Everything you need to learn about controlling and reducing noise. Learn about how to control noise in:- 1. Factories 2. Commercial Buildings 3. Hospitals 4. Judicial and Administrative Buildings 5. Entertainment Industry 6. Flats and Apartments.
1. How to Control Noise in Factories?
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Consideration of the noise problem in factories opens up a vast subject, since no two installations are likely to present an identical acoustical problem. The variety of questions requiring consideration may range from the problems encountered in heavy engineering works to the quite different matters requiring attention in light assembly plants.
Nevertheless, it is possible to suggest a number of basic considerations which are likely to underlie the approach to noise problems in almost any kind of factory. Where they apply, these factors should be taken into account at the planning stage of a new building and it is assumed, in what follows, that this is the case.
The acoustic consultant should be called in at the earliest planning stage and his views can usefully be sought when the site is being chosen, even though the acoustical aspect is only one of the many important factors to be taken into account.
The proximity of heavy road traffic, rail transport or air traffic will all have a bearing on the noise factor and even when it may not be possible to select a site well away from these distractions, at least it may be feasible to avoid the noisier sports, such as in proximity to a traffic-lighted junction (where the noise of accelerating vehicles and squealing brakes can prove a nuisance) or alongside a railway marshalling yard.
Admittedly, under present conditions, choice in the sitting of a new factory may be severely limited or the new factory may, perforce, be an addition to existing premises on a site which had either been badly chosen in the first place or has since acquired a noisy environment by the building of new roads or an increase in traffic density.
In such cases, the actual position of the factory area in relation to the rest of the site and the environmental noise is important. For example, if a noisy road passes along one side of the site, the factory building can be located as far away as possible from this side of the plot and the quieter areas of the factory (offices, laboratories, etc.) placed in that part of the factory which is least likely to be affected by outside noise.
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While these initial plans are being prepared, consideration must also be given to the relative positions of the quiet and noisier areas within the factory itself. If the production area happens to include a particularly noisy process or department, this should be as remote as possible from the areas which require maximum quiet, though, naturally, the special requirements of the production techniques employed must also be kept in mind.
In this matter, as throughout the initial planning of the plant, it is necessary always to strive for a fair and reasonable balance between the contending forces, so that the end result is a factory which combines the best possible acoustical conditions for its employees with the most efficient production techniques.
Although a certain amount can be achieved by adopting the best possible factory layout, direct acoustic action will probably still be needed to prevent unwanted noise from building up in the first place and this may be achieved by the use of sound barriers and/or absorbents to protect the quiet areas from the noisier sections of the plant. It may, similarly, be necessary to take measures to control the entrainment of noise from outside.
Finally, the adverse effect of outside noise on people living in nearby residential areas must also be kept prominently in mind during the initial planning of the factory.
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The paramount objective of the acoustic consultant, when offering advice during the planning of a new factory, is thus to prevent the factory from annoying its neighbours and also to prevent it from annoying itself. To be able to make his recommendations with certainty, he must fully appreciate the main features of the problem.
In particular, account must be taken of the two main methods by which noise is transmitted, whether the problem concerns the people inside the factory or those living outside. Noise is either airborne or structure-borne and it is vitally important that these factors should be recognised and accurately measured, so that each type can be appropriately controlled.
A wise selection of site and factory layout, following the lines indicated above, will contribute considerably towards a favourable acoustical performance, but there are many points of detail which will have to be given careful consideration if the most satisfactory conditions are to be obtained.
The Production Area:
Since, most of the noise problems in factory production areas arise from machinery; it follows that particular care must be taken with the installation of every machine. All machines, in greater or lesser degree, will inject their noise into the structure of the building and this energy must be controlled at source if a serious problem of structure-borne noise is not to be built up.
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Various methods of doing this are available and the choice of the best method will depend on many factors, including the size and type of machine. In general, the procedure consists in isolating the machine from the actual structure of the building so that the vibrations produced by the machine in action are not transmitted to the building itself.
In the case of a light machine shop containing a number of basically similar machines, it may be possible to mount the whole of the equipment in the shop on an isolating raft. This will consist of a concrete platform, perhaps six inches thick, placed on top of the structural floor of the building but isolated from direct contact with it by a layer of a compliant material, such as mineral fibre or wool.
