Brachot Through a Microphone
Does one fulfill one's obligation of a bracha if one hears a bracha through a microphone? One of the primary sources on this topic is the mishna (Rosh Hashana 27b) which states that if someone blows the shofar into a pit, one doesn't fulfill one's obligation if one only hears an echo of the blow.  Based on this, one could have begun discussing whether hearing a sound over a microphone is considered like hearing an echo or the original sound itself. Yet, there is a clear distinction between an echo and a microphone; an echo causes a mixture of sounds, whereas the microphone simply amplifies the original sound.
The main discussion of the poskim, however, centers around whether the sound that is produced by the microphone is considered the original sound that went into it. Rav Moshe Feinstein writes that it seems that one could fulfill any mitzvah, which one fulfills through speech, by hearing it amplified by a microphone. He notes, though, that this leniency would not apply to Kriyat Shema or Birkat HaMazon. He reasons that since the voice is heard as a direct and immediate result of the speaker it is considered like regular speech and not an echo. Even though the microphone converts the sound waves into an electrical signal which is then used to produce amplified sound waves, the resulting sound waves should be considered no different than regular sound waves that are created as a person speaks. He concludes with hesitation being that microphones are a new invention and shouldn't be introduced into Jewish practices.
Interestingly, Rav Shlomo Zalman Auerbach records a conversation he had with the Chazon Ish, in which the Chazon Ish espoused an opinion very similar to Rav Moshe. On the other hand, Rav Shlomo Zalman Auerbach felt that since the microphone converts the sound waves into an electrical signal and produces a new sound, one certainly can not fulfill mitzvot through a microphone since the sound one hears isn't the same one that was original one. A number of poskim agreed with Rav Shlomo Zalman's logic.
- The gemara Rosh Hashana 27b establishes that this only applies to those who are standing on the lip of the pit, but those inside of the pit certainly fulfill their obligation since they hear the blow directly. Shulchan Aruch 587:1 codifies this as halacha. See the Mishna Brurah 587:7 who writes that one should be strict for the opinion of the Rosh who says that in all cases the ones standing on the lip of the pit did not fulfill their obligation.
- Rav Levi Yitzchak Halperin (Torah UMadah 9:1, 5740, p. 3). Beiur Halacha 587:1 s.v. VeIm explains that an echo is a mixture of sounds.
- Igrot Moshe (2:108 and 4:91:4)
- Minchat Shlomo 1:9, Kovetz Mamarim BeInyanei Chashmal (5738 p. 40)
- See the teshuvot of Rav Ovadia Yosef (Yechave Daat 3:54, Yabia Omer 1:19:18, Chazon Ovadia Purim pg. 44-47, Shabbat vol. 5 pg 241-244) with applications to Zimun, Mikra Megillah, and Tekiat Shofar. Rav Ovadia Yosef (Chazon Ovadia Yamim Noraim p. 21) writes that regarding Selichot it is possible to join in with the recital of the 13 middot and amen after kaddish if one is listening to a live streaming of selichot. See also Rav Yitzchak Yosef's Motzei Shabbat Shiurim from Elul 5774 when he said that, though anyone listening to a live feed does not fulfill any obligations, one may still answer Amen, or the Yud Gimmel Middot or even say the Aramaic parts of Selichot, even though he isn't present in that minyan. See Rav Yosef Engel in Gilyonei HaShas (Brachot 25b) who presents a similar approach. He says that hearing sound through a microphone is considered an unnatural way for sound to be transferred.