Investigation of the sound-absorbing performances of pure coffee grounds

Various natural sound-absorbing materials such as rice by-products, coir fiber, date palm fiber, peanut husks, hardwood cross-sections, and forest by-products have been introduced to replace petroleum-based sound-absorbing materials in previous studies, and their sound-absorbing performance was significant. This study investigated the sound-absorbing performance of pure coffee grounds as an eco-friendly sound-absorbing material. After inserting coffee grounds into cylindrical holders with lengths of 20, 30, and 40 mm, the density of the coffee grounds was adjusted from 0.2 to 0.5 g/cm3. Then, the sound absorption coefficients were measured by an impedance tube. As the thickness and density increased, the sound absorption coefficient at low frequencies improved. However, the sound absorption coefficient at high frequencies decreased. The optimal noise reduction coefficient (NRC) of coffee grounds investigated in this study was 0.61 at a density of 0.3 g/cm3 and thickness of 50 mm. This result shows a sound-absorbing performance that is comparable to other natural sound-absorbing materials. This study concludes that coffee grounds have high use-value as an eco-friendly sound-absorbing material.