Abstract
The theory of sound propagation in waveguides with a system of resonators on the wall is given in [1-2]. The papers present theoretical data showing that the use of a chain of identical Helmholtz resonators on the walls of a waveguide reduces the sound pressure levels effectively not only at the resonant frequency, but also at frequencies which are significantly higher than the resonant frequency. This theory was called by the authors of [1, 2] the theory of waveguide isolation (WI). Nowadays, the decades later, the idea of using a set of identical resonators has been widely developed in creation and research of acoustic metamaterials – artificial structures with unusual wave properties (see for example [3-6]). At the same time, the works [1-2] remained almost unnoticed. This paper is devoted to experimental and numerical verification of the WI theory. The design of the studied WI, a simple experimental setup, the results of the experiment and numerical experiment are described.
Highlights
The investigated model of a waveguide insulator (WI) is a small-diameter tube with three identical Helmholtz resonators attached to the pipe wall
The signal from the microphone is sent via the sound card (8) to the computer, where the signal is recorded with the SpectraLab program
Top line 1 corresponds to the levels of the sound passed through the tube, the middle line 2 – to the levels of sound transmitted through a tube with attached WI, the lower one 3 – to the background noise
Summary
The investigated model of a waveguide insulator (WI) is a small-diameter tube with three identical Helmholtz resonators attached to the pipe wall. To reduce the background noise in the laboratory, the box with the inner walls lined with sound absorbing material is used. The sound generated by the speaker propagates through the pipe 4, passing through a WI (5), is recorded by the microphone (6). The outlet of the WI and a microphone are placed in a special box (7) coated with a layer of sound-absorbing material. The generated frequency band of the LFM signal is 1 kHz – 8 kHz. A 0.8 m long tube was used between the speaker, and the waveguide isolator (Figure 3)
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