Alpha College of Engineering & Technology Microphones Prepaid by: Patel Yogen K. ( ) Desai Kishan G. ( ) Dave Bhoomika R. ( ) Guided by: Aneri Pandya. Academic Year:

Type of Microphone  Moving-coil Microphone  Ribbon Microphone  Crystal Microphone  Capacitor Microphone  Carbon Microphone

Moving-Coil Microphone  The moving-coil microphone uses the principle of electromagnetic induction.  When sound pressure variation move a coil placed in a magnetic field, there is a change of magnetic flux passing through the coil.  An emf is,therefore, induced in the coil and this emf forms output of the microphone.

Moving-coil Microphone Figure

Moving-coil Microphone Working Moving-coil microphones are also called Dynamic. Sound waves hit the diaphragm of the microphone. The very sensitive diaphragm vibrates. Vibrations move the coil of wire attached to the diaphragm. The coil is suspended around a magnet. Magnets have a naturally occurring magnetic field. As the coil moves, it disrupts the pattern of the magnetic field. As the coil cuts across the magnetic field lines, an electrical current is induced in the coil. This is an example of electromagnetic principles.

Moving-Coil microphones Characteristics  Sensitivity is 90 dB below 1 volt.  Signal-to-noise ratio is 30 dB.  Frequency Response is 60 Hz to 8000 Hz for ±1 dB.  Distortion is Less than 5%.  Directivity is omnidirectional.

Moving-Coil microphones Application  Mostly live situations, but they are also used a lot in the studio.  Close microphone applications (1-12 inches)  Snare drums, guitar amplifiers, kick drum, vocals and any instrument that can play loud.

Ribbon Microphone  In a moving-coil microphone, high frequency response is poor because of the mass of the diaphragm.  Mechanical mass is equivalent to electrical inductance, and this attenuates the higher frequencies.  Hence, to increase the frequency response for high audio frequencies, a very light aluminum ribbon is used in place of adiaphragm and coil assembly.  The ribbon acts as a conductor as well as a diaphragm.  Such a microphone is called a ribbon microphone.

Ribbon Microphone Figure

Ribbon Microphone Working  Ribbon microphone are considered to be very sensitive and accurate.  They work by suspending a thin metal foil in a magnetic field.  Just like the controlled reluctance elements, moving the ribbon will change the magnetic field.  The ribbon is very thin and folded up so it moves very easily when sound hits it, but they are very delicate and expensive to make and repair.

Ribbon Microphone Characteristics  Frequency response is 20 Hz to Hz for ±1 dB.  Impedance is 200 Ὠ.  Sensitivity is 3 µV or 110 dB below 1 V.  Signal-to-noise ratio is 50 dB.  Directivity is bi-directional.  Distortion is Low about 1%.

Ribbon Microphone Application  In cardioids form it is suitable for group discussions and orchestra.  It is very suitable for dramas.  Music, Broadcast.

Crystal Microphone  A crystal microphone is based on the principle of piezoelectric Effect, which produces difference of potential between the opposite faces of some crystals when these are subjected to mechanical pressure.  The crystals which show this effect are quartz, tourmaline, Rochelle salt and ceramic.  Rochelle salt has high temperature of more than 50° C in outdoor use.  Ceramic is most suitable for crystal microphone as it is not susceptible to moisture and can also withstand high temperatures up to 100° c.

Crystal Microphone Figure

Crystal Microphone Working  When there is a sound wave of compression, it compresses the crystal.  In case of rarefaction, the converse takes place and the crystal is extended and is under tension.  The crystal elements are connected in such a way that the potential difference developed in the elements are added up and we get a good voltage output for feeding to the amplifier.

Crystal Microphone Characteristics  Sensitivity is about 50 mV.  Signal-to-noise ratio is high about 40 dB.  Frequency response is 100 Hz to 8000 Hz for ±1 dB.  Distortion is Low, about 1%.  Directivity is Omnidirectional  Output Impedance is High, about 1M Ὠ.

Crystal Microphone Application  Home recording systems  Amateur communication  Mobile communication

THANK YOU