Okay, so back to our Omni microphone. Uh, I've drawn the diaphragm there and the back plate there. Because this is generally a condenser type microphone, whether electric or externally polarized Mhm, There is an issue here. If this is a truly sealed compartment, right? Guess what? When you go up on top of a mountain or down pressure differences? yeah, that's going to bend the DI frame in or suck it out, etc, etc.

etc. What does that do to it? Well, if it, if it bends in M it's going to increase the sensitivity of the microphone right? Uh, if it bends out, it reduces the sensitivity. There is another Factor if you get too much pressure on it. Uh, you'll actually force it onto that fixed rigid back plate.

Yep, and it'll go dead completely. Uh, yeah. Basically, because it can't move, it's pressed against the back plate. so there'll always be just a little bit of air leakage in there, right? And you can plan that air leakage.

Basically, the idea is, uh, any slow variations in pressure Mhm can put air in or out of there, right? Well, guess what? That forms a low frequency, uh, limitation to the system? It does. Yes and well. You can plan it. You're right.

You can just like speaker box design. Yes, yes. If you make that a very little hole with possibly a labyrinthine path, you can have that time constant. Yeah, Labyrinth labyrinthine.

Uh, you can make that low fre the the diaphragms low frequency pole. You can put it down in the sub one Herz region. So that's a tuned Port It's not tuned not no, could you? uh, you wouldn't is all. Mind you, we will come back to an element where you would, but not at very, very very low frequencies.

I've simply drawn that as uh, Usually what happens is they plan for a bit of air leakage just underneath the seals here or underneath the crimp joint that goes over there that because of the enclosure at the back of it really doesn't For that or is that or quite often on cheap electrics, you're going to have a PCB in here. of course. again, with a kind of crimp roll holding it has the FED in there, and yep, and it just allows a little bit of slow air leakage around. that, right? And that's enough to equalize things.

but it also sets the low frequency pole and you can set that wherever you feel like Mhm. Generally you might set it down in the 20 herish region for a commodity microphone. Uh, because that's Rel relatively high in the scheme of things. so you can have a relatively High degree of leakage there and you don't have to control it that well.

Right to yeah, it doesn't matter on a commodity MK where Where the frequency response is around there as long as it's somewhere below voice range? Who cares. Yep, Okay, um, on a measurement microphone though, they might put it down sub one hurz Mhm. And that's why you wouldn't use them as a vocal microphone Because when you're going P P put with plosives? yep, into such a microphone? uh, you will make the diaphragm stick. Oh, got it.

What about Pro stage mics? Uh, they are generally plan to have around about a 20 HZ is or sometimes as high as 100. HZ Oh, why? Uh, again, for that issue of plosives, right? Uh, if you've got a rock and roll screamer hard up on the microphone, uh, you've got a couple of layers of protection. Uh, you've got the the grill with it spongy stuff there acting as a pop filter, pop filter. And then you've got the intrinsically defined low frency response to the diaphragm so it can take a hit and bounce back.

Mhm, got it. And what's the dynamic range of these, uh, suckers? If you're talking not as good as Dynamic compared to Dynamic Ah, there's a number of limitations on these. Uh, a pure uhh, how do you put it electric? Uh, sorry. a pure condenser microphone without all the electronics hung off behind it? Uh, the main limitation is the linear range of the diaphragm.

There movement, right? And because the space in there is really, really small. uh, it might be of the order of 170 160 DB SPL right before it starts slapping against the back plate or exhibiting other gross nonlinearity. Got it? Sometimes higher, But okay. We pretty much covered the simplest microphone, which, which is the Omni Yes, okay, what is the difference though between a condenser mic and like a proper one and an electric mic? Okay, uh, we might roll this over into the next episode.

But right? I'll give the quick description uh with a both of them have a movable diaphragm which is a conductor and a fixed plate which is also a conductor right in a externally polarized condenser microphone. What do you mean by externally polarized? It doesn't have the electric bit in it, right? Okay, uh. the uh. these are also called externally polarized or pre-polarized Pre-polarized means it's got some electric stuff in there.

Got it? Okay, with externally polarized, we're basically coming along with our own voltage that we've generated somewhere between maybe 50 and 200 volts. applying that voltage to the plates. Yep, so they're They've got a big charge on them and then sensing what happens to the charge. The differential charge on the plates.

