Hello everyone,
I'm going to diy a ribbon microphone, and got the idea to buy arc shaped magnets instead of cilinder, to accomodate a round aluminium foil diaphragm, instead of the typical slice. Do you think this would work? Picture attached
I'm asking beforehand because I'm going on a tight budget and don't want to buy things that won't work
To make a good and efficient ribbon motor we have to observe a few conditions:
1. In the air gap we need to maintain a strong, efficient, and uniform flux, so the magnets should be in quite a close proximity and in parallel to each other. We don't want to place them too close, as then the modern Neodymium magnets will saturate. On the other hand, with distance we loose the filed considerably.
2. Ribbon should be stable, with minimum torsion movements. In general, the best ribbon shape to get a good stability and efficiency (along with low impedance) is rectangular.
3. For a good top end response the front to back distances should be minimal (I posted on this some time ago in depth).
4. Low impedance (DCR).
Let's see what happens if we make proposed circled shape:
1. The rule of the field is 2:4, IOW, if we increase the distance in twice, the filed will decrease 4 times. The optimal distance is about .200"--.250" depending on the magnet size. What happens in the round one--the field in the farthest points will be very weak, producing almost no signal. Also, this is providing you will be able to find the magnets of that shape magnetized in a correct plane.
2. Any 'flaps' will increase mass (without actual reducing DCR) and torsion instability, which results in resonances and all kinds of distortions. This is besides obvious fact the DCR will be weird.
3. The round shape introduces considerable front to back distances. Say 1" round will translate into some 1.750" front to back (including magnets), which translates into -3dB @ 7.7kHz.
That is how the ribbons came to a present (rectangular) form when you optimize each of those parameters and put into a system all together. If you are on the budget I'd definitely suggest to go conventional way in this case.
Best, M
P.S. Somebody posted earlier--against of our intuition the top end is not affected by ribbon mass.