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Parabolic Microphone
Description:
Employing any curved reflector and a microphone will greatly enhance the long distance performance over using the microphone alone. Although the reflector used in this particular project was not truly parabolic, it worked very well. A Hanging Squirrel Baffle was employed although you can use whatever you have. The focal point for the microphone was found to be exactly 6 inches out from the bottom of the reflective surface. To find the focal point of your reflector, first build the high gain audio amplifier listed on this site and then run tests with your microphone on an adjustable rod within the reflector. Place an audio source and speaker about 100 yards away and point the dish at that source...then move the microphone in and out until the maximum volume is achieved. This will yield the exact focal point. The Squirrel Baffle is available at most major home supply stores and is designed to keep squirrels from getting into bird feeders. There are many other reflectors that can be used. Be creative.
How it Works:
Simply put: sound waves strike the concave surface and are directed to the microphone. This tends to concentrate the waves to one spot. This project coupled with the associated amplifier can be used for a variety of applications, just a few being: wild life recording and search and rescue. The application of a high gloss paint to the reflective surface will enhance its reflective attributes. The microphone itself is an electret type element with three wires and does require about 6 volts of DC for operation. On the other hand, it does have excellent frequency response. That, being flat from 20 HZ up to 15 KHZ and with an output of -65dB. In comparison, most dynamic microphones only produce about half that signal amplitude.
Construction:
Note: the following, specifically relates to an 18 inch diameter, 5 inch deep reflector. Cut the following lengths from some 1/2 inch PVC: 2", 1 1/4, 4 1/2, 1 1/4. These pieces along with four 1/2 inch elbows will place the microphone exactly 6 inches out from the bottom of the reflective surface. Cut a 1/2 inch wide piece off of the end of a 1 1/4 slip coupling. Place a 1 1/4 x 1/2 inch bushing through the opening of the reflector (you may have to file the reflector a bit).
Slide the 1/2 inch wide piece over the bushing on the back of the reflector and adhere with PVC cement. After this dries, adhere a 1 1/4 x 1/2 inch Tee to the bushing. As you assemble the 1/2 inch pieces within the reflector it is important that as each piece is adhered in place that the two conductor shielded cable is pulled through. If you wait until all of the curves are complete, it will be almost impossible to pull the cable through the completed work.
Cut a small piece of foam rubber and slide it over the audio cable and then solder the wires to the microphone. After taping the connections, pull the cable and foam cushion back into the 1/2 inch PVC. The red lead from the microphone needs a DC supply and should be soldered to the tip of a stereo 1/4 inch plug. The audio should go to the small ring and the ground (shield) to the base portion of the plug. For the handle, you will need a 4 inch long 3/4 inch PVC nipple and if you wish to mount the handle to a tripod, a 3/4 inch brass cap will be required. Drill a 3/16 inch hole in the bottom of the brass cap and then use a 1/4 -20 tap or whatever matches the threads on your tripod screw.
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