ARCC BU (Architectural Acoustics)

Perforated Resonator

Spaced away from a solid backing, provide a widely used practical application of the cavity resonator principle. Contain a large number of necks, constituting the perforation of the panel thus functioning as an array of cavity resonators. The perforations are circular (sometimes slotted). The airspace behind the perforations from the undivided body of the resonator, separated into bays by horizontal and vertical elements of the framing system.

Foam Baffle

Suspended vertically from their own internal wire frame with corner eyelets. By hanging them in rows and columns it absorbs unwanted echo. It can be used to dissipate sound energy if used within a suspended curtain system surrounding a noise source. This material is used where noise may be expected to originate such as engines, conveyors, presses, pumps, generators, compressors, hydraulic devices, etc.

Intensity Level

Ten times the logarithm of the ratio of sound intensity to a reference sound intensity.

Noise Reduction

The Reduction in level of unwanted sound by any several means (e.g. distance in outdoor space, by boundary surface absorption, by isolating barriers of enclosures, etc.)

Sound Absorption

The ability of a material to absorb acoustical energy. Measured in sabins. The product of area (s) and absorption coeffecient (a). The process of dissipating sound energy by converting it to heat. The reciprocal of sound reflection

100-600 hz

The approximate human speaking voice range.

Intensity

The average rate of sound energy flow per unit area in a direction perpendicular to the area.

Decibel

The basic metric unit for describing the magnitude of sound. It is 20 times the logarithm to the base 10 of the ratio of the sound pressure to a reference pressure of 0.0002 dyne/square meter. This reference pressure is considered the lowest value that the ear can detect.

330 m/s

The considered constant of velocity of sound in air in architectural acoustics.

Sound Transmission Loss

The difference in decibels of the sound pressure level on the receiver side of a barrier or partition from that on the source side.

Wavelength

The distance sound wave travels during each cycle of vibration.

Ambient

The existing surrounding conditions such as air or surface.

Sound Pressure

The fluctuation of pressure about atmospheric pressure. Usually measure in micropascals.

Sound Absorption Coeffecient

The fraction of sound energy absorbed or otherwise reflected by a surface.

Absorption Coeffecient

The fraction of sound energy impinging on a surface that is absorbed by that surface, usually denoted by a.

Gypsum Board

The generic name for the family of products comprised mainly of non-combustible gypsum core and paper facings. Perfectly suited for fire resistance.

Fundamental Frequency

The lowest frequency present in a complex tone.

Sabin

The measure of sound absorption of a surface equivalent to a square foot of perfectly absorptive material; unit of measure of acoustical absorption.

Threshold of Pain

The minimum sound pressure level of sound which stimulates the ear to the point at which discomfort gives way to definite pain.

Masking

The obscuring or covering up of one sound by another.

Sound Propagation

The origination of transmission of sound energy.

Pinna

The outer ear; it is a skin-covered flap of elastic cartilage projecting from the side of the head and funnelling sound into the middle ear.

Acoustical Environment

The overall environment, interior to exterior, that affects the acoustic condition of the space of structure under consideration.

Reverberation

The persistence of sound in an enclosed space as a result of repeated reflection or scattering of sound.

Acoustical Design

The planning, shaping, finishing and furnishing of an enclosed space to establish the acoustical environment necessary for distinct hearing.

Sound Transmission

The propagation of sound energy through various media.

Room Acoustics

The qualities or characteristics of a room, auditorium or concert hall that determine the audibility of speech or fidelity of musical sounds in it.

Sound Power

The rate at which acoustic energy is radiated. Usually measured in watts.

Decay Rate

The rate at which sound pressure level (in db) decreases when the source of sound is eliminated.

Frequency

The rate of repetition of a periodic event. It is determined by the number of times per second a given molecule of air vibrates.

Velocity of Sound

The rate of travel of sound in a given medium.

Acoustical Impedance

The resistance to the flow of acoustical energy, measured in rayls at specific frequencies, affected by density and fiber diameter.

