1992: When Honda Civics were small and their Helmholtz resonators were huge
Cavity Resonance
Exponential Solutions of a Boundary Value Problem of the Helmholtz Equation Related to Change in Phase - Bueckner - 1964 - Journal of Mathematics and Physics - Wiley Online Library
Analytic Solutions of the Helmholtz Equation for Some Polygons with 45 Degree Angles - Wolfram Demonstrations Project