Yamaha experiments with hammer materials & blocking holes in the frame

Recordings from a Yamaha Corporation site. Some are presumably just for fun, but I'm surprised to hear the difference that leather makes--a slightly darker attack?

https://www.yamaha.com/en/musical_instr...sm005.html

But see the notes: Leather does not compress much, and thus soft and hard strikes sound similar.

Perhaps more interesting is Yamaha's experiment with blocking the holes in the frame:

https://www.yamaha.com/en/musical_instr...sm006.html

I like the sound with the blocked holes, actually. Not that it's better, exactly. But it has its own richness in the midrange.