A number of these materials are commercially available and a layer, one-half to two inches thick, will suffice to damp down the vibrations. The exact thickness and density of the isolating layer will depend on the load and the forcing frequency, which can be calculated from the known weight of the machinery to be installed, its revolutions per minute (r.p.m.), the amount of other equipment likely to use the floor and other relevant factors.
As it is unlikely that all the machines will be exactly similar, it will be necessary to give careful consideration to the layout of the various pieces of equipment in order to ensure a balanced floor. The architect and other specialists, in consultation with the acoustic consultant, will take all these factors into account to ensure that the load is evenly distributed over the floating floor and that the floor as a whole fits into the overall concept of the building. Should it prove impracticable to mount all the machinery on the same isolating raft, it may be necessary to construct the floor in sections, each on an anti-vibration foundation of its own.
Where a factory floor contains a mixture of equipment and a few very heavy pieces of machinery are included among a large number of lighter machines, a different mounting procedure may be required. One technique used in such cases is to provide an overall mounted anti-vibration floor on which the light machines can be mounted, the structural floor of the building being allowed to obtrude through the raft at the points where the heavier machines are to be installed.
These structural floor mountings thus resemble islands brought up through holes cut in the anti-vibration raft. The heavy machinery is mounted on these islands, using suitable anti-vibration mountings and techniques for this particular application.
Very heavy machinery can also be successfully installed on an individual mount, which may consist of a concrete block sunk in a pit in the structural floor but separated from contact with the walls and bottom of the pit by a layer of a compliant material. The vibrations transmitted by the machine to the concrete block on which it is mounted are than prevented from entering the structure of the building by the layer of anti-vibration material which entirely surrounds it.
Careful thought given to the mounting of every piece of machinery can do much towards preventing any build-up of structure-borne noise and its transmission to other parts of the factory or to the outside world but, here again, it is essential that any such decisions are made at the earliest possible planning stage, when the special mounting arrangements and resultant structural requirements can be incorporated in the initial plans as an integral part of the building operation.
If such arrangements as isolated floors and anti-vibration mounts have to be added after the building has been completed, the necessary alterations will, at best, be extremely costly and time-wasting while, at worst, they may prove to be quite impracticable.
Compartments and Enclosure:
Where the need arises for a relatively quiet area to be provided on a factory floor on which the machinery in use is noisy, special steps will be required to reduce not only the structure-borne noise but the airborne noise as well. Among the quiet areas which are frequently required on production areas are foremen’s offices, progress control facilities, testing areas and so forth.
On a highly mechanised production line, including a large number of noisy machining operations all under automatic control with automatic transfer from one operation to the next, the entire line may be remotely controlled from a console in a central position in the department. A quiet room is obviously required for such an application as this.
Noise-proofed areas for these purposes can be built, using partitioning systems. The type of structure required will range from a simple partitioning system which may provide sufficient quiet for an administrative section in a not-too-noisy department, to a double-skinned enclosure with specially protected windows, doors and roof, as might be needed for a test area.
An example of a special case can be quoted. This was a department for testing electric motors for quiet running and for which a fairly high level of quiet was required. For economic reasons, however, it was necessary that the motors should come straight off the production line and still on flow line principles, pass through the test and out again to dispatch. On their way into and out of the testing booth, the motors passed through sound locks while the testing enclosure itself was double-skinned to provide the quiet conditions required.
Ducting and Pipework:
Where ventilation ducting and pipework for heating and other services passes from production areas to offices and other quiet sections, factory-generated noise can be transmitted, in addition to any noise which may be produced by the ventilation system itself. Consideration should, therefore, be given to the layout of all ducting and pipework when the building is designed, from the point of view of noise transmission from noisy to quiet areas.
Where circumstances are such that some noise is inevitably transmitted in this way, it can be reduced by the introduction of attenuators at suitable points. The layout of ducting and pipework and the positioning of attenuators should, of course, be carefully planned in the initial design stages.
Special attention must be paid to such ancillary equipment as pumps, which should be isolated from pipework so that vibrations will not be transmitted along the pipes. Even if the vibratory power of a prime mover is successfully isolated from pipework, it may still be transmitted through the water in the pipes. This can be prevented by inserting a flexible connection between the pump and the pipe system it serves.
