This paper reports the development of a non-electrical sound augmentation system that uses acousto-fluidic technology to amplify and transmit voice sounds. Because of the unique religious restrictions of Orthodox Judaism, use of electronic sound reproduction per se to amplify and transmit the voice of a rabbi or cantor is not allowed because it contravenes the prohibition of performing labor on the Sabbath or on holy days. Labor is defined in the Halacha (Jewish Law) as the creation of anything new. Since conventional sound transduction or reproduction involves the creation of several new things or states, that is, the speaker's sound causes a diaphragm to move that was previously at rest (a new state), the diaphragm motion creates an electrical current that did not exist before, the electrical current causes another diaphragm to move, and the diaphragm motion creates a new sound that also did not exist before (albeit sounding the same, it is nonetheless not the same sound), therefore, its use is not kosher and is thus prohibited. Sound augmentation, however, that is the restoration of the original sound to its original level, all the while preserving the actual sound, is permissible as long as no apparent sound level amplification is evident.
Sounds interesting?, see http://www.acoustics.org/press/132nd/2aaa8.html