Broadband sound absorbers via quality-factor modulation

Broadband acoustic absorbers have extensive applications in noise control engineering and room acoustics. In recent years, acoustic metamaterials have provided an avenue for compact low-frequency and broadband absorbers but the complexity of their configurations is commonly increasing with the larger number of component resonators. In this paper, we propose an easy and effective design concept for broadband two-resonator acoustic absorbers by conceptually analyzing the absorption properties based on basic resonance qualities. Then, proof-of-concept structures validate the presented design concept with remarkable broadband absorption performances and simple structure configurations. One of the resonators has a low quality factor (Q) and the other resonator features a high quality factor. The low-Q resonator contributes to the broadband absorption performance while the high-Q resonator leads to high-efficiency absorption as well as a sharp absorption curve at low frequencies. We practically achieve the low-Q resonator by combining a perforated absorber with a porous material (foam) and a straight cavity. The high-Q resonator is realized with another perforated absorber with a foam and a curled cavity. The combination of the two resonators can achieve high-efficiency sound absorption in the range of 300–6400 Hz with a structural thickness of 100 mm. This work presents a simple and effective design approach using only a low-Q resonator and a high-Q resonator to achieve a thin and efficient broadband acoustic absorber, which would have broad application prospects in the field of low-frequency and broadband absorption.