The use of materials based on the mycelial growth on recycled materials is widely studied. The absorbent properties of such composites can be found in a number of articles. However, this one focuses on the possibility of using mycelium-based composites for the design of sound diffusers. Diffusion parameters were determined in the form of normalized and non-normalized diffusion coefficient in a free field according to ISO 17497-2. The measured results show that the use of mycelium for the construction of diffusers is promising. However, the results are not the best, which is due to the architectural design.