We describe an acoustic impedance matching method that permits perfect sound transmission between waveguides of different impedances as set by their cross sectional areas. Impedance matching in this case is based on extraordinary acoustic transmission mediated via a Helmholtz resonator embedded at the junction between the dissimilar waveguides. Perfect transmission occurs at the Helmholtz resonance frequency. However, perfect transmission between different impedance waveguides requires that the two-neck Helmholtz resonator be asymmetric with different areas and lengths of the necks that couple to each waveguide.
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