Reflected Sound

The resultant sound energy returned from a surface that is not absorbed or otherwise dissipated upon contact with the surface.

Architectural Acoustics

The science and technology of controlling sound in and around buildings.

Acoustics

The science of sound, including its generation, transmission and effects of sound waves.

Waveform

The shape of the graphic representation of a sound wave.

Wavefront

The spherical surface of the wave as it travels out in all direction from the source.

Acoustics

The study of how sounds are created, transmitted and received.

Loudness

The subjective attribute of an auditory sensation.

Pitch

The subjective response of human hearing to frequency. It is higher as the number of vibrations/oscillations become greater.

Tone

The subjective response of the ear to the pitch of a sound.

Hearing

The subjective response to sound, including the entire mechanism of the external, middle and internal ear system and the nervous and cerebral operations that translate the physical stimuli into meaningful signals.

Acoustics

The technology of designing spaces, structures and mechanical systems to meet hearing needs.

Engineering Acoustics

The technology of sound production and recording, sound motion pictures, and radio and television, as well as the study of vibrations of solids and their control and the use of high - intensity ultrasonic in industrial processing. Noise is an important aspect here.

Reverberation Time

The time in seconds required for a sound to decay, roughly speaking to inaudibility after the source ceases. (Strictly the time in seconds for the sound level at specific frequency to decrease 60 db in level after the source stops).

Acoustical Treatment

The use of acoustical absorbing or reflecting materials or sound-isolating structures to improve or modify the acoustical environment.

Sound Insulation

The use of structures and materials designed to reduce the transmission of sound from one area to another.

331.5 m/s

The velocity of sound in still air of normal atmospheric composition at 0 degrees celsius.

Complex Tone

The vibration in pressure caused music, speech or noise.

Acoustical Tile

A widely used ceiling material made of mineral or cellulose fibers or of fiberglass. It is usually suspended in a metal grid, but some types can be glued or otherwise attached to solid surfaces. It is prone to damage when contacted and is therefore not recommended for surfaces. Suspended ones provide more low frequency absorption than glued-on. Membrane-faced ones provide less high-frequency absorption than those whose faces are porous.

Porous Materials

Commonly formed of matted or spun fibers. Their basic acoustical characteristic is a cellular network of interlocking pores. Sound absorption is more efficient at high than at low frequencies but their acoustical efficiency improves in the low frequency range with increased thickness and with distance from their solid backing.

Partials

Component of high frequencies.

Focusing

Concentration of reflected acoustic energy within a limited location in a room as the result of the reflection from concave surfaces.

Speech or Communication Acoustics

Considers the production and transmission of speech

Inner Ear

Contains the sensory receptors for hearing.

Vibrating Panels

Conver sound energy into vibrational energy which is dissipated by internal damping and radiation

Thin Porous Materials

Convert sound energy into heat by friction.

Melamine Foam Sound Absorber

Convoluted double hump anechoic wedges. Designed for sound absorption in a wide range of frequencies. Increased surface absorption area.

Volume Resonators

Created by holes connected to an enclosed volume of trapped air. Enclosed body of air confined walls connected by a narrow opening (neck) to the surrounding space, in which sound travels. The impinging sound causes the air in the neck to vibrate, and the air mass caused the entire construction to resonate at a particular frequency. By adjusting neck opening and cavity dimensions, the unit can be tuned to resonate at a desired frequency.

Underwater Acoustics

Deals specifically with all aspects of sound in the sea and its use for detection of vessels and exploration of the seabed.

Musical Acoustics

Deals with the physics of musical instruments.

Sound Conditioning

Designing and equipping a space for effective retention of desirable sounds and maximum relief from undesirable acoustical effects.

Acoustic Transducers

Devices by which any form of energy can be transformed into sound energy and vice versa.

Presbycusis

Diminishing of hearing sensitivity with advance in age without adverse effects from diseases and noise.

