Acoustics for Libraries
By Charles M. Salter, P.E.
Introduction
Principles ：
 Site noise considerations
 Establish noise standards
 Room acoustic considerations
 Sound isolation between use spaces
 Vibration control for mechanical equipment
 Audio/visual system considerations
Sound and noise
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Please differentiate between sound and noise
Define “frequency”
SPL (Sound Pressure Level)音壓
Pa：Pa – Pascal
dB：
dBA：A-weighting curve has been widely
adopted for environmental noise
measurement in roadway noise and aircraft
noise analyses
Sound and noise
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NC Rating：?
NC-25:
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Loudness of all frequencies must fall at or
below the NC-25 curve
以p6為例，人對於 NC-25高頻音(4kHz)能
容忍之背景聲音音壓為? NC-25低頻音
(63Hz)所能容忍之背景聲音音壓為?
Room Acoustics
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Physical characteristics of a space for the
hearing of directed and reflected sound
High level of reflected sound – poor room
acoustics creating unwanted background
noise
Reverberation  the time required for the
sound to be absorbed gradually and
reduced below hearing level
Room Acoustics
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Sound absorbing materials reduce
reverberation
Multi-purpose rooms：
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Musical activities: longer reverberation is
preferred(1.5 seconds – acceptable)
Speech activities: low reverberation is
better (<1 seconds – acceptable); too
long causing interference
Sound Absorption
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Sound absorbing materials used in
building are rated using the Noise
Reduction Coefficient (NRC)
Average of sound absorption
coefficients from 250 Hz to 2000 Hz
(speech frequency)
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Perfectly absorptive – NRC = 1.0
Perfectly reflective – NRC = 0.0
Sound Absorption
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Acoustically transparent materials: fabric,
perforated metal, and spaced wood slats
acoustically transparent allowing sound
energy to pass through and be absorbed by
the material located behind
Absorptive materials:
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Thicker porous materials in lay-in grid ceiling
Thick glass fiber ceiling tile (or adding acoustic
absorption to the space – suspend acoustic
baffles
Sound Insulation
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Purpose: reduce intrusive noise; reduce
the transmission of sound through solid
barriers in buildings
5.1 Principle of sound insulation
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Reduction of sound energy from one area
to another by absorbing or reflecting –
sound transmission loss (TL)
TL of Massive wall > TL of lighter wall
Use of dual panel partition ：increase TL
Sound Insulation
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5.2 Sound insulation construction
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STC (Sound Transmission Class): rating of a
wall, floor or ceiling determined by the
component of the construction.傳音等級
5.2.1 Wall construction
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What is the min STC rating for a conference room
and a office?
What is the min STC rating for a room having
amplified sound systems?
Sound Insulation
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5.2 Sound insulation construction
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5.2.1 Wall construction- What are the
considerations for actual construction of
sound-rated partition?
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Air and sound leaks through cracks
Air and sound leaks through normal openings
Structural connections between double stud
partition 雙柱隔板之結構結合情況
Seal both faces of a concrete masonry （混泥
土工程）
Sound Insulation
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5.2 Sound insulation construction
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5.2.1 Wall construction- movable partitionflexible space utilization
What are the types of operable partition?
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Panel operable wall : better sound isolation
(electronic or manual operations)
Accordion partitions : for visual privacy
Sound Insulation
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5.2 Sound insulation construction
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5.2.2 Floor construction
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Two acoustical functions provided by floor
and ceiling: airborne sound insulation, and
impact insulation
Insulation can be upgraded by decoupling
ceiling from the structure
Mechanical and electrical
systems noise control
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6.1 Space Planning
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Cost-effective noise control technique
Avoid locating mechanical equipment
rooms and electrical transformer rooms
near spaces that require low background
noise level
Floating floor ：neoprene pad + concrete
slab
Mechanical and electrical
systems noise control
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6.2 Noise control for main building
equipment
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Use quietest type fan
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Down discharge fan
Side discharge fan
Mechanical and electrical
systems noise control
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6.2 Noise control for main building
equipment
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Fan noise transmission Duct borne
noise –
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Breakout noise
Mechanical and electrical
systems noise control
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6.2 Noise control for main building
equipment
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Absorption of fan-generated noise
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Provide long duct lengths between fans and the
nearest air register serving a room
Treat the duct internally with duct liner
Mitigation of air turbulence
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Using ducts with ample cross-sectional area
Keeping duct run straight
Round ductwork better than rectangular ductwork
Mechanical and electrical
systems noise control
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6.2 Noise control for main building
equipment
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Crosstalk Silencers
Duct lagging
Mechanical and electrical
systems noise control
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6.2 Noise control for main building
equipment
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Variable speed drives and their cabinets
should be vibration isolated, and never
adjacent to an acoustically sensitive room
Chiller – HVAC (Heating Ventilation Air
Condition )
Audio-Visual
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7.1 Auditoriums, theaters and meeting
rooms ----Configuration
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Podium or lectern located to the left or right of
the screen
Video: maximum depth of the seating – 8
times the height of the screen for video;
Height of screen: 最後一排至銀幕之1/8
Room used for projection: maximum depth
seating – 6 or less times the height of the
screen
Audio-Visual
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7.1 Auditoriums, theaters and meeting
rooms ----Configuration
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30 degrees from the centerline of the
screen – limit for seating in the front rows
Width of the screen determined by aspect
ratio:
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1.3:1 (= 4:3) (長:寬)
Audio-Visual
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7.1 Auditoriums, theaters and meeting
rooms ----Configuration
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Minimum distance from ceiling: 6 inches – avoid
ceiling reflection
Minimum distance from floor: 4 ft
Front projection screen
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距離?
Rear Projection screen: projector located in a
separate room – translucent; better noise
control
Audio-Visual
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7.1 Auditoriums, theaters and meeting
rooms ----Configuration
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Loudspeakers for sound - should be located
as close as possible to the projection
Perforated-type screen: speakers can located
behind screen
Solid screen: speakers placed close to ear
height
Audio-Visual
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7.1 Auditoriums, theaters and meeting
rooms ----Configuration
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Microphone should be selected and located
very close to the lecture or performer
Loudspeaker
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Central cluster: groups all the required
loudspeakers at one location (Fig 25), provide best
match for audio and visuals
Distributed system: works well with low-ceiling
room (Fig 26)
Audio-Visual
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7.2 Teleconference rooms
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Audio, or AV
Cameras and video monitors for projection
Video images transmitted over high-speed
ISDN telephone
One of two floor plans for effective from
camera imaging
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V-shaped table
Curved table
Audio-Visual
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7.3 Electronic classrooms and training
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Distance learning classroom
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Hybrid of presentation and video conferencing
Interaction of local and distant participants
Screens – at front and rear of room
Training rooms
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Different types of training rooms
Audio-Visual
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7.4 Lighting in AV spaces
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Dimmable to allow note taking illumination
Light for speaker – avoid interference with
projection images
Dimming system- control “bright” and “dim”
Adequate emergency lighting