When to use PRD (skyline) &/or QRD

[Ray Sr.]

Hey all, its been a while since I've posted here on GS (haven't had the need, most people have asked similar questions in the past).

I've recently decided to add Diffusors to my home project studio after running some tests using the Room EQ Wizard. I have quite a bit of Absorption going on (maybe too much) but think I need some diffusion to open things up a bit. Also I have a null at about 1500hz that is bothering me. I bought a book a few yrs back in school called Sound Studio Construction on a Budget finally after an acoustics class & reading all of the Ethan (RealTraps) and Glenn (GIKAcoustics) info (throughout the years) I feel I have enough understanding to get my home studio up to par.

The question is, when should I use PRD instead of Qrd's? If the prime root (7) is the same does it make a difference? I read that Qrd's scatter horizontally (when the wells are vertical) & Prd's scatter in an omni direction.

Any advice or input would be greatly appreciated.