Acoustical Noise Reduction Blanket

Effective, economical method of noise reduction in a wide variety of applications such as industrial, commercial studio and other applications. Modular panels used for effective sound absorption and noise reduction properties that join together to form any configuration required. The vinyl-coated facings on the noise-reduction blankets are dirt and oil-resistant, cleanable and designed for industrial use.

Sailcloth and Vinyl Encapsulated Acoustical Baffles

Fiberglass core encapsulated in Polyvinyl Chloride Film or sailcloth; Plain-Type A or Type B mounting Cost effective, lightweight, high acoustical performance, moisture and chemical resistant.

Acoustical Plaster

Fibrous materials with binder. Distinguished by its porosity after it dries. It was originally intended to create jointless surfaces that absorb sound, which ordinary ones does not. Noise reduction coefficient on the order 0.60 have been obtained under controlled conditions, but field installations usually yield much less. It is not a reliable sound absorber.

Tinnitus

High pitched ringing in the ears This is experienced by some people exposed to machinery and other high pitched sound sources. This condition may last a short while.

Compression

In sound, the concentration of the conductor molecules to produce a high pitch layer of sound.

Curtains and Fabrics

Include a range of textiles that are used on their own or as covering for other materials that may are may not be sound absorbing.

Amplification

Increase in intensity level of an audible signal produced by means of loud speakers and associated electronic amplification apparatus.

Dense-pack

Insulation is sometimes blown at a relatively high density into wall or ceiling cavity to resist air infiltration.

Environmental Acoustics

Involves the control of noise pollution, environmental noise includes automobile and other motor vehicles, aircraft, industrial plant and heavy construction equipment.

Wood Decking

It is often exposed as finished ceiling. Owing to its relatively low mass (as compared to concrete), it provides only nominal attenuation unless ballasted with heavier materials. Are generally reflective, but unsealed cracks between boards have been known to contribute a fair amount of absorption.

Slit Resonators

Last type of volume/cavity resonator.

Sound Attenuation

Lessening or reduction of sound intensity, e.g. from 80 db to 70 db.

Glass

Light-tranparent materials made of a mixture of sillicates. It is used principally to glaze windows and other openings that need to be closed, but without excluding light. Despite its mass, it is a marginal sound attenuator because it is thin and the mass per unit area is quite small. Almost totally reflective in the higher frequencies, it resonates and, through this mechanism, can absorb appreciable amounts of low-frequency sound.

Individual Resonator

Made of empty clay vessels of different sizes. Their effective absorption spread between 100 and 400 hz.

Water Resistant Board

Made with water-resistant core and water-resistant face paper, also known as "green" board. This is design as a ceramic tile backing board.

Acoustical Blankets

Manufacture from rock wool, wood fibers, hair felt, etc. generally installed on a wood or metal framing system. Their absorption increases with thickness, particularly at low frequencies. They do not constitute an aesthetically satisfying finish, they are normally covered with suitable type of perforated boards, wood slats, flying screen, etc., placed and fastened to the framing system.1

Sound Conductor

Material that carries or transmits energy from one location to another; must be an elastic material.

Absorbing Materials

Materials that dissipate acoustic energy within their structure as heat and/or mechanical energy of vibration. Usually building materials designed specifically for the purpose of absorbing acoustic energy on the boundary surfaces of rooms or in the cavities of structures.

Sound Absorber

Materials that have the capacity to absorb sound, such as acoustical tile and panels, carpets, draperies, upholstered furniture, etc.

Panel Absorbers

Membrane. Having an impervious surface mounted over an air space. The airspace will act as absorber and will vibrate when struck by sound waves. The incident sound energy is then converted to heat. Use where low-frequency absorption is required and middle and high frequency absorption is unwanted or provided by another treatment. Are often used in studio recordings.

Threshold of Audibility

Minimum sound pressure level that is capable of evoking auditory sensation.

