The Helmholtz resonator with different types of necks

This paper focuses on improving the noise attenuation performance of the Helmholtz resonator (HR) at low frequencies with a limited space. Three different types of necks: an extended neck, a spiral neck and a tapered neck takes the place of the traditional straight neck of the HR. The acoustic performance of the HR with these three types of necks is analyzed theoretically and numerically. The spiral neck is transformed to an equivalent straight neck, and the acoustic performance is then obtained by a one-dimensional approach. A length correction factor for the extended neck is developed through a modified one-dimensional approach to take the non-planar effects into account. A simplified theory of tapered neck resonator is derived to predict its acoustic impedance and resonance frequency. The theoretical prediction results fit well with the Finite Element Method (FEM) simulation results. The results show that significant improvement of the acoustic performance of the HR can be obtained by introducing these necks. The acoustic characteristics of HRs with these three different neck types have a potential application in noise control, especially at low frequencies within a constrained space.