How does one go about determining hi frequency limits for quadratic residue/primitive root sequence style diffusers. I know that low frequency is related to well depth, and high frequency is related to well width, but was is the specific math for these calculations?

Also, based on liturature published by RPG, the low frequency limit also seems to related to the difraction limit of the diffuser based on overall width(not sure if I said that quite right). Does this mean that the diffraction limit is lowered when multiple units are placed side by side? Hope I'm being clear.

Thanks!