Brick

Modular building block made from clay. It attenuates sound well. Exceptionally high orders of attenuation can be achieved with two side-by-side but unconnected. Joints must be fully mortared or otherwise sealed. Absorption is negligible since there is little or no porosity and the material is rigid. It is a good all-frequency sound reflector.

Acoustical Plaster

These acoustical finishes are mostly for noise in auditoriums where any other acoustical treatment would be impractical because of curved or irregular shape of the surface. They are applied in a semi-plastic consistency. Their acoustical efficiency usually best at the higher frequencies, depends largely on such job condition, the amount of binder, the state of undercoat at the time of application, and the manner in which the finish is applied.

Basic Sound Theory

Sound is an aural sensation caused by an oscillation or vibration in an elastic medium (such medium returns to its normals state after sound waves pass through it). Sound energy progresses rapidly thereby producing small changes in atmospheric pressure. Vibrating particles of sound move in an infinitesmal amount to either side causing particles to impart its motion and energy to them. Sound travels in any medium except vacuum because there is no carrier of sound.

Complex Tone

Sound sensation characterized by more than one frequency.

Reverberation Sound Field

Sound that is reflected from the boundaries of and furnishings within an enclosed space.

Airborne Sound

Sound that is transmitted through air by a series of oscillating pressure fluctuations.

Structureborne Sound

Sound transmission through solid material by means of vibrations of waves in the material.

Transondent Facings

Sound transparent facings that may range from 5 to 50 percent or more open area. Tend to reduce the effectiveness of sound-absorbing materials by reflecting high-frequency sound waves. In general, the lower the percent of open area in it, the less absorption of high frequency sound energy.

Echo

Sound waves which have been reflected back to a listener with sufficient magnitude and time delay.

Wood Paneling

These are usually attached to furring and thus kept clear of the wall behind it. When used on a wall, it generally results in negligible improvement over the attenuation provided by basic wall. It absorbs low-frequency sound by resonance and may lead to serious bass deficiency in music rooms unless it is thick and/or well restrained.

Bass Trap

Thick, self-standing, portable flutes of foam that stack on each other int the corners of a room. It helps to combat low impact noise. These are 12x12 inches triangular cut pieces.

Type X Gypsum Board

This is available in 1 and half inch or 5/8 inch thickness and has improved fire-resistance through the use of fibers with gypsum core.

Soffit Board

This is designed for use under protected overhangs and walkways.

Regular Gypsum Board

This is used as a surface layer for walls and ceilings, available in tapered and square edges.

Period

Time required for one complete cycle.

Creep

Transmission of sound along curve surface.

Cycles per second (CPS)

Unit of frequency; SI unit (hertz).

Phon

Unit of loudness level.

Rayls

Unit of specific acoustic impedance or equivalent characteristic acoustic impedance.

Suspended Sound

Units that are installed with all edges and sides exposed, they can provide extremely high absorption per square feet of material because at six surface will be exposed to sound waves.

Bioacoustics

Use sound (particularly at high frequency) in medical diagnosis and therapy as wells as its use in the study of overall behavior of animals in general.

Gypsum Sheathing

Used as an underlayment in exterior walls for structural stability and fire-protection. Available in treated and non-treated core for water resistance.

Reverberation Control

Using sound-absorbing materials to control reverberation so speech will not be garbled.

Source

Basic element in an acoustical situation (human speech, mechanical equipments, etc.)

Receiver

Basic element in an acoustical situation (usually humans, although sometimes animals or sensitive medical equipment)

Geometric Acoustics

Behaviour of sound waves likened to that of light rays and the law that apply.

Acoustical Cotton FIber Composite Panel

Bonded Acoustical Pad, recyclable, fiberglass-free, high density fiber; Soft textured surface, foil on one side. Economical, multi-purpose, high performance absorption combined with STC value.

Hanging Acoustical Baffles

Bonded Acoustical Pad; Soft-textured surface. Economical, multi-purpose, high performance, durable, lightweight.

