Audio Fundamentals Test #2

Transduction

Converts a signal in one form of energy to a signal in another form of energy

Electromagnetic Induction

A current produced because of voltage production due to a changing magnetic field

Electromagnetic Force

Type of physical interaction that occurs between electrically charged particles

Transducers - Ear

• From: Sound waves in air

• To: Nerve impulses in the brain

Transducers - Microphone

• From: Sound waves in air

  • To: Electrical signals in wires

Transducers - Loudspeaker/Record Head

• From: Electrical signals in wires

• To: Magnetic flux on tape

Transducers - Record/playback head/ Analog Tape

• From: Magnetic flux on tape

• To: Electrical signals in wires

Transducers - Phonograph Vinyl Records

• From: Grooves cut in disk surface

• To: Electrical signals in wires

Transducers - Optical Sound on Film

Means of storing sound recordings on transparent film

Electrical Current (I)

The flow of electrons

Amps (A)

Rate of flow of electrons in water  

Electro Motive Force (EMF)

The pressure creating the current

Volts (V)

Electric pressure creating the current

Resistance (R)

Restricts the flow of the free electrons

Ohms (Ω)

Tightens or loosens the current

Power (P)

The amount of energy in the flow of electrons

Watts (W)

Measurement of how much work is being done

Decibel (dB)

Unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale

dB-SPL

Used in loudness measurements and noise specifications

dB-A, B, C weighted

Measurements with frequency weighting, which gives human hearing-like response when measuring SPL

dB-u

Measures voltage

dBFS

Used in digital audio meters

Signal Flow of a simple sound system

Input and output

Mic Level

-70 dBu to -50 dBu

Line level

+4 dBu

Speaker Level

+30 dBu

Output Transducer

Takes in electrical signals and converts them into other forms of energy

Speaker Drivers

• Individual transducer that converts an electrical audio signal to sound waves

• Most common driver types

  • Moving coil

  • Ribbon

  • Electrostatic

  • Piezo

Moving Coil Driver

A fixed magnet that creates a static magnetic field. This interacts with the voice coil’s electrical current, which is forced to move back and forth with the applied signal

Ribbon Driver

Produces a driving force to the applied (magnetic) field

Electrostatic Driver

Work by applying a static electrical charge to a thin film that floats between two perforated metal plates

Piezo Driver

Use crystals which when voltage is applied move in precise ways

Electromagnetism

The interaction of electric currents or fields and magnetic fields

Magnetic Force

Attraction or repulsion that arises between electrically charged particles because of their motion

Voice Coil

• Coil of wire that drives the cone of a loudspeaker according to the signal current flowing in it

Speaker Diaphragm

Thin flexible disk that vibrates in response to sound waves to produce electrical signals

Speaker Enclosure

• Enclosure where speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted

• Modern enclosures are 1 of 3 types:

  • Acoustic Suspension (air suspension)

  • Bass Reflex (Ducted Port)

  • Folded Horn

Acoustic Suspension

Closed boxes that absorb sound

Bass Reflex

Enclosures that have an opening in the box allowing energy from the back of the diaphragm to combine with energy from the front

Ducted Port

An opening in a speaker cabinet that has an airway extending several inches into the cabinet. It improves the quality of sound from a speaker system by equalizing the air pressure inside and outside the cabinet

Horn

Used to improve the driver’s efficiency and to control directivity

Folded Horn

A woofer driver mounted in a loudspeaker enclosure which is divided by internal partitions to form a zigzag flaring duct which functions as a horn

Crossover Network

An electronic device that divides the audio spectrum into individual frequency ranged (low, high, and/or middle) before sending them to specialized loudspeakers such as the woofer(s) and the tweeter(s)

Crossover Frequency

The frequency at which the high frequencies are routed to the tweeter(s) and the low frequencies are routed to the woofer(s)

Woofer

Informal name for a loudspeaker that PRODUCES the bass frequencies 

Tweeter

Informal name for a loudspeaker system that REPRODUCES the bass frequencies

Passive vs. Active Crossover

• Passive

  • Built into the speaker enclosure, after the power amp, and not adjustable

• Active

  • Free standing, before the power amp(s), and adjustable

  • Active means it requires a power supply 

Two-Way System Loudspeaker

Speaker that has two types of drivers which are known as a woofer and tweeter

Three-Way System Loudspeaker

Speaker that produces three individual gadgets called the mid-range, woofer, and tweeter drivers

Time-Alignment (Phase Coherent)

Term applied to loudspeaker systems which use multiple drivers to cover a wide audio range

Passive Speaker System

Speaker that has no build-in amplifier, so needs no power

Powered Speaker System

Loudspeakers that have built-in amplifiers

Frequency Response

Speaker manufacturers will list a bandwidth (EXAMPLE: 20 Hz-20 kHz) and show a frequency response diagram to illustrate the accuracy of sound reproduction for their device

Maximum Power

A specification for passive and active crossover systems using separate amplifiers, but not for self-contained powered systems

Coverage Angle

Defines the vertical and horizontal space in the listening area where the level does not decrease of fall-off more than -6 dB-SPL from on-axis

