First Microphone Design - Care to Review?

[Pariah Zero]

I'm hoping some kind soul can point out any major errors I've made, or improvements I can make to the idea I've drawn up so far.

I've been thinking about making a ribbon mic for a while - I've seen some YouTube videos, and figured they seem simple enough (famous last words...).

I'm not looking for insane quality, so much as making something myself, and having a sort of platform I can start with to play with. I figured I'd start with something vaguely similar to the RCA-44.



I have the Neodymium magnets in light grey, and a steel magnetic shield in the darker grey on the outside

I figured I'd design the upper half using stacked plates separated by spacers - and with cut plywood with spacers -- something like this case:



Then I'd fill the (non ribbon motor parts) with low density A/B foam (and cut holes with a hot wire where needed). That would give me a solid, strong, lightweight sandwich that's hopefully resistant to ringing - which seems (to my ignorance) like a fairly good idea. Worst case, I can use a little bit of CLD material to absorb vibrations.

• The ribbon itself would be a tad bigger than the Original RCA-44, 63.5 mm (2.5") long and 4.7 mm (0.185") wide.
• The YouTube video linked also points to this 0.4 µm Aluminum leaf - I could use it, but I'm find with using something different.
  • I know geistnote sells various thicknesses.
• I could follow the formula in the video for the ribbon size/thickness & transformer -- but I'm open to suggestion.
  • At this point, I'd prefer inexpensive, with the idea being that I know I'll be replacing it in the future (after I've learned more.)

Thanks for any input you have.

I know I have a lot of reading to do - I'm working on it...

 

[Rusan]

Though I've designed and built a few ribbon mics, I'm by no means an expert; others will likely chime in and offer additional/superior advice, especially a few who do this for a living and do it extremely well.

The only thing I really see that could possibly be amiss is the choice of .4 micron foil. While this in itself is not necessarily a bad thing, .4 micron is EXTREMELY difficult to work with, even after you've become accustomed to making ribbons. Unless you have a good corrugator (not one of the plastic crimper thingies), you'll likely go through several failed attempts before getting a good, straight ribbon. Then, you'll likely tear a few while tensioning, until you learn how to handle them. Something like 1.5 micron is about as thin as I'd personally do for my first ribbon mic, especially if you don't have access to a good corrugator. And, maybe a 1:35 transformer in my reckoning.

Having fun while creating something of your own is what DIY is all about, and ribbon mics are a favorite subject for good reason. It's very rewarding and satisfying when you plug it in and get to hear it for the first time (if it sounds good ). Best of luck!

 

[Pariah Zero]

While I'm waiting for shipping... I am refining my design a bit: I'm working on narrowing out and tapering the motor so it has less of a box shape and more of an hourglass shape. The basic frame now extends all the way to the base.



I'm thinking my first pass at the grille will be a less-ambitious but simpler box shape, as it'd be pretty easy to just bend on a brake. Making an RCA-44 positive mold out of hardwood would be fairly straightforward, but a functional negative mold doesn't strike me as simple. (Then again, if I understand the How it's Made video correctly, AES doesn't seem to use a negative, so much as a thick plate with a shaped hole -- and that might be doable, as long as it's reinforced to prevent splitting).

I think I'll take Geistnote's advice and practice making ribbons using the cheap 'fake' silver leaf you can get from Amazon (at $7 for 100 sheets, why not? I've got other projects I can gild anyway.)

I'm going to start with Geistnote's 1:36 transformer, and see how well that works.

 

[Pariah Zero]

Fabrication has been underway: it's been a bit slower than hoped, but it's getting there.

I started by laser printing the outlines and used an acetone transfer to get the image to the plywood:


After cutting & some sanding, I've got some shapes for the motor housing:


I did the same for the inner part of the mic body, which I am also sandwiching with some extruded polystyrene:



Next up I'll cut the edges (inner & outer) with a hot wire, and then add in some smaller wooden blocks on the sides and bottom, so that I have a surface which can be used to mount the base/transformer box and grille to.

 

[Pariah Zero]

It's been a while... time for an update:

After making the sandwich, I've cut the foam to size around the frame, and then my 'lil bud wanted to help, so then I had to fill in places where he 'stopped' and let the wire melt the foam. That's OK, I needed to make a few slots anyway - I filled them in with J-B Weld so I could drill & tap some holes to hard-mount the exterior grille.:

Along the same time, I assembled the ribbon motor assembly - since I have a couple of extra magnets, I'm taking a bit of a risk and am using the magnets themselves as load-bearing structures, but it helps reduce back-to-front distance. The magnets themselves are Neodymium N40 with a 1/4" square cross-section, so I doubt physical strength will be an issue as long as I don't drop 'em.




I've got a set of aluminum terminals, but I think I'll bite the bullet and make a second set, having learned with the first set - I think I can do better. For now, I have a set of MDF Plugs in their place. Once the terminals are set, I can get the majority of the ribbon motor finished.

Then I can start getting something put together to suspend the ribbon motor in the frame, and start working on the transformer box at the bottom, and finally the mic grille.

I'm sort of torn between grille materials - there's the classic perforated metal used by the RCA-44, but it would be fairly hard to shape, I'm afraid. (It's definitely beyond my ability to make one with compound curves like RCA/AEA's) - I'd have to use square bends & cuts, and solder/braze/weld the seams back together.

I'm also thinking of something entirely different - hexagonal perforated aluminum, with big holes: 0.45" holes (Though there is a 0.25" hole size version), and 81% open area.

I'd probably have to use a secondary screen in the middle, but I seem to remember that it's a critical choice, as a fine mesh would filter one set of audio frequencies, whereas cloth would filter another. (I don't, for the life of me, remember where I read that...)

Edit: I found it:
"Another distinguishing feature of these large headbasket mics is the use of a nylon-covered wire mesh box for wind blast protection. While the mesh is very successful at protecting the ribbon from strong gusts of wind, there is a downside: the fabric/wire box is actually a bandpass filter. Like all analog bandpass filters, this blast filter imparts phase shifts in the audio band. Most noticeably, the high pass portion of the filter imparts a phase shift in the bass region. The result is a degradation of time alignment across the lower audio band.

The second effect of this mesh is a low-pass function caused by layers of fabric — an attenuation of high frequency audio."