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Glossary list


The changing of energy to heat which reduces the amount of energy which can be reflected.


The sticking of the gasket material to either or both flanges of a mechanical assembly.

Airborne sound

Sound that arrives at the point of interest, by propagation through air.


A type of steel that contains additional elements to improve the properties of a fastener.


A silvery, white metal that is soft, light, and is electrically and thermally conductive.


The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be "live"; one without much reverb is said to be "dead".

Ambient noise

The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest.


The instantaneous magnitude of an oscillating quantity such as sound pressure. The peak amplitude is the maximum value.


Without echo.

Anechoic chamber

A room designed to suppress internal sound reflections. Used for acoustical measurements.


Antifreeze/Coolant is a combination of chemicals designed to be mixed with water for use in engine cooling systems. Antifreeze most commonly use glycols (either ethylene or propylene) to reduce the freezing point of water.


A coating or surface treatment that prevents the gasket material from adhering to the flanges.

Audible frequency range

The range of sound frequencies normally heard by the human ear. The audible range spans from 20Hz to 20,000Hz.

B100 Biodiesel

B100 is 100% biodiesel. (See Biodiesel.)

Background noise

Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structureborne, and instrument noise.


A free hanging sound absorbing unit used for reduction of reverberation and noise levels.


Periodic fluctuations that are heard when sounds of slightly different frequencies are superimposed.


The elastomer or rubber used in gasket material.


Biodiesel is an ester made from fats or oils (renewable resources such vegetable oils, animal fats, or other types of biomass). B100 is 100% biodiesel.


Biofuels are liquid fuels made from esters, alcohols, ethers, and other biomass chemicals


Occurs when internal pressure tends to push the gasket material out from between flanges. Blowout usually occurs in areas of low flange pressure and high internal pressure.

Bolt fracture

A type of fastener failure that occurs when a fastener is over-tightened and causes the bolt to break.

Bolt Length

A gasket selection and flange design factor that includes the "effective bolt length" (defined as the distance from theunderside of the bolt head to the closest engaged thread), the washer, and the thickness of the compressed gasket.

Bolt Loading

The load generated by a bolt when it is tightened.

Bolt-Hole Distortion

Flange is permanently distorted directly beneath the bolt. Caused by initial bolt torque.

Brinell scale

A method for testing a material's hardness that forces a hard steel sphere under a specified load into the surface of a material and measuring the diameter of the indentation left after the test.

Broad band noise

Spectrum consisting of a large number of frequency components, none of which is individually dominant.

Broken Corner

A corner of a mechanical assembly that is "broken off" instead of being machined into a perfect radius. Usually done to reduce manufacturing costs.


An alloy of copper and tin. Bronze is highly corrosion resistant.

Carbon steel

A type of steel made up of iron and carbon and no other material. Most fasteners are made from carbon steel.

Chemical Resistance

A gasket material's degradation resistance to the fluid or fluids being sealed.

Clamping force

The compressive force that a fastener exerts on a joint.


When the flanges of a mechanical assembly are not parallel to each other.

Cold working

The shaping of metal at temperatures much lower than the metal's molten state. Cold working increases the strength in certain steels.


The amount (%) of material thickness reduction that occurs when the proper external load is applied to a material.

Compression Set

The residual deformation of a material after removal of the compressive stress.


The ability of a gasket material to conform to flange surface roughness and out-of-flatness.

Controlled Swell

A gasket material that exhibits a controlled increase in thickness (swell) in the presence of oil.


See Antifreeze


A reddish-brown metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper fasteners are often used for electrical components.

Corrosion resistance

The ability of a material to resist chemical destruction from an environment. Corrosion resistance is one of the most important physical property for fasteners.

Creep Relaxation

A transient stress strain condition in which the strain increases concurrently with the decay of stress.

Crush Resistance

A measurement of a gasket material's ability to resist initial bolt load and/or extreme stress generated by the expansion of a bolted assembly upon heating.


To cause a loss or dissipation of vibrational energy in solid media and structures.


The frequency response curve which resembles the normal frequency hearing curve for most people. A sound-level meter reading with an A-weighting network simulating the human-ear response at a loudness level of 40 phons.


A sound-level meter reading with a B-weighting network simulating the human-ear response at a loudness level of 70 phons.


A sound-level meter reading with no weighting network in the circuit, i.e., flat. The reference level is 20 uPa.


Ten times any quantity or frequency range. The range of the human ear is about 3 decades.

Decay rate

For airborne sound, the rate of decrease of vibratory acceleration, velocity, or displacement level after the excitation has stopped.

Decibel (dB)

The standard measure of loudness. dB is a ratio of two quantities on a logarithmic scale.


The relative compactness of a material. Density is the mass of a material per unit volume.


