Sound level meter directional response measurement in a simulated free-field

Overview & Synopsis

Sound level meter directional response has to be measured in free-field, a condition that is usually met by using an anechoic chamber. However, using one is not always a possible option for cost or availability reasons. This paper describes an automated method that uses a structure, built to provide a simulated free-field, and a time-selective technique to remove the room reflections from the frequency response, thus enabling the directional response of an instrument to be measured without an anechoic chamber. The proposed method is then compared to the classical toneburst method for validation. Finally, the effects of some parameters (i.e. external noise, temperature, microphone positioning, air fluctuations...) on the obtained results are discussed, as well as their associated uncertainties.