Best way to increase volume of wall mounted 30 note mechanism

I’ve been trying to find a good/easy way to increase the volume of a wall mounted mechanism for use in a gallery context. Currently I have the mech screwed to a wooden box, which in turn is secured to the wall. Would adding sound holes improve the volume further? Any suggestions about preferred resonator design/materials? In testing surfaces I tried holding the mech against a large chambered door and it sounded fantastic - but that’s not an option in the gallery space.