Using the loud speaker in different way!!

[anuk07]

Actually i need to charge a capacitor with a speaker by speaking on to it or say using the speaker as microphone simply..so tell me what are the specification for certain voltage level output from the speakers when used as a voltage generator in accordance with the variation of the voice signal...

[Dr.EM]

As the voice coil impedance of most speakers is very low (compared to that of a dynamic microphone), ie 8ohm compared to 600ohm, I'd expect the output voltage to be lower but the current drive to be higher. A step up transformer may be required, you can obtain small 8ohm to 1k types which might be useful but it depends on the value of capacitor you'd be charging and the voltage it needs to be charged to. A rectifier is also needed, a full bridge will make most sense for this.