Roll your own parabolic microphone

Parabolic microphones are used to listen in from a distance. You see them on the sidelines of NFL football games, but they’re part of the standard issue in detective and spy novels. Now you can build your own parabolic microphone by following this example.

The one component that may be hard to find is the parabolic reflector. You cannot simply use a bowl or other curved object as the precise parabolic shape ensures that sound waves are reflected onto one finite focal point. For this build the reflector was obtained from an eBay seller. But the other parts are scavenged from easy to find sources. The microphone itself is an inexpensive element from Radioshack. It is mounted in the shell from a tweeter speaker, which helps to gather the sound if the element isn’t exactly aligned with the focal point. The setup also needs a preamplification system, which uses many components. Luckily there’s a schematic and other reference material linked in the write up.

You can also build a laser microphone which detects sound waves on a pane of glass.

[Thanks Anonymous]

Comments

  1. RobinJood says:

    “You see them on the sidelines of NFL football games” or “You don’t see them on the sidelines of NFL football games”?

  2. fartface says:

    This is an awfully complex version. just stick a hand held mic at the focal point and call it done.

    http://makeprojects.com/Project/Parabolic-Microphone/16/1#.UGMbE41lSqs using an umbrella to get more sound gathering and far more portable.

  3. rasz says:

    ” the precise parabolic shape ensures that sound waves are reflected onto one finite focal point”

    you mean like EVERY SINGLE parabolic antenna?

  4. spiffwilkie says:

    Couldn’t you use one of the millions of orphaned Dish/DirecTV antennas?

    • Dax says:

      Or you could make one by stretching a membrane across a trash can, and sucking air out of the can to create a parabolic shape.

      • AstronomyFTW says:

        Sorry, removing air from behind a membrane only results in a spherical surface (https://secure.wikimedia.org/wikipedia/en/wiki/Mylar#Science). It can still be useful, just not for the same things a parabolic reflector is useful for.

        From the linked article:

        Films in annular ring mounts on gas-tight cells, will readily deform into spherical mirrors. Photomultiplier cosmic-ray observatories often make use of these mirrors for inexpensive large (1.0 m and above), lightweight mirror surfaces for sky-sector low and medium energy cosmic ray research.

      • Dax says:

        I’m sorry, but Wikipedia is full of shit as always.

        The membrane isn’t exactly parabolic, but neither is it spherical. It resembles more closely a parabolic surface though, and that is why the technique is used in fluidic lenses. A spherical surface would produce bad color aberrations.

        For a microphone dish, it is well parabolic enough to be useful.

    • Cubby says:

      My thoughts, exactly. You even have a boom arm extending out at the correct focal length, plus a mounting bracket on the rear of the dish.

  5. Mark says:

    Reading this guy’s political musings, it seems like he’s not so much interested in using this device at football games as much as he is interested in keeping tabs on the commie jews that control the US government :/

    I especially loved his improvised ceramic knives for evading metal detectors and defending himself against the “shit-skins.”

    There actually is a lot of good electronics stuff on his site, though. Pretty messed up.

    • dude says:

      Who else did you think would have good instructions on how to build this kind of device? The only video he won’t share is how to make his super special tin foil hat. It’s a highly guarded secret he doesn’t want the “commie-jews” and “shit skins” to get.

  6. Nunya Bizniss says:

    You can create a parabolic reflector by filling a container (eg. cookie tin) with fiberglass resin and placing the container on a spinning turntable. The centripetal force distorts the surface of the liquid to form a parabola. The focal length is related to the rotational speed of the turntable. Eventually the resin will harden and you can turn off the turntable.

    • Whatnot says:

      Nice but constant stable rotating platforms aren’t around as much as they used to, although I guess you could source one somewhere, if need be make one from a CD drive motor and some rubber belt.

      The more things become solid state the harder it is to source nice stuff :/
      CD/DVD drives are on the way out, spinning platter HD’s are too. Next all we have is going to be ways to warm things by using chips in devices as heaters.

  7. What the hell is a “commie-jew” and a “shit-skin”? If this is the mindset of Mike S. then WOW! I thought he was much smarter than this. Oh well live and learn…

    Anyway enuf’ with the socio-political BS…

    LISTENING DEVICES

    One thing about parabolic mics are that they are hard to hide in a clandestine operation. Laser mics are a problem because “angle of the dangle” BS? Meaning: You have to be directly across the street from the reflective surface unless you are using a window hidden-prism or optical metamaterial on the target window. And if the target is smart enuf’ to put a buzzer on the window or use a IR detector (night vision goggles, Sony HandyCam w/night vision or a cheapo’ digital camera with IR filter removed) then laser mics are pointless with really savvy targets.

    Did you know you could resonant a window with a microwave signal if it has burglar alarm tape on it? I also heard that you can do it with an ultrasonic signal too. Since they are widebeamwidth you don’t have to be so concerned about “angles & dangles”.

    A really cool but expensive device is the shotgun mic. They are NOT simple to build as you need to tune the tubes to voice band and mount them on a non-resonating holder for them to be effective. Shotguns are very easy to disguise though.

