Sound-insulating Casing with Resonator Elements

Constant exposure to industrial noise has a negative impact on the human body. That is why increased attention is paid to the fight against noise, the rationing of industrial noise and vibrations was adopted. One of the effective methods to reduce the noise emitted by the operating equipment is the use of noise-insulating casings. The casing, as a rule, contains an outer skin made of steel sheet, a sound-absorbing lining of the inner skin, a perforated lining of a sound-absorbing coating. A typical octave spectrum of radiation sound pressure levels near the machine has a maximum near the frequency of 500 Hz, and the highest casing efficiency (insertion loss) is achieved in the frequency range of 1000–4000 Hz. The purpose of the study presented in the article is to improve the acoustic properties of the noise-insulating casing in the medium and low-frequency sound spectrum. To accomplish this task, the author proposes integrating resonator elements, in particular, Helmholtz resonators, into the structure of the noise-insulating casing. The natural resonant frequencies of Helmholtz acoustic resonators are determined considering their necessary frequency tuning, which ensures effective suppression of sound radiation at discrete values of the operating dominant frequencies of operating equipment. To reduce the excitation of structural vibrations and sound, as well as additional sound insulation, the frame walls and casing covers are damped on the outside and inside with a layer of vibration-damping material. Significant absorption of sound waves generated by operating equipment is ensured by lining the casing walls with effective sound-absorbing panels made of porous material, lined, in turn, with an external protective sound-transparent layer. The design of a noise-insulating casing with resonator elements presented in the study has high acoustic properties in a wide frequency range. Helmholtz resonators built into the casing structure provide sound absorption in 1/3 octave frequency bands centered at 400 and 500 Hz, characterized by a resonant amplification of the sound emitted by the equipment discussed in the article.