The question arose at a large wedding where the guests ate a sit-down, catered meal and then prepared to recite Birkat Ha'mazon. It was obvious to all that given the size of the banquet hall, the voice of the Rabbi leading the Zimun at the dais would not be heard beyond the two or so tables situated right in front of the dais. In order to ensure that the Zimun would be heard by all the guests, the Rabbi was given a microphone to use for the recitation of the Zimun. Is this a proper practice? Seemingly, if we assume that everybody in attendance must hear the Zimun, then the recitation of the Zimun through a microphone would not be valid. When a microphone is used, the audience does not hear the speaker's actual voice, but rather the amplifying effect of the microphone. It would thus appear that the person leading a Zimun should not make use of a microphone. Accordingly, Hacham Ovadia Yosef ruled that in the case described above, where the voice of the person leading the Zimun would not be heard by the large audience, it is preferable for each table to recite its own Zimun. Since the hall is too large to allow for a collective Zimun to be heard by everyone in attendance without the use of a microphone, the Zimun should be recited separately by each table. Nevertheless, Hacham Ovadia adds, if a collective Zimun was recited with a microphone, the guests have nevertheless fulfilled their obligation and do not have to repeat the Zimun. This discussion applies only if the voice of the Mezamen (person leading the Zimun) would not be heard at all without the microphone in some parts of the room. However, if his voice could be heard throughout the room, and amplification is needed only to enhance the sound, then it may be used for the Zimun. Since the guests could hear the Mezamen's voice even without amplification, he may use the microphone to enhance his voice. Summary: If a Zimun is recited in a large banquet hall and the voice of the person leading the Zimun cannot be heard without amplification, it is preferable for each table to recite a separate Zimun. Nevertheless, if somebody did lead a collective Zimun with a microphone, the guests have fulfilled their obligation and they do not have to repeat the Zimun.