Fundamentals of Audio Production. Chapter 2 1 Fundamentals of Audio Production Chapter Two: Capturing Sound Electronically

Fundamentals of Audio Production. Chapter 2 2 Converting Sound into Electricity Because sound is essentially a vibration, vibrations must be converted into electricity. Sound is converted into electricity using transducers. Transducers convert one form of energy into another form. In this case: physical energy into electrical

Fundamentals of Audio Production. Chapter 2 3 Understanding electricity Electrical current flow is simply electrons in motion in a conductor. Electrons are negatively (-) charged subatomic particles in all substances. Electrons orbit the nucleus of the atom. Electrons are held in orbit by the electrical attraction of positively (+) charged protons in the nucleus.

Fundamentals of Audio Production. Chapter 2 4 Understanding electricity Because particles with similar electrical charges repel one another, electrons forced to move into the orbit of adjacent atoms will dislodge electrons there, where they will move to the next adjacent atom and dislodge electrons there, and so on…

Fundamentals of Audio Production. Chapter 2 5 Understanding electricity Substances that have more electrons than protons, have “free electrons” Free electrons are easily dislodged from their orbits Substances with free electrons are called “conductors.” The more free electrons in the substance, the better conductor it is – the more easily current will flow.

Fundamentals of Audio Production. Chapter 2 6 Understanding electricity Because electrons do have some mass, there is an opposition for them to leave their orbits. This reluctance to move is called “resistance.” Good conductors, with more free electrons, have lower resistance.

Fundamentals of Audio Production. Chapter 2 7 Understanding electricity When the electrons flow only in one direction, the current flow is called “direct current,” or DC. When the electrons flow in both directions, the current flow is called “alternating current,” or AC. Once sound is converted into current flow, audio signals are AC.

Fundamentals of Audio Production. Chapter 2 8 Transducers Transducers are used to convert vibrating air molecules into electrical current flow. Transducers use principles of electromagnetism, electrostatics, and physical characteristics of some substances to convert vibrations into electricity.

Fundamentals of Audio Production. Chapter 2 9 Transducers Common types of transducers –Dynamic –Condenser (electrostatic) –Ribbon –Piezoelectric –Carbon

Fundamentals of Audio Production. Chapter 2 10 Dynamic transducer

Fundamentals of Audio Production. Chapter 2 11 Dynamic transducer Sound pressure waves cause the diaphragm to vibrate The vibrations in the diaphragm are transferred to the coil As the coil moves within the magnetic field of the permanent magnet, current is induced to flow in the coil

Fundamentals of Audio Production. Chapter 2 12 Dynamic transducer Positive air pressure creates positive voltage Negative air pressure creates negative voltage

Fundamentals of Audio Production. Chapter 2 13 Dynamic transducer Dynamic transducers are physically rugged and will withstand rough handling and field use Dynamic transducers are inexpensive to manufacture

Fundamentals of Audio Production. Chapter 2 14 Ribbon transducer

Fundamentals of Audio Production. Chapter 2 15 Ribbon transducer A thin strip of corrugated metal foil is suspended under tension within a strong magnetic field Sound pressure waves cause the ribbon to flex within the magnetic field The movements of the ribbon within the magnetic field induced current to flow along the ribbon

Fundamentals of Audio Production. Chapter 2 16 Ribbon transducers are delicate and will not withstand rough handling High sound pressure levels or bursts of wind will cause the ribbon to permanently sag Ribbons are not well-suited to field use Ribbon transducer

Fundamentals of Audio Production. Chapter 2 17 Condenser transducers

Fundamentals of Audio Production. Chapter 2 18 Condenser transducers Two plates are placed in close proximity, but separated by a thin air gap –One plate is the diaphragm –One plate is called the back plate Voltage (phantom power) is applied to one of the plates Sound pressure waves cause the diaphragm to vibrate

Fundamentals of Audio Production. Chapter 2 19 Condenser transducers As positive air pressure moves the plates closer together, more current will flow away from the back plate. The electrons on the diaphragm repel the electrons on the back plate. As negative air pressure allows the plates to rebound, less current will flow away from the back plate.

Fundamentals of Audio Production. Chapter 2 20 Condenser transducers Condenser transducers require a power supply –May be in the mixing console –May be from a battery –May be from an external power supply Condenser transducers are capable of wide flat frequency response.

Fundamentals of Audio Production. Chapter 2 21 Carbon transducers Telephone handset carbon transducer Carbon Piston

Fundamentals of Audio Production. Chapter 2 22 Carbon transducers A receptacle is filled with carbon, which will conduct current Air pressure waves cause the diaphragm to vibrate The diaphragm is attached to a piston, which compresses the carbon during the positive phase of the audio wave As the carbon is compressed the current flow increases

Fundamentals of Audio Production. Chapter 2 23 Carbon transducers Carbon transducers tend to reproduce limited bandwidth Carbon transducers are not commonly used for high fidelity audio, but are still used in voice circuits (telephones, intercoms, etc.)

Fundamentals of Audio Production. Chapter 2 24 Piezoelectric transducers

Fundamentals of Audio Production. Chapter 2 25 Piezoelectric transducers Certain mineral crystals will generate a current when stressed Sound pressure waves push the diaphragm which in turn causes the crystal to flex The vibrations in the crystal induce current flow

Fundamentals of Audio Production. Chapter 2 26 Piezoelectric transducers Piezoelectric transducers tend to have poor bandwidth Crystal transducers are used in some inexpensive microphones The Shure™ “Green Bullet” is a popular crystal microphone for harmonica