How to increase the microphone sensitivity ?

[juno93]

Microphone Sensitivity

Hello ! I am trying to make a conferencing sytem using ordinary condenser pc microphones, a laptop/pc and an amplified pc speaker. I connected the microphones in parallel and connected them into the mic port of the pc. The problem is, the user has to speak very near the microphones to be heard. Is there any way to increase the sensitivity of the microphones so that they can speek freely without going very near the microphones? Thanks a lot!

 

[Regnum]

Re: Microphone Sensitivity

What happens when connecting only one mic ?

 

[barrybear]

Re: Microphone Sensitivity

You could build a small preamplifier for each condenser mic .

Bring the amplified outputs into the line in socket via a small mixer.

In the long run I think you will find this is the best way. I would not recomend connecting mics of enytype together directly.

Barrybear

 

[atmaca123]

Re: Microphone Sensitivity

You could build a small preamplifier for each condenser mic .

Bring the amplified outputs into the line in socket via a small mixer.

In the long run I think you will find this is the best way. I would not recomend connecting mics of enytype together directly.

Barrybear

Can you suggest any preamp circuit schematics

 

[batdin]

Re: Microphone Sensitivity

By the way,the MIC in of the sound card is MONO!
The one connector is for the signal,the other is for +5V supply of the microphone.
So just one preamp is needed,if any (most soundcards have +20db boost of the mic in).

 

[juno93]

Re: Microphone Sensitivity

The sound level is the same whether one mic is used or all seven at the same time. The sound quality is also good when the speaker's mouth is 1-2 inches away from the mic and drastically fades when the distance increases. I will try to install a preamp in between the mics and the pc. I am already using the 20db boost from the soundcard. Will report on changes later. By the way, can anyone tell me if there are simple schematics for this preamp that I can build myself? Thanks a lot to all of you who replied.

 

[artem]

Microphone Sensitivity

Following could improve your application :
a. Use auto gain control amp for mic amp
b. use directional mic to reduce noise
c. Use high pass filter to cut low freq environment noise. It is assumed that human voice freq starts from 300 Hz
d. It is proved that speech stereo recording significantly improves speech recognition . So, if possible use stereo mics . I so one article , where speech recognition was imrpoved when using signal phase shift in headphones . If this is true for speakers you can use mono mic with stereo emulated speaker side .

 

[batdin]

Re: Microphone Sensitivity

If You love simplicity as much as I do,you should use the +5V supply provided by the microphone connector of PC to power a low-current opamp such as MCP606.
The internal impedance of the source is 5kohms,that's why the opamp should be economic.
The same power source should be used to power the microphone,too.
The circuit is not too complex ; I will help You if asked.

 

[juno93]

Re: Microphone Sensitivity

batdin,

I am from the Philippines where resources are way too prohibitive. That is the basic reason why I intend to use the cheapest pc mikes available in my inventory. I would appreciate if you can help me in this matter. Thanks!

 

[batdin]

Re: Microphone Sensitivity

I understand,I am from a poor country,too.
Nevertheless MCP606 costs only 0.7$...
I apply here a circuit that should work also . It is built using more standard components.
Be careful to connect it properly for the one mic input of the PC is actually +5V and the other is the real mic input.
Max.gain should be around 20-30.
P.S. Sorry for the deplorable picture

 

[juno93]

Re: Microphone Sensitivity

Batdin,

Thanks for the reply! Have a few questions. (attached an JPG file to explain) Did I get the schematic right? What is 1ms and Rb ? Hope you can enlighten me on this. Thanks a lot for your patience.

 

[batdin]

Re: Microphone Sensitivity

First,I apologize for my terrible handwriting.It is not 1ms,it is 1M5 ; i.e. 1.5 MOhms.This value is approximate since I don't know the exact H21(beta) ot the transistor.Rb also depends on the microphone V-A curve.You'll have to find the value experimentally.
On the left side of the picture (input) is the microphone itself;the right side (output) is connected to the microphone connector of the sound card.It is stereo and has three wires one of which is ground.
It is possible that your microphone has a stereo connector,too.Don't worry,just short-circuit the active ends.They are most probably connected together anyway.
What I described applies to a relatively modern sound card (after 2000).I don't know if there used to exist cards of different types which have a different way to connect to a microphone.
All soundcards that I have seen have a stereo microphone input.However only the one active connector is really input; the other supplies +5V through 5kohms resistor to the electrete microphone.My idea was to use this feature and power up an additional amplifier.

!!!!! By the way,the input capacitor is 47nF,not 47uF.It is important to place the right one .

That's all for now ; don't worry to ask me again if I did not explain something.