On Certain Practical Issues Relating to Constructionof the In-duct Single Mode Synthesizer
Archives of Acoustics
2015
No 2
Łukasz GORAZD, Anna SNAKOWSKA, Jerzy JURKIEWICZ, Artur FLACH
circular hard-walled duct, modal structure, cut-on mode, circular duct modeling
Nauki Techniczne
It is convenient to have a device and a method of generating single cut-on modes in cylindrical hard-
walled waveguides or at least in laboratory models of such systems. This allows to examine, among
other things, properties of various active and/or passive elements inserted in a cylindrical duct by testing
them in conditions when the incident (input) wave comprises only one cut-on mode and determining
the reflection and transmission coefficients for single selected incident modes. As it has been already
demonstrated by the present authors, it is possible to generate single cut-on modes in a circular duct
using a small (although increasing with mode order) number of acoustic monopoles arranged properly
on a duct cross-section and driven with appropriate acoustic volume amplitudes and phases. Laboratory
models of such sources are proposed in this paper and results of tests verifying their directional properties
are presented. The other technical issue relating to practical utilization of the proposed method is the
possible error introduced by the apparatus used for scanning the acoustic field inside the duct model. It
is shown that insertion of the measuring probe changes the total energy radiated into the free space only
by a fraction of a decibel.
Committee on Acoustics PAS, PAS Institute of Fundamental Technological Research, Polish Acoustical Society
ISSN 0137-5075
;
eISSN 2300-262X
10.1515/aoa-2015-0027