3pcf vs. 6pcf rockwool in ceiling mounted absorbers

[coyotekells]

My supply of the denser (3", 6.0pcf) rockwool is limited to only 4 panels (the usual 2x4' size).

In my small vocal booth (3x6, 7.5' high), is it better to use one of the 3" panels on the ceiling? (instead of putting a 1.5" / 3pcf panel on the ceiling, and using all the 6pcf on the walls/corners).

Sorry if this is a negligible acoustical difference, but I genuinely want the best outcome.

One other question: is 1/4" a sufficient amount of space between the panel frame and the wall? (it would actually be about 1/2" between the wall the rockwool, because there's 1/4" overhang of the frame, plus 1/4" airflow how the frame is mounted off the wall)

Many thanks (again)!

[Glenn Kuras]

In my small vocal booth (3x6, 7.5' high), is it better to use one of the 3" panels on the ceiling? (instead of putting a 1.5" / 3pcf panel on the ceiling, and using all the 6pcf on the walls/corners).

Yes if you can go with the 3". BTW 3pcf will work very well.

is 1/4" a sufficient amount of space between the panel frame and the wall?

If that is all you the space leave then go for it. The rule of thumb though is to put equal air space, the thickness of the panel. So if the panel is 3" of mineral wool then leave a 3" air gap.

Glenn