Development of new sound insulators with perforated board and honeycomb layer systems

Abstract

Two newly developed types of sound insulators are introduced in this study. The first type is derived from an analytical model of a vibrating surface with an impedance facing. The model is investigated theoretically; the results indicate the possibility of reducing radiation from the vibrating surface by giving appropriate impedance. To realize this effect, a model using a perforated board with a subdivided air cavity is proposed. It is shown theoretically and experimentally that this insulator can achieve radiation reduction at an arbitrary frequency. The second type is proposed from the viewpoint of the subdivision strategy. It presents the possibility of improving insulation by restricting the air-particle motion at the interface between the vibrating surface and air. This method for noise control has an attractive simplicity and considerable practical benefit. The attenuation mechanism is discussed theoretically and experimentally. Results of this investigation show that the effect of this insulator is characterized by reduction of acoustic radiation at low frequencies near and below the critical frequency of coincidence. Wide use of these two insulators in many fields is anticipated.