CapacitorMicrophone

[alisarhangpour]

Hello,
Well, I'm not sure about the name, I mean wether they're called capacitor microphones or something else. anyway,
They're like small metall cylinders, usually found in telephones. Just how to use them? Do they need to be DC Biased?

 

[audioguru]

Old very high quality microphones are called "condenser" microphones and need a DC bias voltage of about 48V to work.
Modern ones are called "electret" microphones and have the 48V built-in inside the electret material. They have a field-effect transistor inside as an impedance converter that needs a voltage of 3V to 9V at 0.5mA. Usually a 10k resistor feeds it from a 3V to 9V battery.
Electret microphones are made with two wires (common source) or with three wires (common drain).

 

[Nigel Goodwin]

Old very high quality microphones are called "condenser" microphones and need a DC bias voltage of about 48V to work.

Such mikes may be old?, but they are still current, with new models regularly released - they are usually used for specific purposes, such as recording vocals in a studio. Almost any audio mixer will have 'phantom power' built-in, which can be switched to send 48V to the mike.

However, you don't get 'condensor' mikes in phones, as suggested they will be electret ones, cheap and low quality (but FAR better than you need for voice!).

 

[audioguru]

Hi Nigel,
Few people can hear the difference between a high quality studio (very expensive) condenser microphone, and a cheap and common electret microphone.
I still have a high quality studio (very expensive) electret microphone that I use to measure speaker systems. Don't ask how I got it. :lol:

Except for its cardioid directional pickup pattern due to ports in it sides (and the nice deep vocals when upclose) it sounds exactly like the cheap omni-directional electret mics I salvage from toys.

 

[Nigel Goodwin]

Hi Nigel,
Few people can hear the difference between a high quality studio (very expensive) condenser microphone, and a cheap and common electret microphone.
I still have a high quality studio (very expensive) electret microphone that I use to measure speaker systems. Don't ask how I got it. :lol:

Except for its cardioid directional pickup pattern due to ports in it sides (and the nice deep vocals when upclose) it sounds exactly like the cheap omni-directional electret mics I salvage from toys.

Have a look at **broken link removed** where he explains the limitations of cheap electret mikes, and how to overcome them.

 

[audioguru]

Hi Nigel,
I would never use an electret mic with a supply voltage as low as 1.5V.
Also, I would never go near a sound level higher than 110dB!
Actually, I measured peak sound levels reaching 125dB (!!) in a disco years ago, and the meter I used had a real condenser mic.

I used pro-quality Audio-Technica electret mics and copied their electronic circuits, just like Rod Elliot copied Panasonic's circuits.

National Semi have a new preamp IC they hope will replace the lousy Fet in cheap electret mics. Their LMV1031 is in a microscopic "4 bump" package.
It has too much built-in gain to handle sound levels of 110dB or more but its very low output impedance and high level might drive just an unshielded twisted pair. :lol:

 

[Dr.EM]

I built a mic using this circuit just yesterday, from spare parts only.

http://www.mp3forkidz.com/mic/phantxy.html

I got 12 electrets from ebay not long back, and the rest of the parts I have around. You can see it uses the linkwitz mod to help its performace at higher SPLs. I'm not sure how successful that aspect of it is, tests measured that its only able to handle very slightly more, however, it is not a Panasonic capsule and so it may not have been very suitable for it. I would think its acceptable for drum overhead level and mabye for a guitar amplifier, so long as the amp isn't on full :lol: . The main reason I did it was just to see how small I could make it (pointless really I know). My old ones do have the circuitry in the tube, but this one is around 8cm shorter, even though the circuit is more complex.

**broken link removed**

**broken link removed**[/url]

 

[audioguru]

You have a nice balanced mic circuit, Dr. EM.

 

[Dr.EM]

Yeah, that design is exactly what I was looking for. A balanced low impedance output one which utilises the linkwitz mod.

