Carbon Mic Tip

[n8fvj]

Many Military WWII transmitters use a carbon mic. The Shure 104C is a replacement, but the frequency response is a dismal 300Hz to 4KHz. Telephone carbon microphone cartridges have much better frequency response. I find these on eBay. Most telephone carbon mics are 2 inch diameter.

[W7TFO]

When a carbon mic goes bad, I just toss the element on the floor with a bit of force.

Stir up those little granules, most of the time it works.

73DG

[Opcom]

I used to bang it on the desk, then I was told to 'tap' it on the desk.

[W3SLK]

Opcom said:

I used to bang it on the desk, then I was told to 'tap' it on the desk.

Tap, bang, whatever it takes!

[Opcom]

Never throw away a carbon mike input transformer!

[w8khk]

Tap, bang, whatever it takes!

Yup!  Ya just gotta understand the underlying technology.  No need to replace a perfectly good microphone! 

That reminds me of the engineer, talking to his technician, who was having trouble hearing.  The engineer SLAMMED the phone on the desk five times, then softly spoke "Can you hear me now?"  That phrase has been recycled into the wireless era and beyond.  Recently it was heard, repeatedly, in an advertising campaign.

It is no different than when the ole TV box loses vertical sync; a couple earnest SLAMS on the side set it straight.  Kinda like the self-proclaimed know-it-all, they need to be SLAMMED AROUND quite often too.  The technology is well understood, once you practice applying the age-old approved techniques!

[Opcom]

I'll just leave this here..

[wa2oro]

i use a ww2 navy TCS-12 on am 40 meters when i first got the transmitter i used it with a T-17 military mike it sounded real bad then i switched to ww2 military mike with a modern 2 inch telephone cartridge and got great reports on my audio Greg WA2ORO

[W7TFO]

I've transplanted WECo carbon mics into T-17's several times.  Works FB.

73DG

[wd8das]

I suspect the life and long-term performance of carbon mics depends to some degree on how well they are sealed from the outside air, and the environment where they are used or stored.  I have tested truly antique carbon mics that still sounded good, and others that could barely make any audio. 

My reasoning about the seal and environment comes from a couple cases in which I put the troubled mics in a sealed plastic bag with some desiccant to absorb moisture.  After a couple weeks they sounded much better.

Steve  WD8DAS

[w7fox]

Many Military WWII transmitters use a carbon mic. The Shure 104C is a replacement, but the frequency response is a dismal 300Hz to 4KHz. Telephone carbon microphone cartridges have much better frequency response. I find these on eBay. Most telephone carbon mics are 2 inch diameter.

Not having any experience with carbon mics, I hope someone can answer a question.  I was under the impression that 300Hz to 4KHz was an ideal range for communication.  If not, what is an ideal range?  Thanks.

73,
Fox

[n8fvj]

Many Military WWII transmitters use a carbon mic. The Shure 104C is a replacement, but the frequency response is a dismal 300Hz to 4KHz. Telephone carbon microphone cartridges have much better frequency response. I find these on eBay. Most telephone carbon mics are 2 inch diameter.

Not having any experience with carbon mics, I hope someone can answer a question.  I was under the impression that 300Hz to 4KHz was an ideal range for communication.  If not, what is an ideal range?  Thanks.

73,
Fox

Although 300Hz to 4kHz works, it is not high fidelity and anything close to it.

[w7fox]

So....what is the ideal frequency range of a microphone?

[W7TFO]

Depends on the mic.

A carbon, 300Hz to 4kHz usually

A dynamic, 50Hz to 20kHz overall

A ribbon, 30Hz to 19kHz

A condenser, 20Hz to over the human hearing range.

These are averages, certain examples may be better or worse in responce.

73DG

[KA3EKH]

 I always preferred the narrow bandwidth of carbon elements, Things are what they are and they are not what there not. Almost every military transmitter or transceiver I have worked with over the years is designed with a audio passband of 300 to 3500 Hz or there about. That fits well with a carbon element. Also, the carbon elements develop a huge amount of output compared to dynamic and are low impedance compared to something like a high output crystal with all its issues with high impedance audio circuits.
Done enough work on T-368 transmitters to know one of the first Ham hacks of that transmitter is to bypass the audio pass band filter and then hack the input amplifiers for use with a D-104, I always thought the transmitter sounds best with the original band pass filter, limiter and a M-29 carbon microphone, but that’s me.
Done work on a couple 368 before and that’s always been a sticking point with a lot of Hams being they want a high-fidelity transmitter and I always thought trying to do that with a T-368 was something like putting a saddle on a cow.
If you want to work with military radios the old carbon element microphone is King. And the limited bandwidth is part of the experience, if you want high fidelity go do SDR or something modern.
And a final point about High Fidelity Ham audio, In the AM Broadcast world most broadcasters moved to 5 kHz audio bandwidth years ago, they are all limited to 10 kHz by law. Works for them.
There, that’s the end of my rant for today. Sorry if it appears that sometimes I post too much or have opinions that deviate to far off the subject but sometimes you get started in one direction and before too long are going off into some weird diatribe about something completely different.
Just for the record I do not believe beating microphones on the desk is good for them. Maybe remove the element first and just whack that?

