Friday, May 11, 2012

Homemade Ribbon Microphone



            Ribbon microphones have been used to capture sound since the early 1920’s, and though they’re not the most high tech instruments for recording today, they are still highly sought after by musicians and recording studios alike for their silky smooth sound and vintage gleam. But how can something so small and simple capture sound in such a grandiose way? My personal fascination with how microphones work started a long time ago, and though I’ve read plenty of literature that explains their inner workings, I wanted more than anything to find out for myself. Being the hands-on learner that I am, I decided that the only way I’d be able to truly understand how ribbon microphones worked would be to build one from scratch. So that is exactly what I did. Here you’ll find a step-by-step guide to how I went about building my microphone, what I learned along the way, and a few things to consider when making your own. If you’re trying to build your own and have any questions, please feel free to email me: kippermank@gmail.com .
            Before I began building my microphone, I felt that it was important for me to learn as much about ribbon microphones as possible; their history, function, mechanics, electronics, variations, etc. I will go over these topics first and incorporate them into the project wherever I see fit.

(All links and resources used are at the bottom of this post.)

I. What is a ribbon microphone?
            A ribbon microphone is a type of microphone that uses a very thin, corrugated ribbon (made of some type of nonmagnetic metal) and places it between two very strong magnetic pulls (sometimes this is two separate magnets, sometimes it is one large horseshoe shaped magnet). The two ends of the ribbon are attached to an electronic transformer, and when the ribbon is in any way displaced, a small electrical signal is sent to this transformer, which is responsible for turning the signal into an output that we recognize as an amplification of the initial sound. This process is called electromagnetic induction. The transformer also matches the ribbon circuit’s impedance so that the output signal (and therefore sound) is not overly distorted or generally “noisy”.
            Ribbon microphones were initially (and are still mostly) bidirectional, meaning that they pick up sound equally on both their front and rear sides (creating what is often referred to as a “figure-eight” pattern of pickup).  Though bidirectional ribbon microphones are most common, there have been models with more than one ribbon that pick up sound on more than just two sides, as well as unidirectional models which only pick up sound from the front.

The "figure-eight" pattern of a ribbon  microphone.


II. History
            The first ribbon microphone was co-invented invented by Walter H. Schottky (Switzerland) and Erwin Gerlach while the pair worked at Siemens Research Laboratory in the early 1920's. Shortly afterward, they also created the first ribbon loudspeaker, which almost identical to a ribbon microphone except that the circuit is reversed. By the late 1920’s, Harry F. Olson at the Radio Corporation of America (better known as its acronym RCA) had created and marketed RCA’s first bidirectional ribbon microphone: the RCA 44-A.

RCA 44-A bidirectional ribbon microphone.

Dr. Olson also created the company’s first unidirectional ribbon microphone in the 1930’s, the RCA 77-A.

RCA 77-A unidirectional ribbon microphone.

            The microphones were originally used, as mentioned before, in broadcast media for their wonderfully smooth vocal pickups, but as newer models of ribbon microphones improved throughout the 1930’s, 1940’s, and 1950’s, they started to be used for other purposes such as music. Their warm vocal quality was used to pick up singers in the same way that they had been used on news announcers, and became widely used in the music and recording industries.
            Toward the end of the 1950’s, however, newer types of microphones started becoming more developed and were yielding higher quality sound results than they had previously (such as condenser microphones, for example). These microphones became more widely used and the ribbon microphone silently became forgotten. They were rarely used except for the few individuals who held onto them and couldn’t quite let go.
            Within the past several years, ribbon microphones have started to make more of a comeback within modern recording. Though there are other microphones that produce much more accurate sounds today, something about the ribbon microphone’s old, vintage sound has started capturing the ears and dollars of younger record studios today. Most of their draw is believed to be the vintage, “old-timey” sound that one can get while using them, and their old school charm may be the only reason that they’ve been brought back as much as they have. The ribbon microphone can be held in parallel to the vintage Polaroid cameras from the 1950’s and 1960’s – they’re expensive buy and to maintain, not to mention difficult to find, but something about their analog charm has modern day youngsters hooked.

