Room Acoustics

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environment for the eye, the ear and the mind.

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Acoustic Comfort, Esthetic Choice

Home Comfort and Sound Control

"We only can learn what
we can hear"

Speech and hearing

Speech dominates the majority of learning situations. The quality of a room's acoustics can therefore help determine whether teaching is successful or not. Futhermore the indoor environment of all workplaces must help ensure that people feel both mentally and physically healthy.

Hospital bedrooms
A hospital bedroom should provide a calm environment for rest and sleep. However, patients are often disturbed by noise from the corridor, medical equipment, noise from their neighbors, the television, conversations etc.

Recommendation
Tr = 0,5 s for V< 100 m3
A short reverberation time will improve the general comfort and decrease the sound level from disturbing noise. The value of 0.5 seconds - the typical reverberation time of a residential living room - is often aimed at to provide a "homelike" environment.

Canteens and Cafeterias
The typical noise sources (clatter from plates and dishes, clanking trays, noisy machines etc.) in a canteen or a cafeteria interfere severely with speech communication.
A short reverberation time means not only that noise levels decrease, but that people can lower their voices and still be heard by those taking part in a conversation. Hence, the general noise levels decrease more than would be expected from a simple calculation.

Recommendation
Tr = 0,4-0,8 s up to V= 250 m3,
Tr decreasing with decreasing volume.
A special study is needed for greater volumes.
The need for absorption treatment in a canteen depends, among other factors, on the room shape and the density and type of furnishing. Independent of the size of the room, we recommend a good absorber to cover the ceiling. It is often useful to complete with absorbing wall panels on at least one or two walls. In big canteens, there may also be a need to separate the volume by using sound absorbing screens.

Church and Religious Spaces
The problems in the acoustical design of churches and similar spaces are related to the almost equal requirements for speech intelligibility and musical presentations. Reflective and absorptive surfaces must be carefully studied and used in order to support useful reflections and suppress disturbing ones. Uneven distribution of sound, defects such as echoes and sound concentration due to spherical surfaces etc. are common in churches. Some of these problems can be avoided using sound absorptive materials.

Recommendation
Room acoustics in churches and other rooms where people gather for meetings should be studied by specialists.

Cinemas
Since a loudspeaker-system is always used, it is generally necessary to shorten the reverberation time as much as possible with regard to the loudspeaker-system used. The sound emitted by the loudspeakers contain the room acoustical properties that correspond to the image that is shown. The aim is to transmit this sound to the listener without distortion due to the acoustical properties of the cinema room itself.

Recommendation
An acoustical study is needed for cinemas.
It is often recommended to cover both ceilings and wall with efficient absorbers. This is true for a distributed PA system. In old cinemas, where the loudspeakers were placed behind the screen, a part of the ceiling and the side walls could be reflective.

Classrooms
In a classroom, the main consideration is to achieve best possible listening conditions, i.e. the highest possible speech intelligibility.
The speaking conditions should be considered as well. The acoustical solutions may be influenced by the type of education performed, that is traditional teaching from a teacher's desk or education in groups of students.

Recommendation
Tr between 0,4 and 0,6 for V< 250 m3.
Generally speaking, the ceiling should be covered by products with high sound absorption, taking into account even the low frequency absorption. If the depth of the classroom is greater than 8 meters, there is a need for an additional absorber on the rear wall in order to avoid late, strong reflections. There may also be a need for a reflective area above the speaker. This area may be used for low frequency absorption.

Cleantech
There are three main goals concerning noise in workshops : To create an acceptable environment for the people working in noisy areas. Hearing damage must be prevented. A good environment is also supposed to increase productivity. To facilitate speech communication and the perception of warning signals. To prevent the transmission of noise into adjacent areas. This is a question of sound level decrease per doubling of the distance from each sound source. These objectives can be obtained by the use of sound-reducing enclosures and/or by introducing sound-absorbing materials.

Recommendation
Tr = 0,5 s for V 250 m3.
Tr= 0,5-1,0 s for V=250-1000 m3
and h= 5 m. A special study is required for V>1000 m3 or h>5 m.
Our recommendation is to install a maximal amount of good hygiene absorbers both in ceiling and on walls. The very different types of frequency distribution for different sound sources, as well as the local environment must be considered in the choice and mounting of sound absorbers.

Corridors
Circulation areas are often neglected when it comes to acoustical comfort. It seems natural to consider that there is no pronounced need for speech intelligibility, and that a relatively high background noise level can be accepted inside these areas. This way of thinking often makes circulation areas an unpleasant space to be in and - worse - an efficient ground for spreading of noise. One single sound source in a corridor or staircase may disturb a lot of people in adjacent areas.

