Aluminum housing and Copper back plate.
MIROAK is made of aluminum + copper.
There are three types of copper, and the metal coloring is done by “momentum factory Orii” using a traditional Japanese technique.
The copper on the back plate is blue “HANMON GAS SEIDOU Color”.
Each one has a different pattern and color. No two are alike.
The sound is even milder than brass and has a thicker midrange.