Pyramids

2'x2' square, open cell polyurethane acoustic foam panels cut with standard egg shell face. Popular choice for sound control in most industrial establishments. Typically not recommended for use in public buildings where Class A fire rating is required.

Gypsum Core Board

A 1 inch thick panel used in proprietary shaft wall assembles and laminated gypsum assemblies.

Architectural Acoustics

A branch of acoustics that deal with providing rooms and buildings with good conditions for listening to speech and music, it plays an important role in the planning and construction of auditoriums, churches, halls, libraries and music halls.

Harmonics

A component of sound containing more than one frequency which is an integral multiple of the lowest frequency.

Free Field

A field free from boundaries that would otherwise tend to reflect sound.

Cochlea

A fluid-filled chamber containing sensory receptors.

Octave

A frequency band whose upper limit is twice the lower limit; a division of the audible frequency range, the center frequency of which is twice that of the preceding band center frequency. The standard acoustical octave bands are centered at 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000 and 8000 hz.

Plywood

A laminate of several layers of wood veneer. It is used as an underlayment for floors, as sheathing on studs or rafters or as finished paneling on walls. Mainly because of its density, its is relatively ineffective as a sound attenuator. However, it is often adequate in combination with other materials or where high performance is not required. Thin ones, if furred out from a solid wall, is a potent low-grequency absorber. At higher frequencies, it quite effective.

Fireflex

A lightweight, porous, open cell, acoustic melamine foam material designed for maximum sound absorption where Class A fire rating is a must. This material is resistant to most organic solvents, alkalis and diluted acids. The facing is convoluted with eggshell pattern.

Hertz

A measure of frequency

Concrete

A mixture of Portland cement, stone and sand aggregates, and water, cured into a hard mass of superior strength. Like any hard material, it readily accepts and transmits impact sounds. It provides virtually no absorption. There are, however, those aerated and intentionally porous. These are fairly absorptive.

Flutter Echo

A rapid succession of echoes caused by reflection of sound back and forth between two parallel walls.

Fibrous Plank

A rigid (often structural material), usually made of coarse fibers, sich as wood fibers, embedded in a cementitious mix. The fibrous surface absorbs sound. If exposed to the room, it reduces noise and reverberation time.

Laminated Glass

A sandwich of two or more sheets of glass with viscoelastic interlayers that proved damping as the sandwich is flexed. Certain types offer substantially better sound attenuation than an equal thickness of monolithic glass.

Noise Isolation Class

A single number rating derived in the same manner as Sound Transmission Coeffecient (STC) based on Noise Reduction.

Sound Transmission Class

A single number rating of the sound insulation value of a partition, door, window, etc.

Splay

A slight offset in angle from a flat plane such as walls or ceilings.

Diffuse Sound Field

A sound field in which the energy arrives at the receiver in a direct path from the source, without any contribution from reflections.

Resonance

A state in which the forces of oscillation of a system occur at or near a natural frequency of a system.

Diaphragm

A thin body that separates two areas. In sound, the skin of a partition or ceiling which separates the room from the structural space in the center of the partition or ceiling assembly.

Sone

A unit of how loud sound is perceived; it is a non-SI unit.

Curtains

Absorb sound if they are reasonably heavy and, more importantly, if their flow resistance is sufficiently high- to the point of severely impeding, but not stopping, airflow through the material.

Close-cell Foams

Absorbs sound but less efficiently and less predictably. They are more often applied to ringing surfaces, such as large metal plate to provide damping.

Near 1

Absorption coefficient of highly absorptive materials.

Near 0

Absorption coefficient of highly reflective materials.

Sound Diffraction

Acoustical phenomenon which cause sound waves to be bent or scattered around.

Physiological Acoustics

Acoustics that deals with the way humans and animals hear things.

Psychological Acoustics

Acoustics that deals with the way humans and animals interpret sounds.