Acoustical Treatment:
If all the precautions described are taken during the planning of a new factory, a considerable degree of acoustical comfort will be achieved. The use of absorbent materials, however, will further improve conditions, both for those working in the production area and those in adjacent quiet sections. As these absorbent materials will increase the initial cost of the building, it is important to select the most economical method.
A reverberation analysis should be made and optimum reverberation times for each area determined from a reverberation time graph. Calculations of actual reverberation times in the factory can be made or measurements can be taken, using the latest electronic equipment, during a quiet period. In the case of a new building, such measurements will have to be taken in a comparable factory and then applied to the proposed new structure.
Treatment can then devise and applied according to the findings. Structure-borne noise from machines can be controlled, as has been seen, by isolation techniques, while airborne noise is contained by the use of absorbent and barrier materials. If this is not sufficient to provide the desired conditions, consideration may have to be given to enclosing particularly noisy machinery in cabins.
2. How to Control Noise in Commercial Buildings?
Although the amount of noise actually generated in a commercial building will obviously not be as great as that to be expected in a factory, the general noise levels demanded will be lower, while the need to provide insulation from environmental noise will probably be greater. Many considerations must thus be taken into account in the design and construction of large office blocks and other administrative buildings.
When determining the site for a new administrative building, the same considerations apply as were discussed in the case of factories except that, in general, there will be much less likelihood of the building creating a noise nuisance for the neighbourhood, with the possible exception of noise from such services as electrical substations and stand-by generating plant.
The siting of these and other services should also be considered in relation to the noise problem they could produce for the inmates of the building. Careful sound measurements in the vicinity of the site are an important part of the preliminary studies on which the initial plans are based.
Noise levels can be measured at ground level and the results projected to give likely levels at the various floors of a multi-storey block. The effects of aircraft noise at the higher storeys must also be taken into consideration. Some thought should be given to likely future trends of noise, as suggested by known developments, such as the construction of a new road or the expansion of a nearby airfield.
These measurements will enable a decision to be taken as to the necessity or otherwise of considering the installation of double windows, with the attendant acoustical problems of ventilation systems.
Engineering Area:
Only in comparatively recent times has proper consideration been given to the engineering services of commercial buildings as a cause of noise which should and can be controlled by proper action at the design stage. Structure-borne noise from such equipment as pumps, fans and electric motors, formerly considered to be a necessary evil for office workers whose accommodation happened to be near, can be treated.
In large buildings, all the services can be located in a common services area which may, in fact, occupy an entire floor of the building. The normal plan of siting the central-heating plant and other services in the basement is now being varied by selecting other positions and some recent buildings have the services area on the top floor. Where all the services are concentrated on a single floor in this way, consideration may be given to the isolation of the floor from the building structure.
In multi-storey buildings, special attention will have to be paid to lifts. Thanks to the efforts of lift manufacturers, the lifts themselves normally make very little noise in action; the chief acoustical problem arises from the lift motors and from ancillary equipment, especially the contactors. The situation of the lift shaft and motor room in relation to the rest of the building should be carefully considered when the building is being designed so that, as far as possible, the quieter areas are situated well away from this source of noise.
Special arrangements which may be necessary may include acoustic treatment of the lift motor-room, to control both structure and air-borne noise. Holes through which the ropes pass (and which can also permit the emission of noise) should be as small as possible. In some circumstances it may be advisable to treat the lift shaft from the motor-room downwards.
Variety of Rooms:
Acoustic consultants dealing with large modern commercial buildings have to consider a wide variety of differing requirements, particularly in a building which houses the entire administrative headquarters of a large company. Consider, for example, the case of an important construction company specialising in the design and construction of large industrial plant.
A building housing such a company will probably contain, in addition to numerous offices, a drawing office, executive suites and board-room, a cinema, a first-aid post, executive and staff dining-rooms and possibly, a computer centre. All these rooms and areas will require different quietness levels and since rooms with different noise criterion curves will be next to one another, the choice of suitable partitions becomes all-important.
