Speaker as a microphone

[Nathan] sent in his speaker microphone project. Speakers and microphones are physically similar – usually mics are much smaller to allow decent high frequency response. In this case, [Nathan] wanted something to pick up kick drums or bass guitars, without the cost of a commercial version like the subkick. It’s build around a dual coil 6.5 inch subwoofer. The passive circuit design allows the coils in the speaker to be configured for differing impedance, phase and isolation.


  1. lonas says:

    i once saw a guy from Shure re-wire an sm58 as a tiny speaker as a demonstration of this very concept.

    I especially like that he’s wired it up to be more than just a mic.

    Doing cool shit with junk is awesome.

  2. peter hajas says:

    of interest to any people with ipod earbuds:

    stick them in your mic input on your computer, and you can use the left earbud as a microphone. very handy in a pinch, and it also sounds fine through line in

  3. gm says:

    Or anyone with any other earbuds – they all are pretty much the same.

  4. alex mccown says:

    ahhhhhh the oldest trick in the book

  5. Will says:

    Hmmm, not so sure about using headphones as a PC mic, The PC provides a DC voltage to the right bud, I guess that others here might know if that DC voltage was enough to overheat the bud over time.

  6. EthanV2 says:

    Hmm, might have to try this with the Sub from my Logitech Z2300’s when i get my Z5500’s

  7. Bhima says:

    While this is very cool, I am beginning to find the instructables website rather annoying.

  8. Wesley says:

    open headphones work reasonably well as a microphone

  9. eric says:

    I was using speakers as microphones back in 1980. I accidentally discovered it playing with my brand new state of the art cassette recorder. I actually got better sound of the speaker than I ever did any mic that I could hook up to it AND it was significantly more sensitive. I used it to record my parents talking with my uncle 2 rooms away and I couldn’t physically hear them at all with my ears but I could hear them loud and clear through the recorder. Since then I’ve used speakers as microphones several times, even recently.

  10. eric says:

    will: you can solve the dc voltage problem by putting a capacitor in series with the headphones.

  11. Will says:

    I saw this in… “Honey, We Shrunk Ourselves”
    I believe, in his midget status, he scrapes some of the solder off, which does some funky film magic and makes it a microphone…

  12. samurai says:

    this has been a common dj trick since the late 70s… if you dont have a mic at your mixer, just plug your headphones into the mic jack, make your announcement, and plug em back into the cue jack.

  13. strider_mt2k says:

    All hail transducers!


  14. neoxide says:

    This is a classic ‘hack’.

    Since I have virtually no cash, I use a car speaker (found in trash, of course) as my main mic. It sounds terrible, but alright for rough demos. From a 4 track tape recorder.

  15. Stephen-C says:

    Just think, if someone had discovered this 45 years ago, Jack in the Box might have pioneered the drive-up window…

  16. Scrappylaptop says:

    Wow, I mean just wow. In other news, water can be used for drinking AND bathing!
    Seriously, folks. Take apart an old microphone from the 50’s; it’s a speaker!
    Remember in grade school how the PA system speaker was also a microphone?
    This goes waaaay back to when they actually were the same thing; I even have an ancient bakelite telephone where instead of the mouthpiece having a carbon mike, it’…just another speaker!

    So as to not just gripe and groan;

    Other uses for speakers and/or microphones:
    -Poor man’s laser show:
    lay raw speaker on back.
    lay a mirror on it so that one end is supported by the speaker.
    Aim laser pointer at mirror onto ceiling. play music.

    -Poor man’s actuator:
    -strip most of the cone off or make holes so that air movement is reduced.
    use to move parts of halloween display, such as eyelids or lips.
    recorded speech makes a good signal source.

    -passive (resonance) amplifier / frequency selective microphone:
    -take Aluminum tubes about 1/4 inch in dia, cut to various lengths. Bundle together.
    attach speaker to end of bundle (air tight, please).
    Each tube if cut carefully will amplify a single frequency only, picked up by the speaker.

    • nickguitarguy says:

      I totally made the poor man’s laser show when I was in High School!!! What a trip back to memory lane. I remember the best way I made it was to stretch a balloon (like heavy duty one) over the speaker and glue the mirror to it. . . Made some really cool light show effects.

  17. Marco says:

    “Hmmm, not so sure about using headphones as a PC mic, The PC provides a DC voltage to the right bud, I guess that others here might know if that DC voltage was enough to overheat the bud over time.”

    Shouldn’t be a problem. Typically it’s only a 5V bias designed to drive the electret microphone pre-amp at ca. 1 mA. I would be surprised to find a commercial device that does not have some kind of current limiting in case of a short circuit.

  18. cliff says:

    after looking at the circuit, i wonder about impedance of this device since the transformer is a 1:1 and the coils are 4 ohm each. does it react favorably with preamps, and how would it compare with commercially manufactured mics?

  19. Thomas Bailey says:

    I particularly liked the results I got whan I used an 18″ woofer for a microphone. I’ve heard of large-diaphragm microphones, but 18 in (457 mm) is huge.

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