Acoustics for Libraries By Charles M. Salter, P.E.

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 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 ad

opted for environmental noise measurement in roadway noise and aircraft noise analyses

Sound and noise

NC Rating ： ? NC-25:

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

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

Sound absorbing materials reduce reverberation

Multi-purpose rooms ： Musical activities: longer reverberation is

preferred(1.5 seconds – acceptable) Speech activities: low reverberation is bet

ter (<1 seconds – acceptable); too long causing interference

Sound Absorption

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) Perfectly absorptive – NRC = 1.0 Perfectly reflective – NRC = 0.0

Sound Absorption

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: 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

Purpose: reduce intrusive noise; reduce the transmission of sound through solid barriers in buildings

5.1 Principle of sound insulation 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 5.2 Sound insulation construction

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 What is the min STC rating for a conference room

and a office? What is the min STC rating for a room having ampl

ified sound systems?

Sound Insulation

5.2 Sound insulation construction 5.2.1 Wall construction- What are the cons

iderations for actual construction of sound-rated partition? Air and sound leaks through cracks Air and sound leaks through normal openings Structural connections between double stud p

artition 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 5.2 Sound insulation construction

5.2.1 Wall construction- movable partition-flexible space utilization

What are the types of operable partition? Panel operable wall : better sound isolation

(electronic or manual operations) Accordion partitions : for visual privacy

Sound Insulation 5.2 Sound insulation construction

5.2.2 Floor construction 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

6.1 Space Planning Cost-effective noise control technique Avoid locating mechanical equipment roo

ms and electrical transformer rooms near spaces that require low background noise level

Floating floor ： neoprene pad + concrete slab

Mechanical and electrical systems noise control

6.2 Noise control for main building equipment Use quietest type fan

Down discharge fan Side discharge fan

Mechanical and electrical systems noise control

6.2 Noise control for main building equipment Fan noise transmission Duct borne noise

– Breakout noise

Mechanical and electrical systems noise control

6.2 Noise control for main building equipment Absorption of fan-generated noise

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

Using ducts with ample cross-sectional area Keeping duct run straight Round ductwork better than rectangular ductwork

Mechanical and electrical systems noise control

6.2 Noise control for main building equipment Crosstalk Silencers Duct lagging

Mechanical and electrical systems noise control

6.2 Noise control for main building equipment Variable speed drives and their cabinets sho

uld be vibration isolated, and never adjacent to an acoustically sensitive room

Chiller – HVAC (Heating Ventilation Air Condition )

Audio-Visual

7.1 Auditoriums, theaters and meeting rooms ----Configuration Podium or lectern located to the left or right of

the screen Video: maximum depth of the seating – 8 time

s 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

7.1 Auditoriums, theaters and meeting rooms ----Configuration 30 degrees from the centerline of the screen

– limit for seating in the front rows Width of the screen determined by aspect rati

o: 1.3:1 (= 4:3) ( 長 : 寬 )

Audio-Visual 7.1 Auditoriums, theaters and meeting room

s ----Configuration Minimum distance from ceiling: 6 inches – avoid

ceiling reflection Minimum distance from floor: 4 ft Front projection screen

距離 ? Rear Projection screen: projector located in a se

parate room – translucent; better noise control

Audio-Visual

7.1 Auditoriums, theaters and meeting rooms ----Configuration 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

7.1 Auditoriums, theaters and meeting rooms ----Configuration Microphone should be selected and located

very close to the lecture or performer Loudspeaker

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

7.2 Teleconference rooms 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 V-shaped table Curved table

Audio-Visual

7.3 Electronic classrooms and training Distance learning classroom

Hybrid of presentation and video conferencing Interaction of local and distant participants Screens – at front and rear of room

Training rooms Different types of training rooms

Audio-Visual

7.4 Lighting in AV spaces Dimmable to allow note taking illumination Light for speaker – avoid interference with

projection images Dimming system- control “bright” and “dim” Adequate emergency lighting