Many recent poskim have dealt with the question of a microphone, a telephone, or a live radio broadcast. Most say the listener does not discharge his obligation via these means, on the grounds that he does not hear a human voice, but rather a human voice that has been transformed into sound waves and then recreated as electronically produced sound.

In footnote 9, the Piskei Teshuvot cites the Maharsham as comparing a microphone or telephone to an echo; if you hear only the sound of an echo, you have not discharged your obligation. The position is elaborated by Rav Shlomo Zalman Auerbach in the Minchat Shlomo. Rav Shlomo Zalman consulted with experts on how electronic systems worked and compared the electronic reproduction of sound to the waving of flags in the enormous sanctuary in Alexandria, so that the congregation would know when to respond Amen. Rav Shlomo Zalman said that one may not answer Amen to a blessing heard over the telephone or radio, because one is not hearing the person at all, just a sound produced by the membrane of the device. Under such circumstances, the Amen would be recited in vain. (He added that those who are lenient on this subject fail to understand how the devices work and are under the mistaken impression that they are hearing a human voice.) If, on the other hand, the listener is in the synagogue or immediately outside it and hears the blessing through a microphone, he is “dragged along” with the congregation and may respond Amen. This method is not available, however, for any other mitzvah that requires hearing a human voice.

For Rav Shlomo Zalman, hearing an electronic sound through a microphone is like listening to a tape, and does not constitute listening to one who has an obligation. Therefore, he adds, those who wear hearing aids also fail to fulfill their obligation and should read the Megillah to themselves. Rabbi Kermaier added that he knows of a case of an individual who wears hearing aids and, for Megillah reading, removes them and stands close to the reader, so as to hear the sound of the Megillah directly.

Some poskim are lenient, however. Even without using a microphone or telephone, they argue, the only way we hear is through the transmittal of sound waves and after a delay of time. No one disputes that that kind of listening is anything but a human sound. So, too, the microphone and telephone work to gather sound waves and transmit them over a distance. Thus, listening over a microphone or telephone is analogous to listening to an echo mixed with the original voice, and is permissible. Even these poskim, however, say that this leniency should be used only under extenuating circumstances. Rav Moshe Feinstein allowed for the possibility of a microphone, but concluded that there was insufficient basis to rely upon its permissibility, and thus the minhag has spread not to use a microphone.

Rabbi Kermaier further cited three teshuvot of Kollel Eretz Hemdah. First, they ruled that if one is sitting in a location where it would be possible to hear the reader of the Megillah without amplification, then the presence of a microphone does not prevent him from fulfilling his obligation. It’s as though he’s hearing the human voice mixed with another sound. The problem of a mixture of two sounds being halachically inaudible does not apply to Megillah, because it is deemed a beloved mitzvah, so the listener will pick out the sound that he wants to hear.