Dollar Store Parabolic Mic

Step 9 Take it for a Test Ride

Plug your new parabolic mic into the microphone input of your favorite recorder. Use headphones to monitor your work. Then point it at something interesting. You are in for a pleasant surprise. Try recording the same sound without the parabolic set up.

Haven't made one yet? Hey, that's okay. I did it for you. Here is a link to an '''a short MP3 file''' that lets you hear how well it works. First you will hear a recording of a growling squirrel with the mic element by itself followed by the same squirrel recorded with the parabolic set up. That is followed by a similar sequence recording a cardinal chirping in the distance, first without the parabolic setup, then with it. The segments are separated by short tones. I think the differences are pretty amazing.

So, make one for yourself and let me know how it comes out.

Comments

[KingOfCatfish]

I love this Instructable!
So you know those really crinkly emergency blankets that resemble foil? Would lining the inside of the umbrella (using spray adhesive or the like) with that help provide better sound? My reasoning with this thought was that the metal-like surface would reflect sound waves better than just the vinyl.

[jurtle]

Glad you like the Instructable. It was fun to put together. As for lining the umbrella with the rescue blankets, I think you would get only marginal improvement if any at all. Those blankets are usually made of mylar, another plastic-like material. Adding another really thin layer of plastic (and glue) to the umbrella might make the whole thing slightly more rigid, thus making it slightly more reflective. My guess is that one would hardly be able to tell the difference in an A-B test. Don't confuse the shiny, almost mirror-like, look of the mylar with good acoustic reflectivity. It will make a much better reflector of light but not of sound.

[KingOfCatfish]

Thank you for getting back to me. My eyes have now been opened, ha-ha. So I was looking at some pieces of Lexan that are at my house from another project and was wondering is forming it into a parabola would work. What do you think the outcome would be?

[jurtle]

I assume you are talking about flat pieces of lexan. Yes, you can fabricate a parabolic reflector from that material. It will require some cutting and gluing. Here is a link that will get you started: http://vzone.virgin.net/ljmayes.mal/var/parabola.htm Otherwise, just do a google search for something like "Make a parabolic reflector." Lots of idea out there. Good luck.

[scraggy12]

Hey , can I use an old direct tv dish?

[jurtle]

Yes, but because the dish is so shallow, the focal point is farther away from the surface. It will work but you won't get as much gain. See an earlier comment/reply on this subject. Good luck

[wingo395]

Oh one more thing - You showed in the photos but perhaps it is worth mentioning - you want the microphone element pointed IN to the center of the umbrella, not outwards.  This is to pick up all of the reflected sound bouncing off the surface of the umbrella and to the focal point.

[jurtle]

Good call. I did show the mics facing inward in the photos but nothing is said about it in the text. I will probably amend to make the addition. Thanks for the input.

[jurtle]

I have amended the text to point out that the mic should face inward toward the umbrella. Thanks for the input.

[wingo395]

Very nice project!  If you really want to get accurate (as accurate as possible given the flexible nature of the umbrella hat), you can calculate the focal point.  All you need to know is the diameter of the dish and the depth of it.

A simple google search will turn up oodles of info:
http://www.google.com/search?q=calculate+the+focal+point+of+a+parabola

I once bought a parabolic dish (without the mic) from a college, and I bought a very sensitive electret microphone (electets have batteries in them to amplify the signal).  I don't know if it was omni or unidirectional.  My guess is omni might be better, but would need experimentation.  The funny part?  I have yet to put it all together!!

[jurtle]

Glad you liked the project. Yes, one can easily calculate the focal point from diameter and depth in a true parabola. That said, there is no reason to believe the umbrella is actually made to conform to such standards. As I have said in previous posts, the focal point on this device is fuzzy at best. Better to use the methods suggested to get the best result. Much of the physics (and math) that applies to parabolic focus with point sources from infinite distances (therefore parallel rays) just does not apply with variable wavelength sonic sources from variable distances and angles. Too much accuracy is overkill.

[SLUTSONLY]

nice work ....... how do i use one witout being in plain view ....... dose it work threw screens ??? thanks

[SLUTSONLY]

do you , by any chance.. know about a shotgun mic ... and how it works ??? i have hot to hear what the heck my new neighbors across the street are arguing in the driveway about ..... thanks

[jurtle]

Begin your research into microphones here:
http://en.wikipedia.org/wiki/Microphone
I am going to stay out of that business with your neighbors. You probably should too.

[SLUTSONLY]

just bored and she's kinda cute ..LMAO .... thanks for your help ...

[jurtle]

Glad you like it. This is probably not your best bet for secretive recording. It does stand out. My guess is that it will work through a screen but I have never tried it. Good luck.

[hellequin]

Excellent demonstration... In your sample, I found that as with most parabolic reflectors – professional or otherwise that I have on occasion used, there is quite a bit of base rumble in the 40 > 100 Hz area. But a lot of this can be filtered out using various low-pass filters and EQ. A very commendable effort and a great solution... Bravo!

[jurtle]

Thanks. You are right about the low end emphasis. I think a more rigid reflector would probably take care of some of the problem. Some sort of shock mount for the mic would help as well. The challenge would be to make such modifications while staying within the "dollar store" range. Thanks again. Glad you liked the project.