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Glossary of Vibro-Acoustic Terms

These terms have been simplified to be self-explanatory to most readers.

Absorption: The process of dissipation of sound or vibrational energy

Acceleration: The rate of change of velocity, measured in "g's"

Accelerometer: A sensor used to measure the motion of a vibrating structure

Acoustic: Having to do with sound or the transmission of sound

Acoustic Impedance: A measure of "resistance" of a medium or area to the movement or transmission of a sound wave, defined as the ratio of the sound pressure to particle velocity.

Acoustic Phonograph: A phonograph which reproduces sounds without the use of electronic amplification.

Airborne: Energy (sound or vibration) which travels through air

Amplitude: The maximum value of a sinusoidal signal

Analyzer: A computerized device which processes vibration or acoustic signals

Averaging: The process of taking the average value of a signal over time

A-Weighted Sound Level: A sound pressure measurement which has been modified to correspond to the frequency response of the human ear. A weighted measurement provides better correlation to subjective sound volume.

Band: A segment of the frequency spectrum or range

Bandpass Filter:
A filter which allows a selected range of frequencies to pass, and which attenuates all others above and below preset values

Complex Waveform: A wave consisting of sinusoidal components of different frequencies

Compliance: The inverse of stiffness. A measurement of how a structure bends or deforms to an input force.

Cycle: One complete interval of a sinusoidal waveform from zero to positive through zero through negative and back to zero.

Cycles per Second (CPS): The numbers of cycles of a wave which occur in one second. More commonly called Hertz

Damping: Dissipation of energy in a system, either through time or distance

Decibel (dB): A unit of amplitude which is the logarithmic ratio between two quantities. For most sound pressure measurements, dB = 20 log [ Sound Pressure (measured) / 20 uPa]. The decibel corresponds well to human hearing, as a subjective doubling of sound level is equal to a 10 dB increase.

Diaphragm: The flat membrane which, when coupled to the vibrations of the stylus, vibrates to produce the planar soundwaves in the tonearm

Diffracted Soundwave: A wave which has encountered an obstacle in its path, and has changed direction in some way other than reflection

Direct Sound: Sound which reaches a location in a direct line from the source

Displacement: The movement of an object measured in units of distance

Distortion: Unwanted modification or changes to a signal.

Dynamic: Relating to forces which are constantly changing or in motion.

Dynamic Stiffness: A measurement of the rigidity of a structure to vibrational energy. Most structures become less stiff at higher frequencies, and tend to couple less energy through them. Measured as deflection per unit input force vs. input frequency

Exponential: A quantity that grows as a power of a number, for example 20...21... 22 ...23... = 1...2...4...8...etc

External Horn Phonograph: A phonograph wherein the horn is located outside of the base or cabinet

Filter: A device for separating components of a signal on the basis of frequency

Frequency: The number of times a signal repeats itself in one second. Measured in Hertz (Hz.)

Fundamental Frequency: The lowest frequency component of an instrument or sound generating mechanism.

Goose-Neck: The curved pivot mechanism for the soundbox

Harmonic: A sinusoid whose frequency is a whole number multiple of the fundamental frequency.

Harmonic Distortion: The adding of unwanted harmonics to a signal due to the flexing of a structure or component

Hertz (Hz.): Unit of Frequency. Same as Cycles per Second

Horn: The gradually expanding hollow structure in a phonograph which routes the soundwaves from the tonearm, and provides the final impedance match to the listening room.

Horn Elbow: The connecting "tube" between the tonearm and the horn of a phonograph

Impact: A collision of a mass in motion with a second mass

Internal Horn Phonograph: A phonograph wherein the horn is located inside the cabinet or base

Laser Vibrometer: A sensing system which uses laser beams to measure the motion of a vibrating surface

Lateral Cut: A technique of cutting records wherein the stylus vibrates from side-to-side when the record is played

Linear (Linearity): Having a response directly proportional to the amount of excitation or stimulus at all amplitudes or frequencies

Loud-Tone Stylus: A thick stylus which tends to reproduce records with an increased volume

Loudness: The subjective volume of a sound

Masking: Noise which tends to "cover" a sound or sounds

Microphone: A sensor which measures the magnitude of a sound pressure wave

Natural Frequency: The frequency at which a structure will naturally vibrate when stuck or excited

Noise: Any disagreeable sound or sounds or unwanted acoustic disturbance

Octave: The interval between two sounds whose frequency ratio is 2

Octave Band: The amount of sound or vibrational energy within a band one octave in width

Offset: The lateral distance from the centerpoint of a tonearm's pivot point to the outer diameter of the turntable.

