Ribbon microphone.

                                    Ribbon microphone

In ribbon microphone aluminium ribbon is used which acts as a diaphragm as well as coil when the ribbon is placed in magnetic field is made to move at right angle to the magnetic field by force of sound pressure there is change in magnetic flux through the ribbon conductor due to this change of magnetic flux and EMF is induced across the ribbon this EMF proportional to the rate of change of kinetic flux which is proportional to the force of sound waves striking the ribbon.

Q - Why ribbon microphone  is velocity microphone ?

when the sound wave strike the ribbon and EMF is induced in it because induced EMF is proportional to velocity of ribbon it is also called velocity microphone.

Characteristics 

* sensitivity is low .

* because of low mass of ribbon frequency response is very good almost flat about 20hz to 12khz.

* output impedance is very low less than < 0.5.

* distortion is less than 1%.

*signal is high about 50dB.

Applicatin

* suitable for broadcasting purpose .

* suitable for dram and theater.

                                   Crystal microphone

A crystal microphone is based on the principle of piezoelectric effect. when the sound wave strike on the  diaphragm

it  vibrates and compress the crystal. In case o rarefaction converse take place and crystal is standard and is under tension due to this compression and rarefaction. a varying potential difference is generated which is proportional to the applied mechanical  pressure by sound wave the  crystal elements are connected in such a way that the  potential difference developed elements are added up and get good output voltage.

Characteristics

* distortion is low , about 1%.

* omnidirectional.

* output impedance is very high , about 1Mohm.

* signal to noise ratio , about 40dB.

* flat  frequency response from 80 to 

   8khz.

* sensitivity is good , about 50 mv for sound pressure of 0.1 pa.

 

 Application

* used for recording system.

* used for mobile communication.

condenser microphone pdf

                                 Condenser microphone

when the sound wave strike the diaphragm it moves compression increases capacitance and rarefaction decreases in capacitance change in capacitor results in change in voltage since, charge on capacitance remain same.

                                 V = Q  /  C             ........1 equation

              

                           C =  kA / D   ............2 equation

( k = dielectric constant)

( A = area of capacitor )

( D = width of two plates )

( Q = charge held by capacitor )

                                      equation 2 value put the equation 1.

                                                     V = QD / kA

Q, k, A are constant for capacitor microphone then , Q / kA = K

                  then , V = K

 Differentiating     ds V  = K  ds  D

Thus, variation in output voltage depend on charge in distance between the plates which entered depends on the pressure variation due to sound wave.

Characteristics 

* distortion is low , about 1%.

* omnidirectional.

* output impedance is very high, about 100 ohm,s.

* signal to noise ratio is high , about 10dB.

* very good frequency response  from 40hz to 15khz.

* sensitivity is low therefore it has in built amplifier .

Application

* used as standard microphone for calibrating  other microphone.

* used in sound level meters.

* used in professional high fidelity recording.

condenser  micro