Regarding nose cone material, I run the center conductor / spring through a piece of Teflon insulating tubing. The material of the rest of the cone is relatively unimportant.
I consider to 3D print nose cones as well, but haven't decided on the material yet. Which material would have the best properties in terms of surface and bulk resistance and moist absorption, if those matter at all for the given dimensions? Anyone having any experience? And what should be the maximum gap between tube and cone? I guess a wide gap will cause FR anominalies.
The MOST important thing is to have the rest of the microphone body sealed from the cavity behind the cardioid capsule.? So your conductor/spring needs to be a close fit to its hole and the 'cone' to the tube.
If there is too much 'space', the tube and the hole/space act as a Helmholtz resonator in the audible range.? If you see a sharp suckout in the frequency response between 1kHz & 20kHz, see what happens when you fill the space/hole with glue
The slots in the tube and the cavity behind the capsule are another resonator so make the slots as open as possible and the cavity small to get this above 20kHz.? I never bothered with cones (which reduce the cavity) and the stick Calrecs simply had a flat Perspex cap sealing off the tube.?
See the Saturnsound page for picsThe first 'slot' also need to be as close to the front of the capsule as possible thought this is a path length effect rather than Helmholtz.
You don't need slots with omni capsules but these have other problems.
If the front of the capsule is in a shallow cavity, you can use this to raise the top end of your frequency response slightly .. eg if you are -3dB @ 20kHz and you want it flat to 20kHz.? There's a couple of other dirty tricks ... I mean subtleties of design ... you can pull on a stick mike which aren't available on a side address mike :)
BTW, CGO/NPO ceramics are probably the BEST capacitors you can buy.? If size, value & voltage are appropriate, use them.? Replacing these with polystyrenes will introduce microphony.? Guru Scott Wurcer did some trials in Jurassic times when he was active here.? He might have reprinted some of it in his more recent Linear Audio articles on mike design.
As far as 9dB spl noise spec, you could work out the?
electrical noise from a circuit sim.? The fact that they are driving only one side of the XLR in an impedance balanced circuit suggests they are trying as that can have a dB or so advantage.? Then the sensitivity of the mike will tell us if they are cheating by just quoting electrical noise.? Excuse me if I dun do da hard sums as dis daze, mi hed huts :(
