DonsDeals Blog: Use a Speaker as a microphone (How To)

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Thursday, November 22, 2012

Use a Speaker as a microphone (How To)

I use to use my Stereo Speakers as Microphones, back in the 1960's and 70's. I don't remember exactly when I discovered that speakers would work as a Mic. But, I vaguely remember hooking up a Speaker to the Mic Input Jack on my Realistic Cassette Recorder. Just to see what would happen. Back when I was a kid, in the 60's. Later on, in the 70's - 80's. After I was grown and married and had kids of my own. I Hooked up all of my Home Stereo Speakers to my Teac Stereo Recording Cassette Deck. And used them to Stealthily Record all of the sound and everything everyone said in the whole house. It sounded like everyone was down in a Barrel. But, it was easily understandable and allot of fun to play with. I had my Speakers (all 4 of them) spread throughout the house. So, that I could listen to my Zeppelin, ZZTop, Yes and Who, everywhere. I even rigged some toggle Switches, so that I wouldn't have to keep Plugging and unplugging my Speakers (when I wanted to Record). Before I added the Switches. I would have to unplug the speakers from the output on the Stereo and plug them into the Mic Inputs on the Tape Deck. What a Drag, Man... I used some Adapters, that went from RCA to 1/4 inch male, to accomplish the this. Of course I bought all my parts at Radio Shack. The go to place for Electronics, back then. Yes, Kiddies... Once apon a time... Radio Shack was Cool. To us AV and Electronics Geeks, that is!;) Anyway, I still have those Toggle Switches. Which I didn't buy. But salvaged from some 120 volt Parts that I found or took out of something that was in the garage, when I was growing up. I still have a bunch of my old parts. I'm sure I will use them for something cool. Any Day now!;) But, back to the Point of all this... I have always thought. There must be a way to get rid of that Down in a Barrel Sound and make my Speaker Mic's work like a real Metabolic Microphone. That's what they were, in effect. I have also tried out 4ohm Car Speakers and they work well and are very sensitive. The 4 or 5 inch Car Speaker that I used, the last time I tried this. Along with a little old Radio Shack Mixer (this was just about 12 years ago in 1999 or so). Actually made a better sounding recording, than the Home Stereo 8 to 10 inch Speakers. I set it on the Roof and Recorded the Bugs, the Breeze, the Cars on the Highway near by and If anyone was talking I could Record that too. So, I find this How To, with added Electronics and a nice looking Case. Very interesting. Check it out...

Don

Intro

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

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.

Step 1

Materials and Tools

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)