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I'm trying to transfer sound from an electret microphone to my speaker.

I'm copying a simple circuit from the Internet with 5V source from USB and a 1Kohm resistor. However, because I don't have a capacitor here, I removed it from the circuit.

The output is connected directly to the speaker. After finishing it, I tested my project by saying some words into the electret microphone. It can reproduce my voice when I bring my mouth very close to the microphone and talk 'uuuuuuuuu' 'aaaaaaaaaaa'. It can record my breath when I blow to it. But it cannot reproduce any other sound around me or 'real human voice' as a working microphone. What am I doing wrong in my project?

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    \$\begingroup\$ The problem is you removed the capacitor. \$\endgroup\$
    – Connor Wolf
    Jun 24, 2014 at 12:13
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    \$\begingroup\$ And you connected a high impedance microphone directly to a low impedance speaker. \$\endgroup\$
    – Matt Young
    Jun 24, 2014 at 12:24
  • \$\begingroup\$ Is there not an amplification stage for the actual signal? The capacitor is there to block the DC offset from the 9V battery, so you are driving your speaker with a high DC component which means higher continuous current flow through the speak coils. Can you drive a speaker without amplifiying the mic signal? \$\endgroup\$
    – sherrellbc
    Jun 24, 2014 at 12:31
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    \$\begingroup\$ @ConnorWolf What does the capacitor do in this circuit and which type of capacitor should i use for this project ? \$\endgroup\$
    – user46199
    Jun 24, 2014 at 15:11
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    \$\begingroup\$ youtube.com/watch?v=LycH4cXgx7Q \$\endgroup\$
    – Fizz
    Oct 4, 2015 at 1:01

1 Answer 1

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The eletret microphone requires a dc bias to enable it to function. However, you only need to detect the audio (ac) signal to amplify and feed to a speaker. The capacitor blocks the dc bias, whilst passing the audio signal to the amplifier. There must be an amplifier to generate the required power to drive the speaker. The speaker will have a low impedance, typically 8 to 16 ohms. The amplifier must provide the power and a matching output impedance _ else won't work!

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