[n8fvj]

I always preferred the narrow bandwidth of carbon elements, Things are what they are and they are not what there not. Almost every military transmitter or transceiver I have worked with over the years is designed with a audio passband of 300 to 3500 Hz or there about. That fits well with a carbon element. Also, the carbon elements develop a huge amount of output compared to dynamic and are low impedance compared to something like a high output crystal with all its issues with high impedance audio circuits.
Done enough work on T-368 transmitters to know one of the first Ham hacks of that transmitter is to bypass the audio pass band filter and then hack the input amplifiers for use with a D-104, I always thought the transmitter sounds best with the original band pass filter, limiter and a M-29 carbon microphone, but that’s me.
Done work on a couple 368 before and that’s always been a sticking point with a lot of Hams being they want a high-fidelity transmitter and I always thought trying to do that with a T-368 was something like putting a saddle on a cow.
If you want to work with military radios the old carbon element microphone is King. And the limited bandwidth is part of the experience, if you want high fidelity go do SDR or something modern.
And a final point about High Fidelity Ham audio, In the AM Broadcast world most broadcasters moved to 5 kHz audio bandwidth years ago, they are all limited to 10 kHz by law. Works for them.
There, that’s the end of my rant for today. Sorry if it appears that sometimes I post too much or have opinions that deviate to far off the subject but sometimes you get started in one direction and before too long are going off into some weird diatribe about something completely different.
Just for the record I do not believe beating microphones on the desk is good for them. Maybe remove the element first and just whack that?

300Hz to 3.500kHz is about a SSB bandwidth. I prefer fidelity on my AM signal from 100Hz to 6000Hz.

[W7TFO]

The fone bands aren't crowded today, so who gives a whit about bandwidth?

One should pay more attention to +peak levels, as most of us have radios that can't resolve them above 120% anyway.

The Commission sure isn't listening, so don't harp up some crap about rules.

If you like PTT sound, go for it.  I don't.

So there!

73DG

[KA3EKH]

Not trying to tell anyone what to do, what to like or whatever. Think that just in the context of carbon microphones and military radios, the sub section that we are in the passband audio is 300 to 3500 Hz. Everyone is free to do what they want, including things like modifying a T-368 to have a flat response out to 20 kHz if they want, good luck with the modulation transformer! But there is also a group of Flatheads like me that are into the original configuration and that’s our thing.

Flathead Definition- Nothing to do with shoes, Ford designed a side valve engine back at the beginning of time that was a favorite of Hot Rod and Rat racers, Primitive design and was soon replaced by better technology but still some embraced that technology long after the world passed it by.
I am a proud Flat header from way back. I view AM and nineteen fifties technology as my bucket T.

 

[w7fox]

Thanks for all the input, it sounds like the main issue is not enough bass from the carbon mic.  I am getting a couple of ART-13 transmitters going, and I was planning to use a dynamic mic.  I'll be sure to try the carbon mic too.
73

[K1JJ]

OK... let me say this about carbon mikes....

Unless we have a great voice for radio, a carbon mic will not do us justice.  I have heard friends who have great voices (that lower bass powerful punchy sound) and sound absolutely FB on a carbon mike.... not hi-fi, but actually pleasing to listen to ALL because of their robust, BC quality voice.  

But then let someone with an average, mid-bassy voice (like mine) speak into the same mic system and they sound like crap.   Bumpy 300-3500 Hz audio NEEDS a punchy voice to do any good.

I believe human voice "quality" is a bell curve.  The majority of men have an average voice with little deep lows or that low punch. This majority have to use EQing and a broadband mic to artificially fill in or cut these desirable audio gaps to achieve "hi-fi audio," whatever that is to you personally.  BUT, many can sound great once audio processing is done. And many guys sound totally different in person as a result.  Like make-up on a woman in a way.

