统地变化。机翼的曲率似乎是声脉冲平均频率的决定因素。我们的发现可用于预测小型飞行动物的声学，其中类似的潜在脉冲的重复音高，以更高的翼拍率重复成为主导。由翼拍产生的脉冲的相位模式随记录角度系统地变化。机翼的曲率似乎是声脉冲平均频率的决定因素。我们的发现可用于预测小型飞行动物的声学，其中类似的潜在脉冲的重复音高，以更高的翼拍率重复成为主导。由翼拍产生的脉冲的相位模式随记录角度系统地变化。机翼的曲率似乎是声脉冲平均频率的决定因素。我们的发现可用于预测小型飞行动物的声学，其中类似的潜在脉冲的重复音高，以更高的翼拍率重复成为主导。