To solve such problems that, if a large-capacity resonance box is set to design a resonator with the intention to achieve a low-hertz intrinsic acoustic frequency, solid resonance frequency of the resonance box itself becomes low, so that it easily corresponds to the low-hertz intrinsic acoustic frequency to resonate the resonance box itself and thereby to amplify resonance, despite the intention of attenuating acoustic energy.

Rigidity of the resonance box itself is significantly increased by integrally forming a support in the resonance box, and the resonance frequency of the resonance box is significantly increased, so that the above problem is solved.