A change in the direction of propagation of sound energy in the neighborhood of a boundary discontinuity, such as the edge of a reflective or absorptive surface.

Diffuse field

An environment in which the sound pressure level is the same at all locations and the flow of sound energy is equally probable in all directions.

Dimensional Stability

How well a cut gasket retains its original dimensions when exposed to temperature and humidity extremes.


The ability of the material to deform before it fractures.

Elastic Modulus

See Young's Elastic Modulus.

Electrical conductivity

The ability of a material to conduct an electrical current.


As a descriptive audio term, usually refers to a coloration or inaccuracy that none-the-less may be sonically pleasing.


A type of fastener failure that occurs when a fastener is subjected to repetitive loading or stressing. Fatigue can cause catastrophic failure

Feedback, acoustic

Unwanted interaction between the output and input of an acoustical system, e.g., between the loudspeaker and the microphone of a system.


A metal that contains iron. Carbon steels are common ferrous metals


A curved or rounded portion of a mechanical assembly.


A rib or rim for strength, guiding, or attachment of one object to another. In a gasketed joint, a flange performs all three of these functions.

Flanking transmission

Transmission of sound from the source to a receiving location by a path other than that under consideration. These noise flanking paths can defeat noise reduction techniques.

Free field

An environment in which a sound wave may propagate in all directions without obstructions or reflections. Anechoic rooms can produce such an environment under controlled conditions.


All sounds can be described by their frequency or their mix of frequencies, and can be measured on a scale in units of Hertz (Hz), expressing the number of cycles per second.


Frequency-time curve.


The lowest frequency of a note in a complex wave form or chord.

Fusion zone

All reflections arriving at the observer's ear within 20 to 40 msec of the direct sound are integrated, or fused together, with a resulting apparent increase in level and a pleasant change of character. This is the Haas effect.


A material, combination of materials, or a device used to create and maintain an impervious barrier against the transfer of fluids across the separable surfaces of a mechanical assembly (joint) that do not move relative to one another.

Gasket Extrusion

Refers to the tendency of a gasket to flow from between flanges, particularly around bolt holes where stresses are concentrated.


A category that fasteners are grouped in according to their strength.

Grain Listening term

A sonic analog of the grain seen in photos. A sort of "grittiness" added to the sound.


Sulphuric acid is a strong mineral acid. It is soluble in water at all concentrations

Haas effect

See fusion zone. Also called the precedence effect. Delayed sounds are integrated by the auditory apparatus if the fall on the ear within 20 to 40 msec of the direct sound. The level of the delayed components contributes to the apparent level of the sound, and it is accompanied by a pleasant change in character.

Hard room

A room in which the surfaces have very low values of sound absorption and are therefore highly reflective.


The resistance to indentation. Usually measured with a durometer.


Also called overtones, these are vibrations at frequencies that are multiples of the fundamentals. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic second, fourth, sixth, etc.-is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.

Heat treatment

The heating and cooling processes used to change the structure of a material and alter its mechanical properties.

Hex-head bolt

A type of bolt that has a head with six sides.


The opposition to the flow of electric or acoustic energy measured in ohms.


A very short, transient, electric or acoustic signal.

Impulse response

Sound pressure versus time measurement showing how a device or room responds to an impulse.

In phase

Two periodic waves reaching peaks and going through zero at the same instant are said to be "in phase."

Initial Flange Pressure

The stress on a gasket attained when a joint is initially tightened.


Acoustic intensity is sound energy flux per unit area. The average rate of sound energy transmitted through a unit area normal to the direction of sound transmission.


The combining of two or more signals results in an interaction called interference. This may be constructive or destructive. Another use of the term is to refer to undesired signals.


A dampening mechanism made a part of the assembly or system, which reduces structure borne vibrations from passing through the structure.


Term used for a mechanical assembly or gasketed assembly.


Thickness reduction that occurs with a given gasket material at various known applied external loads, thereby establishing a load/compression curve.


An exponent of 10 in the common logarithms to the base 10. For example, 10 to the exponent 2=100; the log of 100=2.


A subjective term for the sensation of the magnitude of sound. The subjective response to a sound level.

Low-carbon steel

A type of carbon steel that contains less than 0.3% carbon.

LS Diesel

Low Sulphur Diesel Fuel(< 50ppm sulphur content)

Mass law

An approximation that describes the Sound Transmission Loss (TL) of a limp, flexible barrier in terms of mass density and frequency. For each doubling of the weight or frequency of a partition, mass law predicts a 6 dB increase in TL.

Medium-carbon steel

A type of carbon steel that contains between 0.3% and 0.5% carbon.


Monoethylene Glycol. (See Antifreeze.)