III. Building my own ribbon microphone
            When I first decided that I wanted to build my own microphone, I started trying to find examples that other people like myself have been able to make recently. No one I knew had ever attempted to make one, so the first place I went was to the magic of the internet. Initially, the only site that I came upon was a site that sold kits for making ribbon microphones. For an expensive sum of money, they would send you all of the precut pieces and give you video tutorials on how to assemble it (in supposedly less than three hours). I didn’t want to do this, necessarily; what in the world would I learn from using a kit? I considered just paying the money to get access to the video tutorials, but decided that I didn’t want to use those either. This was an independent project, and I was determined to work completely from the ground up. I’d read about ribbon microphones in several audio recording/engineering books, and had also done a fair amount of research on how they worked online, so I gave it a shot.
            After much searching, I finally found two people who had made ribbon microphones from scratch within the past few years – one was a student who made his in his college dorm room out of PVC piping and a ladies nylon, and the other was a photographer/musician who had built a very nice looking one in the old casing of a flashlight. These were the two examples I had, so I ran with them, substituting in my own frugality and common sense (also probably lack of common sense in some cases).

Here’s exactly what I did and exactly what I learned from it:
Materials that I needed:
1 - small piece of ¼” thick hard plastic
4 - pieces of thin but sturdy aluminum
(if I were to do this again, I’d use copper)
2 - (1” x ¼” x 1/2 ”) neodymium magnets with polarities running “through” them
(if I were to do this again, I’d use 2” x ¼” x ½” neodymium magnets)
1 – EDCOR RMX1 ribbon microphone transformer
Extra wire, electrical tape, solder, a soldering iron, wire cutters, wire strippers,
super glue (that will adhere to both metal and plastic), a male XLR jack, a scroll saw, a hand drill, some mesh (for the housing - I got mine from the fabric store), and whatever paint/housing materials you think you’ll need – jazz it up!

Planning everything out:
            Initially, I drew out (to perfect scale) what the inside “backbone” of my ribbon microphone should look like. This was important because it needed to hold the two magnets in place without letting their attraction pull them loose from their positions. I also wanted a place for the transformer to sit, so I added that as well.
Here is my initial drawing of the inside of my ribbon microphone:

The initial drawing and dimensions of the inside of my ribbon microphone (including dimensions of transformer and magnets).

            The next step was gluing the magnets onto the plastic. After searching through a lot of different types of glue and quizzing the man at the hardware store, I finally found one that I thought would be strong enough. Most importantly, it adhered to both plastic and metal which was important because I couldn’t file down the sides of the magnets so that they would stick better (neodymium magnets are highly flammable and very dangerous because they’re so strong – the box that they came in had a giant WARNING label on it that said specifically not to file the magnets down as the dust that came off of them sounded like it would do horrible things to me).


The plastic piece and the glue before I added the magnets.

            I had to pry the magnets apart (which took more work than you’d think, they’re strong little buggers!) and glue them one at a time in their places, always making sure that within the final product they’d be attracting one another across the small opening for the ribbon. After they were glued, I went back and added extra glue around them (you can never have them stick too much!) and let them sit for about 24 hours before I did anything else, just to be safe.

The magnets glued in place and the two bottom aluminum pieces are attached to the plastic.
The other two will come into play once everything else is wired.

The next step in the process, was attaching the pieces of aluminum (hopefully in your case this will be copper so that you can actually solder to it) that would hold the ribbon in place and that I could attach the transformer’s wires to. These should go close to the magnets, but should not touch the magnets at all. I’d also recommend trying to file down the plastic in between the magnets where the ribbon will go, as this could reduce the chance of the ribbon hitting the plastic and messing up its signal later.

Wiring the transformer:
            This is the manual that came with the EDCOR RMX1 transformer that I used for my project:

The EDCOR RMX1 Ribbon Microphone Transformer's circuit.

Let's try to make some sense of this:
- The BLUE wire is the "input" wire, meaning that it will be attached to one of the ends of the ribbon (in my case the top of it). This wire will be taking the small electrical signal that is made by the ribbon being displaced by noise, and bring it to the transformer.
- The RED wire is one of the two "common" wires, meaning that it will be attached to whichever end of the ribbon that the BLUE wire is not attached to (in my case the bottom of it). In this case, the "common" wire is a sort of reference wire that will tell the transformer what the output of the ribbon (going through the BLUE wire) is in comparison to "nothing" (for lack of a better term) or "ground" in electricity speak.
(NOTE: The RED and BLUE wires should be twisted together as much as possible so that they'll insulate each other and help to create less electrical noise in the circuit.)
- The GREEN wire is the "output" wire, meaning that this is the live wire that the transformer will be sending its amplified signal out of. The GREEN wire will later be soldered to the XLR jack (at PIN 2) so that the microphone can be plugged in and output its intended sound.
- The YELLOW wire is another "common" wire (like the RED wire) and should be twisted with the GREEN wire. It can then be soldered to the XLR jack (at PIN 3).
- The BLACK wire is called the "shield" wire. We don't need to know much about this in this particular case except that the BLACK wire can optionally be soldered to the XLR jack (at PIN 1), which I did in my model.

