Materials that produce Diffuse Acoustic Reflections

[dimensionless]

Are there certain materials that reflect acoustic waves diffusely? Would the material need to have large (visible) surface features to produce this kind of reflection or can the surface be smooth? Are there materials that reflect acoustic waves in accordance with Lambert's cosine law?

 

[geonat]

Are there certain materials that reflect acoustic waves diffusely?

Constructions that do this are commercially available, see for example http://www.rpginc.com/

Would the material need to have large (visible) surface features to produce this kind of reflection or can the surface be smooth?

Not necessarily - variations in acoustic impedance may also produce scattering.

For non-smooth surfaces: The roughness usually needs to be of the same order as the wavelengths for efficient diffusion.

 

[dimensionless]

Thank you for your reply.

Are there standard materials that diffuse (e.g. wood, concrete, tile, wall board, etc.)?

Are there many contruction materials that have non-uniform acoustic impedance?

 

[geonat]

It is difficult to achieve uniform and significant diffusion with standard materials - the dominant factor is rather the macroscopic irregularities (required roughness typically about 30 cm for 1 kHz).

Non-uniform acoustic wall impedance is effected by placing many patches of different materials (and/or different air gaps behind them) close to each other. Each patch may have constant acoustic wall impedance over its own surface.

The safest method is however probably to use quadratic residue diffusors (QRD) with documented values of diffusion coefficients. It is also important to keep track of the absorption coefficient of the diffusor, so that the reverberation time doesn't become too low by mistake.