Metric sabin [L2]

The unit of measure of sound absorption in the metre-kilogram-second system of units.


Sodium Chloride (vulgar table salt)


Sodium hydroxide (NaOH), also known as lye or caustic soda, is a caustic metallic base. It is widely used in industry, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, and detergents

Near field

Locations close to the sound source between the source and the far field. The near field is typically characterized by large sound pressure level variations with small changes in measurement position from the source.


Interference of an electrical or acoustical nature. Unwanted, bothersome, or distracting sound.


A metal that does not contain iron. Aluminum, copper, and zinc are nonferrous metals.


An octave is a doubling or halving of frequency. 20Hz-40Hz is often considered the bottom octave. For example, each octave you add on the bottom requires that a speaker move four times as much air!

Octave bands

Frequency ranges in which the upper limit of each band is twice the lower limit. Octave bands are identified by their geometric mean frequency, or center frequency.


A component of a complex tone having a frequency higher than the fundamental.


Monopropylene Glycol. (See Antifreeze.)


Phase is the measure of progression of a periodic wave. Phase identifies the position at any instant which a periodic wave occupies in its cycle. It can also be described as the time relationship between two signals.

Phase shift

The time or angular difference between two signals.


The unit of loudness level of a tone.

Pink noise

Noise with a continuous frequency spectrum and with equal power per constant percentage bandwidth. For example, equal power is any one-third octave band.


A subjective term for the perceived frequency of a tone.


The load that sufficiently stretches the bolt/screw to give a tight joint and overcome any forces tending to pull the joint apart. (See Proof Load.)

Pressure zone

As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface.


Device that measures flange surface roughness.

Proof Load

The amount of stress that the fastener can withstand without experiencing deformation. Proof load is often used interchangeably with yield strength. (See Yield Strength.)

Pure tone

A tone with no harmonics. All energy is concentrated at a single frequency.


The portion of a sound wave in which molecules are spread apart, forming a region with lower-than-normal atmospheric pressure.


For large surfaces compared to the wavelength of impinging sound, sound is reflected much as light is reflected, with the angle of incidence equaling the angle of reflection.


The bending of sound waves traveling through layered media with different sound velocities.


A natural periodicity, or the reinforcement associated with this periodicity.

Resonant frequency

Any system has a resonance at some particular frequency. At that frequency, even a slight amount of energy can cause the system to vibrate. This is its natural or resonant frequency.


The persistence of sound in an enclosed or partially enclosed space after the source of sound has stopped.

Reverberation time

The tailing off of a sound in an enclosure because of multiple reflections from the boundaries.

Rockwell scale

A method for testing a material's hardness that uses an indenter to test the material's resistance to deformation as a load is applied.

Root Mean Square (RMS)

Term used to express surface texture. It is the average deviation from the mean surface.


The weighted sound reduction index (excludes the effects of flanking transmission)


The apparent weighted sound reduction index (includes the effects of flanking transmission)

Seal Point

The minimum stress needed on a gasket material to achieve an effective seal.

Sealing Stress

The amount of flange pressure present in a flanged joint assembly to compress and seat a gasket material in order to create an effective seal.

Sine wave

A periodic wave related to simple harmonic motion.

Socket screw

A type of capscrew with a round head and a hexagonal indentation for tightening purposes.


The unit of measurement for subjective loudness.


Sound is vibrational disturbance, exciting hearing mechanisms, transmitted in a predictable manner determined by the medium through which it propagates. To be audible the disturbance must fall within the frequency range 20Hz to 20,000Hz.

Sound absorption

(1) The process of dissipating sound energy.
(2) The property possessed by materials, objects and structures such as rooms of absorbing sound energy.
(3) A: [L2]; metric sabin---in a specified frequency band, the measure of the magnitude of the absorptive property of a material, an object, or a structure such as a room.

Sound attenuation

The reduction of the intensity of sound as it travels from the source to a receiving location. Sound absorption is often used as, for instance, in a lined duct. Spherical spreading and scattering are other attenuation mechanisms.

Sound energy density, D

J/m, the quotient obtained when the sound energy in a region is divided by the volume of the region. The sound energy density at a point is the limit of that quotient as the volume that contains the point approaches zero.

Sound energy, E

J-energy added to an elastic medium by the presence of sound, consisting of potential energy in the form of deviations from static pressure and of kinetic energy in the form of particle velocity.

Sound insulation

The capacity of a structure to prevent sound from reaching a receiving location. Sound energy is not necessarily absorbed; impedance mismatch, or reflection back toward the source, is often the principal mechanism.

Sound intensity, I

W/m2, the quotient obtained when the average rate of energy flow in a specified direction and sense is divided by the area, perpendicular to that direction, through or toward which it flows. The intensity at a point is the limit of that quotient as the area that includes the point approaches zero.

