Category Archives: DIY Recording Studio Gear

A Ribbon Microphone- Design 001, Rev A

Since I have to give away the Austin Ribbon Mic that I built, I decided that I wanted one of my own. I purchased raw materials for four more ribbon mics and have been working diligently on another mic. It isn’t completed yet, but I’ve done enough (and it looks good enough) that I can show off some preliminary photos.

My progress so far on ribbon mic no. 2, which incorporates a large number of design changes from the previous mic.

This microphone is similar to the Austin ribbon, but it’s a completely new design inside. The body style is similar, and I’m using a similar motor frame of clear acrylic plastic with drilled vent holes as a frame for the motor, but that’s where the similarity ends.

The Austin mic sounds great, but my outboard preamps are… well… let’s just say they aren’t top-of-the-line models. (Except for my lovely pair of VP26 pres from Classic Audio Products of Illinois, but I don’t have a Lunchbox yet to mount them in. I’ll get them racked one of these days, but the studio needs to generate some income first.)

So as a result of my gear, I’m having to crank the preamps up a good bit on the Austin mic. It sounds great on a source like an acoustic guitar, but for voice it requires a super clean preamp. (The Crest preamp that I recently purchased is a significant improvement.) This new design is an attempt to increase the output a little so that I can get a better signal with more common equipment.

My redesigned ribbon motor frame with magnets in place. A central groove is milled in the plastic for positioning the ribbon. The magnet spacer is just a piece of 4mm aluminum.

I’ve redesigned the motor frame using magnets that are slightly larger at 5mm x 10mm, and a ribbon that is slightly narrower, about 3.5mm. It’s counterintuitive, but narrower ribbons have a higher output. I’m using a 2.5 micron aluminum ribbon foil. The plastic frame is machined with a slot down the middle to hold the ribbon, and a pair a milled aluminum clamps to hold the ribbon in place. I didn’t want to use copper here because of galvanic reaction concerns. Everything is held in place by 4-40 capscrews, which are magnetic & will probably be a pain in the ass to install, but we’ll see. I’m waiting until most of the work is completed before I install the magnets and the ribbon, since the magnets will attract bits of ferrous crud in handling & the ribbon is so very fragile. That’s why they aren’t in place in the photo above.

The frame installed on the motor mounting tube. The ribbon clamps have been machined and are in place. I’ll probably secure the wiring with a dab of glue once the ribbon is installed.

Another difference is in the motor mount. I’ve built a secondary can that slides inside the mic body from a small piece of galvanized fence tube with a fender washer silver soldered to the top. This will shield the transformer almost as well as a Mu-metal can, and it makes a sort-of “mic-within-a-mic.” This same type of construction is used with great results on the Electro-Voice RE50 reporter’s mic, one of my favorites. This sub-assembly is isolated from the outer shell of the mic with a wrap of foam. This will be of limited benefit, since a ribbon mic is never handheld except when used as a prop in music videos. But I did want some way to take the mic apart and put it back together as a single unit… the Austin design has the motor pressed against the mic body with strips of neoprene foam. It works well, but isn’t ideally suited to taking the mic apart. I expect to do that a bit more with this mic, as I experiment with things like silks around the ribbon or waffle-plate resonators.

I’m calling this one Revision A, since I redesigned & rebuilt the mount to correct a grounding problem. I’m already working on Revision B, which will be largely similar except for the ribbon clamps and  more space at the bottom of the frame for mounting the motor with screws. (Revision A’s mount is secured with glue.) I’ve got some other ideas to try with magnet sizes and frame designs, but I need to give these an extensive listening test first.

I’m still waiting on a few parts… the transformer and the XLR, mainly… but I hope to have this project finished soon, and I’m anxious to hear the results. In the meantime, I’ve started milling parts for another one.

The semi-completed shell. I still need to machine the brass cap at the bottom and mount the XLR connector. Overall length is just about six inches.