Then there are the outliers who don't even need EQing.  These are the guys who could do voice-overs.  These are the lucky ones who sound great in person or on the air without processing.  And there are many in-between.    Finding the right mic, processing and voice style  is different for everyone since we are all relying on a complex rat's nest of muscles, tendons and brain matter to control it for our own sound. We are all analog voice generators, so we're all different.

So, assuming we have a reasonably "flat" transmitter, based on the bell curve, to achieve hi-fi BC type audio, the majority of us should consider a good mic, like a $100 B1 or whatever, and an EQ.  Add on the limiting and processing later if desired.  The hi-fi mic and EQ are all we really need.    If you want to play the stock ART-13 and carbon mic game, just remember what I said here and don't be disappointed if you never receive a glowing, unsolicited hi-fi FB audio report....

T

[n8fvj]

OK... let me say this about carbon mikes....

Unless you have a great voice for radio, a carbon mic will not do you justice.  I have heard friends who have great voices (that lower bass powerful punchy sound) and sound absoultely FB on a carbon mike.... not hi-fi, but actually pleasing to listen to ALL because of their robust, BC quality voice.  

But then let someone with an average, mid-bassy voice (like mine) speak into the same mic system and they sound like crap.   300-3500 Hz NEEDS a punchy voice to do it good.

I believe voice human "quality" is a bell curve.  The majority of men have an average voice with little deep lows or that low punch. This majority have to use EQing and a broadband mic to artificially fill in the gaps of these desireable audio gaps to achive "hi-fi audio," whatever that is to you personally.  BUT, many can sound great once audio processing is done. And many guys sound totally different in person as a result.  Like make-up on a woman in a way.


Then there are the outliers who don't even need EQing.  These are the guys who could do voice-overs.  These are the lucky ones who sound great in person or on the air without processing.  And there are many in-between.    Finding the right mic, processing and voice style  is different for everyone since we are all relying on a complex rat's nest of muscles, tendons and brain matter to control it for our own sound. We are all analog voice generators, so we're all different.

So, based on the bell curve, to achieve hi-fi BC type audio, the majority of us should consider a good mic, like a $100 B1 or whatever, and an EQ.  Add on the limiting and processing later if desired.  The hi-fi mic and EQ are all you really need.    If you want to play the ART-13 carbon mic game, just remember what I said here and don't be disappointed if you never receive a glowing, unsolicited hi-fi FB audio report....

T

That telephone carbon mic replacement fixes the low bass issue to about 200Hz response.

[K1JJ]

BTW, the punchy, resonant, broadcash-type extreme lows voice peak curve I'm talking about resides somewhere between 75-110 Hz.   And the mid-bass cut is naturally somewhere between about 110 - 200 Hz.  If you ever hear Jay, N3WWL on AM, listen closely and you will hear it personified.

Because as they say, Jay has the "Lowest Voice in America."   :-)

Jay, can you post that old "Lowest Voice" audio file here?

T

[Opcom]

I like to have a choice of a carbon mike and a hi-fi mike.  Experienced the difference many times talking with Dennis W5FRS. Beside the bandwidth difference, the sound of Carbon is different. Makes things more interesting.

Just like the choice of narrow or wider voice filters, one can be put inline after the carbon mike and another used for the braodcast mike.

Every time I read "Courtesy Filter" I smile internally because it is indeed courteous to use a filter that covers the intended bandwidth and matches the mike.

[n8fvj]

I like to have a choice of a carbon mike and a hi-fi mike.  Experienced the difference many times talking with Dennis W5FRS. Beside the bandwidth difference, the sound of Carbon is different. Makes things more interesting.

Just like the choice of narrow or wider voice filters, one can be put inline after the carbon mike and another used for the broadcast mike.

Every time I read "Courtesy Filter" I smile internally because it is indeed courteous to use a filter that covers the intended bandwidth and matches the mike.

Carbon mic I used on a TBX-8 used 12 volts. Hi-fi mics have like 50 millivolts output. You use an amplifier with hi-fi mic on carbon mic transmitter?

[Pete, WA2CWA]

300Hz to 3.500Hz is about a SSB bandwidth. I prefer fidelity on my AM signal from 100Hz to 6000Hz.

Ouch! Definitely PUA (Puckered Up Audio)
300Hz to 3.500Hz - 296.5 Hz audio bandwidth  
Watch the punctuation - it means different things depending on the country.

ed.: And Jim, watch how you quote - I had to fix your previous post  - your response was inside the section you were quoting.