Where the noise criteria curves of two adjacent rooms are about the same, the partition may need to be little more than a room divider, whereas in the case of, say, a general office next to an executive’s room the partitioning selected will have to ensure a considerable noise transmission loss. It must be remembered, however, that the occupants of each room want to be able to hear comfortably inside that room and the partitioning must not only provide the required noise transmission loss but must also play its part in the general acoustics of the room.
Another factor to be considered when designing partitions is to prevent acoustical ‘soft spots’, where noise can leak out round the edges of the partition. Suspended ceilings can be a source of trouble here if partition heights terminate at ceiling level.
Where rooms which require a reasonably high quietness level are adjacent to a corridor, consideration may have to be given to the installation of sound-resistant doors. It follows, of course, that corridors should always be the subject of careful thought and a high degree of acoustical treatment.
There are some cases where the problem may not be so much the prevention of noise entering a room as controlling the emission of noise from a room. A typical example is in the case of executive areas or personnel departments where, for one reason or another, conversations must be kept private.
Conference and Board-Rooms:
Special attention must be paid to acoustical conditions in such rooms as conference and board-rooms. Preliminary work on their hearing capabilities will include very careful measurement of reverberation times and the selection of specific measures. This must take into account the fact that speakers are likely to address the members present from more or less any point in the room (for example – when seated round a large table), with or without reinforcement by microphone and amplifier system.
A high syllable articulation percentage is important here and tests have been devised for assessing this quality in a room. Certain selected words are spoken from various points in the room, while listeners, also in different parts of the room, write down the number of words heard. This is known as articulation testing.
Open Planning:
Office floors consisting of a large number of departments without separate rooms (‘open planning’) have become very popular in recent times but this arrangement poses considerable problems for the acoustic consultant. A meticulous study must first be made of the grouping of activities in respect of the noise levels and the acoustic consultant must be called in at this stage. Specific measurements must be made of the various types of noise to be expected in the various areas and careful attention paid to the geometries of the area.
Even in open planning, it is important to consider the place of any partitions used to divide the various areas. Even if they are only a few feet high, these dividers can be detrimental to the general acoustical position unless made of suitable material. Partitions can also produce too much reflective noise, though, on the other hand, their reflective properties and those of desks and office equipment can be utilised to direct unwanted noise towards absorbent panels.
It is particularly important to examine the overall picture and to take account of all factors, including, for example, the use of carpets, soft furnishings, etc., where appropriate.
Drawing Offices and Libraries:
A drawing office can be treated acoustically as a large office and as an area where a considerable degree of concentration is demanded of the occupants, the noise level must be given close consideration. Fortunately, a drawing office almost invariably contains a great deal of paper and this, together with the drawing boards, provides a fair amount of noise absorbent material which will assist in any necessary acoustical correction. Even so, it is always of advantage to install an acoustic ceiling in such rooms, provided that its design is based on an acoustical analysis.
Libraries, especially where facilities are to be provided for visitors to sit and consult books and documents, should also be given special consideration. Whilst it is true that the large numbers of books and the shelving will act as noise absorbents, it is also necessary to ensure that extreme conditions of quiet are provided, especially in respect of the entrainment of noise from outside.
Computer Rooms:
With the increasing commercial use of computers and data processing equipment of all kinds, designers of buildings have been faced with a number of new problems and these are perhaps particularly noticeable in the field of acoustics. Staff members operating computer facilities are engaged on work which calls for considerable concentration and therefore require reasonable conditions of quiet.
Whilst computers themselves cannot be always classes as noisy machines, some of the ancillary equipment, such as punch-card machinery and print-out equipment, can produce a noise level which, both because of its nature and its continuity, becomes annoying to those working near. Computers also require air-conditioning, so the steps must be taken to control any noise from this source.
Entrance Halls:
A company will, naturally, want its brand-new building to have an imposing entrance hall, but an impressive entrance loses much of its effect if visitors find distracting echoes are making it difficult for them to explain their mission to the commissionaire. The current popularity of certain prestige materials (marble being perhaps the best example) means that acoustics must be kept well in mind when planning the design of the entrance hall.
The entrance hall is also likely to front on to the road on which the building is situated and this must be taken into consideration when designing doors and windows, together with the possibility of the visitors’ car park also being situated near the main entrance.
