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Acoustics

Fundamentals

Environmental Technology IV

Professor Tango & Parker Spring 2009

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Acousticsis usually very broadly defined as "the science of

sound."

Room AcousticsThe shaping and equipping of an enclosed space

to obtain the best possible conditions for faithfulhearing of wanted sound and the direction andthe reduction of unwanted sound.

Room Acoustics deal primarily with the control ofsound which originates within a single enclosure,rather than its transmission between rooms.

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The balance of keeping

wanted

soundsand eliminating

unwantedsounds

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Sound Waves

What is a wave?

http://www.kettering.edu/~drussell/Demos/waves-

intro/waves-intro.html

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frequency;

vibration cycles per second

wave length:

distance between identical points on a wave

amplitude

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The human ear can detect sounds between

20 HZ and 20,000 HZ.

Most sensitive in the range of 100HZ to 5000HZ

Hear it: http://www.surendranath.org/Applets.html , then select: menu/new applets/new menu/ waves/ hear the beats.

Speakerdiameter

(cm)

Frequencies

(Hz)

Woofer 30 20-2,000

mid-

range12 2,000-5,000

tweeter 65,000-

10,000super-

tweeter3

10,000-

20,000

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20 HZ 56 feet

20,000 HZ - 11/16

The length of a sound wave

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VelocityRate at which sound travels through a conductor

Air:

Wood:

Steel:

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VelocityRate at which sound travels through a conductor

Air:

Wood:

Steel:

1128 feet per second

11,700 feet per second

18,000 feet per second

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Sound Pressure/

Amplitude

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Sound Pressure/Amplitude vs. Frequency

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Complex Waves

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The Mobility of Sound

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Direct Sound

Since sound travels in all directions from the

source, each listener will hear just the segmentif the overall sound wave that is traveling in adirect line to his hear (in a space free fromreflecting surfaces). As the distance from the

source increases, the sound pressure at thelistener's ear will decrease proportionately.

(Example: goodHeadphones)

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Reflection

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Diffusion

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Diffraction: The Sound Squeezes Through

Sound waves are not always reflected or

absorbed. When an obstacle is the same size asthe wavelength or less, the sound can bendaround obstacles or flow through small openings,and continue onward. This is called diffraction.

This action is more likely for deeper sounds (oflow frequency, and this with longer waveforms).

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ReverberationReverberationThe perpetuation of reflected sound within a space afterThe perpetuation of reflected sound within a space afterthe source has ceased is calledthe source has ceased is called reverberationreverberation. The time. The time

interval between reflections is usually so short thatinterval between reflections is usually so short thatdistinct echoes are not heard. Instead, this series ofdistinct echoes are not heard. Instead, this series ofreflections will blend with the direct sound to addreflections will blend with the direct sound to add"depth". Reverberation is a basic acoustic property of a"depth". Reverberation is a basic acoustic property of aroom. It can enrich speech and music in all areasroom. It can enrich speech and music in all areas ---- oror

it can slur speech and generate higher noise levelsit can slur speech and generate higher noise levelsthroughout a room, depending upon the room volume,throughout a room, depending upon the room volume,timing, and absorption.timing, and absorption.

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Room Acoustics

Shape

Volume

Materials

Room Acoustics

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Room Acoustics

Sound re-enforcement

Reflect

Absorb

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The shape of a space

determines the sound

path within the space

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Room Acoustics

AA

B

C

Reverberation

A

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Parallel reflective

surfaces generates

unwanted

reverberation

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Reverberation time mustmatch room function

Pure speech requires short

reverberation time

Symphony blends notes with long

reverberation time

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The lower part of the band is best for rooms intended primarilyfor speech, the upper part is better for music rooms, and themiddle portion is recommended for general purpose rooms.

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Studies based on the audibility of speech andmusic reveal that the most desirablereverberation times generally fall within the

ranges shown below. These values are based ona sound frequency of500 Hz (approximate pitchof male speech).

Reverberation time in secondsSpeech

Small offices 0.50 to 0.75Classrooms/lecture rooms 0.75 to 1.00Work rooms 1.00 to 2.00

MusicRehearsal rooms 0.80 to 1.00Chamber music 1.00 to 1.50Orchestral/Choral/Average church music 1.50 to 2.00

Large organ/liturgical choir 2.00 to 2.25

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Live!

DEAD

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A classification of typical rooms by acousticalenvironments

"Dead" : Very Absorptive

"Live: Highly Reflective

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Absorbing MaterialsCarpet

Soft ceiling tile

Rigid foam

people

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Reflecting Materials

Masonry

Wood smooth panels

Smooth concrete

Glass

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Medium

Cafeterias (school or office)Reduce overall noise level.Use highly sound-absorptive ceiling; also use quietequipment such as rubberized dish trays.