The cost for this project is fairly high, mainly due to the amount of time that is spent in construction. If you add in the cost of the machine tools, the cost goes from fairly high to astronomical. I’m using a benchtop drill press, a 7×10 Chinese lathe and Taig milling machine to make these. All three have been essential for various parts of the work. While it would be theoretically possible to build a mic with hand tools, it is a lot easier to get good-looking results in less time with some heavy machinery. (If you lack the tools, Rick Wilkinson’s Austin ribbon mic kit is highly recommended, see my previous post.) And actually, my setup is pretty minimal… I could use a larger lathe & a CNC mill for faster and better results… but now we’re talking about an investment that would require going into business as a mic manufacturer, which isn’t my intent. These are experiments. I’ll probably make a few available for sale at some point, just to recoup some of the cost of the parts. And I expect the price on them to be rather high, just because they take so very long to make. But these are primarily built for my own satisfaction. It won’t hurt the resume, either.

I owe a great debt to Rick Wilkinson and Les Watts (former mic designer with Shure and EV) for teaching me a large majority of what I know about building ribbon mics. Their help is very much appreciated.

UPDATE: I’ve very nearly completed this mic… I recut an existing XLR connector on my lathe, so now it fits the microphone. The magnets were fitted to the frame, and I mounted a 2.5 micron ribbon yesterday. I’m guessing it’s about 3.6 mm wide. It’s a nice, tight fit. The ferrous capscrews were a pain in the ass, but not impossible to deal with.

The ribbon motor completed, with magnets and ribbon installed. Using 2.5 micron ribbon material is much easier than signwriters leaf, though it’s still not a simple process to install.

Now I’m just waiting on the transformers to arrive. These will be a special custom-wound ribbon transformer that should meet or exceed specifications from the usual suppliers. Unfortunately, it probably won’t arrive in time for the DIY seminar… I was hoping to have this working before then.

This mic comes with a custom walnut mic box that I had built by a local cabinetmaker. Nothing on this mic is sourced from Chinese suppliers… that sort of thing is easy enough to get from just about anywhere these days. If nothing else, this mic will be different from the common stuff that is so prevalent these days.

UPDATED UPDATE: When I went to use this mic recently, I discovered that the glue had failed on one of the magnets and it had separated from the frame, bringing the two together and turning the carefully-placed ribbon into aluminum dust. So while this is an easy-to-build example of how ribbon mics work, it isn’t the best design in terms of longevity.

My new design incorporates a steel frame rather than plastic. This is slightly better from a magnetic perspective, and it’s naturally stronger for threads, etc. I’m thinking of trying a frame made from small pieces of 1/4″ square steel. Machining from solid would be a possibility, or I could even get crazy and go to the blacksmith shop and forge something… I was formerly a full time blacksmith and still have access to some large and heavy tooling. And I’m pretty sure that nobody else is hot forging their ribbon mic parts.

But the key design element will be a small notch to hold the magnets apart. I should have done this before, as it could be incorporated into my earlier frame design. It’s yet another thing to put on my long list of projects.

The finished mic in its custom-built, handmade walnut box.

Austin Ribbon Mic Completed

The completed Austin ribbon mic. This one will be given away at the Producer’s and Engineer’s Summit at Welcome To 1979 in Nashville, coming up in November.

Here’s a look at my Austin ribbon mic, I completed it yesterday. Building this mic certainly was actually really easy, except for one part… installing the ribbon in the frame. I had to do this several times… six, to be exact. I  had various problems. One, for example, didn’t show it’s ugly head until I’d completed an installation… tiny tears all along the edge of the ribbon. I learned they were caused by the ruler I was using, which had a cork backing that was set slightly behind the ruler’s edge. This small unsupported space allowed the foil room to stress and tear. I corrected this by using a length of rectangular aluminum as a straightedge, this pressed down on the foil right at the cutting edge.

Another problem I had was corrugating the ribbon. I was trying to protect the ribbon by corrugating it with the release paper on the top and bottom, but doing so a) causes the ribbon to curl up, and b) makes the corrugations shallower. If the ribbon isn’t sufficiently corrugated, it is extremely difficult to get it tensioned properly. The tension is important… the ribbon can neither sag in the frame, nor should it be too tight. I had the latter problem, and the ribbon developed a longitudinal curl, so scratch that ribbon.

