General theory and design of microperforated-panel absorbers

A general theory of microperforated absorber is proposed on the basis of eguivalent circuit. The characteristic parameters of the absorber are its relative acoustic resistance r, the diameter d of the perforations and the resonance freguency f₀, the later two form the perforate constant k=d \sqrtf_0 / 10, which, together with r. decides the structure and characteristics of the microperforated absorber. The maximum value of the absorber. band width Δf/f₀ is (4/π) tan^-1 (1 + r) as k approaches zero. and it does not change much as far as k is less than one, and the cavity depth is nearly a quarter wave length of the resonance frequency. For large values of k, the absorption band narrows down significantly and the cavity depth repuired becomes a small fraction of the wavelength. The properties of the microperforate absorber are discussed.