In a pre-polarized microphone. We come along with a material such as Teflon or one of the other flurocarbon type Plastics to which we've applied a charge and locked it in place. and we put that in there. And that is the moral equivalent of applying an external voltage.

Got it. And that's what's in all the cheap ass mics, and likely the one you're almost certainly the one you're and I'm wearing right now. And there's a few different methods of construction too. Actually, I might go over into construction of typical cheap and cheerful electric microphones.

First of all, we'll start off off with a tubular body. Let's put a well diaphragm there and we'll pretend that that's a thin enough material that it will vibrate quite happily with applied sound pressure. Uh, we'll put a fixed plate in there and then figure out what do we do next. Okay, um, one of the things that we can do is we can put okay this material here.

The red stuff will make that Teflon or something like that to which we can apply the charge. And incidentally, the way that they apply the charge apparently is they uh, during the forming process when it's molten, as it's cooling, they they apply a polarizing voltage across, you know, from the top to the bottom side of the film, and as it solidifies, it locks that charge in place within the body within the material of the plastic. Got it? And forever. Is there any yes? Over time, there can be, and it depends on the resistivity of the material, right? If the material has poor resistivity as some of the early uh, Beeswax type materials did, they'd only last a few years and then the charger just dribble away within itself.

Mhm Teflons though. U They've got time constants of a couple hundred years years. y they're enormous. yeah, and very useful material.

Uh, in fact, at the Cs uh, back in 2000, I saw their they done measurements over a period of I Think about 20 years on an electric material and it had not changed by I Think it was something like 0.1% It was about .1 of a DB over the last 20 years. Nice. So that material really does lock the charge in place. Okay, let's put a gold diaphragm there.

Oh no, we can't put the gold diaphragm there. Why not? Why? Because if we got the charge that side, there's actually no charge between those two things. Yes, B B So in fact, the conductor has to go on that side. so we make electrical contact to that bit there and to that bit there.

MH that electric film, which is, you know, polarized with, say, positive, that side. negative That side. Yep, whatever. Uh, it acts as the polarizing Vol between the two plates.

Mhm. That works pretty well, but you're limited by the fact that the diaphragm material is also doubling as your dialectric. and stuff like Teflon might not necessarily make a great uh diaphragm material. y Lovely, lovely electric di lovely electric material, but not so good at those diaphragms.

Okay, so you might take a slightly different approach. and again, we'll put a uh, a diaphragm there, which might be Myar or something, which is a little bit better behaved as a diaphragm material right. This time, we'll put the gold plating on the inside where it's a bit harder to scratch and take the electrical connection off there. And where do we put our electric material? Uh, I'm running out of colors here.

We put the electric material there. All right. That's called a back electric. Okay, do they advertise them as that or you just don't know? Uh, usually if you're buying them from a hobbyist shop, you don't know.

You don't know if you're buying them from a manufacturer. They'll tell you. Does it matter a huge amount? Yes, the back El Electric types are much more stable, right? in terms of what? uh in in terms of all of the properties of the microphone, that frequency response, uh yeah, and sensitivity and charge retention is better with a back dialectric. Okay, uh, it's uh, they sound better all around.

Yeah, yes, generally it's probably Fair way of saying it. Why doesn't everyone make them like that? More expensive? Basically because it's cheaper to put a lump of Teflon on the front right, rather than have the multi-layer construction there. So your cheapest and nastiest microphones are probably going to be uh Teflon with the gold PL on the front right, which is more susceptible to damage. Uh, more susceptible to erosion and just don't sound as good because the Teflon is not as good at diaphrag.

What sort of typical Dimensions we talking about here? Yeah, Minimum and maximum I can make these. The largest I've seen is about 15 mm. Jeez yeah, uh, the smallest ones about 2 mm. Now the 2 mm ones are typical of the kind of thing that you might get in, for example, a hearing aid, right? Okay, yeah, I know it's got to be tiny, right? Yeah, Yeah.

um. and of course, the hearing aid microphones are more likely to use this back electric construction. Uh, because they're after quality and stability. Got it? They're living in a pretty adverse environment.

Uh, you know, who knows what kind of creepy crawlies are floating around people's ears.