In most countries, sound from dueted and non-dueted fans is .measured in reverberant room facilities. The inconvenience and cost of such expensive facilities have resulted in extensive efforts in the last fifteen years to develop a less costly, yet still satisfactory in-duct fan sound measurement system. (1-12) The British produced an in-duct standard in 1966 (13) for octave band measurements, and several other European countries and the US have done work on such standards. However, many problems have had to be solved.

During the past two years, the International Standards Organization (ISO) has been developing Standard ISO/TC 43/SCl "Sound Measurement Procedures for Air Moving Devices Connected to Either a Discharge Duct or an Inlet Duct." (14) Also the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) has been developing Standard 68P, "Method of Testing Sound Power Radiated into Ducts from Air Moving Devices."

The ISO and ASHRAE drafts have offered solutions to the practical problems and, hopefully, will soon be adopted. Research done at Herrick Laboratories of Purdue University on in-duct fan-sound power measurements provided much of the background material that went into these standards. It is the purpose of this paper to summarize this research.