Chapter 8

Auditoriums

Allowing adjustments to acoustics is good; curtains that retract; reflector panels that adjust on ceiling

Noise Reduction Coefficient (NRC)

Averages sound absorption coefficient at 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz

Acoustic Design Main Points

First, the architect or the interior designer must define the character of the sound problem Next, consider acoustics of individual rooms, including any structural precautions that must be taken

Staggered-stud Partitions

Framed with two separate rows of studs arranged in a zigzag fashion and supporting opposite faces of the partition. Fiberglass blanket can be inserted between rows of studs

Sound Transmission

Involves the transfer of sound from one part of a building to another Airborne Sound- changes directions easily (ex. talking) Structure Borne Sound- from an impacting source directly contacting the building structure (ex. someone bouncing a basketball in the apartment above)

Compound Barriers

It's very effective to use multiple layers of gypsum wallboard with a resilient channel between the two faces of the partition and with absorptive material in the staggered stud space

Acoustical Fiber Ceiling Panels

Made of treated wood fibers bonded with inorganic cement binder High structural strength and are abuse resistant

Materials and Acoustics

Massive Materials- concrete and brick are big reflectors Reflective Materials- glass reflects higher frequencies almost completely, but absorbs low frequencies fairly well since it resonates

Impact Noise

Controlling Impact Noise: Attenuation Impact Insulation Class (IIC): Rating for floor construction. Higher rating is better.

Design Process

Acoustic Consultants- for special acoustic issues, bring in a consultant as EARLY as possible DIRECT implications for the interior designer

Ceiling Products

Acoustic Tile: mineral fiber tiles have NRC ratings between 0.45-0.75 Some faced fiberglass tiles have NRC of 0.95

Flanking Paths

Acoustic short circuit, most common is a plenum with ductwork, registers, and grilles, which turns into an intercom (use duct lining)

Speech Privacy

group spaces similarly. Three levels.

Room Acoustics

how sound behaves in a given room depends on the shape, size, and proportions of the room. when little sound is absorbed , sounds are mixed together. when steady sounds are mixed together, they reverberate (get noisier) which may be bad for understanding speech but good for music

Transmission Loss

measure of how well a building material or construction assembly prevents transmission of airborne sound

Schools

need privacy between classroom spaces; dining areas should keep kitchen and serving areas separate from eating area; nothing will quiet the excessive noise in a gym but use an absorbent ceiling

Building Noise Control

noise affects design decisions regarding building siting, space planning, exterior and interior material selection, and natural ventilation (let in air but also noise)

Sound Transmission Class

rates how well a building material or construction assembly prevents transmission of airborne sound Open doorway STC= 10 Normal construction= 30-60 Special construction > 60

Mass

the more mass of a barrier, the less likely sound will make it vibrate/sound be transmitted

Measuring Office Acoustics

variety of ratings used. absorption coefficient is typically best

History of Vitruvius and Acoustics

wrote The Ten Books of Architecture

Resilient Furring Channels

Separate the wall's structure from its surface material, making the wall less stiff and inhibiting the transfer of vibrations to the other side

Music Performance Spaces

Services of acoustical consultant are essential; needs to distribute and reinforce sound evenly throughout the audience; relatively long reverberation time needed; good sound path = good visual path

Controlling Exterior Noise in Buildings

Solid exterior barriers must be close to either the source or receiver to be effective, as sound may pass over barriers or in-between locations Window and door openings can be oriented away from the sources of undesirable noise, or multiple glazing of windows can be used Make sure walls, floor and ceiling of the protected room are heavy and airtight. Weather stripping can also reduce wind noises and cut transmission of outdoor noises

Acoustics Codes and Standards

Some building codes have added limits on noise ASTM has established methods for measuring , analyzing, and quantifying noise ANSI sets scientific parameters and criteria used in acoustic analysis ASHRAE determines sound levels for mechanical systems in buildings

Public Toilet Rooms

Surround with corridors and mechanical spaces; use a steady masking sound like a noisy fan; music works very well

Assistive Listening Systems

Uses a hard-wired or wireless system to transmit an audible signal 2010 ADA Standards require these in assembly areas where audible communication is integral to use of the space

Sealing Penetrations

Very important to keep sound from traveling flanking paths

History of Modern Acoustics

Wallace Clement Sabine, developed reverberation equations and absorption coefficients for many common building materials

Increase STC

-Double-glazing for windows -Properly installing acoustical sealant -Select solid core doors or hollow core doors filled with sound-absorbing material. No louvers. -Extend partitions to slab above

3 Basic Ways to Control Noise in a Building

1. Reduction at the source through proper selection and installation of equipment 2. Reduction along the paths of transmission through proper selection of construction materials and construction techniques 3. Reduction at the receiver through acoustic treatment of relevant spaces

Residential Acoustic Considerations

Bathrooms are inherently reverberant; separate from bedrooms with intervening closets and hallways; do not use undercut or louvered doors even for ventilation; avoid back to back electrical outlets between bathroom and bedroom Do not place laundry areas where they will disturb sleeping areas Think about toilet location! Where will the rush of water in the pipes go? Wrap and resiliently wrap pipes Put a closet as a buffer space between kitchen and bedroom

Sound Absorption Coefficient (SAC)

Describes performance of sound absorbing materials. Runs 0-1 with 1 being total sound absorption

Controlling Interior Noise in Buildings

Equipment Noise- select quiet equipment and locate it away from inhabited parts of the building Mechanical System Noise- AHU- specify quieter HVAC and use passive design Plumbing System Noise- Normal sound of rushing water and "water hammer" knocking noise in a pipe turned off rapidly

Office Spaces

General Recommendations- minimum clear ceiling height of 9 ft with highly absorptive materials Open Plan Office Ceilings- Sound problems are exacerbated by sound reflecting off ceilings at 45-50 degree angle; avoid metal pan air diffusers or flat lighting fixture diffusers Glass Surfaces- increasingly popular (walls); use full height partitions, possibly heavy drapes; locate confidential spaces in groups, buffer with storage areas Floors in Open Offices- Ideally carpet to reduce chair movement/footfall Masking Sound- Use background sound system close to frequency of speech

Doors and Transmission

Hollow vs solid core doors Two gasket doors with space for a door swing between= Sound Lock Stagger doors in hallways (not directly across from each other)

Lecture Rooms

Important to have good sound reflection in teacher's space; use absorbent treatment at rear wall, perimeter of ceiling, and side wall areas between seating and standing height

Resiliency

In a stiff material, sound energy motion is passed from molecule to molecule, conducting sound efficiently

Perforated Metal Pans and Panels

backed by acoustic fillers easy to clean, not combustible

Architectural Acoustics

branch of acoustics concerned with achieving good quality sound within a building