Sound isolation

The degree of acoustical separation between two locations, especially adjacent rooms.

Sound level

Of airborne sound, a sound pressure level obtained using a signal to which a standard frequency-weighting has been applied.

Sound power level, Lp

Of airborne sound, ten times the common logarithm of the ratio of the sound power under consideration of the standard reference power of 1 pW. The quantity so obtained is expressed in decibels.

Sound power, W

W, in a specified frequency band, the rate at which acoustic energy is radiated from a source. In general, the rate of flow of sound energy, whether from a source, through an area, or into an absorber.

Sound pressure level (SPL)

Given in decibels (dB) is an expression of loudness or volume. A 10 dB increase in SPL represents a doubling in volume.

Sound pressure, p

Pa, a fluctuating pressure superimposed on the static pressure by the presence of sound. In analogy with alternating voltage its magnitude can be expressed in several ways, such as instantaneous sound pressure or peak sound pressure, but the unqualified term means root-mean-square sound pressure. In air, the static pressure is barometric pressure.

Sound Reduction Index, R

The airborne sound insulation of a material in a particular frequency range, expressed as a decibel value

Sound spectrograph

An instrument that displays the time, level, and frequency of a signal.

Sound transmission class, STC

A single-number rating, calculated in accordance with Classification E 413 using values of sound transmission loss. It provides an estimate of the performance of a partition in certain common sound insulation problems. A single number rating that indicates the sound transmission loss of a partition or ceiling system between adjacent closed rooms, abbreviated STC.

Sound transmission loss, TL

Of a partition, in a specified frequency band, ten times the common logarithm of the ratio of the airborne sound power incident on the partition to the sound power transmitted by the partition and radiated on the other side. The quantity so obtained is expressed in decibels. The reduction in sound level when sound passes through a partition or ceiling system.

Sound waves

Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves.


The distribution of the energy of a signal with frequency.

Spherical divergence

Sound diverges spherically from a point source in free space.

Stress Riser

A small band or rib, machined or embossed into the mating surface of a flange. Helps to strengthen the flange and to concentrate the sealing load onto a smaller area.

Structureborne noise

Generation and propagation of time-dependent motions and forces in solid materials which result in unwanted radiated sound.


An externally threaded fastener that is often threaded at both ends and can be used with a nut. Unlike bolts, studs do not have a head.

Surface Roughness

The deviation of the topography of an actual surface from an ideal atomically smooth and planar surface.

Temperature Resistance

A material's ability to withstand defined temperatures.

Tensile Strength

The maximum stress applied in the plane of the material (not perpendicular to its surface) while stretching a specimen to rupture.

Thermal Conductivity

The ability of a material to conduct heat.

Thermal expansion

The tendency of a material to increase in size as it increases in temperature.

Thread stripping

A type of fastener failure that occurs when a fastener is over-tightened. Thread stripping causes the fastener threads to appear deformed.

Threshold of feeling

The sound pressure level that makes the ears tickle, located about 120 dB above the threshold of hearing.

Threshold of hearing

The lowest level sound that can be perceived by the human auditory system. This is close to the standard reference level of sound pressure, 20uPA.


The unwanted but acceptable deviation from a specified dimension.


A tone results in an auditory sensation of pitch.


A measure of force applied to an object to create a rotational or twisting effect about some point.


Loss The percentage of initial bolt torque that is lost after operation of finished assembly.

Torque Retention

A term used to express how much of the initial bolt torque remains on the bolts after an assembly has been exposed to operating conditions.


The higher frequencies of the audible spectrum.

Typical Values

Estimates of gasket material properties that are used until enough statistical data can be accumulated to write accurate product specifications.

Ultimate Tensile Strength

The final amount of stress sustained in a tensile test at the exact moment the object ruptures.

Vibration isolation

A reduction, attained by the use of a resilient coupling, in the capacity of a system to vibrate in response to mechanical excitation.

Vibration loosening

A type of fastener failure that occurs in a bolted joint due to excessive motion, which causes the bolt to rotate loose.

Vickers scale

A method for testing a material's hardness that uses a pyramid-shaped diamond to exert pressure on the surface of a material for a standard length of time. The diagonal of the indentation is measured under a microscope to determine the hardness value.


Colloquial equivalent of sound level.


The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency.


Adjustment of sound-level meter response to achieve a desired measurement.

White noise (ANS)

Noise with a continuous frequency spectrum and with equal power per unit bandwidth. For example, equal power in any band of 100-Hz width.

Yield Strength

The maximum force that a fastener can withstand before it experiences permanent deformation.

Young's Elastic Modulus

The ratio of tensile or compressive stress to corresponding strain below the proportional limit of the material.

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