Acoustic Dissipation and Modal Coupling in Server Computers

Abstract

Interest in the interior acoustics of server computers is growing as noise generated by air movers (fans) is increasingly observed to impact the performance of hard disk drives (HDD) inside these computers. In a typical server, a backplane cavity is located between an array of air movers and an array of HDD such that the HDD may be within a fan diameter of the air movers. The possibility of functional degradation requires careful management of air mover noise with respect to HDD susceptibility to acoustic noise disturbances and motivates understanding the physical phenomena underlying the acoustics. A previous investigation demonstrated the importance of coherence between acoustic standing wave modes in the backplane cavity. In this paper server interior airborne acoustics are further investigated by focusing on acoustic dissipation and inter-modal coupling in the backplane cavity. Various dissipation models are developed and used in conjunction with a previously formulated modal cavity acoustic model to generate cavity transfer factors. The transfer factor predictions are compared to measured transfer factors to draw further insights into the physical phenomena governing the interior cavity acoustics.