Periodic arrays of cylinders, sometimes called Sonic Crystals, are known to produce useful sound attenuation in narrow frequency bands, known as stop bands. These result from multiple scattering within the cylinder array. For sonic crystals to be useful as highway noise barriers, methods must be found of reducing the angle-dependence of the stop bands and ensuring that the first stop band corresponds to the main peak in the traffic noise spectrum. Two possibilities have been explored that may be useful in designing noise barriers and are based on resonant scattering. Data for the insertion loss spectra of single cylinders and arrays of cylindrical PVC tubes with vertical slits (acting as Helmholtz resonators) and thin-walled latex cylinders (capable of breathing modes) are compared with data for single PVC tubes and arrays of PVC tubes, of the same diameter and with the same filling fractions, without any slits. The effects of concentric latex and PVC cylinders with slits are investigated also. The single cylinder and array results show low frequency insertion loss peaks. The resonant arrays are found to give rise to relatively angle-independent stop bands in a useful range of scaled frequencies.
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