A friend was sitting near another's ringing mobile phone, stoically ignoring the noise. When I advised him to cover the dynamic with a finger, he replied that it may break it.
Is it really so? I think the energy should be dissipated in finger/casing and is too weak to break anything anyway.
Managed to find a reference with [remotely] similar opinion, although here the aperture is covered to make it louder as opposed to silencing it http://www.e-katalog.ru/opinion_ie.php?resolvedName_=NOKIA-1280 "И динамик не стоит на обратной стороне заклеивать или закрывать пальцем,на много проще перевернуть телефончик обратной стороной к уху и слышимость становится просто-супер!А заклеенный динамик со временем испортится." -> "And you should not block the dynamic on the reverse side with finger or with duct tape. Simply turn around the device and lean the back side your ear - audibility is superb. And glued (with a duct tape) dynamic will eventually spoil."