Capacitor/Condenser Microphones

Sennheiser make RF-based microphones. The MKH range is what you want.

d Pearce Consulting

Yes, I seem to recall that some early designs used RF, but likely nothing in the last 50 years.

There are some microphone historians that may know over on news:rec.audio.pro

I once thought about making a "direct digital" mic by using a condenser mic capsule in an RF oscillator circuit and a high-speed freq counter to generate the digital samples.

I got lots of hits on Google with: rf condenser -interference -wireless (because many sites mention "RF interference" and/or wireless mics)

(If my previous posting didn't get cancelled properly, ignore it!)

Hi Richard,

How can you cancel a post to an unmoderated newsgroup? Just curious.

Regards, Joerg

Canceling a message (only your own, of course!) is a fundamental part of Usenet and the NNTP protocol.

How it is implemented is dependent on which news-reader application you are using. I use MS Outlook Express and the function is found in the menu bar under "Message". In the drop-down menu is a selection for "Cancel Message"

Note, however, that because of the speed of the modern internet infrastructure, your Usenet message may have already been forwarded to hundreds (thousands?) of news servers and may have already be read/downloaded by thousands of readers before the cancel message can go out and do its thing. Usenet was a "store-n-forward" or a kind of "peer-to-peer" sharing protocol long before Napster, et. al. came along. Because of that, cancelling a message is a rather unreliable exercise.

OK, lessee-

Send a post using this syntax:

(start)

Newsgroups: sci.electronics.design,sci.electronics.misc Subject: cmsg cancel Message-ID: Control: cancel References: Supersedes: X-Cancelled-By: snipped-for-privacy@removethispacbell.net Approved: snipped-for-privacy@removethispacbell.net Sender: snipped-for-privacy@removethispacbell.net From: snipped-for-privacy@removethispacbell.net X-No-Archive: Yes

cancel

(end)

Here is a template, ready for you to enter your info:

Newsgroups: Subject: cmsg cancel Message-ID: Control: cancel References: Supersedes: X-Cancelled-By: Approved: Sender: From: X-No-Archive: Yes

cancel

I saw it at 2:07pm PST. My newsreader says that you posted your message at 2:02 But the timestamps are not particularly reliable, either IME.

I have used quite a few old condenser mikes, but I think the only OLD ones that used an RF oscillator/detector/discriminator were the Stevens Tru-Sonic units, about 1949-1950. The most popular of the line was the Stevens C-2S, which was used with the OD-4 oscillator demodulator unit.

Kind of a counter-intuitive setup, the OD-4 contained a crystal oscillator, and the microphone head contained the capacity element and a small inductor. The oscillator ran of course at a fixed frequency, but the microphone proper was part of a discriminator circuit. Microphones were tremendous, sound wise, but a real pain otherwise. Because everything was tuned, the mike and the O/D unit needed matching serial numbers, and cable damage was generally catastrophic, as the cable capacitance was part of the discriminator circuit.

I don't have a link, but I do have a schematic and specs here.

Other than that, I don't know of any other mikes that used RF. By far the vast majority just used a DC polarized capacitor element with an amplifier in the mike head.

Whuffo you doing this?

If it's of interest QST ran a couple of articles a while back on home brewing your own condenser mics, but they use HV DC and FET preamps to extract the signal. Pretty clever -- the author was claiming high audio quality from aluminum foil and other household items, but then it always sounds better when you do it yourself...

Think micro-microphones ;-)

...Jim Thompson

Not only that but most servers don't honor the cancellation either, something known as Dave the Resurrector I recall...

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

Fascinating!

I clicked cancel about four seconds after I clicked "send"!

Well, maybe ten.

The thread isn't up at google yet, but it's only been a few minutes.

Cheers! Rich

On Sat, 06 Nov 2004 16:44:15 -0700, Jim Thompson wroth:

You gonna integrate it onto a hunk of silicon? MEMS-like?

Aren't there integrated pressure sensor chips around. All you need to do is make one with high enough frequency response. Gain shouldn't be a problem since the amp can go right on the same piece of silicon.

Jim

Your browser is supposed to know how to do it, but IIRC, you post a cancel message to the control newsgroup. See one of the many Usenet FAQs that are out there, and also the relevant RFC(s).

curious.

Well, if you tried to cancel this message, then it didn't work, obviously...

to

audio

always

Well, the telephone sets that we have at work have an electret mic element in the body of the set for the speakerphone. It's about 3/16" diameter and even less in depth. That's pretty small, and I'm sure that the electrets could be made smaller. How small did you have in mind?

I believe the D (Dave) version was superseded by the G version a few years ago. I don't know what version it's on now. Thanks to Hipcrime.

But I think the resurrector is for rogue cancellations, not for cancellations from the originator. So it may not prevent you from cancelling your own posts. But I think AOL is one of the major usenet servers that doesn't honor cancels. But that's from what I knew about it several years ago. :-P

Hipcrime.