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3_microphones

# 3_microphones - M i c ro p h o n e s Juan P Bello Early...

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Microphones Juan P Bello

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Early recording Early recording and reproduction was entirely acoustic Sound was captured by a horn terminated on a diaphragm that vibrated in sympathy with the sound The diaphragm was attached to a stylus which cut grooves on foil or wax Performers had to clutter around the horn. Little control of individual levels
Sound in electrical form Sound in electrical form can be amplified, mixed and recorded. We can convert the acoustical waveform into an electrical waveform of the same shape Amplitude becomes voltage (V), and air particle motion becomes electrical current (I) - electrons playing the role of air particles. The current’s direction of flow changes with cycles of compression/rarefaction creating an alternating current (AC) The flow of electrons in a conductor is impeded by a certain amount of resistance (R) The relationship between V, I and R is regulated by Ohm’s law: V = I × R. Their relationship with Power (W) is: W = I 2 × R = V 2 /R In AC systems resistance is replaced by impedance (which also includes reactance). Impedance is frequency dependent

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Electro-magnetic induction Electromagnetic transducers convert mechanical motion (as produced by, e.g., an acoustic wave) into an electrical signal An electrical current is induced (and voltage is produced) if: (i) a static conductor is situated in a changing magnetic field, or (ii) a conductor moves in a static magnetic field This phenomenon is characterized by Faraday’s law of electromagnetic induction ( http: //msdaif . googlepages . com/demo_faraday ) The direction of motion (perpendicular to the lines of flux) controls the direction of current flow in the conductor (e.g. a wire). Back and forth movements result in an alternating current (AC) related in frequency and amplitude to the wire’s motion Magnet Magnet N S Electro-magnetic field wire Motion of wire
Microphones Microphones are transducers that convert acoustical energy into electrical energy.

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3_microphones - M i c ro p h o n e s Juan P Bello Early...

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