Diffusive surfaces can be optimally designed for both acoustic and aesthetic purposes. Adapting to the parametric demands of interface design, fractals are widely applied as a fusion of mathematical calculation and artistic design. The Sierpinski triangle is a self-similar structure with a more impressive appearance than conventional acoustic diffusers. However, the acoustic performance of Sierpinski fractal patterns has not been considered. This paper proposes a design of an acoustic diffuser based on the construction rules of the Sierpinski triangle to broaden the effective frequency range. The diffuser is made of triangular blocks of different sizes attached to a plane surface. A series of case studies are examined through numerical simulations based on the boundary element method (BEM) to investigate the effects of the number of iterations, the randomness of block arrangements, and the inclination of block tops. The diffusion performance of a conventional quadratic residue diffuser (QRD) is compared to confirm the advantage of the designed diffuser for broadening the effective frequency range. Furthermore, a workflow of the design and evaluation processes is presented to fabricate samples that could be used to tune the design parameters according to their in-field application demands.@en

This paper proposes a new design of an acoustic diffuser based on the construction rules of the Sierpinski triangle in order to broaden the effective diffusion frequency range. The diffuser is made of triangular blocks of different sizes attached to a plane surface. The effects of the number of fractal iterations, the height of triangular blocks, and arrangements of the blocks on the normal-incidence diffusion coefficients in the near field are examined through numerical simulations based on the boundary element method (BEM) in the frequency range of 100 Hz – 5 kHz. Furthermore, measurement results will be presented to validate the diffusion performance presented by the numerical simulations. The diffusion performance of a conventional quadratic residue diffuser (QRD) is compared to confirm the advantage of the designed diffuser for broadening the effective frequency range. It shows that the fractal patterns with various sizes of blocks improve diffusion performance compared to the conventional QRD of the same size, especially in the mid-low frequency range below 1 kHz.@en