What surface roughness makes for a good diffractive side wall ?

[Wes]

Depth and spacing of surface elements...

Note - elements could be the peaks on a brick.

 

[Hipper]

I would have thought that the sonic behaviour of a wall with a rough surface would be more determined by the material from which it is made then the coarseness of its surface. Remember that the sound wavelengths are relatively large (20kHz has a wavelength of 1.7cm).

When you look at diffusor panels their relevant dimensions are much bigger then this.

Of course I could be completely wrong!

 

[JohnPM]

Height differences reaching 1/4 of the wavelength of the lowest frequency you want to diffuse, so a lot of height variation. "Roughness" doesn't quite capture it