Design of an undamped Helmholtz resonator

Optimizing low-frequency performance within enclosed spaces is often achieved through solutions involving acoustic absorption, including Helmholtz resonators. This thesis specifically focuses on the design of a "damped" variant of these resonators, characterized by the absence of sound-absorbing material inside. The main objective is to experimentally explore and validate the differences between the effects of a real resonator and a theoretical one, also confirming a modal division phenomenon previously observed in simulations. Within the scope of this thesis, the methodology, both simulation-based and experimental, that guided the design and realization of the resonator is carefully discussed. In designing this resonator, it is crucial to identify the frequency to focus on to adjust the resonator's absorption. The work begins with the selection of a suitable environment for acoustic analysis, followed by experimental measurements and theoretical modal analysis, essential for determining the reference modal frequency. The actual design of the resonator starts with simulations that generate an accurate model of the resonator's behavior based on its fundamental properties. Thanks to the development of a custom simulation system, key parameters are estimated. This initial phase allows for outlining the design before its physical realization, culminating in an experimental phase that further refines the design, specifically identifying the hole dimensions through experiments with the impedance tube. After identifying the technical characteristics of the device, a piston system is implemented on the back of the resonators during the production process to allow dynamic adjustment of the cavity depth and, consequently, the resonance frequency of the resonator. Once the construction of the resonator is completed, its effectiveness is tested first in an anechoic chamber, then in the initial semi-reverberant environment, and finally in a reverberant chamber. To ensure a robust research sample, four identical resonators are produced and tested simultaneously in various configurations to assess their impact on the acoustics of the environment. Finally, the results obtained from the experimental measurements are compared with the theoretical simulations and expectations, providing a detailed analysis of the possible causes of the observed discrepancies.