Thin multi-tone sound absorbers based on analog circuit shunt loudspeakers

The noise generated by large machines and equipment with periodic rotating or reciprocating excitations often contains low frequency harmonic components, which is a challenge for some applications where current active and passive noise control methods cannot be adopted. This article investigates the feasibility of designing thin multi-tone sound absorbers based on analog circuit shunt loudspeakers, which use only close-box loudspeakers and some electronic components to produce nearly perfect absorption at the designed frequencies. The advantages of the proposed thin absorbers are their low cost and flexibility of tuning the absorption frequencies. The implementation procedure of the proposed circuit is presented, and a thin prototype targeting at the transformer noise is made and tested as an example. Both simulation and experiment results validate the feasibility of the proposed circuit and design procedure.