Recommendation
A 2/3 % of the floor area.
This is a recommendation of a reasonable amount of absorption in order to get a sufficiently short reverberation time and a convenient sound level decrease per distance doubling. The recommendation expressed above as an absorption area can, roughly, be obtained by the use of absorbers rated as follows : Class A : 75% of the floor area or Class B : 85% of the floor area or áw = 0,9 : 75% of the floor area or áw = 0,8 : 85% of the floor area áw = 0,7 : 95% of the floor area.

Disco and Night-club
The sound levels from music in discos and night-clubs are often very loud. The main goal is to limit the high sound levels to the dance floor and reduce them in other parts of the room, in order to permit conversations and avoid disturbance to adjacent spaces. This demands a good PA system and absorption treatment on reflecting surfaces.

Recommendation
An acoustical study is needed for discos and night-clubs.

Examination Rooms
The noisy environment of a hospital affects as well the personnel as the patient. The examination room should be treated with the aim to obtain an as quiet and peaceful - "homelike" - environment as possible.
A short reverberation time will also indirectly improve the sound insulation between rooms.

Recommendation
Tr = 0,5 s
A short reverberation time increases comfort and eases communication. This makes the patient feel more relaxed and improves the working conditions for the personnel.

Gymnasiums and Sports Halls
The reverberation time should be as short as possible in order to suppress noise and facilitate communication and instructions. Flutter echoes between hard, parallel surfaces must also be considered.

Recommendation
Tr = 0,5 s for V< 250 m3.
Tr = 0,5-1,0 s for V= 250-1000 m3.

A special study is required for V>1000 m3.
Our recommendation is to install absorbers with high sound absorption in the ceiling and on part of the walls.

Ice Rink
The reverberation time should be as short as possible in order to suppress noise and facilitate communication and instructions. Flutter echoes between hard, parallel surfaces may also have to be considered.

Recommendation
Ice rinks require an acoustical study.
Our recommendation is to install absorbers with high sound absorption in the ceiling. Surfaces that may cause flutter echoes or sound concentrations should receive an efficient absorber.

Kitchens
Kitchens are noisy environments where there is a need to suppress the noise as much as possible and get a maximal sound level decrease per distance doubling.

Recommendation
Tr = 0,6-0,8 s up to V= 250 m3,
Tr decreasing with decreasing volume.
A special study is needed for greater volumes.
Our recommendation for big kitchens is to install a maximal amount of hygiene sound absorbers on both ceiling and walls. The way of mounting may have to be varied in order to cover a large spectrum of noise sources.

Libraries
Every reasonable effort should be made to provide the quiet environment essential for studying or reading. A short reverberation time will improve comfort and ease concentration by a decrease of the sound level from disturbing noise.

Recommendation
Tr = 0,4-0,6 s up to V= 250 m3.
Tr = 0,6-1,0 s for V= 250-1000 m3 and H= 4 m. . For greater volumes than V=1000 m3 or heights above 4 m, a special study is required.
Our recommendation is to install excellent sound absorbers all over the ceiling.

Lounges
The lounge is a kind of multipurpose room: people come here to talk, to read, to play cards, to watch the television or simply to relax. There are two important points to consider: the promotion of word intelligibility, the suppression of noise from radio, television, external noise sources (traffic and activities in the corridor etc.) and conversations. The aim should be to create a homelike environment.

Recommendation
Tr = 0,5 s
The reverberation time of 0,5 seconds correspond roughly to the reverberation time in a normal living room. The required amount of additional absorption depends on the volume and shape of the room as well as on the furnishing, the presence of curtains, textiles and carpets.

Meeting Rooms
Depending on size and use, different acoustic measures are required. Generally, there is a need for good speech intelligibility and talking conditions.

Recommendation
Tr = 0,5 s for V=100 m3
Tr = 0,5-0,8 s for V=100-250 m3,
Tr decreasing with decreasing volume.
A special study is required for V=250 m3.
The first thing to consider for meeting rooms is whether or not the speech transmission is to be made by a loudspeaker-system. The following recommendations suppose non reinforced speech transmission : For smaller rooms - less than 100 m3 - we recommend the whole ceiling to be covered by a product with high sound absorption. In medium size rooms the same type of ceiling is required, but there may be a need for a reflective area between the speaker and the listeners to support useful reflections. In big rooms there is an additional need for reflective areas above the speaker/scene and on the side walls to give further support to the voice. These questions must be considered by specialists. When loudspeaker-systems are used, there is generally a need for a very short reverberation time and thus a maximal amount of absorption. The optimum conditions depend on the quality and distribution of the loudspeaker-system,- they need to be studied by a specialist.

