Alas, I do not have the recording equipment to make a proper recording for you. I can ask around and see if there is a recommended sample of half-muffled ringing that I can point you to. Still, it would have been nicer to give you a sample where I was one of the ringers.

Also, your first guess as to how the muffles work is the right one.

If you ever come to visit, I simply must bring you to one of the towers where I ring so that you can (a) see it for yourself, and (b) give it a go if you wish. I have brought several P**T***ns on such trips by now, but it does require a trans-Atlantic flight, first!