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Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources.

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The other way to use these is in the original way they were designed.  That is to directionally listen to sound from far away using the parabolic reflector with built in microphone.  However, in the classroom, you are only able to do this with the headphones on, which means that only one student at a time is able to experience the effect.  If you hook the parabolic reflector with microphone to an amplifier and speaker, you will start to get uncontrollable feedback, mostly due to the reflection off the classroom walls of the signal you are amplifying.