A simple three-dimensional (3-D) sound intensity probe

An important property of sound intensity measurements is that the free-field properties of a sound source can be determined, although the source is positioned in a reverberant environment. The standard intensity probe consists of two closely spaced, accurately matched pressure microphones (p-p probe). A 3-D intensity probe consists of three pairs of matched microphones. The necessity of accurate matching makes such a probe large, complicated, and expensive. As an alternative for the p-p probe a p-u probe has been published [104th AES Convention Amsterdam; preprint 4651], where the particle velocity (u) is determined using the Microflown. It consists of two heated wires, 40 mm apart. The temperature difference of both wires is linearly dependent with the particle velocity (u) and can be measured accurately. A 3-D intensity probe will be reported consisting of one (pressure) microphone and three particle velocity sensors placed orthogonal for the velocity vector (u) determination. Experiments have been performed in an anechoic and a reverberation room. It was found that the free-field properties of a sound source, as determined from experimental results in the reverberation room, coincide with the experimental results in the anechoic room, showing that this 3-D intensity probe works satisfactorily.