GymnasiumsInstructor must be heard over background noiseUse acoustical material over entire ceiling to reducenoise; walls remain untreated to permit somereflected sound.

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Medium Dead

Elementary-grade classroomsTeacher must be heard distinctly; reduce noise levelproduced by children.Acoustical ceiling essential. Supplementary acousticalspace units on upper rear and side walls are

desirable.

Music rehearsal roomsUnlike music hall, instructor must hear individualnotes distinctly; minimum reverberation desired.

Entire ceiling, sidewalls, and wall facing musicianswould be treated; wall behind musicians may be leftsound-reflective for proper hearing. Room should belocated away from normal use rooms.

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Dead

KindergartenMaximum noise reduction.Maximum acoustical treatment on ceiling; space units

on available wall surfaces.

Vocational classrooms and shopsMaximum noise reduction.Acoustical tile or lay-in panel ceiling, plus acousticaltreatment of available upper wall areas; locate awayfrom normal use rooms.

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Reverberation time (in seconds) =

.05 x volume of room______________________________

sabins

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Sabin

The amount of sound absorbed is measured insabins. One sabin is equal to the soundabsorption of one square foot of perfectlyabsorptive surface. The sound absorption

equivalent to an open window of one squarefoot. (theoretical, since no such surface exists).

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Measuring Absorption:Sound Absorption Coefficient

The fraction of the energy absorbed (at aspecific frequency) during each reflection isrepresented by the sound absorptioncoefficientof the reflecting/absorbing surface.In the building industry, this is a meaningfuland widely accepted quantitative measuring

of sound absorption, and applies to allsurfaces -- whether they be of reflective orabsorptive materials.

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Reflective Surfaces

Hard, massive, non-porous surfaces, such as

plaster, masonry, glass and concrete, absorbgenerally less than 5% of the energy ofstriking sound waves and reflect the rest.Such materials heaver absorption coefficients

of .05 or less.

Ab ti S f

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Absorptive Surfaces:

Porous materials such as acoustical tile,

carpets, draperies and furniture are

primarily absorptive. They permit thepenetration of sound waves and are

capable of absorbing most of the soundenergy. These materials may haveabsorption coefficients approaching 1.00(one sabin per sq. ft.).

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Poor acoustical characteristics in this lecture room.

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Reflective surfaces near the speaker.

In lecture rooms more than 40 feet long, the rear wall

should be absorptive to prevent echoes.

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Why Sound Conditioning??

The objective of sound-conditioning isto create a haven for the occupant,shielded from annoyance anddistractions. With such an environment,individuals show increased productivity,tenants complain less, turnovers andvacancies are reduced, and propertyvalues rise.

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Structure borne sound

Steel Frame

Plumbing Pipe

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SourcePath

Receiver

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Isolation Of Equipment

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Isolation Of Equipment

Low-end RTUs (roof top units) are

typically loud . No isolation springs /

poorly balanced

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Background Noise

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Acceptable Background Noise Levels

As a rule, we can tolerate, and even welcome, acertain amount of continuous sound before itbecomes noise. An "acceptable" level neitherdisturbs room occupants nor interferes with the

communication of wanted sound.

Recommended category classification andsuggested noise criteria range for steady

background noise as heard in various indoorfunctional activity areas as indicated in the

Preferred Noise Criterion (PNC)Curves.

Type of Space (and acoustical requirements)

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Type of Space (and acoustical requirements)

PNC curveConcert halls, opera houses, and recital halls (for listening to

faint musical sounds)

10 to 20 dbLarge auditoriums, large drama theaters, and churches (for

excellent listening conditions)Not to exceed 20 db

Broadcast, television, and recording studios (close microphone

pickup only)Not to exceed 25 dbSmall auditoriums, small theaters, small churches, musicalrehearsal rooms, large meeting and conference rooms (for

good listening), or executive offices and conference rooms for50 people (no amplification)

Not to exceed 35 dbBedrooms, sleeping quarters, hospitals, residences,

apartments, hotels, motels, etc. (for sleeping resting, relaxing)25 to 40 db

Private or semiprivate offices, small conference rooms,

classrooms, libraries, etc. (for good listening conditions)30 to 40 db

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Type of Space (and acoustical requirements)PNC curve

Living rooms and similar spaces in dwellings (forconversing or listening to radio and TV)

30 to 40 dbLarge offices, reception areas, retail shops and stores,

cafeterias, restaurants, etc. (for moderately good listeningconditions)

35 to 45 dbLobbies, laboratory work spaces, drafting and engineering

rooms, general secretarial areas (for fair listeningconditions)40 to 50 db

Light maintenance shops, office and computer equipmentrooms, kitchens and laundries (for moderately fair listening

conditions)45 to 55 db

Levels above PNC-60 are not recommended for any officeor communication situation.

