Analysis of Some of the In-Duct Acoustic Pressure Measurement Errors

The article analyses discrepancies in the results of the acoustic pressure measurement carried out for measuring points located on the duct axis at a chosen distance from the sound sources. The measurement set-up consists of a self-designed single mode synthesizer located inside anechoic termination and a measuring section with the microphone moving along the waveguide radius. Several measurement series were carried out for each of the generated consecutive single modes, i.e. (0,0), (1,1), (2,1), (0,1) and a frequency wideband signal for an axisymmetrical and non - axisymmetrical position of a single sound source. For each case, calculations of the mean value and the type A standard uncertainty were executed by means of the classical method but also by the bootstrap estimate of the mean value and the bootstrap estimation of the uncertainty. The results obtained applying each of the listed methods were discussed and compared with each other. The non-zero result of the standard deviation indicates some eccentricity in the measurement set - up and so it can serve as a hint to improve axiality of the system.