Acoustic Limitations in Notebook Thermal Design

The fan is responsible for the majority of platform cooling in all but the lowest power notebook computers, and is also a major noise source. Fan performance is acoustically limited, and sufficient airflow must be provided within some acoustic target. Data from fan vendors is inadequate for designing a notebook thermal solution since it reflects neither the degradation in performance due to inlet restriction nor the associated noise increase which occurs when installed in the system. Constant sound power, or iso-acoustic, fan curves can be used to properly size the thermal solution, and are shown to correspond to actual system sound power levels. Operator position sound pressure as a function of flow for several systems indicates a wide range of performance among designs, and it is recommended that system impedance be kept as low as possible to maximize flow at a given noise limit.