EXPERIMENTAL STUDY INTO THE HELMHOLTZ RESONATORS' RESONANCE PROPERTIES OVER A BROAD FREQUENCY BAND

We have investigated the distribution of sound pressure levels in the Helmholtz resonators over a wide range of frequencies. Computer simulation of the sound field at the resonator was performed by using a finite element method and an experimental research. We have established the existence of many resonance frequencies at the resonator and show the distribution of the maxima and minima of sound pressure levels within the volume of the resonator. It has been revealed that the distribution of the resonator's resonance frequencies does not obey the harmonic law. That makes it possible to consider resonance properties of the resonator similarly to the oscillations in a membrane or a bell. The second resonance frequency of the resonator is 6‒9 times higher than the first resonance frequency corresponding to the Helmholtz resonance. Simulation of sound field in the resonator showed the presence of nodal lines in the distribution of the sound pressure in both the resonator's volume and its throat. It has been established that the number of nodal lines for the first frequencies is one unity less than the resonance number. A common feature to all distributions is that when a measuring point approaches the edge of the resonator throat, the level of sound pressure decreases. In addition, the study has found the possibility to generate resonance only within the resonator's volume without distinct nodal lines in the throat. Comparative analysis of data acquired from experiment and during computer simulation has revealed a high level of reliability of the results obtained. Error in determining the resonance frequency did not exceed 0.8 %. That makes it possible, when further determining the sound field in the systems of resonators, to employ computer simulation instead of resource-intensive experimental studies. The existence of many resonances at the Helmholtz resonator enables the construction of broadband devices, which could be based on using a given type of resonator