When sound reaches the end of a closed duct, some of the sound waves bounce back, generating acoustic reflections. Reducing this effect is the aim of research conducted by Dr. Jie Deng, a researcher at La Salle - Universitat Ramon Llull, and Dr. Oriol Guasch, Head of the Acoustics and Audio research line, Coordinator of the Human Environment Research (HER) research group and Full Professor at La Salle - Universitat Ramon Llull. The research also involved PhD student Junjun Li from La Salle-URL and a group of Chinese researchers led by Dr. Nansha Gao, a Full Professor at Northwestern Polytechnical University in Xi'an. The research has led to the development of a sonic black hole, a device capable of absorbing sound without the need to modify the duct walls.
We have been conducting cutting-edge research on acoustic black holes at La Salle-URL for years. Our challenge is to develop increasingly efficient and lightweight methods for reducing noise and vibrations, overcoming the limitations of conventional solutions, which often require adding mass to improve their attenuation capacity.”
Dr. Oriol Guasch, Full Professor at La Salle-URL
An acoustic solution with practical applications
The sonic black hole is a structure of rings and cavities that promotes the absorption of sound waves and reduces reflections inside ducts. The physical principles underlying its operation are quite different from those used in conventional designs. Compared to these, it has a lower reflection coefficient and is effective over a wider frequency range. The main innovation of the device is that it is manufactured as a separate component that can be inserted into the end of a duct, featuring a removable design that facilitates the integration of acoustic absorption solutions into existing installations.
To test its performance, the research team combined numerical models with experimental tests and manufactured a prototype using 3D printing. The results are consistent with the simulations and demonstrate the potential of a low-cost solution that can be adapted to ducts of different geometries and materials and installed without modifying their walls.
This research opens up new possibilities for developing more flexible and accessible acoustic control solutions, applicable to ventilation systems and other installations where sound reflections need to be reduced. In this regard, the study exemplifies La Salle - Universitat Ramon Llull's commitment to applied research that transforms scientific knowledge into solutions that address real-world challenges and contribute to improving people's lives.
Reference article: Deng, J., Li, J., Gao, N., Zhang, Z., Li, Y., & Guasch, O. (2026). A plug-in sonic black hole for duct terminations. Applied Acoustics, 243, Article 111119. https://doi.org/10.1016/j.apacoust.2025.111119