Type C Gypsum Board

Additional additives give this product improved fire-resistance, required in some fire-tested assemblies.

Volume Resonators

Also called Hemholtz, reduce sound energy by friction at opening and by inter reflections within cavity.

Middle Ear

An air-filled chamber connected to the pharynx by the Eustachian tube, thus equalizing the pressure on the two sides of the eardrum.

Fiberglass

An excellent sound absorber. The manufacturing process ensures consistent porosity at a very fine scale. Compressed blocks or sheets are also used to form resilient supports/ hangers or as joint filler where rigid ties are to be avoided. Its absorptivity depends on flow resistance, which, in turn, is affected by the material's thickness, its density, and the diameter of the fibers.

Sound

An oscillation in pressure of the atmosphere which is capable of being detected by the human ear.

Distortion

Any change in the transmitted sound signal such that the sound received is not a faithful replica of the original source sound.

Sound Generation

Any change of stress or pressure producing a local change in density or a local displacement from equilibrium in an elastic medium can serve as a source of sound.

Masonry

Any of a large variety of stone-like materials. Acoustical properties vary, but in general are comparable to those of brick, concrete, and concrete masonry units.

Carpets

Any of a variety of soft floor finishes made of synthetic materials such as nylon or natural materials such as wool. It is either glued directly to the floor or installed over an underlayment of hairfelt or foam rubber. Are used as versatile acoustical material because it reduces, in some cases, almost completely eliminate surface noises.

Fibrous Spray

Any of a variety of sprayed-on insulating material, often specified for fireproofing application. Most contemporary sprays contain cellulose or mineral fibers of various descriptions. It is inherently porous and therefore absorptive.

Noise

Any unwanted sound, it is annoying and interferes with speech and hearing, or intense enough to cause hearing damage.

Metal

Are any family of alloys, but especially steel, which is commonly used to provide structural support.

Open-cell Foams

Are excellent sound absorbers, provided they are sufficiently thick. Their uses include padding for upholstered theater seats to stabilize reverberation regardless of occupancy.

Inverse Square Law

At a distance from a source, under free-field conditions, sound intensity varies inversely with the square of the distance from the source, resulting in a decrease in sound pressure level of 6 db for each doubling of distance.

Fabrics

Attached directly to hard surfaces that do not absorb sound. However, if stretched over materials such as fiberglass, and provided they are not airtight, they make an acoustically excellent finish that fully preserves the substrate's absorptivity.

Pitch

Attribute of an auditory sensation which enables us to order sound on a scale extending from low to high frequency.

Gypsum Liner Board

Available in 3/4 inch or 1 inch thick board used primarily in area separation wall systems.

Path

Basic element in an acoustical situation (air, earth, building materials, water, etc.)

Concrete Masonry Units

Modular building blocks made of concrete. They are usually manufactured with hollow cores. The attenuation provided depends mainly on their weight. lightweight units may be adequate in non-critical cases. Normal-weight units, especially if solid or if their cores are filled with sand or mortar, attenuate sound very well. Exceptionally high orders of attenuation can be achieved with two side-by-side but unconnected. Since its surface is somewhat porous, it is slightly absorptive, unless painted or otherwise sealed.

Background Sound

Noise from all sources in an environment, exclusive of a specific sound of interest.

Infrasound

Noise of the frequency less than 20 cycles per second, below the normal lower audible limit of the human ear.

Frequency

Number of complete oscillation cycles per unit of time. Unit often used is the hertz.

Absorption through Resonance

Occurs when a stiff but not totally rigid system is set in motion by sound. The system will absorb and dissipate the energy if its natural frequency corresponds to that of the incoming sound.

Absorption through Friction

Occurs when sound has access to the fine pores and interstices that one finds in porous and fibrous material. The air molecules are restrained from continuing their cycle of compression and rarefaction. The energy this lost is converted to heat.

Cycle

One complete displacement.

Longitudinal Wave

One in which the vibration of the medium is (forward and backward) parallel to the direction of the propagation of the wave.

