Make a LoFi Mic From an Old Telephone Speaker


Introduction: Make a LoFi Mic From an Old Telephone Speaker

About: Bitcoin, electronics, music, robots

The speaker in an old telephone makes a great lo-fi mic. Just wire a 1/4 inch jack straight up to the speaker and enlarge the telephone jack hole to mount it. A small piece of towel helps to muffle some of the air noise.

You can hear an audio sample on our blog entry. Made by recompas and friends.

Tools and supplies needed:

-old phone headset
- 1/4" audio jack
-about 20" of hook-up wire
-solder / soldering iron
-screw driver
-small piece of towel

Step 1: Unscrew the Speaker and Microphone Caps and Remove Innards

The covers simply unscrew. The only part you'll be keeping from the insides is the speaker. Get rid of everything else, including the telephone jack.

Step 2: Drill Out Telephone Jack Hole to Make Room for 1/4" Audio Jack.

Enlarge the existing telephone jack hole with a 5/16" drill.

Step 3: Solder Wires to and Install 1/4" Audio Jack

First solder wires to the audio jack, then install in the newly enlarged hole. Cut the wires to be long enough so you can easily attach them to the speaker (next step) after the audio jack is installed. The audio jack won't fit through the body of the phone, so you need to install the jack before screwing the wires to the speaker.

Step 4: Screw Wires to Speaker

Some phones will have a resistor across the speaker. Just leave that there.

Step 5: Screw the Caps Back on With a Little Piece of Towel on the Speaker

To help reduce some air noise, put a little piece of towel underneath the cap that goes over the speaker (the new lo-fi mic). Screw both caps back on and you're done.

Again, an audio sample on our blog entry.



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    25 Discussions

    well I took this same idea and planted the plug in to the bottom of a soup can.

    I mounted the speaker over the plug inside the can(yes I made a plastic holder).

    Now I have a sexy tinny sound while I play one of my harmonicas.

    Fun project I liked.

    Awesome, i wanna try this sometime!!

    how long did it take you?

    HEY ;) !! If the sound from the microphone is too weak, theres a way to "amplify" it : just solder a 9v battery to the wires , and add a on/off switch ;)

    I used telephone speeker and telephone mic.
    Mic worked but it was to noisy, quiet and I soldered badly.
    Telephone speaker worked good untill I realized that opened soledring between to cables is bad. I taked off short pre wired cables. I but longer ones and it stop working.

    Hello People,

    I just picked up an old telephone and intent to make one of these mics. However there are two on instructables as you might know. The other one, by Randolfo is found here:
    Now I hear some of you are talking about a preamp. Is this what Randolfo has done? And is that the difference with this one? Or is it essential to get it to work to add a little voltage on the mic, like with a condenser microphone. I don't understand this very well and I'm new at the whole electronics and diy-business. So if someone could explain me the difference between the two, I would be very thankfull.

    Thanks for the great posts all of you. I really love this site.



    2 replies

    I'm working on my second right now (the first shifted into another project before I finished it as a mic).

    I have had no problems running mine directly into a PA or a guitar amp. I get full volume, in fact I generally get a lot of feed back.

    You're fine without it, but you're probably done by now either way.

    Yes, I'm done by now and it works perfectly. But what did was slightl different from your original design; I used the speaker as mic and that did the trick for me. Thanks for the reply though.

    There is not much difference in the design of a speaker and a dynamic microphone.  The main difference is that one is optimized for making sound and one is optimized for hearing sound.  Beyond that, the guts of the two are very similar.  This is probably why the microphone in this project is "lo-fi."

    to be more precise, they are the exact same thing. the only difference between a microphone and a speaker, is the impedance of the driver. a speaker will usually be 4, 8, 16, 32, or some amount of ohms like that. a microphone is generally 600-1000ohms. when sound waves cause the driver to vibrate, it creates a signal, which is transmitted to your pre amp, and then to the amp. the higher ohms allows the signal to be much higher. take a pair of headphones and plug it into your mic input. it will work as a mic, but youll have to raise the input, and talk very closely, because the low ohms means a lower signal is transmitted.

    You miss my point. Yes, they contain the same electrical parts. However, each is mechanically tuned for its purpose. Compare the woofers in your speakers to a stage micropone. Even if you used an impedance matching transformer to fix the mismatch, a dynamic element would probably sound poor unless it is optimized to be used for both purposes (say an intercom).

    you are correct there, however you can use a 5 1/4" extended range driver, and get an accurate reproduction of most frequency, and would be able to use it for very very low budget recording, but honestly you would be better off just buying a cheap 20$ sure mic, as there isnt much difference in the mics in the under 100$ range. as for the optimization however, that is simply the much higher impedance of mics, and the use of thin polypropylene as a diaphragm, which allows very easy manipulation of the diaphragm by the vibrations put off from your source.

    Is Rondofo's instructable better for using one of these as a mic through an amp to sing into or would I just need to build one of these and use a mic preamp?

    what do you suggest me to do with the rest of the telephone? (:

    Just picked up two phones from salvation army (most thrift stores will allow you to root through their newly donated stuff outback), and made some mics.  A lot of phones are not as simple as this one (they might have green ground wires or other mystery wires attached to stuff).  Usually the extra wires are attached to the stuff that is getting thrown out, so don't worry.  This was way fun, and the mics sound awesome.

    i quite enjoyed doing this project, and was eager for more things like it to do, so i opened up the carcass of an old, non-functioning keyboard under my bed and hook up its old volume knob to the telephone mic, however, I'm not sure where to conect the wires from the mic to the knob, and from the knob to the out put.
    any ideas?

    does it actually record sound when plugged into a computer?

    i just finished mine and i love it! the instructions were very simple and it actually doesn't sound as bad as i expected!

     the audio jack i can only provide it from the link site? (