    But in any event they all can be circumvented with white noise (i.e. running water, radio hiss, or some babbler voice masker I just read about – a complex gadget invented by some con-artist thieves in jail).

    An interesting device I ever heard of is something the Israelis thought up (a Trojan Horse program). I can’t remember the name but it can circumvent Skype and other secure-VOIP too. It involves bypassing the program all together it taps into the PC’s headset’s audio and feeds the audio back to HQ via TCP/IP. I wish I could remember the name of the software. It was in the news recently.

    Back on parabolas… I found some DishNetwork replacement parabola shells. I think they could be used for this if you could find the audio “sweet spot”. I’ve used the parabola algorithm to find focal point. It works pretty good. However, trial and error works too if you have the patience and audio equipment.

    You could disguise a parabola inside a makeshift bag made of speaker cloth from old speakers in the trash. Then it would appear to be some dirty laundry bag or something sundry and unremarkable.

    I think the best “bug” I ever heard of (besides the Russian’s American Embassy (Moscow) cavity resonator – simply amazing bug from 1960’s) is the “plumbing bug” we (USA) inserted in the Russian Embassy in Wash. DC. It was a wired mic that was waterproof and could be raised and lowered in the vertical riser pipes. I’m not sure if was water feeder pipe or the sewer stand pipe. In any event I heard it picked up a lot of Slavic conversations until it was discovered by Russian security officers.

    I guess if you want to go all high-tech and you had the money and the special black-bag skills you could install a digital spread-spectrum transmitter in the target’s wall outlet. I think a “store & forward” version is also way cool too. It records VOXed audio for days onto a gigabyte memory card then uploads data in burst via a transmitter when remotely interrogated by the spook.

    OK I’m rambling now… over & out! (LOL)

  8. William Pretty says:

    Try Fisher Scientific for parabolic parts …

  9. There’s this guy I think is in the same “party” with Mike S. named Joe Loritz. He has plans for ANY TYPE of device you need. I don’t agree with is very radical and specious politics but his science & technology trade craft is awesome.

    Check it out:

    http://72.52.208.92/~gbpprorg/mil/shotgun/index.html

    Make sure you don’t transpose the 9 with the A in his Ham Call sign or you’ll know too much!!! Now I know why ‘they’ kicked this guy out… (LOL)

  10. echodelta says:

    It would seem that the focal point is too close into the dish. I wouldn’t trust math or measurements, just pick a target with different sounds in the field. Then manually focus for gain and tightness of field. This can be done in stereo as well, just use 2 mics in close spacing. The feedhorn on the mic will broaden the pickup point.
    Look into sound location ranging of aircraft in the years before radar, everyone had their version all in stereo.

  11. xrayspex says:

    1. Calculate the wavelength for audible sound waves.

    2. Calculate the size of a parabola needed to focus sound waves effectively.

    3. Realize that a “parabolic microphone” doesn’t do what you think it does.

    4. Profit from the disappointment.

  12. DaveO says:

    Wouldn’t a piece of cloth naturally form a parabola under the influence of gravity? You could impregnate some fibreglass or some other cloth with resin and let it drape into a ring-shaped former and let it harden. Cut it out, paint and smooth etc…

  13. Dojo66 says:

    This technique works, but it is not very stealthy. You can get the same effect if you make an array of microphones (either in a grid or a logarithmic spiral), and then electronically combine the signals with the correct phase shift.

    You have special jackets, laptop bags, … sold to law enforcement with this system integrated. Most people think that someone who is facing them with their backside cannot hear what they say, especially at the other side of the street.

  14. Joe says:

    Just moved this week. Called Directv about getting the dish hardware. They told me to take my reciever to the new location and to just throw away the dish. There was a lot of metal there and a 1 year old dish. Just wait around for any end of the month apartment switch over weekend and drive around an apartment complex trash area. You’ll be able to find a bunch of these. :)

    • @Joe – Also do some dumpster-diving in back of any Radio Shack and you might find a crap load of DirectTV or DishNet parabola shells. You only have to figure out how to mount the microphone as the shells are sans (w/o) feeder arms. Not hard to make though. Could simply be a long carriage bolt with the mic taped to one end. The nut/bolt arrangement on the shell side could make the thing adjustable to find the focal point. You could make a tripod mount with a block of wood bolted on the shell and a 1/4″-20 nut secured to the bottom to mate with the tripod bolt. You can disguise the thing with a inverted large canvas bag with speaker cloth sewn to the front. The speaker cloth is needed to not absorb the sound (invisible to the audio) as the bag would muddle-up the audio.

      • BTW the DishNet feeder-arm has to be removed for a different focal point arm as the DishNet/DirectTv LNA is not really mounted at the focal point for an audio signal. It is mounted for a microwave signal and I’m not sure that the mfg mounted it at the parabola natural focal point for an RF signal.

        Also if you use a canvas bag you will also have to cut out with scissors the area where you sew in the speaker cloth. Match colors too. Or you could just mount a smaller parabola inside a stereo’s wooden speaker enclosure (with speaker cloth). That would be a good disguise too. A loudspeaker is always somewhat innocuous too.

  15. samuel says:

    Is there a way to get full analysis on the circuit?Thank you

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 96,656 other followers