            First, I soldered longer wires onto each of the transformer’s leads, as they were kind of short and I thought I’d need more slack (for twisting and such). Then I glued the transformer into place within the plastic and looked at the manual to figure out how to wire it to the rest of the microphone.

Soldering extra wire onto the leads.
          Then, I stripped some of the red wire and some of the blue wire, twisted them, and attached them to their respectful pieces of aluminum (at the top and bottom of where the ribbon will go), as explained previously.

The red and blue wires are twisted, part of the red wire is stripped so that
 it can be attached to the bottom piece of aluminum.

The red and blue wires continue to be twisted after the red wire makes contact
(and in this case is sandwiched between) the two bottom aluminum pieces.
Next, the blue wire will be stripped and attached to the top pieces of aluminum in the same way.
(NOTE: It would be better to use copper instead of aluminum here because instead of sandwiching the wires between the two pieces of aluminum, you would only have to use one and could solder directly to it.)

          Once the red and blue wires are all set, it's time to solder the green, yellow, and black wires to the male XLR jack so that the microphone can later be plugged in. As I mentioned above, the green and yellow wires go on the second and third pins of the XLR jack, and the black one goes on the first.

Make sure that the yellow (purple), green, and black wires are pulled
through the jack's housing before you start soldering,otherwise you'll have to
unsolder everything and start over with the wires through the housing.


Take a lot of care soldering these, if they come apart, your microphone won't be
able to work plugged in and you'll have to solder these connections all over again.

The end result should look like this.
Ready to plug in as soon as you're finished with the rest!
Preparing the ribbon:
            The time has come! In my case, I was trying to save money on the actual ribbon for my microphone, which was a terrible idea. Instead of buying actual ribbon microphone ribbon (which is quite expensive, but is perfect for what I needed it for) I thought I’d try other things that may work. I found this “Mona Lisa” brand silver leaf at the craft store and thought, it’s metallic and it’s thin, why not? I think it would have been perfect except for the fact that no matter how hard I tried, I couldn't separate it from the paper that it was attached to without breaking it into a million little pieces. It may have been too thin. I did try it with the paper still on it, however, and it did work. I wouldn't recommend it necessarily, but it wasn't a complete failure.

Mona Lisa Products' Silver Leaf

            The other thing that I had on hand and tried was just plain old aluminum foil (tinfoil). I sort of knew from the beginning that it'd be too thick and too rigid, but I figured it was worth a try anyway. This also worked, but was a lot less sensitive than the silver leaf. In the future, I'd definitely just bite the bullet and invest in some actual .8 micron thick ribbon microphone ribbon, as I'm sure that'd work perfectly.
            Regardless, the ribbon needs to be corrugated in order to work. With it being so thin, it's difficult to accurately make little bends in it. I saw on another site that molding it around the top of a medicine bottle would work, and it did - perfectly.

Corrugate the ribbon by rubbing it against the ridges in a medicine bottle cap.

Installing the ribbon:
            Installing ribbons into ribbon microphones is a lost art. People used to (and a few still do) make a lot of money repairing ribbon microphones by  hand when they were broken (which happens a lot,  as you can imagine – they’re so thin!). My advice would be to do your best not to breathe on it (I’m serious, wear a bandana over your mouth and nose or use a snorkel so that you can breathe over your shoulder), and to position it so that it’s just pulled tight enough – you don’t want the corrugation to come out, but you also don’t want the ribbon to be sagging. It took me dozens of times, even with silver leaf and tinfoil, to get it just right.

One of my almost successful tries at getting the
ribbon correctly into the microphone.
Even this one's a little saggy.
            Once you think you've got it, you can plug your microphone into an amplifier, soundboard, preamp, whatever suits your fancy, and see if it works! You may have to play around with how thick the ribbon is cut, etc. but if it works you're almost done!

