Characteristics of Low-frequency Broadband Sound Absorption of Combined Helmholtz Ventilated Absorbers
In order to solve the problem of poor ventilation and sound absorption effect in low frequency band,a sub-wavelength thick neck embedded Helmholtz ventilation metamaterial absorber was proposed.This absorber consists of a cen-tral ventilation opening and peripheral arranged multi-harmonic oscillators.Through precise design of each resonant unit,the acoustic absorber exhibits excellent sound absorption characteristics in the frequency range of 445-678 Hz,and the sound absorption coefficients are all higher than 0.85.The thickness of the structure is 40 mm,which is only 1/20 of the wave-length of 445 Hz.The sound absorption mechanism embedded in the neck was analyzed.It was found that the structure has strong viscosity to dissipate sound wave energy at the neck position,and the resonance frequency shifts to lower frequency side with the increase of neck embedding length.Subsequently,it was verified through experiments that the transmission loss of the ventilation sound absorber is in good agreement with the calculated results,and the average transmission loss within the target frequency band can be increased by 6 dB.Therefore,the feasibility of the ventilation sound-absorbing material with this functional structure to achieve high sound absorption capacity in the low-frequency domain has been verified.
acousticsacoustic metamaterialssound absorption and noise reductionventilation structureembedded necksub-wavelength thickness resonator
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