English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

To reduce noise, Helmholtz resonators are widely used in internal-combustion engine intake systems, in the rocket engine’s combustion chambers and building wall materials. As a bass-reflex-type loudspeaker, Helmholtz resonators may also be used to increase the sound pressure level. The advantage of using a Helmholtz resonator is that the frequency used to change the sound pressure level can be easily controlled by the resonance frequency and can be more easily applied to lower frequency noises than can porous sound-absorbing materials. A Helmholtz resonator is usually described in one-degree-of-freedom systems, wherein the neck portion is modeled as a mass, the damping of the neck as a damper, and the cavity as a spring. The noise reduction effect of a Helmholtz resonator (as in porous materials) is evaluated by its normal incidence sound absorption coefficient or acoustic impedance. Meanwhile, the effects obtained when the resonator is added to the main acoustic system are described in the same way as are the effects of the mass-tuned damper used to reduce mechanical vibration; such effects are determined by comparing the acoustic transfer functions of the main system with the main system after a Helmholtz resonator is added. This study first describes the two-degree-of-freedom mass-spring-damper model, which represents an acoustic system with a Helmholtz resonator. Next, the equation of the two-degree-of-freedom acoustic system is shown to be the same as that of the vibration system with a mass tuned damper when the damping coefficients are zero. Finally, the transfer function of the acoustic system using a Helmholtz resonator with heavy damping was found to approach that of the acoustic system without a resonator.

Estimating the noise reduction effect of the Helmholtz resonator using a two-degree-of-freedom mass-spring-damping model