Building the housing:
            You can build whatever type of housing you’d like, as long as the front and back of the ribbon are exposed enough to pick up sound. I made one out of plastic, painted it, and then glued some fabric mesh on the inside of it to make it look like a microphone. Get creative, bedazzle it, put it in a soda can, make it into a hat, do whatever you want!

My housing while the paint was drying.
How mine came out and what I’d do differently next time:
            I got my microphone to work pretty successfully a few times, I could hear myself talking pretty clearly, but its output wasn't nearly as strong as I needed it to be. Here's why I think this happened: for starters, the magnets I got in the mail were the wrong ones - they were supposed to be 2" long and the ones I got were only 1", but I didn't notice it until they were already glued down (which was a huge bummer). If the magnets were longer, this would allow for the ribbon to be longer, and would make it more sensitive to the sound waves hitting it, therefore theoretically increasing its input (and therefore its output) signal. Second, as I already mentioned, it would have been great to use copper instead of aluminum for the four plates that the ribbon was attached to. This would have allowed me to solder directly to the plates instead of having to strip and sandwich the wires, which would yield a much stronger connection and much more accurate/controllable results. I also would have definitely bought actual ribbon microphone ribbon which is a lot thinner than what I used (and doesn't have a paper backing). This would also make the ribbon itself more sensitive to sound waves and would up its output. If you're going to build your own ribbon microphone, pay close attention to those particular elements as they're all important in how well your microphone is going to sound.

           Overall, I had a lot of fun with this project and learned a lot. Yes, it did end up taking me more than the three hours that the ribbon microphone kit promised, but it also didn't cost the $200 that that kit did. I learned a lot more by doing it all myself, and though it's not perfect I know and understand what I can improve on with my next one.


            I'm going to try to build a new ribbon microphone using all of the things that I learned from building this one, and hopefully avoiding all of the mistakes that I made while constructing this one.
            I'll post those findings, photos, and hopefully recordings as soon as it's finished.

            A big thank you to the Hampshire College Lemelson Center (Glenn, Don), Professor Fred Wirth, my "Musical Acoustics" class, Larry Berger (for the use of some of his personal library), Steve Banzaert, and everyone else who helped me with any part of understanding and building this.

            Good luck to you, if you're going to build your own!
            Please let me know if you use this and how helpful it is!

            All of the sources used throughout this article and my construction process are listed below.

Works Cited 
"Homebrew Ribbon Microphone." Homebrew Ribbon Microphone. Web. 11 May 2012. <http://www.rimagraphics.com/microphone.html>. 
"How I Did It." How I Did It. Web. 11 May 2012. <http://make_a_ribbon_mic.tripod.com/id3.html>. 
Huber, David Miles. Modern Recording Techniques. 2nd ed. Print. 
"Live Sound: The Benefits Of Using Ribbon Microphones In Live Sound Applications - Pro Sound Web." Live Sound: The Benefits Of Using Ribbon Microphones In Live Sound Applications - Pro Sound Web. Web. 11 May 2012. <http://www.prosoundweb.com/article/benefits_of_using_ribbon_microphones_in_live_sound_applications/>. 
"Microphones." Microphones. Web. 11 May 2012. <http://hyperphysics.phy-astr.gsu.edu/hbase/audio/mic.html>. 
Owsinski, Bobby. "Chapter 1: How Microphones Work." The Recording Engineer's Handbook. 2nd ed. Boston: Course Technology, 2009. 1-27. Hampshire College. Web. 13 Apr. 2012. 
"Relics Reborn: Ribbon Microphones Rally for Vintage-Audio Geeks." Wired.com. Conde Nast Digital, 11 Jan. 2011. Web. 11 May 2012. <http://www.wired.com/rawfile/2011/01/gallery-ribbon-mics-part-1?pid=568>. 
"Ribbon Basics." Royer Labs -. Web. 11 May 2012. <http://www.royerlabs.com/ribbonbasics.html>. 
"Shure Notes Issue #37 - All About Ribbon Mics." Shure Notes Issue #37 - All About Ribbon Mics. Web. 11 May 2012. <http://shurenotes.com/issue37/article.html>. 
"Twelve Mics That Made History." Twelve Mics That Made History. Web. 11 May 2012. <http://www.coutant.org/12mics/>. 


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