A subwavelength ventilated structure for efficient broadband sound insulation

Multifunctional structures such as ventilated sound barriers, have become the focus of recent research on the noise reduction and environmental comfort. However, its large size and complex inner structure hinder its potential applications. Novel structures with side-branch sectorial Helmholtz resonators and double-layered perforated slit plates enlightened by macro-perforated plates to enhance the soundproof performance and facilitate natural ventilation are proposed and experimentally validated. Compared with simple muffler ducts, the combinations with slit plates provide a smoother transmission loss (TL) curve with a broad and continuous TL band. We also study the influences of the independent parts and interactive effects of the assembly on the sound field, including the frequency migration and plate vibration. The proposed sub-wavelength structures with a thickness of 15 mm can obtain TL values up to 25 dB with a broad bandwidth from 930 Hz to 1600 Hz. Moreover, soundproof walls can be fabricated by using these structures with plenty of ventilated slits to freely exchange air and heat. This ventilation sound barrier is suitable for acoustic landscape buildings as it covers the main frequency spectrum of a human equal loudness contour.