Mic stuff for short essay

[mattr]

Whilst this is a microphone question, I thought it would be more suited posted here

Basically I have to do a short physics research-project thing in the next week or two on a subject of my choice. Guide of around 2-3000 words. Microphones came up as one of the suggestions by the teacher so I thought I would snap that up, as I already know a fair bit and there's plenty of physics involved that I could write about.

So far I've thought of the following topics to cover...

Electromagnetic induction in dynamic mics.
Electrostatic / capacitance stuff in condensors.
How venting is used to create polar patterns.
Possible some basic stuff on resonant chambers in dynamics.
Advs/Disadvs of different diaphragm sizes (i.e. comb filtering when wavelength < diameter if diaphragm, mass of diaphragm and momentum changes, etc).

Whilst I won't be going into that much detail, everything I do has to be related back to the underlying physics, and it all has to answer an overall question. I think I will be working under the title of "How does microphone design relate to application?"

So are there any other topics that anyone would suggest exploring? Any suggestions for how I could approach the ones I've covered? Links to useful sources?

Any help would be gratefully received! Thanks

 

[mshilarious]

Uhhh . . . have you read the stickies in the microphone forum

 

[mattr]

Yup, and I've read through most of Harvey Gerst's mic FAQ which is very interesting, but apart from that most of the stuff in the mic forum is just opinions about different mics in different applications, etc.

I'm being expected to look into the theories, and maybe run through a few equations and calculations to show how these theories are put in to practice, e.g. typical voltages produced through electromagnetic induction by a dynamic mic coil. Just been doing some work on electrostatics and charge in electric fields so I guess I could include that as well.

I thought this was like the electrical-engineering type part of the board, hence why I asked here rather than the mic section. Just looking for any other ideas for principles that I could look into.

 

[mshilarious]

Microphone selection comes down to three criteria, from my admittedly biased point of view:

- polar pattern (including proximity effect)
- transient response
- noise vs. distortion

Frequency response is not that important as you can equalize that however you like after the fact. But it's tougher to remove noise and impossible to improve transient response. Even digital noise removal techniques cannot recover signal below noise; they simply make the noise less apparent vs. the signal that is above the noise, but at a different frequency.

Thus, I would always select the smallest diaphragm microphone of the required polar pattern that is capable of the required noise/distortion performance.

If you know that you can a goal of slower transient response and falling high-frequency response, you can save time by selecting a dynamic mic or large diaphragm condenser microphone if you don't want things that slow. But it's not too difficult to create a similar response via DSP using a more transparent microphone.

My higher math skills are not sufficient to explain these phenomena in pure mathematical terms. I used to have some good links, but I lost all of my bookmarks a few months ago

PS Dynamic capsules are typically -66dBV/Pa to -60dBV/Pa, and are usually followed with a step-up transformer as the capsule's output impedance is rather low.