Far Field Monitoring

Monitoring sound at the listening position from large, powerful frontal loudspeakers several feet away and usually built into the mixing-room wall

Near-Field Monitoring

Speakers placed to reduce the influence of the room acoustics

Low Frequency vs. Placement of Speaker

The apparent low frequency response of the speaker systems in small rooms is heavily influenced by location

System Calibration

• Necessary to check loudspeakers are working…

  • 1.) to insure accurate representation of all frequencies 

  • 2.) all frequencies are evenly reproduced

Spectrum Analyzer

Device that displays the frequency response of an electrical waveform in relation to the amplitude present at all frequencies

Real-time Analyzer (RTA)

A device that shows the total energy present at all audible frequencies on an instantaneous basis

Headphones (“cans”)

• Used extensively in the studio and sometimes in live concerts

• Advantages:

  • Isolation 

  • Elimination of listening room acoustics

  • Feel for consumer experience

• Disadvantages:

  • Coloration

  • Lack of listening room acoustics

  • Unrealistic stereo sound field

Noise-canceling Headphones

Use microphones on ear pieces to send an out-of-polarity signal into ear causing cancellation

In-ear Monitors

• Fit into the auditory canal

  • Excellent isolation 

  • Custom fit can be very comfortable

Circumaural Headphones

• Covers and surrounds the ear

  • Good isolation

  • Can be uncomfortable

Supra-Aural Headphones

• Sits on top of the ear

  • Poor isolation 

  • Lighter and more comfortable

Closed or Open Back

• Closed back

  • The outside of the headphones are sealed up

• Open back

  • The outside of the headphones are exposed

Microphones

A transducer that converts acoustic energy into electric energy

Dynamic Microphone

A microphone that transduces energy electromagnetically. Moving-coil and ribbon microphone are dynamic

Moving-coil Microphone

A mic with a moving-coil element. The coil is connected to a diaphragm suspended in a magnetic field

Ribbon Microphone

A microphone with a ribbon diaphragm suspended in a magnetic field

Electrostatic Transduction

The generation of a voltage signal as a result of the disturbance of the magnetic field of an electromagnetic element

Capacitor Microphone (Condenser)

A microphone that transduces acoustic energy into electric energy electrostatically

Phantom Power

Operating voltage supplied to a capacitor microphone by an external power source or mixer, thereby eliminating the need for batteries

Tube Microphone

A capacitor microphone using a tube circuit in the preamp

Pressure vs. Pressure-gradient

Pressure operated means that the capsule picks up sound evenly from all directions. Pressure gradient means that the capsule picks up sound differently from different directions

Polar Response Pattern

The graph of a microphone’s directional characteristics as seen from above. The graph indicates response over a 360-degree circumference in a series of concentric circles, each representing a 5 dB loss in level as the circles move inward toward the center

Omnidirectional

Microphone that picks up sound from all directions

Bidirectional

Microphone that picks up sound to its front and back and has minimal pickup at its sides

Unidirectional

A microphone that picks up sound from one direction

Cardioid

A microphone having approximately uniform response over 180 degrees in front and minimum response in back, a polar curve representing its directional response being a cardioid

Acoustic Delay or Phrase Shift Network

The phase relationship of two signals at a given time, or the phase change of a signal over an interval time

Off-Axis Coloration

A distortion or change in the frequency response of the reproduced audio signal

Frequency Response

A measure of an audio system’s ability to reproduce a range of frequencies with the same relative loudness; usually represented by a graph

Flat

Frequency response in an audio system that reproduces a signal between 20 Hz and 20,000 Hz (or between any two specific frequencies) that varies no more than  3 dB.

Overload

Feeding a component or system more amplitude that it can handle and thereby causing loudness distortion

Maximum Sound Pressure Level

The level at which a microphone’s output signal begins to distort, that is, produces a 3 percent total harmonic distortion

Proximity Effect

Increase in the bass response of some mics as the distance between the mic and its sound source is decreased

Bass Roll-off

Attenuating bass frequencies. The control—for example, on a microphone—used to roll off bass frequencies

Multidirectional or Variable Pattern

Microphone with more than one pickup pattern

USB Microphone

A digital microphone developed for recording directly into a computer without an audio interface, such as a consol, control surface, or mixer

Wireless Microphone System

System consisting of a transmitter that sends a microphone signal to a receiver connected to a console or recorder

Guitar Pick-up as Transducer

The pick-up takes the physical vibration of the string and turns it into an electric signal

Direct Box (D.I) “Direct Insertion”

Used an an interface to connect the output of an electric instrument like a guitar “directly” into a microphone connection on a console or mixer board 

Close Miking

Primarily used in multitrack recording and live production to mic specific instruments

Distant Miking

Primarily used for ensemble recording

Coincident Miking

Technique that uses two microphones with the diaphragms placed as close together as possible, usually directly on top of each other

X-Y Mic Technique

Uses two unidirectional (cardioid) mics angled to cover the sound source left and right

Middle-side (M-S)

Uses bi-directional mic to pick up the side information and a unidirectional mic to pick up the middle information

Near-Coincident Miking

Uses two mics with the diaphragms spaced apart yet angled to pick up left and right sound