Fundamentals of Hard Disk Drive Acoustics

FIGURE 1 Acoustic Intensity Spectrum for a Typical Disk Drive Under Idle and Seek Operation Conditions. INTRODUCTION In the hard drive industry, drive acoustics are becoming more important than ever. With the introduction of hard drives into new emerging markets in which the consumer is more keenly aware of and sensitive to radiated acoustic noise issues, technical professionals are facing enormous challenges to meet customer demands. Drive manufacturers are under severe cost limitations, many times unable to incorporate all the noise control devices necessary to make drives as quiet as possible. Often times a trade off between performance issues and drive acoustics is required. As drives have gotten cheaper and cheaper, expectations on quietness, as well as performance, have increased. As in many other industries, the consumer views a quiet product as one of high quality. The job of meeting these increasingly difficult noise goals also falls on those manufacturers that are the end users of disk drives. One example of this is in the area of set-top box systems, typically characterized as “smart VCR’s” using the disk drive as the storage medium. Since these units are often used in consumers’ bedrooms where background noise levels are much lower than the traditional office environment, the bar for low acoustic output is set very high. Radiated sound power requirements for such products are desired at levels less than 30 dBA, with seek noises virtually indistinguishable over idle conditions (less than 2 dBA louder). To accomplish this feat costeffectively, a detailed technical understanding of drive acoustics is essential to successfully developing optimized noise control strategies. This article attempts to outline some of the fundamentals of hard drive acoustic issues confronting those working in this industry.