Other Rooms and Facilities:
Other rooms and accommodation normally found in large commercial building include dining-rooms and cafeterias. These may range from small intimate dining-rooms for directors and visitors, to large dining-halls where hundreds of meals may be served in a day. Each type of dining facility poses its particular acoustic problem and each must be considered on its merits.
The old-time factory canteen, in which every dinner has to shout to make himself heard above the general hubbub, has no place in a modern commercial building, where dining-rooms, subject as they are to the clatter of utensils and the buzz of conversation, must be acoustically treated to a high level to produce comfortable conditions.
Other parts of commercial buildings where special acoustic problems may arise are the rooms set aside for duplicating equipment, comptometer operators, addressing machines and so forth. Nor should lavatories and toilet facilities be neglected from the acoustic point of view, especially as such compartments are usually lined with ceramic tiles which are highly reflective of sound. Special attention must, therefore, be paid to partitioning and to ceiling materials and hygienic acoustic tiles are now available which combine the necessary cleanliness with the reasonable noise level.
Overall Approach:
Although the acoustic problems of commercial buildings are extremely varied, they are all, to some extent, interrelated and the time to ensure that no built-in noise problems are allowed to arise is at the initial design stage of the building. For this reason, the acoustic consultant should be called in at the earliest possible opportunity and his services utilised throughout every stage of design and construction.
3. How to Control Noise in Hospitals?
The provision of reasonable quiet for patients and staff is, one of the most important aspects of hospital management and control. Noise levels will vary from one part of a hospital to another, depending on the needs of the various areas. At one extreme, maximum conditions of quiet are needed in operating theatres and in wards where seriously ill patients are under surveillance; at the other end of the scale, what may be described as ordinary comfortable home conditions are acceptable for general wards.
In fact, a controlled degree of noise at these levels is often regarded as being beneficial, since people tend to associate everyday noises with a normal sense of well-being, such as they have previously experienced outside and to which they are expecting to return. Furthermore, if all but the dangerously ill patients are kept for a long time in a very quiet ward, they can hear their own heart beats and other internal noises, which can cause annoyance or even worry.
As in the case of other structures, there are two aspects of the noise problem in hospitals. One is that of noise entrained from outside; the other, of noise created inside the building itself. So far as noise from outside is concerned, this is largely dictated by the siting of the building and the problem is not eased by the fact that many hospitals were originally built in large centres of population to be within easy reach of those who would need their services. Even where the site was originally in a relatively quiet area, traffic developments may since have turned it into a very noisy site indeed.
Inside the hospital, there are a number of medical and other requirements which, at any rate in the past, have tended to produce noise almost as a side effect. The importance of hygiene and the need for easy cleaning and maintenance, have encouraged large unbroken areas of walls, ceilings and floors, often tiled or plastered with as smooth a surface as possible, all of which give rise to undesirable acoustical phenomena. Long, unbroken corridors are necessary for easy communication between wards and other hospital areas, but they can also produce persistent noise problems.
Similarly, many essential hospital services are the cause of much unwanted noise. These include both central services, such as the boiler house and associated central-heating and hot-water system, ventilation and air-conditioning systems and stand-by electric generation equipment; quite apart from other services provided at ward level, such as sluices and local water heaters. All these and many other noise problems must be considered when a new hospital is to be built, while, in many existing hospitals, remedial measures are constantly being put in hand.
New Hospital:
Not very many completely new hospitals are built, in the sense that a green field site is selected and a new building erected upon it. In most cases, an existing building is reconstructed or additional buildings erected on an existing hospital site. However, when a new hospital is to be constructed and there is the possibility of selecting a site, as distinct from having to make use of one already earmarked for the purpose, similar considerations apply as when selecting a site for any other kind of building.
Obviously, the most important criterion is the amount of likely noise from passing traffic, from possible future air traffic or from industrial or other installations already in the neighbourhood or likely to be located there at a later date. It is, therefore, necessary not only to consider the present situation in the locality, but to attempt a projection into the future, taking into account known development plans and the possibility that a hospital in that particular spot may of itself attract other building development in due course.