But thanks in no small part to Rick’s patient support via several emails, I finally got one in. It wasn’t perfect… it could be centered just a hair better… but it looked ok, so I closed it up and finished the mic.

And considering everything, it sounds quite lovely. The last time I used a ribbon mic was 25 years ago, when I did my thesis recording using a pair of RCA TK77’s that the university owned, so I don’t have much of a frame of reference, but it seems to have a nicely balanced frequency response. From what I understand, construction errors show up as poor highs or lows. I don’t have a frequency analyzer set up yet so I can’t give any numbers, but my subjective analysis says “nice.” Now, like all ribbons, the output is rather low, and I did my testing using a rather crappy mic preamp. On voice, one has to crank the gain up quite a bit, and this gave me a lot of preamp noise. For someone who is a low talker, this wouldn’t work. But I got a rather useable level on my acoustic guitar.

Again, I can recommend Rick’s kit quite highly, especially if you’ve never built a mic before. He’s done everything that can be done to insure a good outcome, and the one I built certainly worked out well. That’s not to say it’s simple… you need patience, and good, steady hands will help as well. But I’ve already got parts here to build four more for myself!

The Austin Ribbon Mic

I recently received an Austin Ribbon mic kit from Rick Wilkinson (Rickshaw Records) out in California. Unfortunately, I can’t say I’m the proud owner… this mic is going to be built and given away as a door prize at the DIY panel at the Producers and Engineers Summit at Welcome To 1979 in November.

I haven’t finished the build yet, so I can’t give a complete review of the mic, but I can make some comments about the kit and the resources that come with it. Building a ribbon mic is not that complex- IN THEORY. It’s just a thin metal ribbon suspended between two magnets. There isn’t much electronic inside the mic, just a transformer. The design has been around since the 30’s.

The theory is simple. But like most things, it’s the Devil in the details. You can find articles and instruction on the web for free. And that’s what I started to do years ago. I got halfway through the project and shelved it… there wasn’t enough detail for me to be successful.

Or you can spend some money and increase your chances. Rick sells plans for ten bucks, or his ribbon kit for $275 with a Cinemag transformer. (There is a less expensive version with a stock transformer, and I understand the stock transformer is exceptionally high quality. It’s sold out right now, but should be available again shortly) Rick sent me a kit with a Cinemag transformer, so that’s the version I’m reviewing here.

The kit itself is extremely well done. The mic tube is powder coated brass, 1 1/2″ diameter, and exactly machined. All the holes are already drilled, so you don’t need a drill press. The motor frame (a critical part) is a machined piece of plastic. The fit was perfect. I especially liked his design… I designed my own once, and it was a cumbersome mess. Ricks is elegant, simple, strong, and works well. (some folks claim that metal frames are superior. Perhaps they are… I’m not sure… but I think that at least part of the reason behind this claim is that’s what is available from China.)

The greatest value for me, though, is Rick’s instructional materials. When you buy a kit (or his plans), he sends you a link where you can download  PDF instruction manual and several videos where he goes through the process of building a mic. These videos are really helpful, especially when it comes to corrugating and installing the ribbon.

Commercial mics use ribbons that are anywhere from 5 microns to 1.8 microns thick. The ribbon material that Rick supplies is about 0.8 microns. (Thinner ribbons increase high-freq sensitivity.) This is similar to “imitation silver” guilding leaf, it’s readily available on the internet. I’ve bought some from Hobby Lobby before and tried to cut a ribbon from it. I can say without hesitation that it ain’t easy. But that’s the beauty of these videos. Once you see someone doing it, you understand the method better… much better than just reading about it. And you can see that it is possible to make a well-functioning ribbon from scratch, but understand that it’ll take some practice. Even breathing can cause a cut ribbon to fly off your bench. So be ready to make several practice ribbons before you get one correctly made and mounted in your mic frame. And if you just can’t get it, there is an internet source for commercial ribbon foil now. A company called Lebow sells pure aluminum foil in a variety of thicknesses, including 1.8 and 2.5 microns. This would be vastly easier to handle, but it’s also vastly more expensive at $25/sheet. (There may be other sources as well, but this was the only one that I could find. I ordered two sheets to use in my own mics, but they aren’t in yet.)