Minimize Background Noise Level

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Minimize Background Noise Level -Overall noise levels which may interfere with wantedcommunication should always be anticipated and corrected. To

provide maximum quiet, typical methods include the following:

1. Elimination of outside noise by sound attenuation in walls,ceilings, and floor

2. Use of quiet mechanical equipment wherever possible.

3 .Control of remaining noise by absorption -- carpeting,upholstery, and acoustical treatment placed above and behindaudience.

4. Individual handling of unusual noise sources -- for example,isolation of a noisy movie projector.

5. Electronic amplification of the wanted sound level above the

background noise level -- usually done as a last resort.

Masking:

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Masking:

Creating Background "Noise

When an undesirable background sound can't bereduced or eliminated, it can sometimes bemasked (made less objectionable by introducing a

different sound). For example, piped-in music inrestaurants can mask the din of dish clatter andmultiple conversation.At the other extreme, a masking sound may beintroduced to correct an oppressively quiet room.For example, a telephone ring or a slight coughcan be distracting in a very "dead" room, andspeech privacy would be impossible. In manycases the heating and air conditioning systems

will provide a sufficient amount of masking noise.

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white noise

pink noise

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Sound Isolation

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The control of intruding sound ideally begins with theinitial building concept and continues to be aconsideration through the life of the building. Total

sound conditioning affects

1. site selection

2.

building orientation on the site3. room orientation within the building4. design, detailing, specification5. construction6. inspection.

Predictable sound attenuation can be achieved bycareful attention to detail during all phases ofplanning and construction.

Site Selection for Sound Control

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Site Selection for Sound Control

Orientation

Room Arrangement

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Room Arrangement

1. What is the STC rating of the outside kitchen exterior wall?

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sound barrier

Sound Barriers

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If the noise source is intense and no naturalsound barrier exists, a man-made sound

barrier should be considered as part of thedesign. A solid fence-type barrier mayremovefrom 10 to 20 db from the noise level. High-frequency sounds will be reduce more than low

frequency sounds. The cost of an outsidebarrier may be less than the cost of reducingthe sound transmission in the construction.This type of sound barrier must completely

shield the building from the noise source. Itshould be placed as close to the sound sourceas possible to obtain the greatest sound-shadow angle. If a fence or wall is used, no

louvers or openings should be permitted.

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Acoustical Zoning

A r orne oun

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Airborne sound includes conversation, outdoornoises, music and machine noises (machines

usually also produce impact sound). It is themajor source of intruding sound from roomson the same floor and from the outdoors. It iscontrolled by:

1. Mass (weight),2. Isolation (decoupling),3. Absorption4. Limpness of Construction.

These must be combined with airtight sealingand the elimination of flanking paths (routesby which the sound travels around a partition

rather than being stopped by it).

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Impact Sound

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Impact Sound

Impact Isolation

If the surface receiving the impact, such as a floor, can beisolated from the structure, the impact sound will not betransmitted. Likewise, if the structure can be isolated from theceiling below, the impact sound will be restricted from travelinginto the room below.Isolation of the ceiling of the receiving room can be accomplished

with resilient mounting of the drywall panels or lath. This stillallows some sound from above to enter the structure and travelto other rooms. Resilient subflooring materials such asinsulation board and underlayment compounds are effective, as isheavy carpet over thick under pad. A combination of these

methods is necessary to produce ideal attenuation of impactnoise.Other sources of structure-borne sound, such as motors, flushingtoilets, dishwashers, garbage disposals, blowers, and plumbing,can be isolated from the structure by resilient mountingprocedures.

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Isolation (Decoupling)

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Isolation (Decoupling)

staggered 2x3 studs on a single sill plate with alternate

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staggered 2x3 studs on a single sill plate, with alternatestuds connected to opposite diaphragms

d bl f d ill l

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double row of studs on separate sill plates

2x4 studs with one diaphragm attached

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2x4 studs with one diaphragm attachedthrough sound deadening board.

2x4 studs with one diaphragm attached

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p gby means of resilient channels

R ili Ch l

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Resilient Channel1/2

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Absorption

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AbsorptionThe amount of sound energy dissipated depends on thethickness of the material, its density (which determines

the amount of difficulty that the sound encounters intraveling through), and it's resiliency (flexibility with theability to spring back to its original shape). Mineral woolinsulation because of its porous yet dense character, ishighly effective in this application. Sound attenuation

blankets are manufactured with higher density thanthermal insulating blankets to obtain optimumattenuation. Mineral fiber sound attenuation blankets,placed between the studs in a resilient partition withresilient channels, retard movement of the air columnand convert considerable sound energy into heat.However, if the diaphragms are directly connected to rigidstuds, the partition will act as a single diaphragm,rendering the wool ineffective in dissipating sound

energy.

