Low‐cost qualification of a small (170 m3) reverberation room dedicated to fan sound power measurements

Abstract

The qualification of a reverberation room for measurement of sources of discrete frequency sound is not an easy task. Especially if the room is small (the room has to handle 25 000 CFM) and when in an industrial content, the budget is very limited. Many articles have been written on the advantages of using a rotating diffuser in a reverberation room. [J. Tichy and P. K. Bade, J. Acoust. Soc. Am. 56, 137–143 (1974); D. Lubman, J. Acoust. Soc. Am. 56, 523–533 (1974)]. However, the majority of the proposed diffuser designs does not offer the possibility of changing easily the panel's orientation and consequently the shape of the diffuser. An original low‐cost design that was used to qualify the room will be presented and special attention will be devoted to the panel attachment device. The figure of merit of the diffuser will be reported and the influence of the panel's orientation on the variance will be discussed. Some instruments required in the qualification procedure [ANSI S1.32‐1980 (ASA 12‐1980)] are very specialized and their purchase is sometimes difficult to justify. To get round this problem, new approaches have been developed, expecially with respect to the sine wave signal generator. Furthermore, the important effects of the analyzer filter's shape on the loudspeaker's qualification will be discussed. During the qualification process variations in the measured variance between two close locations of loudspeaker have been noticed. Experimental data, sustaining this, tend to indicate that the qualification criteria may be too lax on this point.