The components for the second two Space Rocks needed to take up less space. In the case of Undarum, the amplifier was too large. Shown here is the circuit on a new PCB (version 3) using an Adafruit Mono 2.5W Class D Audio Amplifier (PAM8302), which has a much smaller footprint and height than the previous self-assembly amplifier kit I was using.
Two revised Space Rock circuit sketches. One (above) showing positions of magnets to be used as a closing mechanism. The other without a sensor, as I hope to use the RSSI data from X Bee to influence the sounds from the Space Rocks, meaning no additional sensor required.