Considerations other than those relating to noise will have to be taken into account when selecting the site, such as the position of the hospital in relation to the area it is designed to serve, the availability of land and so forth. Inevitably, it will be necessary to effect a compromise, but even if a site has to be accepted which is less than ideal from a noise point of view, there are steps which can be taken in mitigation.
Surrounding grounds can, for example – be laid out with trees and dense planting and these will act to some extent as a noise ‘filter’. The layout of the actual building on the site should be such that the areas where the quiet conditions are most essential are as far away as possible from the main source of outside noise. Another point to be borne in mind is that patients’ rooms and wards should be as remote as practicable from approach roads used by ambulances; service Lorries and staff and visitors’ cars.
As in all other forms of new building, particular care should be taken with the preliminary acoustical survey, which should be carried out by a qualified consultant. The survey should include readings taken at various locations adjacent to the site at different times of the day and night, both inside and outside the site and calculations should be made to secure the exact requirements.
Night readings are of special significance when a survey is being prepared for a hospital, since it is during the night that quiet conditions are often most necessary. After the report based on the readings has been prepared and submitted, it will form the basis of discussions between the architects and other specialists and the Hospital Governors and officials concerned.
So far as the structure of the building is concerned, special attention should be given to the basic design of the fabric in order to reduce structure-borne noise from plant and equipment areas, such as those concerned with hospital services. Kitchens, utility rooms, dining-rooms, X-ray facilities, research sections and administrative offices should be located away from patients’ accommodation.
If physical separation cannot be achieved within the requirements of the overall design, acoustical techniques must be employed to achieve the necessary isolation. The acoustic consultant can advise on all such schemes so that the basic design of the hospital provides built-in solutions of noise problems, as the final conception of the building materialises on the drawing board.
When considering the design of a typical ward, all decisions should be taken by reference to the specified predetermined noise level, which, for general purposes, will probably be of the order of NC35, this being approximately the level acceptable to nearly all patients and which can normally be attained without introducing specialised structures at prohibitive cost.
Particular attention will generally have to be paid to ceilings and windows. Consideration can be given to the installation of a suspended ceiling, if the designed height of the ward permits this and if it has been decided to include an air-conditioning and ventilation system in the plans. In a ward which was recently designed for a large hospital, air for the ventilation and air-conditioning system was drawn in from outside through intakes located above the false ceiling.
The air had to be cleaned, corrected for temperature and circulated. The noise problem which arose involved the control of the noise of the intake and circulation fans, as well as the noise entrained with the air from the environment. Design techniques had to be applied to reduce the noise to the specified level, over eight octave bands.
Within the false ceiling, sound-resistant enclosures were constructed, immediately above the windows. These enclosures housed the intake and extraction fans and the incoming air were drawn in through the louvred top section of the window. Air passed through the fan, was filtered and discharged into a specially-designed attenuator which reduced the noise level to the required NC35 noise criterion.
At this stage, the incoming air had been partly filtered and ‘quietened’, but to meet specifications, a further filtration was necessary before the air passed through a heater and refrigerated cooler unit to provide the necessary strict temperature control, monitored through room thermostats.
Before the air is distributed to the ward through the duct network, it is passed through a bacteria destructor so that, when it eventually reaches the ward, it has been filtered, strictly temperature-controlled and freed of noise, whilst its bacteria content has been greatly reduced.
Extraction of air by fan can also produce a noise problem and in this particular case, the air was passed to atmosphere through an attenuator, while special measures were taken to prevent noise travelling against the air stream, which would otherwise have nullified the noise prevention precautions already taken.
Depending on the degree of environmental noise and the transmission loss which is required to produce the desired conditions inside the wards, it may be necessary to install double-glaged windows. This may entail using different weights of glass, raked to given angles and the lining of reveals, heads and sills with absorbent materials.
A recent trend in hospital design is for wards to be divided into a number of compartments, as compared with the former long, gaunt rooms. Consideration must, therefore, be given to the compartmentation of wards by the installation of sound rated partitions designed to give the required, calculated noise transmission loss. The level should be set to provide the interior quiet which the patient needs, without inducing a feeling of complete isolation, which could be psychologically harmful.
