Thin absorptive structure in low frequency by extending the neck of Helmholtz resonator

It is well known that a large air space is needed when we absorb sound in low frequencies by using porous material and many types of resonator are needed when we apply resonator absorber to absorb sound in low frequencies. Therefore, both porous material and resonator absorber are neither realistic nor practical for use of absorbing walls or ceilings in small room such as a living room in a house. On the above aspect, sound absorption characteristics of resonator absorber by extending the neck of resonator inside the cavity of it to thin the structure and by combining several types of resonators to expand the absorbing frequencies are examined by numerical simulation based on FDTDM and the experiment of tube method. As a result, it is found that extending the neck of resonator inside the cavity is effective to decrease absorbing frequency of resonator and combining several types of resonators provides multiple absorbing frequencies. This suggests that extending the neck of resonator and combining several types of resonators are effective for a thin absorptive structure in low frequencies