pdf for ppt in microphone short note.

                                           MICROPHONE

A microphone is a transducer which convert acoustical energy into electrical energy.

In microphone amplitude of electrical signal are proportional to intensity of sound wave.

working principle

* When a user sound wave created by voice carry energy towards the microphone.

* In side the microphone  the diaphragm moves back forth when the sound wave hit its.

* The coil attached the diaphragm move back forth as well.

* The permanent magnet attached to the coil produce in magnetic field that cuts through the coil as the coil moves back and forth and electric current flow through it.

* The electric current flow out from the microphone to an amplifier or sound recording device.

characteristics of microphone

*Sensitivity

sensitivity of microphone is its ability to pick up the weakest sound. This can be measured by voltage obtained at the output of mice at given sound pressure.

       It is expressed  in ( mill volt /micro bar ) Or in dB.

sensitivity dBv = 20 log (sensitivity / output )

*Signal to noise ratio

SNR is ratio of signal power to noise power corrupting the ratio compare the level of  a desire signal to the level of noise.

      SNR = output in presence of noise / output when noise is not present.

Frequency response

The frequency response of a microphone is define by the bandwidth of audible frequency in the output of microphone.

Distortion 

*NON- liner distortion

Non liner distortion is that the relative amplitude of different frequency in the electrical output is not same as the sound wave.

*Frequency distortion

It means that some frequency is not present in the sound signal as appear in the input.

*Phase distortion

It means that enter phase relationship between different frequency component in the output is not same as in the input.

Directivity 

Directivity is defined as the ratio of actual output. when placed in direction which an omnidirectional microphone in the same direction would have given keeping the sound intensity constant .  

Output impedance

The output impedance  of microphone is expressed in Ohm.

It is an important parameter which is used to determine which type matching transformer is needed to transfer the power efficiently from microphone to transmission line than to the amplifier.

 

            Z2 / Z1 = ( N2 /N1 )^2

( Z is a impedance of transformer )

( N is a number of turn in winding for transformer )