@E_Schaaf Enlightening, thank you. Do Foster require you to provide some proof of purchase from authorized seller as well? What do they cost the drivers? Sounds like it’d be less of a headache to just start with a complete TH900. I think Tore down HR5C. Accidentally destroyed a driver when a screw fell into and held tight by magnet. Noob. Pics here. HR5C definitely inspired by Sennheiser. Cups dont work out though. The notches and crevices don’t align. I could dremel, but I think I’m just going to try adhering with tape and sealing up. This would make interior volume larger (see pics). Then try alternate pads, and adding mass and reflection absorption, etc. I bought a materials sample kit from second skin audio including sealent.