Does impedance match matter for mic to preamp?

Well it could be very low Q. Hmm OK... I know nothing about mics, but air damping goes as the velocity squared. So it really stinks at low velocity. So there is no other mechanical damping in a mic?

Oh, you're saying the damping is a radiated sound wave from the mic?

Like radiation resistance?

OK I'm not sure. I'm not disagreeing that Brownian motion will cause noise in a mic. I'm just wondering about other noise sources.

Oops.. I read your first answer wrong. I know about impedance matching with transformers. In the voice of Emily Litella (Gilda Radner) "Never mind".

George H.

I found this,

GH

Why would you want to achieve maximum power gain in an audio application? Voltage gain is what you need. And any audio source, even a moving coil mic or guitar pickup has gobs of power available from the source as compared with what's available from say an AM radio wave 30 miles from the antenna

I don't think so, I got mine on Ebay. \ Mikek

The freq response is going to be pretty bad if I use a folded horn or a parabolic reflector. Low freq cutoff. I'll shoot for voice recognition first and then worry about birds. Mikek

Are there mics that can see the Brownian motion noise? If so I'd love to put one in a vacuum and see how it changes.

OK this has a lot of stuff, but they do measure the noise change in vacuum.

George H.

I'm by no means a practicing expert in this subject, but I think your line of reasoning here is missing a step (or is incorporating a false assumption), as follows:

All OK so far, I think.

However, you've neglected to identify the amplitude of that current noise.

That's correct, insofar as it goes... but you're implicitly assuming that the noise current is _independent_ of the load resistance, and thus that increasing the load resistance increases the induced noise voltage. I don't think that's correct.

If the noise voltage is being generated in the source (the mic), then the total noise current flowing through the circuit will be a function of the noise voltage, and the total impedance of the circuit (the mic plus the load). The higher the total impedance in the loop, the lower the amount of noise current that can flow (reciprocal relationship).

If the load impedance is >> that of the mic, then the load impedance will dominate the magnitude of the noise current. Double the load impedance, and you'll cut the noise current roughly in half... and then, working into the doubled load impedance, you'll end up with almost exactly the same induced noise voltage.

Similarly, if you cut the load impedance in half, you'll halve the induced noise voltage per uA of noise current... but you'll roughly double the noise current and you'll be right back where you started.

Thus, in this regime (loadZ >> micZ), changes in the loadZ "wash out", pretty much.

You could claim that the high load impedance causes the generation of a high load-related noise voltage... but since the high load Z is shunted by the low Z of the mic, you never see that noise voltage when the mic is connected.

That's how I see it. Corrections welcomed!

** Bizzare.

** No - it's completely rediculous

Like all you f****it ideas.

..... Phil

** That is cheap electret capsule with inbuilt JFET pre-amp.

There is nothing YOU can do to improves its s/n ratio.

** Rediculous.

** Absurd crap.

** The end result is a pile of junk.

There nothing so pathetic as the blind leading the blind.

FFS, go away a do something useful wit the rest of your life.

..... Phil

How about being helpful and tell me what the problem is using that amp. Mikek

Why do you post if you don't want to explain why something is wrong? Your just name calling, is that useful to anyone, I suspect its not even good for you. Mikek

ut

.

amp that has about 1K input Z via n XLR connector.

I think it is just a matter of dynamic range. Whatever noise you have is l ower in comparison if your signal is larger. A friend used to work in high end audio, not to people listening to music, but the people who make and r ecord music.

They were still using strictly analog with large voltages to improve the dy namic range which makes the noise lower in comparison. Seems the people bu ying the equipment can actually hear the difference.

I expect there is a LOT more digital in the mix (pun intended) these days.

I thought the power used by this sort of mic was low enough a battery would last a long time. Four 12 volt batteries would give you 48 volts.

-300-196

What is the end use for this mic? If you want something with high gain the re are various designs for getting the most signal to your mic.

Rick C.

Please note that the frequency response is only valid if the transformer sees the specified impedances at its connections. Without proper terminations the response is prone to be peaky.

The frequency range is OK for speech, but pretty narrow for music.

I'd avoid the transformers as far as possible.

--

-TV

A 49M source, at say 10nW power is 700mV RMS: you need current gain more than voltage gain. A 47M source won't be much different, except for having harder arithmetic

--
  When I tried casting out nines I made a hash of it.

It'll probably work fine. But it's not a very sophisticated design, and the 2SK117 is discontinued and hard to get, B&D has some, but doesn't specify the Idss grade (it's got a 1.2 to 14mA range).

--
 Thanks, 
    - Win

Phil is right, if your project is based on a commercial electret capsule,

they universally have a built in FET which is the front end of your system.

And even using these inexpensive mics, in most applications the electrical noise is not the limiting factor.

m

I discussed noise sources with a microphone designer at Knowles when I was working in the hearing aid field. He told me that the design objective is for brownian motion noise to be roughly equal to the electrical noise from the FET buffer (in hearing aid microphones).

John

** In-ear hearing aids are very special case of microphone use - not relevant to other microphones which do NOT face the same restrictions on size and location.

.... Phil

OK that makes sense. With a big enough area/ mass microphone element (the moving bit) the thermal air noise doesn't matter so much. So then where are the noise limits? All electrical? Any good articles?

The article I found above was a nice read. Various holes in the thing added thermal noise. I can only picture the Brownian motion of air impeded by the hole. (I've never read Einsteins "Brownian motion" paper.... I think this is it.. or a later copy.)

George H.