Architectural acoustics

(civil engineering) The science of planning and building a structure to ensure the most advantageous flow of sound to all listeners.

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The science of sound as it pertains to buildings. There are three major branches of architectural acoustics. (1) Room acoustics involves the design of the interior of buildings to project properly diffused sound at appropriate levels and with appropriate esthetic qualities for music and adequate intelligibility for speech. (2) Noise control or noise management involves the reduction and control of noise between a potentially disturbing sound source and a listener. (3) Sound reinforcement and enhancement systems use electronic equipment to improve the quality of sounds heard in rooms.

Room acoustics

One essential component of room acoustics is an understanding of psychoacoustics and the qualitative evaluation of sounds heard by people in rooms. Psychoacoustics is the study of the psychology of sounds. It includes studies conducted in laboratories and in actual listening rooms of how people react to the level, frequency content, direction, and arrival time of sounds. These studies have established a set of relationships among the acoustical qualities that have been found to be important in the perception of sound, the room surfaces that contribute to these qualities, and the physical components of the sound field in a room that contribute to these properties. See also Psychoacoustics.

Several important design concepts are used to provide good listening conditions in rooms for speech and music. First is to provide good access to the direct sound for all people in the room. This usually involves raising the source of sound on an elevated stage, altar, or podium at the front of the room and sloping the floor surface to elevate the ears of people above the heads of those seated in front of them. The width and depth of the room should also be limited so that the natural direct sound can project from the speaker or instruments at the front of the room to the listeners. Second is to limit the background noise level in the room so that people can hear the sound they want to hear above the level of the ambient sound. Third is to limit the reverberation time in the room so that sounds are heard clearly and fully, while providing enough reverberant sound energy that sounds are heard as “full” and “live.” If there is too much reverberation in a room, the persistence of an initial syllable will cover up or mask the one that follows it, making it difficult to understand what is being said.

Noise control

Acoustical planning concepts for buildings include placing noisy activities away from activities that require relative quiet and locating noise-sensitive activities away from major sources of noise. Buffer spaces such as corridors or storage spaces are often used to separate two rooms that require acoustical privacy such as music rehearsal rooms in a school. Intruding noises from the exterior or from adjoining rooms can be reduced by using walls, ceilings, windows, and doors with appropriate transmission losses. A compound or double wall assembly can be used to reach a relatively high transmission loss with low mass per unit wall area. The separation between the two leaves or surfaces of the wall must be maintained as completely as possible for this to occur.

It is essential to control noise from building services. The location of air-conditioning plants on a site should be chosen so as to reduce propagation of noise to neighbors. Mechanical rooms in buildings that house air handling units, pumps, and other equipment should be located away from noise-sensitive rooms. Noise control treatments in the air-conditioning system include providing vibration isolators for equipment; providing flexible connections between ducts, conduits, and pipes to equipment; designing air ducts to operate with air velocities that will not create turbulent flow noise; and installing silencers or attenuators in the ducts to reduce noise produced by fans from traveling through the duct work. See also Mechanical vibration; Vibration isolation.

Sound reinforcement

Sound reinforcement systems, electronic enhancement systems, and sound amplification systems are used in many buildings. A sound reinforcement system amplifies the natural acoustic sounds in a room that is too large for people to hear with just “natural” room acoustics. This type of system reinforces the natural sounds that come from the room, increasing their apparent loudness with a series of loudspeakers.

In an electronic enhancement system, loudspeakers act as virtual room surfaces to create the perception that sounds are reflected from these surfaces at the proper times and with the proper loudness. These systems usually have a network of loudspeakers located throughout a room and connected to a microprocessor. The microprocessor can delay the signals to arrive at times corresponding to reflected sounds from the virtual room surfaces. It can also add reverberation and other special acoustic effects to create a virtual acoustic space.

A sound amplification system makes all sounds played in a space louder. It is usually not designed to supplement the natural room acoustics or to provide subtle virtual room effects to the amplified sounds.

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Architectural acoustics is the science of noise control within buildings. The first application of architectural acoustics was in the design of opera houses and then concert halls. More widely, noise suppression is critical in the design of multi-unit dwellings and business premises that generate significant noise, including music venues like bars. The more mundane design of workplaces has implications for noise health effects. Architectural acoustics includes room acoustics, the design of recording and broadcast studios, home theaters, and listening rooms for media playback.