www.usg.com

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www.usg.com

search forSA 100 - Fire Resistant Assemblies

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www.usg.com

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SAFB:sound attenuation fire blankets

Effective mass is contributed by the gypsum panels or plaster.A common wood-stud partition with 5/8-in. SHEETROCK FIRECODE

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p /"C" Gypsum Panels on each side will test STC 34. Using double-layer panels on each side will increase the rating to STC 41,an improvement, but certainly not optimum. Increasing the mass

beyond this point is of little value since other, less expensivemethods of achieving better performance are available. Gypsumpanels decoupled on one side with RC-1 SHEETROCK ResilientChannels, will have sound attenuation ofSTC 49; STC 59 with theaddition of 3-in. THERMAFIBER Insulating Blankets.

The performance of an assembly can vary as much as1

5 STCpoints with the quality of the workmanship

The performance level being sought will usually

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p g g yfall in the STC range of 45 to 60. Thepartitions used in most single-family dwellings

today would test about STC 35 (although theactual performance is often even less due toleaks and flanking paths). On the other end ofthe scale, STC-60 partitions are found

increasingly in luxury multi-family dwellings,and other quality buildings. Partitionperformance ofSTC 60 will, for practicalpurposes, reduce an 85 db noise level (the

maximum normally encountered in a residence)to a 25 db background sound (comparable to anight-time rural sound level) -- near ideal forsleeping rooms.

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Noise Reduction Coefficient (NRC)

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Noise Reduction Coefficient (NRC)The average amount of sound energyabsorbed over a range of frequencies

between 250 Hz and 2,000 Hz.

NOR

MAL SPEECHR

ANGE

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Wh t i CAC?

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What is CAC?

A: CAC, orCeiling Attenuation Class, is a measure of thesound transmission loss as noise travels between rooms.

Essentially, it is the ability of a ceiling panel to block sound

between rooms.

Q: What spaces require CAC values?A: CAC values are essential in interior spaces that require

physical separation from other areas such as conference and

board rooms, private offices, bathrooms, and corridors.

Q: Is CAC important in open plan offices?

A: Actually, CAC is important to assure privacy for areas

outside or adjoining an open plan such as private offices or

conference rooms.

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Details, Specifications

and Construction

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Flanking Paths

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Flanking PathsFlanking Paths

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Flanking PathsFlanking Paths

HVAC

Good

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Sound Control

Negative impacts

Flanking Paths

Electrical Boxes

Especially back-to-back

HVAC

Perimeter Seals

Doors

Other penetrations

50 STC

Example: Back-to-back

electrical boxes

Flanking Paths

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Flanking Paths

BestBetter

Flanking Paths

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CUTOUTS

g

Cabinet

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Eliminating a flanking path with a non-

resilent material

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SoundSound SealSeal

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STC 53

SoundSound SealSeal

Acoustical

Sealant

STC 29Unsealed

2 Layers

5/8 Gypsum

Board

Insulation

Sound Path

SoundSound SealSeal

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STC 53

2 Layers

5/8 Gypsum

Board

Insulation

SoundSound SealSeal

Sealed

Acoustical

Sealant

Sealing

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Sealing

figure 50A. 29 STCUnsealed

figure 50B. 53 STCBoth Base layers sealed.No relief on face layers.

figure 50C. 53 STCSealant applied to runnertrack and board.

figure 50D. 53 STCSealant beneath and on edgeof runner track. Base layernot relieved. Face layer

relieved and sealed.

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S d C t l

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Sound Control

How to achieve SoundAttenuation

Increase STC by:

65 dB 15 dB

50 STC

Isolation

De-coupling

Absorption

Mass

Usually the

Dimension of theFraming 3 5/8

RC-1 or resilient channelInsulation either SAFBor fiberglassto absorbsound energy

Drywall or engineered panel

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Improving Sound TransmissionLoss

Doubling Partition Width =

5 dB Transmission Loss Improvement

Doubling MASS =

5 dB Transmission Loss Improvement

Rules ofThumb

Improving STCImproving STC

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STC 48

p gp g

STC 54 STC 61

STC 43 - 25 ga. Steel stud

ST

C 40 - 20 ga. Steel stud

ISOLATION

MASSDECOUPLINGRC-1Resilient Channel

STC 37 - Wood stud

ABSORPTION3 1/2 Insulation

STC 43 - 25 ga. Steel stud

Doors & Door Frames

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Doors & Door Frames

High

STC Partitions

High

STC Partitions

Fill

Solid Core

Gasket

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last Environmental Tech class : - (

Next Thursday: Dave Duda With Newcomb BoydSecurity Designthen

Final Exam Review