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SPKR MiK: How to make a microphone from a speaker.

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How to make an inexpensive microphone capable of picking up low frequencies that doubles as a speaker and direct box.

The large diaphragm of this microphone will pick up more of the low frequencies when recording a kick drum or bass guitar.

Sound recording engineers have been using this trick for years, and Yamaha has also made a commercial speaker microphone called the SubKick, that usually retails for around USD$300.

I was able to build this mic for under $20 by "scrounging" various parts out of old junk. Even if you need to buy all the components, you should be able to build this mic for a fraction of the price of the retail version.

This design goes slightly beyond the SubKick, as far as electronics are concerned, with a dual coil design, and internal direct injection (DI) box.

You should be comfortable using a power drill and a soldering iron, and be able to read a schematic diagram. There is a little sewing, but it isn't too difficult.
 
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Step 1: Materials and Tools

components.jpg
Materials

  • 6.5" dual coil woofer speaker (4ohm). I pulled this one from an Altec Lansing multimedia system that had a blown amplifier.
  • 10" drum. Cheap is okay, but you'll want something with lugs that screw into the shell, not springs or T-rods that screw into couplers. I found this one for $2 at a second hand store.
  • Two miniature bungee or elastic cords. I got a 4 pack for $2.50
  • Crimp on terminal rings. I paid $2.50 for a dozen
  • Adjustable hose clamp (the same diameter as the magnet of your speaker). This was about $1.50 at the hardware store.
  • Female mounting flange for 3/8" microphone stand and small bolts to mount it. I got this at Parts Express
  • 2 sq. ft. of speaker grill cloth. Also at Parts Express
  • Thread
  • Male XLR 3pin panel mount connector and mounting screws
  • Two 1/4" TS (mono) female phone jacks (at least one needs a tab for a normalling connection)
  • A six-pole four-throw rotary switch (I scrounged my switch from a 4-way printer "data" switch box), or you can use Mouser part no. 105-SR2921F-34S
  • 100 ohm potentiometer, also called a variable resistor
  • two knobs (for pot and rotary switch)
  • Two DPDT toggle switches (on-on)
  • A SPST toggle switch
  • Resistors: 100k ohm, two 10k ohm, 10 ohm
  • 100nF capacitor
  • 1:1 ratio audio isolation transformer (pulled from a second hand 270-054 I got for $1)
  • metal container to hold and shield transformer, and mounting hardware
  • heat shrink tubing or electrical tape
  • connecting wire. 22ga or 24ga is fine.
  • short microphone stand (another second hand store find)

Tools

  • Small adjustable wrench
  • Drill
  • Soldering iron and solder
  • Wire stripper/crimper
  • Scissors
  • Sewing needle
  • Screwdrivers
  • Small hack saw
  • Ruler, or other measuring device
  • Sharp hobby knife
  • Marking pen

Optional

  • Rotary tool
  • Drum key
  • Pliers, tweezers, or other soldering aids
  • Adjustable calipers
  • Cutting mat
  • label maker
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Z.K.2 years ago
Nice tutorial though unfortunately I am not a musician so I don't know where I would use a thing like that. Still, it is interesting though to make it more interesting I would have used one of the free schematic programs rather than drawing it by hand. Also, you should include a short video to show what it actually does. Great work though, the finished product looks nice.
He explained at the start with what it can be used for. Many uses if the frequency response is decent, although mainly for low frequencies. If you use this in accordance with another Mic that has a better frequency response for instruments you can mix the two and add body using this Mic to the signal (ie kick drum or bass)
wriggan1 year ago
Never mind, got a hold of what I'm looking at
wriggan1 year ago
I am an amateur with wiring diagrams. Is there anyway to get a more specific wiring. Example, DPDT switch had 6 connectors but I can't tell from the schematic which poles are relevant. Forgive my stupidity
Vonbakker412 years ago
Cool Design! In the beginning stage of collecting parts and have a very basic knowledge of ee, so was wondering how the components might vary if I have an 6" 8ohm speaker to start with?
Aud1073cH (author)  Vonbakker412 years ago
That should work nicely. If it is a normal speaker with only one coil, you can eliminate the coil selection switch and the damping pot.
memanuel13 years ago
Thank you to post it. A lot of time I search for this informations to make a home made project. I just wanna use a speaker and a mic.
The speaker will be used to the low frequency and the mic to the mid and high.
Can I just wire the speaker (4 ohm) in series with a mic (600 ohm) like a solution to the low resistence (impedance) prolblem?
Speaker + mic = 604 ohm. The mixer input works well to 600 ohm.
Is there some power (watt) problem in that wire. Thanx.
Aud1073cH (author)  memanuel12 years ago
I must have missed this question when it was posted -

