The echo fits, but in comparison to your image it's very deep!
top surface is 4mm lower then the printed part and that's not what I had expected.
If you can afford with the acoustics you can find out by listening to the 2 short clips in the 7z archive file.
I'm a little bit sad about the destroyed print. the flex sheet of the MK3 didn't release on 1st layer, the part had separated a few bottom layers the quality of the remaining is quite good so far.
It's stonefil terracotta by Formfutura.
Expires 2018-04-23 due to 30 day limit
stuck very hard to the bed. like PETG on the PEI sheet...