As the space program transitions to longer duration manned missions, the need to provide a quieter environment assumes increased importance. Fans are a significant noise source and require special acoustic attention. Effective optimization of a quiet fan package involves trade-offs between fan source noise and muffler design. This paper addresses the impact of fan speed on source noise acoustic profile, power and volume. It further addresses muffler characteristics to be included in the trade study and resulting design. For the ISS Avionics Air Assembly, this trade-off resulted in a 50,000 rpm air bearing fan design. This paper addresses the acoustic source noise of both a 30 cfm design and a 130 cfm design. The cooling packages containing these fans meet NC-40 and NC-45 respectively.