A lot of sustain but low volume

[Mike Mandelas]

Dear friends we have in our orchestra a fully carved Romanian double bass with beautiful flamed tonewoods, two years old. The bass has a warm, focused sound with a lot of sustain but the sound's volume in pizzicato playing is low. Compared with some other instruments in our collection (some carved, some hybrids) it produces the most mellow sound but also the lowest. We tried a lot of solutions, dealing with strings, soundpost, bridge, mode matching etc, to no avail. As times goes by and the instrument matures it produces more sustain but the volume remains unaltered. I wonder if it is a matter of construction or of a poorly made set up. As a decent luthier is nonexistent around here, any opinion is welcome.
Michael