Orthophonic: Any of a series of acoustic phonograph models manufactured by the Victor Company in the mid to late 1920's which utilized higher efficiency acoustic techniques to reproduce sound

Particle Velocity: The speed at which an air molecule vibrates when excited in a sound wave

Pascal (Pa): The basic unit of sound pressure. 1 Pascal = 1 Newton/meter2 or 0.000145 lbs/in2

Peak Sound Level: The highest instantaneous value of a sound pressure measurement

Peak-to-Peak Value: The magnitude of the extreme maximum and minimum values of a sinusoid. The peak-to-peak value of a sinusoid is twice its amplitude.

Period: The duration (in time) of one cycle of a sinusoid

Phase: A measurement of the "offset" between two sine waves, usually specified in degrees. One complete sine wave cycle encompasses 360 degrees.

Pitch: The subjective perception of frequency

Pivot: The fulcrum point in the stylus support structure which supports the structure in the vertical direction and permits lateral vibration movement

Planewaves (Plane Progressive Waves): Soundwaves which are flat and straight (planar) in the frontmost section.

Pure Tone: A soundwave which is a simple sinusoidal (no harmonics)

Reflected Sound: That portion of a soundwave which bounces off a surface and reverses direction

Reproducer: Another term for the Soundbox

Resonance: A phenomena wherein an excitation force (sound or vibration) coincides with the natural frequency of the system, resulting in large and unstable responses.

Root Mean Square (RMS) Measurements: A measurement representing the "average" effective power content in a waveform. For simple sine waves, the RMS value is 0.707 times the peak amplitude

Scattering: The irregular diffraction and reflection of sound waves in many directions.

Soft-Tone Stylus: A thin stylus which tends to reproduce records with reduced volume

Sound: The hearing sensation caused by a physical disturbance in the surrounding air

Soundbox: The structure of a phonograph which contains the stylus, stylus bar and diaphragm

Soundbox Tube: The tube connecting the soundbox to the tonearm

Sound Power: The amount of total power of a sound generating source, measured as the rate per unit time at which the total sound energy is radiated from the source.

Sound Pressure: Measurement of the average sound wave pressure variations as the sound wave passes by a fixed point

Sound Pressure Level: The sound pressure, calculated in dB's as: dB = 20 log [ Sound Pressure (measured) / 20 uPA].

Speed of Sound: The speed at which the sound wave passes a fixed point. This is due to the transfer of energy from molecule-to-molecule in the listening area. In air, the speed of sound is 944 feet/second.

Spindle: The "axle" of the turntable motor, and center support of the turntable itself

Stylus: The needle of a phonograph

Spectra (or Spectrum): A plot of a waveform as a function of Amplitude vs. Frequency

Standing Waves: Sound waves which do not "move" through a space due to interference and reflection effects.

Static: Relating to forces which are unchanging or steady

Static Stiffness: A measurement of the rigidity of a structure to a constant force, defined as the deflection per unit force of input. Most structures maintain a constant static stiffness until they reach their yielding point and begin to deform

Structureborne: Energy (sound or vibration) which travels through a structure

Stiffness: A measurement of the resistance of a structure to bending or deformation with an input force

Stylus Bar: The metal bar which connects the stylus to the soundbox diaphragm

Stylus Control Springs: Springs which hold the stylus assembly in place to the soundbox pivot, and still allow it to vibrate to reproduce the recording

Taper: The gradually expanding area inside a tonearm or horn

Thumbscrew: The screw which holds the stylus in place

Tone Arm: The hollow tube which directs soundwaves from the soundbox to the horn of a phonograph

Tracking: The ability of a tonearm or stylus to dynamically conform to the grooves of a record

Tone Arm Elbow: The connecting tube between the tonearm and the horn of a phonograph (sometimes called horn elbow)

Transducer: A sensor which converts physical measurements into a voltage signal for analysis

Transmission Loss: The amount of energy that is lost as it travels through a structure or medium into another structure or medium

Transient: A "burst" or sudden change in a signal

Turntable: The rotating plate of a phonograph on which the record is placed

Vertical Cut: A technique of cutting records wherein the stylus vibrates up and down when the record is played

Vibration: An oscillatory motion of a structure or object

Wave: A disturbance propagated through a medium such as air, where the amount of disturbance can be measured as a function of time

Wavelength: The distance across one complete period of a wave as it travels through a medium


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