The Sifsei chachamim makes an interesting diyuk in the parsha. By 9 of the makkos when Moshe davens to remove the makkos the Torah uses the loshon of 'vayetar". However, by the frogs the loshon used is 'vayitzak ". The Sifsei Chachamim explains that the frogs were making so much noise that Moshe couldn't hear himself daven. Therefore, hehad to scream in order to hear himself.
This leads to the question what is the geder of hearing yourself during davening. The halacha is that l'chatchila one must hear yourself daven but b'dieved you are still yotzei sayin it quietly. The chakirah is the following, by not hearing myself daven is it a chisaron in my dibbur and it is as if I am not saying anything or is it a halaca in tefilla that a ma'aleh of tefilla is that you need to hear yourself. (The chazon ish has this chakirah on the sugyah in Berachos). A nafka mina is if you are talking in a normal voice but you can't hear yourself because it is very noisy. According to teh first tzad-it could still be considered dibbur acc. to the 2nd tzad it is still a problem.
By Megillah, a cheiresh who can't hear is possul. The Avnei Nezer discusses the question if someone can't hear himself cause he has earplugs can he be motzi someone? It could be toloi on the above chakirah. The Avnei Nezer says a cheiresh is really a bar chiyuv just he can't be motzi someone cause his speech is not dibbur since he can't hear himself. So too someone who can't hear himself-his speech is not dibbur. (Rabbi Akiva Eiger holds a cheiresh isn't a bar chiyuv).