how to reduce electret microphone sensitivity

[panneerrajan]

HI,

I have used electret mic and its output connected to 2.2k pullup resistor with vcc3.3V and series 10uF Alu.El. Capacitor than its connected to CPU MIC input channel
It has sensed 5 meters voice also, so i received unwanted noise. But my requirement voice to be sense maximum 1 meter only.
How to reduce mic sensing level? Pls suggest me

Rajan

 

[FvM]

As long as the signal isn't overloading the microphone and causing distortion, there's no purpose of reducing the microphone sensitivity. Just use less amplifier gain.

An electret microphone will hardly be overloaded from a voice in one meter distance.

 

[panneerrajan]

Thank you
Please find mic interface circuit,
this is used for call box application, Box amplifier used 3W only,
If i called from my call box to PC/server i hear long distance sound also in PC**broken link removed**. that why i need to reduce Mic. sensitive in call box side
PC side i used headset

 

[FvM]

You can reduce the "pull-up" resistor, actually a load resistor for the electret microphone amplifier transistor. Sensitivity is reduces linearly with the resistor value.

 

[panneerrajan]

You can reduce the "pull-up" resistor, actually a load resistor for the electret microphone amplifier transistor. Sensitivity is reduces linearly with the resistor value.

Hi,
I will check and let you know,
Pull up VCC 3.3V is enough or need to reduce?

 

[Audioguru]

What is a "call box"? Is it a speakerphone?
Why is the mic preamp circuit of the call box too sensitive for your electret mic? Because it uses a different kind of mic like a dynamic (coil and magnet) mic?

Your attachment does not work maybe because there is no space between it and the word "PC". I need to hear the attachment because you did not describe "long distance sound". Is it an echo? is it reverberation? Is it acoustical feedback howling?

 

[panneerrajan]

Yes, it's like VOIP based speaker phone
I am using Electret condenser type Mic. only
actually call box Mic. should sense voice Max. 1 meter distance only . But my call box mic sense upto 5 meter sound also,
So I want reduce my Mic. sense distance, Bze it has sensing unwanted signals

Also i received echo in PC (computer) side, PC side i used headset interface only.
No Echo in Call box.
Our call box MCU (controller module) have inbuilt audio codec chip for echo cancellation. But still we received echo. if i reduce amplifier volume level in call box- echo also reduced, but that volume level not enough my application.

Thank you

 

[Audioguru]

If you speak into your headset mic and hear your own echo then the sound comes out the speaker in the speakerphone and into its mic then back to you if the echo canceller is not working and if the speakerphone mic is too sensitive or if the speaker is too loud.

Here is an attenuator for the electret mic in the speakerphone:

 

[panneerrajan]

If you speak into your headset mic and hear your own echo then the sound comes out the speaker in the speakerphone and into its mic then back to you if the echo canceller is not working and if the speakerphone mic is too sensitive or if the speaker is too loud.

Here is an attenuator for the electret mic in the speakerphone:

Yes, how to connect attenuator to mic and reduce mic. sensitive. i didn't find attenuator

 

[FvM]

The "attenuator" is a simple resistor, review the previous post. An even more simple way was suggested in post #4.

 

[Audioguru]

I recommended loading the electret mic with an AC voltage divider because the datasheets for some electret mics recommend using only 1.5V and a 2.2k resistor to power it. With the 3.3V supply if lower resistor value is used to power it then its current and its heating might be too high for its tiny Jfet enclosed inside. A few electret mics have a maximum allowed voltage of only 2VDC.

 

[panneerrajan]

The "attenuator" is a simple resistor, review the previous post. An even more simple way was suggested in post #4.

Hi, I tried with low value resistance, but no improvement.
i have covered Mic. with some mess, then sensing level was reduced

which Mic. is suitable for speaker call box application electret condenser OR dynamic Mic?
Please suggest

Thank you

 

[Audioguru]

Hi, I tried with low value resistance, but no improvement.

Your schematic is not clear. Is the resistor that powers it 2.2k ohms? Then a 330 ohm resistor as I showed reduces the mic sensitivity about 8 times which is -18dB. Maybe the input of the mic preamp already has a low resistor value?

which Mic. is suitable for speaker call box application electret condenser OR dynamic Mic?

Digikey lists 733 different electret mics, most are inexpensive and have excellent performance. They stock only one dynamic mic and it is very expensive.
I have worked with many intercom systems and speakerphones. All used an electret mic except the cheap awful sounding intercom on the gas pump at a gas station that uses the dynamic speaker as its microphone.