Ribbon-making details is a big advantage of his instructions, but it isn’t the only one. For example, I learned that you can use a brass footrail cap on the bottom of your mic to hold the XLR connector. These things are nice, solid castings, and if you shop around, you can find them at about $5 apiece. (I wish I’d thought of that.) Circular Switchcraft connectors fit well in these caps.  This would be a good solution for any tubular-bodied homebuilt mic.

The videos do have a slight downside. You have to remember that Rick has built a lot of mics, so some of the things he does in the videos look easier than they will be to folks like you or I. It’s really difficult to explain the things that practice teaches you. But I’m pretty sure that I’ll have a working ribbon mic once the dust settles… I’ll keep you posted.

UPDATE: I finally got up the nerve to install the ribbon today. It worked on the second try, which really isn’t bad. I’m pretty sure that my success with this is pretty much due to Rick’s instruction. Like I said previously, I’ve tried this before and failed miserably. Seeing it done (in a video) makes all the difference.

A just-placed ribbon in the motor frame. This job requires lots of patience, but it can be done.

That is not to say, however, that it was easy. The foil is the definition of flimsy… if it were any thinner I think it’d fly off my bench because of the rotation of the earth. Using the more expensive 2.5 micron foil should be easier (though I expect still no picnic), and that’s what I’m planning for my own ribbon motor frames. (I figured this one should be made as a stock kit, in order to give a fair review.) There will be some slight differences, like slightly thicker magnets… I’m still in the design and prototype phase. But if they work, it’ll be fun to try some design variations like waffle plates (resonators) and silks.

Simple Broadband Absorbers

Here’s how I built a pair of simple broadband absorbers to cut down the room sound in my studio. These work as good as specialized acoustic treatments, but cost far less, and their absorption is good down to the 500Hz region, and it’s fairly flat across the spectrum. Note that absorbers don’t stop outside sounds from getting into the studio… they do shorten the reverb time of instruments as they are played in the room.

The absorber starts with a simple 1×3 wooden frame.

It’s really nothing more than a simple wooden frame with fiberglass fill, covered with cloth. Mine measured about 5’6″ by 30″. I used cheap 1×3 lumber (which is really about 5/8″ x 2 1/2″), but a true 1×4 would be better. If you use cheap wood, count on spending more time building them… I had to pre-drill all the nail holes to prevent the weak wood from splitting. I also used construction adhesive on all the joints.

The frame gets filled with plain R13 fiberglass. A few staples helps hold the fiberglass in place.

Once the frame is built and the fiberglass positioned, all you have to do is attach the cloth. I used a staple gun. They are fairly light, so they can hang on the wall with a simple screw. There may be times when I’ll want more room sound… then it’s a simple matter to move these somewhere else. Or stack them around a guitar amp, for example… they’re very handy to have around.

I turned the absorber over and stapled cloth to the backside, and it’s finished.

The finished absorber in place

A Mixer Table and Gear Racks

Here’s a look at my mixer table that I just completed. Since the Soundcraft 800 didn’t come with any kind of stand, I had to build something. This table is built entirely from two sheets of 3/4″ birch plywood and cost about a hundred bucks. It had a pair of slope-front gear racks and a removable “bridge” for the speakers and computer monitors. Thanks to the panel saw at Home Depot, I was able to put this together fairly quickly… less than two days.Image

I still need to order rails to mount the gear. And of course, I need to get the master section of the mixer rebuilt by Creation Audio Labs in Nashville before I’ll be functional. But it’s been a good bit of progress… hopefully we’ll be mixing in a matter of weeks.Image

While you can buy much nicer studio furniture from some of the suppliers listed in Mix Magazine, I firmly believe that it’s imperative to keep overhead costs as low as possible in almost any recording studio, especially considering the current state of the industry. This is what killed us at On Line Audio (my old studio in Charleston). Some months, business would be good, others not so good and income would be down… but the bills kept coming in like clockwork, and Robert (the owner) couldn’t afford to keep covering the losses.