The page above claims w/ o theory that dinging a bell results in
ringing; harder, louder, but if cracked, if dinged very lightly,
will ring; harder and pitch lowers and the ring is more a thud.
Static and dynamic friction immediately suggest the reason. I
thought some day to try it; strobe maybe, etc. And then I
accidentally cracked a beer (tall) glass and tried it. Wow it's
true, tho couldn't control the dinging to get the ring w/ pitch
change. Then taking the advice of several clocks group posters I
glued the crack w/ cyanoacrylic. Back to normal! Later I tried
"really" dinging it; thud. Yup the glue joint was broken; a re-glue
worked.
bc, kitchen physicist.
p.s. we have some squeaky chairs; searching for glue at the local
iron mongers we found "Tite Chairs". "Instant loose Chair Repair"
20 gm for $10, IIRC. such a deal and includes capillary dispenser.
Was what I used on the glass.