Diffuser Calculator — QRD Well Depths

N=7 is the most common choice, giving a good balance of diffusion quality and construction complexity. N=5 is simpler but less effective. N=11 or N=13 provide better diffusion but require more wells and deeper maximum depth. Higher primes give wider bandwidth diffusion.

The design frequency is the depth-quantum reference that sets the well-depth steps, not literally the lowest diffused frequency. For rear wall studio diffusers, 1000-2000 Hz is common. Useful scattering runs from roughly half the design frequency up to c/(2w) where w is the well width. Lower design frequencies require deeper wells. Note the low end also depends on panel size: the period width must be comparable to the wavelength, so a single short period will not fully scatter the lowest stated frequency — use a double or triple period for genuine low-frequency diffusion.

Well width determines the upper frequency limit of diffusion. Narrower wells (30-40 mm) diffuse higher frequencies. The upper limit is approximately the speed of sound divided by twice the well width. Keep wells narrow enough that the highest frequency of interest is covered.

Yes. QRD diffusers are commonly built from MDF or plywood dividers with a solid back panel. The wells must be rigid and non-absorptive — hard, smooth surfaces reflect sound into the diffusion pattern. Paint or varnish the interior surfaces. Ensure accurate depth cutting for each well.