Contents 1 Building skin envelope 2 Inter-space noise control 3 Interior space acoustics 4 Mechanical equipment noise 5 See also 6 External links 7 References

Building skin envelope

This science analyzes noise transmission from building exterior envelope to interior and vice versa. The main noise paths are roofs, eaves, walls, windows, door and penetrations. Sufficient control ensures space functionality and is often required based on building use and local municipal codes. An example would be providing a suitable design for a home which is to be constructed close to a high volume roadway, or under the flight path of a major airport, or of the airport itself.

Inter-space noise control

The science of limiting and/or controlling noise transmission from one building space to another to ensure space functionality and speech privacy. The typical sound paths are room partitions, acoustic ceiling panels (such as wood dropped ceiling panels), doors, windows, flanking, ducting and other penetrations. An example would be providing suitable party wall design in an apartment complex to minimise the mutual disturbance due to noise by residents in adjacent apartments.

Interior space acoustics

This is the science of controlling a room's surfaces based on sound absorbing and reflecting properties. Excessive reverberation time, which can be calculated, can lead to poor speech intelligibility.

Sound reflections create standing waves that produces natural resonances that can be heard as a pleasant sensation or an annoying one.^[1] Reflective surfaces can be angled and coordinated to provide good coverage of sound for a listener in a concert hall or music recital space. To illustrate this concept consider the difference between a modern large office meeting room or lecture theater and a traditional classroom with all hard surfaces.

Interior building surfaces can be constructed of many different materials and finishes. Ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate. Fabric covered panels are one way to heighten acoustical absorption. Finish material is used to cover over the acoustical substrate. Mineral fiber board, or Micore, is a commonly used acoustical substrate. Finish materials often consist of fabric, wood or acoustical tile. Fabric can be wrapped around substrates to create what is referred to as a "pre-fabricated panel" and often provides the good noise absorption if laid onto a wall. Prefabricated panels are limited to the size of the substrate ranging from 2'x 4' to 4' x 10'. Fabric retained in a wall-mounted perimeter track system, is referred to as "on-site acoustical wall panels" This is constructed by framing the perimeter track into shape, infilling the acoustical substrate and then stretching and tucking the fabric into the perimeter frame system. On-site wall panels can be constructed to accommodate door frames, baseboard, or any other intrusion. Large panels (generally, greater than 50 square feet) can be created on walls and ceilings with this method. Wood finishes can consist of punched or routed slots and provide a natural look to the interior space, although acoustical absorption may not be great.

There are three ways to improve workplace acoustics and solve workplace sound problems – the ABC’s.

A = Absorb (usually via ceiling tile)

B = Block (via workstation panels, wall placement and workspace layout)

C = Cover-up (via electronic sound masking)

While all three of these are recommended to achieve optimal results, C = Cover-up by increasing background sound produces the most dramatic improvement in speech privacy –– with the least disruption and typically the lowest cost.

Mechanical equipment noise

Building services noise control is the science of controlling noise produced by:

• ACMV (air conditioning and mechanical ventilation) systems in buildings, termed HVAC in North America
• Elevators
• Electrical generators positioned within or attached to a building
• Any other building service infrastructure component that emits sound.

Inadequate control may lead to elevated sound levels within the space which can be annoying and reduce speech intelligibility. Typical improvements are vibration isolation of mechanical equipment, and sound traps in ductwork. Sound masking can also be created by adjusting HVAC noise to a predetermined level.

See also

• Acoustic transmission
• Noise health effects
• Noise mitigation
• Noise Reduction Coefficient
• Noise regulation
• Noise, vibration, and harshness
• Room acoustics
• Sound transmission class

External links

• Acoustical Society of America
• American Institute of Architects
• National Council of Acoustical Consultants
• Institute of Acoustics
• Speech Privacy Calculator
• diracdelta.co.uk room mode calculator.
• An on-line version of an exhibition on concert hall acoustics originally shown at the South Bank Centre, London
• Aural Architecture
• WikiRecording's Guide to Recording Studio Acoustics
• Acoustic Modelling using Google SketchUp
• Concert Hall Acoustics (UnOmaha)
• Concert Hall Acoustics
• Everything You Always Wanted to Know About Concert Hall Acoustics

References

1. ^ "Handbook for Sound Engineers"Glen Ballou, Howards Sams Editors, page 56.

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