My first thought was to make some kind of ring clamp, but that would require a large diameter brass tube and was starting to look quite expensive and bulky. So I came up with this…
It is simply a folded strip of aluminium screwed to a threaded brass cylinder. The bass of the cylinder is threaded to fit a 5/8″ mic stand. The mic slides into a slot in the aluminium and is held by its own ground clamp.
Some shrink sleeve ensures that the signal outputs are not shorted by the new mount.
This is what happens when one dissects a couple of Beyerdynamic ribbon mics: bodies, grills, motors, transformers, XLR or DIN output connectors. Nothing surprising there….
But what are those grey plastic tubes?
These are in fact acoustic chambers that provide back pressure to the ribbon, changing it from its natural figure-8 pattern towards being hyper-cardioid. It is also critical to the microphone’s sound – if you make an M260 without one, it sounds pretty awful.
There is one more important ingredient to the mic, and that is a piece of string. This is stuffed into the chamber to break up internal reflections. Sometimes simple works!
Here is Tannoy’s cardioid ribbon microphone – the MD422.
Tannoy MD422 ribbon mic, front
Firstly, Tannoy lose a point for the name. ‘MD’ should surely mean “microphone dynamic” in any sensible society! Perhaps the D stands for “directional”? Who knows, but it puts them at odds with other the Sennheiser MD421, and it is just plain confusing.
Tannoy MD422 ribbon mic, rear
Whatever the D stands for, the mic itself has an industrial look, and this one is finished in a bronze-ish coloured paint. To the best of my knowledge this is the only cardioid ribbon model that Tannoy ever produced, and it uses an acoustic labyrinth to provide the necessary back pressure to the rear of the ribbon. The chamber is the black cylinder in the photo below.
Tannoy MD422 ribbon mic, chamber
Some of the parts were made to a budget, or perhaps a short production run, with thin stamped metal for the base and top cap, along with two layers of off-the-shelf mesh to protect the mic from dirt and wind.
The ribbon assembly and magnets are the same as found in the type 2 Tannoy ‘pitchfork’ microphone, which would have saved costs by sharing components.
In the report, the bi-directional BBC-Marconi AXBT was used as a comparison, which was much more expensive, a different pattern, and therefore a tough benchmark. Cardioid (and non-directional) ribbon mics generally use an acoustic chamber on one side of the ribbon to apply pressure, and this damps the ribbon motion, reducing the output compared with its natural bi-directional response.
Drawing of the Tannoy MD422 from BBC technical document.
Unlike my mic, the BBC’s example had a yoke mount rather than a fixed base, although there are mounting screw holes in the side of mine.
Despite my irritation with the model number, and the BBCs damning assessment, I like this microphone very much. It has a gentle warm tone. More importantly, it was an attempt at technical innovation, which is always to be celebrated.