Re: Variable sound quality, JBL PRX rig
To start with the DRPA+: When used with the factory settings for PRX, it overprotects the speakers and totally squashes the sound when you get to any useful level where the PRX comes into their own. This is fairly easy to fix though, turning the input of the PRX up by at least 6 dB from the recommended setting enables you to use the full dynamics of the PRX without too much interference from the DRPA+.
Secondly, when using the auto EQ with pink noise, and providing that the microphone position isn't totally compromised (and in this particular setting, the chances are that it is because of the nature of the room), one really need to review the result and pull down the big boosts that will probably have been applied in a couple of places (again the nature of the room). I've stopped using the DRPA on the mains.
The main problem in a room of this nature is the speaker placement, there really is no good place for a speaker in a room with sealed brick or concrete surfaces. Being close to the wall, there will be a primary null projecting into what one would assume to be the primary listening area in the upper bass, with multiple lobes in the lower midrange. If the wall can't be eliminated from the equation, the best compromise is often to place the speaker as close as one absolutely possibly can to the wall for maximum coupling as high up the register as possible, and turn the speaker away from the wall so that the directivity of the horn can take care of the frequencies higher up.
In the case of the PRX615, it would be tempting to place it on the wall in the monitor position, ie. putting the 45deg side flush with the wall and securing it using additional fly-points to augment the under-speaker support. Even turning one of the speakers upside down to achieve this on both sides (with proper fixing to compensate for the lack of 35mm hole).
To take care of the reflections thay cause havoc in the upper bass and midrange, I'd try and place absorbers on the wall immediately adjacent to the speakers. Having a couple of efficient 6" by 2' by 4' absorbers made up can be a good investment. A multi layer damper-absorber, one layer of 1/2"-1" high density rubber suspended between two sheets of 2" high density mineral fibre, clad with heavy molton. Such devices can be problem solvers in many situations.
Another solution would be to fly the speakers horisontally above the stage, having a 90deg vertical to 50deg horisontal pattern, using them as you would a small constant curvature array.
Two PRX615 should easily fill the room with adequate levels, the problem is probably too much interference from the DRPA+ and serious nulls that influence main listening areas including FOH
