I know it sounds bougie as hell, but it's really quite a nice effect.
Also do you know the material of the metals? I wonder if it'd be worth it to have them in different metals for different timbres. Like two different instruments
Exceptional circumstances excepted of course.
ECEOC?
I have used 'BOCTAOE' (but of course there are obvious exceptions) in the past, but, guilt by association, kinda stopped all that.
There are plenty of 9-hour long YouTube videos (example [1]) cycling through the frequencies. Apparently to be played while you sleep.