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Ribbon microphone
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200 Watt Class E AM Transmitter
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Ribbon microphone
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On the performance of short antennas
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My home-made ribbon microphone

Below are pictures of a toy ribbon microphone that I constructed from a few pieces of scrap wood, a strip of aluminum foil (standard kitchen wrap), a few screws and other hardware items, and a pair of cylindrical neodymium alloy magnets (0.75 inch diameter, 1 in length, 3/16 inch mounting hole through the axis).
 
It works!
 
I am experimenting with different ribbon designs and different acoustic cavity designs (the first version, shown below, has two pieces of cardboard taped to the front) to enhance the pressure difference between the front and the back of the ribbon.

Engineering Requirements:

Required: Produce an electrical output signal that can be used, in conjunction with an amplifier and a speaker, to produce an intelligible reproduction of the arriving, voice frequency sound wave

Not required: Compact, magnetically shielded, light weight, durable, shock resistant, low maintenance, high output, flat frequency response, low distortion, low noise, manufacturability, aesthetically pleasing

ribbonmicrophone1.jpg

ribbonmicrophone2.jpg

ribbonmicrophone3.jpg

ribbonmakingtool.jpg

Ribbon corrugating tool

Improved version (below)

sdp1.jpg

Improved version with: pop filter made of non-metallic window screen fabric, acoustic cavity back wall made of peg board material, 1:2 audio step up transformer, and brass hardware

sdp4.jpg

sdp5.jpg

Improved ribbon corrugating tool

ribbonmicrophone10.jpg

The picture, above, shows the ribbon microphone on a home made stand made of iron pipe and associated pipe flanges. Obviously, this stand is not totally consistent with the use of non-magnetic hardware elsewhere in this project.

ribbonmicrophone12.jpg

Above and below are pictures of the "final" version of the microphone and its stand. Note that the wires which run between the top and the bottom of the ribbon and the microphone cable have been shortened and twisted to minimize the area of the loop formed by the ribbon and these wires. This is important to minimize hum pickup. You can also see the 3.2 ohm-to-1600 ohm audio step-up transformer (1:22 turns ratio) that was added between the ribbon and the cable. The brass screws at the that hold the ribbon in place have been replaced by nylon screws.

ribbonmicrophone11.jpg

schematic.jpg

Here is a schematic of the ribbon microphone I built. The ribbon on the schematic is shown as being 2" long. The ribbon in my microphone is 4" long, but 2" would be better. To minimize hum pickup (a serious problem with ribbon microphones) keep the area of the loop formed by the ribbon and the connecting wires (before they are twisted) as small as possible. In my micropohone, the area of the loop is about 1 sq inch because the ribbon is 4" long and the spacing beteen the ribbon and the connecting wires is about 1/4 inch.

Final version

final1.jpg

Above and below are pictures or the front and the back of the "final" version.
 
I replaced the Reynolds Wrap (R) ribbon with a piece of thinner aluminum foil (~10 microns thick), and I used a steel spring with about 25 turns per inch, in conjunction with a mousepad, to emboss corrugations on the ribbon.
 
I added a piece of 1/2" pvc pipe... that can be raised and lowered by turning two brass screws... to make an adjustable anchor point for the top of the ribbon. This allows me to install the ribbon with a loose tension, and then to adjust the tension for the best sound.
 
After all was done and said, I decided that the microphone sounded better without the pegboard backing... so I removed that.
 
Overall... this was a fun project, and the microphone sounds pretty good with appropriate equalization. The output is about 25 dB less than that of my RE-27 N/D dynamic microphone at 1 kHz.

final2.jpg