Architectural Acoustics: Building Sound Design

Acoustics Overview

• Acoustics is the science and engineering of achieving good sound within a building
• Acoustics is a branch of acoustical engineering

Architectural Acoustics

• Architectural acoustics, also known as building acoustics, is the science of achieving good sound within a building
• Architectural acoustics aims to design spaces, structures, and mechanical systems to meet hearing needs
• "Wanted" sounds can be heard properly, while "unwanted" sounds or "noise," can be attenuated to minimize annoyance with proper design
• The first application of modern scientific methods to architectural acoustics was done by American physicist Wallace Sabine in the Fogg Museum lecture room
• Sabine applied this knowledge to the design of Symphony Hall, Boston

Wallace Sabine and Architectural Acoustics

• Wallace Sabine was the U.S. physicist who founded the science of architectural acoustics
• After graduating from Ohio State University in 1886, Sabine did graduate work at Harvard University and later joined the faculty
• When Harvard opened the Fogg Art Museum in 1895, its auditorium had seriously defective acoustics caused by excessive reverberation
• Sabine's discovery that the product of the reverberation time multiplied by the total absorptivity of the room is proportional to the volume of the room is known as Sabine's law
• The unit of sound-absorbing power, the sabin, was named after Wallace Sabine
• The first building designed in accordance with principles laid down by Sabine was the Boston Symphony Hall, which opened in 1900

Goals of Architectural Acoustics

• Architectural acoustics can be about achieving good speech intelligibility in a theatre, restaurant or railway station
• Architectural acoustics can be about enhancing the quality of music in a concert hall or recording studio
• Architectural acoustics can be about suppressing noise to make offices and homes more productive and pleasant places to work and live in
• Architectural acoustic design is usually done by acoustic consultants
• Achieving good acoustics has become more difficult due to reduced construction material weight for cost reasons, leading to increased sound transmission
• A large portion of a building's budget is allocated to mechanical systems, which often contribute to noise

Elements of Acoustics

• All acoustics situations have three common elements: source, transmission path, and receiver
• The source can be made louder or quieter
• The transmission path can be made to transmit more or less sound
• The listener's reception of sound can be influenced

Building Skin Envelope

• Building skin envelope science analyzes noise transmission from building exterior envelope to interior and vice versa
• Main noise paths include roofs, eaves, walls, windows, doors and penetrations
• An example of building skin envelope is providing a suitable design for a home near a high-volume roadway or airport flight path

Inter-Space Noise Control

• Inter-space noise control is limiting noise transmission from one building space to another to ensure space functionality and speech privacy
• Typical sound paths are ceilings, room partitions, acoustic ceiling panels, doors, windows, ducting, and other penetrations
• Technical solutions depend on the source and path of acoustic transmission
• An example of inter-space noise control is providing suitable party wall design to minimize noise disturbance between apartment residents

Interior Space Acoustics

• Interior space acoustics controls a room's surfaces based on sound absorbing and reflecting properties
• Excessive reverberation time, which can be calculated, can lead to poor speech intelligibility

Mechanical Equipment Noise

• Building services noise control manages noise produced by HVAC systems, elevators, electrical generators, and other building service infrastructure
• Inadequate control may lead to elevated sound levels that are annoying and reduce speech intelligibility
• Typical improvements include vibration isolation of mechanical equipment and sound attenuators in ductwork
• Sound masking can be achieved by adjusting HVAC noise to a predetermined level

Role of Acoustics

• Knowledge in acoustics is important for many professionals, including engineers, architects, medical doctors, psychologists, biologists, oceanographers, and media professionals
• Acoustics promotes the creation of environments with good listening conditions and reasonably free from harmful noise and vibrations
• Acoustics is a discipline of great importance for a sustainable development

Acoustic Terminology

• Absorption Coefficient: The fraction of incident sound energy absorbed by a surface
• Anechoic Chamber: A sealed room with all surfaces designed to completely absorb all sound
• Attenuation: A reduction in sound level
• Background Noise: Ambient noise
• Break-in Noise: Transfer of noise from surrounding space into a duct through duct walls
• Break-out Noise: Transfer of noise from inside a duct into space outside the duct
• Dead Room: Room with unusually large amount of sound absorption
• Decibel (dB): Unit of measurement for sound pressure, intensity, or power level
• Diffraction: Change in sound propagation direction due to bending around a barrier
• Diffuse Sound (field): Sound with equal intensity from all directions
• Direct Sound: Sound arriving directly from the source without reflection
• Echo: Reflected sound with sufficient time delay
• Environmental Noise: Exterior background noise
• Fidelity: Faithful reproduction of a sound source
• Flutter Echo: Rapid, repetitive sound succession from multiple reflections in a space with hard, flat, parallel walls
• Frequency: The number of full cycles per second
• Impact Noise: Noise by the collision of two objects
• Infrasonic: Sound below human audible frequency, below 20 Hz
• Insulation: Isolation
• Intermittent Sound: Discontinuous sound where pressure level falls below measurable level
• Inverse Square Law: Sound intensity varies inversely with the square of the distance from the source
• Isolation: Lack of acoustical connection
• Leak: Small opening allowing airborne sound to pass through
• Live Room: Room with an unusually small amount of sound absorption
• Loudness: Auditory sensation depending on sound pressure level and frequency
• Masking: The increase in the threshold of audibility of a sound to be heard in the presence of another
• Noise Isolation Class (NIC): Single-number rating of noise reduction between two rooms
• Noise Reduction (NR): Reduction in sound pressure level of noise.
• Noise Reduction Coefficient (NRC): Single-number rating of sound absorption coefficients at 250, 500, 1000 and 2000 Hz
• Outdoor-Indoor Transmission Class (OITC): Weighted single-number rating of sound reduction effectiveness of a partition separating an indoor space from the outside.
• Pitch: A listener's perception of the frequency of a pure tone
• Reflection Coefficient: Measure of a surface's sound reflective property
• Resonance: Large amplitude vibration when source frequency equals a room's natural frequency
• Reverberant Sound Field: Sound field from repeated reflections from boundaries in an enclosed space
• Reverberation: Continuation of sound in an enclosed space after the initial source stops
• Reverberation Time (RT): Time for sound intensity to decay by 1 millionth after the source stops
• Sabin: Unit of measure of sound absorption
• Scattering: Irregular diffraction of sound in many directions
• Sound Insulation: The ability of a barrier to prevent sound from reaching a receiver
• Sound Intensity (SI): The average rate of sound energy flow through a unit area in a given direction
• Sound Intensity Level (SIL): Quantity expressed in decibels of airborne sound.
• Sound Lock: Small space acting as a buffer between a source room and a receiving room
• Sound Pressure: Fluctuating pressure of sound superimposed on the static air pressure
• Sound Pressure Level: See sound intensity level
• Sound Transmission Class (STC): Single-number rating of the sound insulation rating of a partition
• Structure-Borne Sound: Sound propagated through a solid structure
• Transmission Coefficient: Ratio of transmitted sound energy to incident sound energy
• Transmission Loss (TL): Measure of sound insulation of a partition
• Wavelength: Distance between two adjacent compressions or rarefactions in a sound wave
• White Noise: Noise with uniform energy over a wide range of frequencies, analogous to white light and sounds hissy