Transverse Wave

One in which vibration of particles of the medium are perpendicular to the direction of motion of the wave energy.

Acoustical Foam

One of a variety of cellular materials, usually made of polyurethane. Manufactured with either open cells (air can be blown in and through the material) or with closed cells (each cell is sealed; the material is airtight). The cellular structure of the foam allows the sound to be trapped and dissipated. This creates an efficient method of energy transfer that works much better than curtains or draperies. Helps absorb sound to slow down echo and reverberation. For treating the inside of a room to help deaden or dampen echo .

Nosocusis

Other hearing loss that may be attributed to sickness.

Melamine Foam Linear Wedges

Pattern offers excellent absorption and allows to create many different designs. Install vertically, horizontally, diagonally, checkerboard as well as create your design.

Sociocusis

Permanent hearing damage cause by prolonged and repeated exposure to daily intense sound and noise.

Polyurethane Foam Composite Sound Containment System

Polyurethane Acoustical Foam bonded to 1 lb.sq.ft. mass loaded vinyl noise barrier with polyurethane foam vibration decoupler; Flat surface.

20-20,000 hz

Range of audibility for humans.

Sound Deadening

Recycle Wood Fiber Residue

Low Frequency Sound Absorber

Recycled Bonded Acoustical Fiber; Soft gray, ideal behind acoustical fabric, perforated or slotted panel surfaces.

Damping

Refers to energy dissipation in an oscillating system. A damped system cannot oscillate freely.

Sound Reinforcement

Refers to the beneficial reinforcement of a sound signal provided by sound-reflecting surfaces or by a loudspeaker system.

Subjective

Related to condition of the brain and sense organs rather than direct physical actions.

Polyurethane Foam Sound Absorber

Scientifically engineered patter designed to absorb the widest range of frequencies. Effectively reduces reflected noise and reverberation time to produce safe and enjoyable surroundings.

Porous Expanded Polypropylene Acoustical Wall Panels

Semi-rigid Porous Expanded Polypropylene Acoustical Bead Foam; Non-abrasive, slightly textured, porous. Lightweight, impact-resistant, moisture, bacteria and fungi-resistant. Tackable surface, UV stable.

Loose Fill Insulation

Similar to fibrous batts and blankets, except that it can be blown or dumped in place. It serves much the same purpose as batts within a partition; that is, it improves attenuation. Comes in bags and is usually blown into cavities with special equipment.

Ultrasonic

Sound above the audible range, frequency greater than 20,000 cycles per second.

Liquidborne Sound

Sound caused by pulsations of liquid pressure about the mean static pressure.

Fibrous Batts and Blankets

Usually made of fiberglass or mineral fiber, and are among the most common forms of acoustical (also thermal) insulation in use today. If exposed to the room, as a wall finish or as a ceiling finish, they absorb sound and thus reduce noise and reverberation time in the room. Performance depends on thickness and on the properties of the facing. If used between two faces of a partition, batts and blankets improve attenuation. They do it by absorbing sound that is in transit though the partition's cavity. If cavity is braced by rigid ties, there is little improvement.

Pure Tone

Vibration produced at a single frequency.

Prefabricated Acoustical Units

Wallboard and tileboard. These include various type of perforated, unperforated, fissured or textured cellulose and mineral fiber tiles, lay-in panels and perforated metal pans with absorbent pads constitute typical units in this group. Most sound-absorbing tiles and panels are not sufficiently durable for wall application. For walls, use fibrous materials with protective open facings. Use membrane-faced or ceramic tile materials for humid environment.

Sound Diffusion

When sound travels in all directions.

Fibrous Boards

Works like batts and blankets but is of higher density. Are excellent sound absorbers. They are available with a variety of sound-transparent (usually fabric) facings , for use as walls or ceiling panels. Less porous or thinner boards, such as those made of mineral fiber, are somewhat less absorptive.