Multipurpose Rooms
The multipurpose room is one of the most complicated spaces to treat from an acoustical point of view. Different activities demand different acoustical criteria. The needs are not the same for musical performances and speech, for instance. If the needs for music are aimed at when planning a multipurpose room, it is possible that this room will be very uncomfortable for speech, and the contrary. Usually, the aim is set somewhere in between the ideal conditions for each type of activity that is to be performed. Most of the time, this works out fairly well, but there is always a risk that the users feel that the acoustical environment doesn't fe first thing to consider for meetinit either activity.

Recommendation
Tr between 0,6 and 0,7 for V< 250 m3.
A special study is required for greater volumes.
Since there are many difficult problems involved regarding acoustics in multipurpose rooms, it is recommended to let a specialist make a study even for small rooms. One problem in big multipurpose rooms is the flat audience area that is required for exhibitions, bazaars etc. This makes it difficult to provide enough direct sound all over the audience, and may cause flutter echoes between the floor and the ceiling. Therefore, the ceiling should be covered by products with medium to high sound absorption, taking into account even the low frequency absorption. The ceiling above the speaker should be reflective, as well as the side walls near the speaker. It is often necessary to use reflective panels that may be oriented in order to cover the audience area. The back wall and the rear part of the side walls should be absorbent or diffusing enough not to cause late reflections or echoes. If a speaker system is to be used for all kind of performances, it is recommended to shorten the reverberation time as much as possible, taking into account the quality and the distribution of the loudspeaker-system.

Museums and Exhibitions
Every reasonable effort should be made to provide the quiet environment essential for the contemplation of works of art. A short reverberation time will improve comfort and by decreasing the sound level from disturbing noise and conversatione first thing to consider for meetins.

Recommendation
This kind of room always needs a special study.
Our recommendation is to install sound absorbers all over the ceiling.

Music Rooms
The acoustical evaluation of a room for music is often quite subjective. The music rooms discussed here concern only rooms for training. Rooms for performances and larger training rooms must be studied by a specialist.

Recommendation
Tr = 0,4-0,8 s (125-4000 Hz) up to V= 250 m3. The lower values concern training booths.
For smaller rehearsal rooms, the floor area, room height, shape and volume must be carefully studied. Parallel opposite walls must be avoided. A sufficient amount of sound absorption must be introduced. It is often recommended to cover two adjacent walls with sound absorbing materials. The treatment of the ceiling will depend of the room height.

Offices
The individual office is a private working space, dedicated to intellectual work. To reduce noise from office machines, conversation, footsteps etc. and promote concentration and mental effort, the reverberation time should be relatively short. Too short reverberation time, however, would give the impression of working "in a sack". Once people share an office, there is always a need for efficient suppression of noise. This is to decrease the disturbance from telephone calls, conversations etc. When many persons are to work in the same office, the design of the office and the choice of materials have to be considered carefully. In landscaped offices, the optimum conditions are found on a thin line between an acceptable level of background noise and a signal-to-noise ratio that to some extent provides privacy.

Recommendation
Individual Office : Tr = 0,6 s. In offices for 2-5 persons, this value should be decreased to 0.4-0.5 s.
A special study is required for offices that will be used simultaneously by more than 5 persons.
For individual offices, we recommend moderate sound absorption in order to achieve the goals and give good comfort. In offices for 2-5 persons, we recommend a ceiling with excellent absorption, as well as wall absorbers or absorptive screens between working spaces. In offices for more than 5 persons - or landscaped offices - a special study is required to achieve acceptable working conditions. The aim should nevertheless be to shorten the reverberation time and suppress noise as much as possible.

Open Space Offices
Generally speaking, offices shall have an acoustic environment that facilitates communication and supports efficiency. When there is more than one person in an office, the disturbance paths must be suppressed as much as possible. There is also a need to mask speech from neighbors, which can be achieved by a suitable amount of meaningless background noise. The background noise from the ventilation is often sufficient. Sometimes, recorded noise (ventilation or environmental noise) is introduced with the intention to provide privacy. This method has been pleaded and contested by specialists for a long time. It is most difficult to judge the effects of disturbance from speech etc. versus the tiring effects of meaningless background noise...

Recommendation
A special study is always required for open space offices.
In open space offices we recommend maximum absorption in the ceiling, even in lower frequencies. This is in order to avoid disturbance from the activity in adjacent working spaces.

