Noise due to Surface Turbulence on Printed-Circuit Cards
William Warner Lang, Russell E. Wise · The Journal of the Acoustical Society of America · 1963
The surface turbulence produced by air moving over printed-circuit cards sets the lower limit on the acoustic noise levels of a computer cooling system. The sound power generated by two types of components mounted on printed-circuit cards was compared by measuring acoustic power levels in a 230-m3 reverberation chamber. The components were mounted on phenolic cards, 1.5×65×100 mm. Over 200 cards were installed in a flow chamber so the cooling air moved between parallel rows of cards spaced 11 mm apart. Miniature components (transistors, etc.) were mounted on one type of card; microminiaturized components were mounted on the other. The air velocity was varied up to the maximum normally encountered in air-cooled circuitry: 25 m/sec. The fraction of energy radiated as sound power to total energy of moving air stream, as well as the acoustic conversion efficiency per card, was determined for both card types.