A comparison of impulse-like sources to be used in reverberation time measurements

Abstract

an impulse-like source that will comply with certain demands concerning its spectral content and sound pressure levels it can provide. Although the relevant standards state that such kind of sources should be avoided due to the lack of measurement repeatability, their use has proved to be necessary due to inability of conventional omnidirectional loudspeakers to provide adequate sound pressure levels, especially at the low end of the frequency range of interest, thereby ensuring sufficient dynamic range. Therefore, the emphasis of this investigation has been made on peak sound pressure levels and the amount of low frequency content each source is able to provide. The investigated sources include 6 mm and 8 mm pistols, firecrackers with different amount of explosive compound and explosive mixtures of acetylene gas.

Review of Acoustic Sources Alternatives to a Dodecahedron Speaker

“…Regarding frequency response, the balloon does not offer adequate excitation at the low frequencies [68]. The spectral content of balloon bursts clearly indicates the direct relation between balloon size and the overall spectrum.…”

“…Relating to sound pressure levels, Horvat et al [68] measured differed sized balloons and found levels ranging from 133 to 138 dB. Results from Pätynen et al [67] ranged from 121 to 137.5 dB.…”

“…However, the impulse response of a balloon burst is not ideal. Measurements can be found in many kinds of research and for different balloon sizes [67,68]. "When a balloon is burst perfectly, the resulting acoustic disturbance should have the shape of the letter N" [69].…”

“…In reality, there are deviations in the expected N shape of the acoustic disturbance which results in an N wave spectrum containing nulls [70]. As Horvat et al [68] states, "balloons require more time to release the acoustic energy (compared to other sources) due to the certain amount of time required for cracking the balloon wall".…”

“…Concerning the question of repeatability, the balloon does not satisfy this requirement, but only under certain conditions. Studies by Griesinger [71] and Horvat et al [68] have shown that the balloon has poor repeatability. Also, Topa et al [75], in order to evaluate the repeatability of measurements and the effect this has on the acoustic parameters, performed measurements with balloons for the same source and microphone positions.…”