 

[Nigel Goodwin]

Yeah, that design is exactly what I was looking for. A balanced low impedance output one which utilises the linkwitz mod.

OK for recording, when you can place a mike reasonably far away from the drums - but for multiple miking a drum kit for a gig, dynamic mikes have much better high level response :lol:

I use four of my cheap Behringer mikes, bass drum, snare/hi-hat, and two overheads - lack of money is VERY much the driving force 8) but they perform pretty well, and you can't beat them for the money!. Along with two vocal mikes, this leaves me with one spare mike - but no spare channels on my mixer/amp (4 drum mikes, two vocal mikes, guitar DI, bass DI, keyboard, CD player).

 

[audioguru]

One time I connected 8 electret mics in parallel, fed them enough current, turned up the gain and they all worked fine.

 

[Dr.EM]

Yep, always need to use dynamics for unnatural sound pressures like inside a bass and snare mics, the one on the bass has to be a special one for studio recording, designed for the job. I have 3 of these electret mics now and one dynamic, my dynamic is very poor, if I get a real drum kit sometime or do any louder recording, i'll bear those behringers in mind. You should get improvements in your sound using even electret condensers for overheads, dynamics are never recommended for overhead use.

 

[Nigel Goodwin]

Yep, always need to use dynamics for unnatural sound pressures like inside a bass and snare mics, the one on the bass has to be a special one for studio recording, designed for the job. I have 3 of these electret mics now and one dynamic, my dynamic is very poor, if I get a real drum kit sometime or do any louder recording, i'll bear those behringers in mind. You should get improvements in your sound using even electret condensers for overheads, dynamics are never recommended for overhead use.

You use what you've got :lol: Check specific drum mike sets, they mostly are all dynamic mikes, no electrets!.

They sound fine!, bear in mind it's only a question of giving a bit of boost to the drum levels.

 

[Dr.EM]

The convention is that all close mics are dynamic (snare, tom mics, hi-hat and definately bass drum) but overheads are always condensors, though they arn't always supplied in the sets. The reason for not using dynamics as overheads comes down to thier reduced sensitivity, and more importantly "proximity effect" aswell as not being so effective at higher frequencies. With extra gain and providing the rest of the kit is close miked well, I expect good enough results can be achieved.

 

[Nigel Goodwin]

The convention is that all close mics are dynamic (snare, tom mics, hi-hat and definately bass drum) but overheads are always condensors, though they arn't always supplied in the sets. The reason for not using dynamics as overheads comes down to thier reduced sensitivity, and more importantly "proximity effect" aswell as not being so effective at higher frequencies. With extra gain and providing the rest of the kit is close miked well, I expect good enough results can be achieved.

Just asked my daughter what they are using on her sound engineering course? - they are using D112 for bass drum, SM58's for snare and hi-hat, and C1000 condensers for overheads. Notice how they are called 'condensors' and not 'capacitors'?, I wonder why?.

Mike sensitivity isn't much of a concern for drum mikes, even when using dynamic mikes as overheads - there's a MASSIVE amount of volume from a drum kit :lol:

 

[Dr.EM]

Yeah, drum kits are very loud up close. C1000 must be a popular choice, we use them at college for overheads, and as a general purpose mic. We use SM57 for close mics, the SM58 is similar only more tailored to vocals. We also use that D112. Capacitor is generally the American term, I normally call them condensers myself, seems less confusing.

 

[Nigel Goodwin]

Yeah, drum kits are very loud up close. C1000 must be a popular choice, we use them at college for overheads, and as a general purpose mic. We use SM57 for close mics, the SM58 is similar only more tailored to vocals. We also use that D112. Capacitor is generally the American term, I normally call them condensers myself, seems less confusing.

Apparently there's almost no difference between an SM57 and an SM58, I seem to recall a webpage that showed you how to convert them?.

'Capacitor' replaced 'condensor' back in the 1960's in electronics, but the motor trade have never changed, and it looks like the audio trade hasn't either :lol:

 

[alisarhangpour]

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