Brad,
All the prior posts about having it done right, and making sure anything installed is fireproof is good advice.
However, all the ideas so far mostly only deaden the high frequency, which often make lower frequency problems even more apparent by comparison.
Another approach not mentioned so far that works quite well in small and larger scale rooms is a type of diffuser panel I encountered in an orchestral rehearsal room.
The room was a typical ballroom type room, about 70’ x70’ and 10’ ceilings. I expected it to sound like the usual boom boom room, but was surprised to find I could run my system at upwards of 115 dB (where it was running out of headroom) without any of the flutter echoes, boom or the other crud associated with that type of room shape.
I later built the same type of panels for a friend who wanted to turn his cinderblock single car garage (probably roughly the size of the stage you are trying to fix) into a rehearsal/recording studio.
Each panel uses a piece of 4’x8’ 1/4” ply bent on arcs which are cut from 2”x12” material. Picture the cross section of a parabolic satellite dish vertically attached to a frame, like an airplane wing, or a giant roll and pleat.
The back side of the frame has fiberglass insulation installed. The sections I made, and the ones I copied, used 4’x8’ 1/4” ply. If your ceiling is higher, the “wing” could be made higher.
The arcs were cut to a 4” depth if I recall correctly, with a 1.5” frame thickness, for a total depth of just under 6” in the center. The arc is a section of a circle with approximately 57.5” radius. Four arcs per 4’x8”, and 1.5” angled “studs” on either side. The left to right dimension is slightly under 48” because of the arc, so you need to lay one up to figure exactly how many sheets you need for the finished length.
The reverse parabola scatters, rather than absorbs the sound waves, the spectral content stays roughly the same, while the standing waves and HF chatter are largely eliminated. The 1/4” material flexes enough that it (with the fiberglass behind) eliminates much of the mid-bass build up common to a small room.
I can not normally stand to be on a small live stage without hearing protection with even a moderately loud drummer. With this type of treatment not only do drums sound good, but everything is easy to hear distinctly throughout the room. Stage volume escalation should tend to be less than on a “dead” stage, where musicians crank up because their apparent volume seems less, or a too live stage where they crank up to hear themselves over the wash.
Cutting the arcs with a band saw took a while, but the rest of the construction is about the equivalent of doing a sheet rock wall of the same size.
Art Welter
P.S. Really large sonotubes could be cut up for a similar effect as what I described above, and would be a snap to install.