Near Field Problems of Measurements Using Toneburst Techniques
Toneburst techniques are employed in room acoustics to evaluate sound reflections from different room surfaces. The existence of single (detrimental) echoes can be recognized from the sound energy decay curve. Assuming the pulse width is small in comparison with the room dimensions, approximately even wave patterns can be assumed and phase shifts can be neglected. If the reflecting surface area is close to the sound source, nearfield wave patterns (e.g. spheroidal ones) must be considered. The measured sound levels can then be interpreted as the summation of the emitted intensities of the infinitesimal sound sources distributed on the reflecting surface. In that case, phase shifts must be considered. In this paper, formulas for the "area of influence" as a function of the pulse width and for the entire sound pressure as a function of the source and microphone positions are given.
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