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The aim of the paper is to present results of examination of the acoustic pressure field inside a model of a cylindrical duct. Measurements of the root mean square acoustic pressure were carried out using a new measurement setup, first in conditions allowing for propagation of the plane wave only, and next - by increasing the excitation frequency - with successive higher modes also taken in account. Two types of hard-walled cylindrical ducts were examined corresponding to mathematical models known as the infinite duct and the semi-infinite duct. A dedicated measurement setup is presented as well as the successive stages of its modification. In order to verify the modified measuring system, the first stage of the research work consisted in excitation of the axisymmetric modes only and assessing the degree of symmetry represented by the measurement data Significant improvement of the compatibility of the obtained measurement results with theoretical predictions was observed in the explored frequency band 800-5500 Hz that for the duct inside radius of a = 0.077 m corresponded to the reduced frequency range 1.13 < ka < 7.76.

Modification of the Measurement Setup for Examination of Acoustic Field Distribution Inside Cylindrical Ducts for Axisymmetric Excitation