The best option is to run the speaker an mic separately into two separate channels of the mixer, and mix them together using the mixer. This way you can use the EQ in the mixer to remove the high frequency component from the speaker signal.

I would not use them in series as you describe. The speaker coil may reduce too much of the high frequency of the microphone, and the speaker may try to drive signal into the microphone.
jon_dave4 years ago
does the watt rating of the resistor matter? thanks :)
Aud1073cH (author)  jon_dave4 years ago
when using it as a microphone, there is little power. normal 1/4w resistors are fine.
If I have a 50 watt @ 4 Ohms speaker, using as a Mic and the Low Z output is not giving me enough juice to get to the preamp, What type of impedance transformer (Low z to High z) should I be using.. I was told to use a 1:100 Audio Input Transformer, shielded and get it to somewhere between 400 to 800 ohms Im having a hard time finding one.. would I also need a Isolation transformer as well to balance the signal as well? and is that important? Thanks for your help on this.
Aud1073cH (author)  Renegade Studios2 years ago
The first thing I would try is to solder a 1/4 in. connector to the speaker terminals, and plug it into a DI box. The DI will have the right output impedance for your preamp.

Balanced is better when using longer cable runs, and/or in electronically noisy environments- simply, it helps reject noise. Over short runs you can run unbalanced. Be careful about going directly into a high-z preamp with a 50W rated speaker. you may want to have a pad/attenuator to start with.

I used a simple 1:1 transformer to balance the signal, although it probably does not do a very good job at impedance matching. If you use an impedance matching transformer, you can balance the signal with that at the same time. you do not need a second transformer.
mtschles3 years ago
Your rotary has me a little confused. What is coil B doing when coil A is being driven by the input, and is the dampening output solely coil B? Also, which position are you in when you're using it as a DI?
Aud1073cH (author)  mtschles3 years ago
I did make that complicated didn't I?
I hope this answers some questions.  If not, just reply to this comment, and I'll do my best to help.

Here I have quoted from my original text, in italic, and added notes in between in normal text:

Circuit ExplanationThe configuration of the coils can be changed by the rotary switch (S1).

Position 1 Single: A single coil of the speaker is used
(Coil B) (4ohms), both 1/4" jacks are wired in parallel with the coil. Coil A is disconnected. Any input will drive both Coil B and the DI's input.

Position 2 Series: Two coils are wired in series(8ohms), with the two 1/4" jacks wired in parallel. either input will drive the coils (a 8 ohm load) and the DI input

Position 3 Parallel: Two coils are wired in parallel (2ohms), with the two 1/4" jacks wired in parallel. Either input will drive the speaker coils (now a 2 ohm load) and the DI input


Position 4 Damping:
Coil A is normalled to the 100ohm potentiometer, which will electromagnetially
(and perhaps inductively) dampen coil B. When a 1/4" plug is plugged into CN1, the potentiometer is disconnected, and the input (CN1) directly drives coil A only.
Coil B is wired in parallel with the 1/4" output jack
CN2. A signal input here will drive coil B (at 4ohms) and the DI input.

In all positions, the output then passes through the phase flip switch, through a -20db pad, to one side of the transformer. The transformer's secondary outputs through the XLR jack. (The pins on the XLR jack are labeled.)

There's always some coil connected with the DI side.  You can use either input in any position of the rotary switch and get sound out of the DI. Since there are different coils, loads etc. (that I haven't experimented with) each will affect the sound differently.