Operation Theaters
The noise levels in operating theatres may from time to time exceed 100 dB(A). Even though the equivalent noise levels normally don't suppose any danger for hearing damage, there are good reasons to pay attention to these noisy conditions. The noise from unfamiliar machines and the activities preceding the operation may affect the patient even when he is under light anaesthetics. The speech intelligibility is of course of greatest importance to the operation team. A sudden, strong noise may detach the attention in a critical moment, etc.

Recommendation
Tr = 0,6 s
Except for the human beings, there are no natural absorbers at all in an operation theater. It is therefore important to cover the ceiling and, if possible, the upper part of the walls with good hygiene sound absorbers.

Playrooms
Playing children generate noise - it is a part of the game. The main consideration for a playroom should therefore be to suppress noise, without creating a "dead" environment.

Recommendation
Tr = 0,6 s
A resistant ceiling with good absorption is recommended. The need for a short reverberation time is greater when personnel spend their working day in a playroom, than when children are playing independently.

Public Areas and Reception Halls
Public areas in a hospital or in industrial building are mainly the reception area - an often crowded and very noisy space. Here, the considerations regarding the acoustical environment concern speech intelligibility and privacy.

Recommendation
Tr = 0,6-0,8 s up to V= 250 m3,
Tr decreasing with decreasing volume.
A special study is need for greater volumes.
We recommend a maximum of good absorbers in the ceiling.

Restaurants and Bars
The typical noise sources (clatter from plates and dishes) in restaurants and bar's interfere severely with speech communication. A short reverberation time means not only that noise levels decrease, but that people can lower their voices and still be heard by those taking part in a conversation. Hence, the general noise levels decrease more than would be expected from a simple calculation.

Recommendation
Tr = 0,6 s for V= 250 m3.
A special study is needed for greater volumes. We recommend a good absorber to cover the ceiling.

Showroom
The acoustical considerations regarding showrooms concern mainly noise attenuation. There is also a need for accurate speech intelligibility when speaker announcements are to be made.

Recommendation
Tr = 0,6-0,7 s up to V= 250 m3.
Tr = 0,7-1,0 s for V= 250-1000 m3.

We recommend a suspended ceiling with good absorption even at low frequencies.

Staff Rooms
The staff room should be a calm place where the personnel can have a little rest.

Recommendation
Tr = 0,5-0,6 s
The extent of the required acoustical treatment will depend on the furniture, the presence of textile, carpets and other natural absorbers. A suspended ceiling with good sound absorption is recommended.

Staircases
Circulation areas are often neglected when it comes to acoustical comfort. It seems natural to consider that there is no pronounced need for speech intelligibility, and that a relatively high background noise level can be accepted inside these areas. This way of thinking often makes circulation areas an unpleasant space to be in and - worse - an efficient ground for spreading of noise. One single sound source in a corridor or staircase may disturb a lot of people in adjacent areas.

Recommendation
A 1/3 (landing surface + horizontal step surface.
This is a recommendation of a reasonable amount of absorption in order to get a sufficiently short reverberation time. The recommendation expressed above as an absorption area can, roughly, be obtained by the use of absorbers rated as follows : Class A : 40% of the landing and horizontal step area or Class B : 45% of the landing and horizontal step area or áw = 0,9 : 40% of the landing and horizontal step area or áw = 0,8 : 45% of the landing and horizontal step area áw = 0,7 : 50% of the landing and horizontal step area.

Swimming Pools
The reverberation time should be as short as possible in order to suppress noise and facilitate communication and instructions. There is also a need to support warnings and cry for help. Flutter echoes between hard, parallel surfaces must also be considered.

Recommendation
Tr = 0,5-1,0 s up to V= 1000 m3,
Tr decreasing with decreasing volume.
For greater volumes than V=1000 m3, a special study is required.

Our recommendation is to install absorbers with high sound absorption in the ceiling and, when possible, on part of the walls. Flutter echoes between hard, parallel surfaces must be considered. The products used must be adapted to the humidity conditions.

Workshops
There are three main goals concerning noise in workshops : To create an acceptable environment for the people working in noisy areas. Hearing damage must be prevented. A good environment is also supposed to increase productivity. To facilitate speech communication and the perception of warning signals. To prevent the transmission of noise into adjacent areas. This is a question of sound level decrease per doubling of the distance from each sound source. These objectives can be obtained by the use of sound-reducing enclosures and/or by introducing sound-absorbing materials.

Recommendation
Tr = 0,5 s for V= 250 m3.
Tr = 0,5-1,0 s for V= 250-1000 m3
and h= 5 m.
A special study is required for V>1000 m3 or h>5 m.
Our recommendation is to install a maximal amount of good absorbers both in ceiling and on walls. The very different types of frequency distribution for different sound sources, as well as the local environment