|MadSci Network: Physics|
What a parabolic dish is A parabolic dish is nothing more than a concave surface - it looks like the inside of a bowl. This bowl is made in such a way that if a light was shined into the bowl, all of the light rays would reflect off of the inside of the bowl, and would focus on a point in the center of the bowl - probably suspended in the middle of the air in the bowl. The parabolic dish also reflects sound the same way, and focuses it in the middle where the vertex (focus point) is. The microphone is usually placed at this vertex, pointing into the bowl to catch all the reflected waves. A car's head lights are parabolic with the light bulb at the vertex, as well as the reflector of a flash light (usually silver in color). Yes, you can take the reflector of a flash light, measure where the light bulb filament (coiled wire) sits inside the reflector, and mount your microphone on that same spot. Remember to point the microphone inside the reflector. If nothing else, a plastic bowl will do just fine. You can make your own parabolic reflector dish if you use the equation (y)^2 = (4)(v)(x) where y^2 is y squared (y times itself) where x and y would be numbers like 1,2,3, and v would be the distance you need to mount the microphone from the center of the dish. I calculated some of the numbers here as an example, assuming the microphone would be 10 inches (or centimeters) from the center bottom of the dish. Then the rest of the dish must follow the curvature on the graph. v= 10 X Y^2 Y 0 0 0 1 40 6.325 2 80 8.944 3 120 10.95 4 160 12.65 5 200 14.14 6 240 15.49 7 280 16.73 8 320 17.89 9 360 18.97 10 400 20 11 440 20.98 12 480 21.91 13 520 22.8 14 560 23.66 15 600 24.49 16 640 25.3 17 680 26.08 18 720 26.83 19 760 27.57 20 800 28.28 21 840 28.98 22 880 29.66 As far as construction material, try to use substances that are hard or have a flat surface. Avoid constructing with foam or paper as they tend to absorb sound instead of reflecting it. Also, since the microphone is placed at X=10, you don't need to go beyond 10 when constructing the dish. And remember to face the microphone inside the bowl. This will be a tuff but fun project. Don't give up. Let me know if you need more guidence with the microphone or the construction techniques. Abtin Spantman SPANTMAN@EXECPC.COM
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