A study of acoustic noise generating mechanisms of small form factor HDDs

A combined experimental and numerical study of the acoustic noise from a small form factor hard disk drive (HDD) is made to investigate the relative contribution of structure-borne idle noise to the total generated noise. Initially, the idle noise of a 1.8″ HDD was measured in an anechoic chamber, and a clear high-frequency peak is found in its total idle noise frequency spectrum. Then the modeling and simulation (M&S) of the top cover vibration and the associated sound radiation are performed to identify the dominant source and transmission path causing this noise peak. The M&S process consists of a 3D structural finite element (FE) modeling of the HDD to calculate the frequency-domain vibration response of the top cover, and a boundary element (BE) modeling of the HDD for calculating the radiated sound pressure. The loading specified in the FE model is motor torque ripple: the dominant electromagnetic excitation of fluid dynamic bearing spindle motor for HDDs. Finally, the obtained acoustic BE results of the sound pressure levels at a selected field point are compared to those measured physically in the chamber. It is shown that for the HDD considered, the coincidence of a high-frequency resonant mode with the fifth harmonic frequency of motor torque ripple is responsible for the high-frequency peak noise in the idle noise spectrum.