If you want a straight DI, disconnected from any speaker coils, you can install a switch to disconnect the coils from the input jacks. Or use a normalling jack for CN2, and the coil side connects to the normalling contact. (I just built myself a couple of regular DI boxes as separate units)

s omer3 years ago
MAN VERY NICE BUT BOOORING
ptwornicki3 years ago
But where's the fun in that?
pointless13 years ago
I built this using an old 8 ohm sub. It works very well but it has to be aprox. 2-3 feet from the bass drum. I used the simple schematic and just added the -20 pad, but when I switch it on it goes from very sensitive to very unresponsive. Any suggestions what my next step should be? :)
Aud1073cH (author)  pointless13 years ago
Perhaps instead of a regular pad, use a variable pad/pot - I would try a 500k ohm guitar volume pot.

With the back of the pot facing you, and the three leads pointing down (toward you):

wire the lead on the left to the positive of the speaker (+) ,

the middle lead of the pot goes to the
-positive of the output -the tip of 1/4 in. jack,
-or pin 2 of XLR (if you are using my bitmap schematic in the comments)
-or pin 3 of XLR for yamaha schematic

the last lead of the pot on the right goes to connects with
-the common of the speaker (-),
AND either the
-shield of the 1/4in.
-or pin 3 of XLR (my schematic)
-or pin 2 of XLR (if using yamaha schematic)

maybe a little confusing, but you should have a variable volume control. You could mount it with a knob, or you could just hot glue it to the back of the speaker to set it once and forget it.

hope this helps :)
aar0nc0le4 years ago
Is there an easy way to modify this to help it to pick up higher sounds from a guitar?
Ojd4 years ago
Looks like very nice instructable. So its ok to just connect +/- wires from speaker to 1/4 jack to mixer? I think it just might work, if preamped. I just thought how to get this low-low kick sound from the real kick, tuned a lot, but still beater thump and overtones were present (more that i needed), sample you recorded looks like a cure. Also have you tried it to use with bass cabinets? (Bass-guitar>bass combo>subkick)? I think its very possible to get old dub-like bass.
Aud1073cH (author)  Ojd4 years ago

Yes it should work directly into the mixer.  You may need to use a mic level input.   Some mixers have mic/line switches on the 1/4in. jacks, others you need to use the XLR jack.
   Yamaha wires the hot (+) lead of the speaker to XLR pin 3 (cold), the cold (-) lead of the speaker to XLR pin 2 (hot), and XLR pin 1 (ground) to a lug of the drum. (closest thing to ground.)
Here's a pic of the Yamaha I found online:

 Of course, this instructable is for the more complicated dual-coil with DI box.
    I may suggest running it through a compressor if you have one. It is meant to be mixed with a normal microphone. 
I have not tried it with a bass guitar cab yet.  But you should get some really low bass.
yamaha subkick.jpg
bigredlevy4 years ago
After reading this instructable i constructed my own sub kick using a 10" sub and an old 14" drum shell.
It has fantastic bass response, and i have been using it to mic my drum kit. It sounds great.
DSC00103.JPG
Aud1073cH (author)  bigredlevy4 years ago
Awesome! Thanks for the pic. That looks way cool. :)
iif 
draxgon5 years ago
hey i have a blaupunkt TSw1200 12" 4-ohm subwoofer that i use to use for car stereo system but i havent for a few years now. could i replace the 6.5" sub in this instructable with my 12" sub?
Aud1073cH (author)  draxgon5 years ago
You may have trouble squeezing a 12in. sub into a 10in. drum shell.

Feel free to modify my design however you like.  Use the original speaker box, or use a larger drum., or let it hang in mid-air. its up to you.

I have not tried such a large speaker. try it -and write a post about how it sounds :)
 A few years ago, I was experimenting with this idea, although my version was "quick and dirty." 
I've got tons of speakers, parts, etc. laying around. I simply took an extra 15" woofer and laid it on it's back, on a folder blanket, inside the kick drum.
I left the front head and hoop off of the kick and wired an XLR connector to the speaker.
From what I remember, it sounded awesome! It provided ridiculous sub-frequencies (like big r&b/hip hop kick.) Of course, it was possible to dial back that excessive bass to taste.
Also, when I threw a blanket over the drum, the signal was completely isolated, even while recording in close proximity to bass and guitar.  I would assume that this was because the 'mic' diaphragm was so huge and not easily moved by more distant sounds. 
I experimented with suspending the speaker inside the drum, but that forced me to change the angle and wasn't nearly as good. I don't remember exactly how so. It could have been that it focused the sound too much on the beater.
It's also possible that part of the mojo of lying the speaker on its back was simply due to mass and resonance. After all, I was using a high quality woofer with a heavy magnet. Possibly an EV.

