Can I swap a plastic for aluminum in this ribbon microphone design?

July 26, 2024 5:24 PM

I want follow a youtube ribbon mic tutorial, but I don't want to do the fussy metalwork. Will replacing the aluminum part with plastic reduce the humbucking/shielding effect?

5 pic imgur gallery of tutorial snapshots if you don't want to watch a video: https://imgur.com/a/Ksfv0nM

If I apply the copper tape as illustrated in the tutorial, will I achieve a similar effect? Or is the aluminum frame necessary for either the shielding to really have an effect, or is it necessary for the operation of the microphone just because of how it affects the magnetic field?

posted by Jack Karaoke to Technology (2 answers total)

Dealing with reducing hum & noise in circuits like this is a pretty tricky business, and I am the exact opposite of an expert in that area.

But if I were guessing, they chose the aluminum because it is relatively neutral in affecting the magnetic field characteristics of the magnets, but at the same time it is electrically conductive, so can be connected in with the copper ribbon that is tied in to the ground to (between the copper ribbon & the aluminum parts that are electrically connected to them) create a grounded shield that almost completely encloses the entire unit.

It doesn't completely enclose the entire unit, but it encloses it with a conducting material pretty much to the degree possible - given the function of the circuit as a microphone, where the element needs to be exposed to the atmosphere.

So if you use plastic instead, you will maintain the neutrality as far as the magnetic fields go, but lose the shielding effect that the (grounded) aluminum pieces would.

You could try it without the extra shielding and just see how that goes, or use something like aluminum foil cut to cover the same basic areas the aluminum channel pieces do, and glued in place to the plastic case, and just make sure that is electrically connected/grounded through the copper ribbon cable.
posted by flug at 7:20 PM on July 26

I've never made a ribbon mike. I think the aluminum channel could be replaced with similarly sized plastic to no ill effect. Shielding may be slightly affected, but this is such a low impedance device, I'd be surprised if the difference would be noticable. The aluminum may have an effect on the eddy currents induced in the magnetic field, but I think it'll be most significant in the ribbon itself, rather than the aluminum "chassis" in this arrangement.

I'm mostly curious how efficient this design is with the way the magnetic poles seem to be oriented. A quick search gives ambiguous results on optimum pole orientation. I don't have the patience to do a deeper dive right now. Maybe it's not significant, but I would have thought the magnetic circuit itself in relation to the ribbon would be important in the design.
posted by 2N2222 at 8:56 PM on July 26