Sound Analysis Method for Warble Noise in Electric Actuators

Multiple automotive applications exist for small electric motors that are activated by vehicle occupants for various functions such as window lifts and seat adjusters. For such a motor to be described as high quality, not only should the sound it produces be low in amplitude, but it also needs to be free from pulsations and variations that might occur during its (otherwise) steady-state operation. If a motor’s sound contains pulsations or variations between 2 and 8 cycles per second, the variation is described as warble. To establish performance targets for warble noise at both the vehicle and component level a way to measure and quantify the warble noise must be established. Building on existing sound quality metrics such as loudness and pitch variation, a method is established by which processed sound data is put through a secondary operation of Fourier analysis. Thus warble can be reduced to a single value, and in this way, noise engineers have a basis to measure and report warble, and to facilitate product development with A/B comparisons. Depending on its source, warble is manifested as either a sinusoidal variation in loudness, or as a sinusoidal variation in a motor’s rotational speed. Regardless of source, pulsations between 2 and 8 Hz are particularly annoying and portray a low-quality perception of a sound that is expected to be steady and even. By using the methods and calculations presented in this paper, a clear indicator of both loudness warble and pitch warble can be discerned from any recorded steady-state motor noise.