Aud1073cH, your design looks great. I've got some junk drum shells lying around. I'm gonna have to try making one like yours, sometime.

To everyone else, just experiment. This is a safe and fun project to play with, and can teach you about both mics, speakers, and how they work.
To ever

themancable4 years ago
That is an excellent looking subkick. Amazing to see how much detail you put into it -- great work!
aceLED4 years ago
i can make a smaller model right pm bck on that please;p

Aud1073cH (author)  aceLED4 years ago
you can use whatever size speaker you have available.  Feel free to experiment. :)
Hey i was wondering what is the best type of speaker to use for this? Large or small? we've got a lot of guitar cabs around here that I could steal a speaker from, but I want to know if getting a cheap-o stereo speaker from a pawn shop would work better. Thanks!
Aud1073cH (author)  forget12343215 years ago
Unfortunately there's not really a straight answer. (sorry- probably more info than you wanted) most microphones have diaphragms 2" and less, but we're not after "normal" here. The larger diaphragm of a speaker works better to pick up the very low frequencies we're after, but the higer mass, and slower response mean that it also rejects higher frequencies. It is my guess that a cheapo would work better, but still pick one sufficiently large. anything from 4" up to 12" should work, but I'm guessing that a better choice will be a 6.5" or 8" cheapo sub that has a fairly small voice coil -usually given away by the smaller magnet. (think radioshack cheap.) My best suggestion would be to try a few out and listen to them first before building them into a nice drum shell. make up something with a mic stand, rubber bands, and paperclips to temporarily hang each speaker in front of your kick or bass cab. Then pick a sacrificial guitar cable, and strip one end to wire to each of the speakers, and plug it into a DI box, to your mixer. If you have any single cabs to sacrifice, then you could just plug the speaker cab (not the amp!) into the DI or mixer. hope this helps - and good luck on your project. :)
Yes. I have a 4 inch, 4 ohm, 3 watt, radioshack woofer. Do you think it would sound okay? I got it for free.....
Aud1073cH (author)  iamtoats5 years ago
I think it would work.   try it and see.

I've got an 8in. and a 10in. radioshack woofers that I want to try myself.
im just wondering why do peeps all think everything outa radio shack is cheepy stuff ? ive a pair of old speekers from them {15yrs.old} that have dipole tweets in them an they sound still better than any thing around plus there 360 output each , have you ever tryed to make a mike outa tweets to catch the high ends ? ive played around with a few mikes as im a amtur radio guy an some of the mikes ive used have whats called talk back were it works still as a mike but a speaker as well is this were you got your idea from?
Aud1073cH (author)  riverreaper5 years ago
True, Radioshack has carried some good stuff. (especially 15 years back).  I have a NOS (new old stock) metal project enclosure on my shelf that is as solid as some of the Hammond enclosures.  If you see any of the Radioshack PZM microphones around (discontinued) - try it out. they are quite handy.  I think they may have been manufactured for RS by Crown? (can anyone confirm?-please post links)

I have not tried tweeters as mics yet, but a dynamic tweeter would probably work.

I knew that some radio and many intercom systems used the speaker as a microphone in half-duplex systems.  Recording engineers have been using this trick for ages.
My idea was to build my own nice-looking low frequency mic for cheap, and using a drum shell was inspired by the Yamaha SubKick, as I stated in the introduction.


Make life a bit easier, and simply get a mesh head - typical of those used on e-drums.
Aud1073cH (author)  Angry_Monkey5 years ago
That would be a lot quicker. 
using an ns10 woofer would make that subkick sound awsome
Aud1073cH (author)  it_dont_work5 years ago
destroying an original NS10 would make me sad. 
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