In your first post you said, "I have used electret mic ...." then did you replace an existing mic or did you make the call box? Can't you reduce the gain of the mic preamp?

 

[panneerrajan]

Your schematic is not clear. Is the resistor that powers it 2.2k ohms? Then a 330 ohm resistor as I showed reduces the mic sensitivity about 8 times which is -18dB. Maybe the input of the mic preamp already has a low resistor value?


Digikey lists 733 different electret mics, most are inexpensive and have excellent performance. They stock only one dynamic mic and it is very expensive.
I have worked with many intercom systems and speakerphones. All used an electret mic except the cheap awful sounding intercom on the gas pump at a gas station that uses the dynamic speaker as its microphone.

In your first post you said, "I have used electret mic ...." then did you replace an existing mic or did you make the call box? Can't you reduce the gain of the mic preamp?

Hi,
I am using electret mic only, I wanted to confirm if I can choose electret mic. for speaker phone (like VOIP based call box) application. I didn’t use any preamplifier. After biasing circuit, with one series capacitor I directly connected to Micro processor (MCU) MIC input channel. Pls. find attached image

Electret microphone datasheet mentioned operating voltage is 2VDC and output impedance 2.2Kohm, But I provided 3.3V VCC, if I making 2VDC source can I use zener diode or two dropping (1n4007) diodes, Also let me know attenuation resistor value. Please find the attached image

Image2= with Zener


Image 1 = Diode drop voilt


How to calculate attenuation network resistor value w.r.t. to dB (sensitive)

Thank you for your support
Rajan

 

[c_mitra]

You can reduce the output of the microphone by (i) reducing the applied voltage (upto 0.8V, I believe) and/ or (ii) by reducing the load resistor (upto 1k perhaps). They are usually operated with a 1.5V button cell that lasts till the battery voltage goes down to 0.8V.

 

[Audioguru]

I have seen and designed many circuits with electret mics and most are powered by a 9V battery. The Jfet in the mic draws 0.5mA so the resistor powering it is 10k ohms. The 9V is filtered by a series 1k resistor and a 10uF capacitor. Then the mic has 3.5V across it when the battery is new. I have never seen a low voltage zener diode or some series diodes reducing a voltage like you have.

Your circuit has R2 killing the DC voltage across the mic, it should be at the output of the output capacitor to attenuate the AC signal from the mic.

The attenuator is simply a voltage divider of the 2.2k output impedance of the mic circuit (mic parallel with the resistor powering it) to the extra resistor: 240/(2.2k + 240)= 1/10th.

What kind of cpu do you have with too much gain and an AC mic input??

 

[panneerrajan]

Hi,

I want to provide Mono audio output and I have chosen Mono audio amplifier IC, But my audio source have provision for stereo (Headphone-L & Headphone-R,) As per attached image Can I loop two signal (Headphone-L & Headphone-R,) for making single output? Is it creating any problem? Please suggest



Also I plan to provide fixed volume control instead of trim pot. Which GND reference should provide for Resistor divider network (GND or AGND_AUDIO). Please find attached image and suggest me

Thank you
Rajan

 

[c_mitra]

I want to provide Mono audio output and I have chosen Mono audio amplifier IC, But my audio source have provision for stereo (Headphone-L & Headphone-R,) As per attached image Can I loop two signal (Headphone-L & Headphone-R,) for making single output? Is it creating any problem?

Stereo signals (L and R) can be combined (L+R) to give mono output. However, to prevent unwanted loading, you need to add about 10K before you connect them together. Use two 10K resistors before you connect L and R. Use the amplifier level control to reduce output; if you decrease the input signal, you will be adding unwanted noise.

 

[panneerrajan]

Stereo signals (L and R) can be combined (L+R) to give mono output. However, to prevent unwanted loading, you need to add about 10K before you connect them together. Use two 10K resistors before you connect L and R. Use the amplifier level control to reduce output; if you decrease the input signal, you will be adding unwanted noise.

Hi,

Instead of resistor divider network for audio volume control, could you please share Amplifier level control concept/circuit.

Thank you
Rajan

 

[Audioguru]

The AGND is the computer's audio ground that should be connected to the shields of your audio cable that connects to the audio ground of your amplifier.
As C_Mitra said, do not short together the stereo outputs of the computer, connect 10k resistors in series with each one then short the free ends of the resistors together to make mono.

Why did you talk about using a trimpot that we do not see on a schematic? Why do you show a resistor divider? Doesn't your computer have a volume control? Doesn't your amplifier have a volume control? You will have too many volume controls.