In addition to the noise problems of general wards, it will be necessary to consider other accommodation, such as maternity and nursery rooms and side-wards for seriously ill patients, whose occupants may be liable to cause noise disturbing to other patients. Special acoustical methods will have to be employed and the installation of sound-absorbent materials will prove helpful.
Other hospital rooms and areas which may require special treatment could include audiometry rooms, lecture rooms, clinics and rooms for administrative meetings and conferences. In addition to normal acoustic treatment to control noise coming in or going out, the treatment will also have to provide optimum conditions for speech.
Reference has already been made to the acoustical treatment of the air-conditioning system of a single ward. In most cases, a common system will provide these facilities for the whole of the building and the noise problems which arise must be given general as well as detailed treatment.
Acoustical consideration must be given to every duct run, apart from the noise from fans, compressors and ancillary equipment. Attention must be paid to the central-heating and hot water systems, through the suitable isolation of heating boilers, pumps and other plant and it should be remembered that pipe runs can also convey noise throughout the building unless effectively controlled.
Most hospitals are multistorey buildings and lifts are essential for the movement of personnel, patients and stores. Noise from lift mechanisms and the transmission of noise by way of lift shafts must be suppressed by suitable means, including the covering of the inner walls with absorptive materials. Once again, it is vital to plan such measures before the building work begins and to incorporate properly-designed acoustical control methods before the lift shafts are built and the equipment installed.
A Big Field:
Control of noise in hospitals is a vast subject in itself and it has been possible to do no more than indicate the nature of the problem and the approach which should be adopted. Certainly, far greater attention is now being paid to the problem than ever before and it is to be hoped that no new hospital will in future be built without acoustical advice at the very start of the planning.
So far as existing hospitals are concerned, the need to provide proper acoustic conditions for patients and staff is urgent indeed. Although it is true that ideal conditions are virtually impossible of achievement in many cases, it is equally true that a great deal can be done to improve the situation and case histories exist to prove it.
4. How to Control Noise in Judicial and Administrative Buildings?
Whatever personal reservations the individual citizen may have about the qualities and abilities of those who walk the corridors of power, there will surely be general agreement that all who make and administer our laws, whether at national or local level, should be accorded the best possible facilities for their important tasks. Prominent among these facilities is the provision of accommodation, such as council chambers, committee rooms, court rooms, offices and other rooms, specially designed for their respective functions.
As the transaction of a great deal of public business depends on the spoken word, the acoustics of all judicial and administrative accommodation are, obviously, a major consideration. Yet, as anyone will know who had has business with a local government committee or has visited the public gallery of a council chamber or court of law, the acoustics of the average administrative building leave very much to be desired. Here, then is yet another important field in which the acoustic consultant has a role to play, both in the construction of new buildings and in the modification of existing accommodation.
Following the pattern which will have become familiar in the first stage at which the acoustic consultant should be called in when a new building is being planned is on selection of the site. Since all administrative buildings must necessarily be at the heart of affairs, the site is likely to be in or near the centre of the town where traffic is certain to be heavy and the problems of external noise acute.
All that will be possible, as a general rule, at this stage, will be to orientate the building on the site in such a way that the areas within the structure which require the quietest conditions are situated as far away as is practicable from the sources of greatest noise.
Once the selection of site has been made and the layout of the building determined, a detailed acoustical investigation is necessary, account being taken of the special requirements of the different types of accommodation in the building.
If it is considered that judicial and administrative buildings can be grouped together for the purposes of this survey, then four principal types of accommodation, more or less common to both these main classes of buildings, can be defined.
These are – court rooms, legislative chambers and council chambers, assembly rooms, committee rooms and other rooms where meetings or conferences may be held; public and private offices, judges’ and magistrates’ retiring rooms, typing and general offices; rooms for rest, relaxation and refreshment and special plant rooms.
Court Rooms, Council Chambers, Etc.:
It will be obvious that in this group of rooms, where everything depends on the accurate transmission of the spoken words everything possible must be done to provide optimum conditions for clarity of speech, whatever the relative positions of speaker and listeners. It follows that reverberation times should be closely controlled in order that good hearing conditions are maintained throughout the room.
Since, the premises are likely to be in a busy part of the town, the problems of the entrainment of noise will also have to be considered. This will usually entail the sealing of windows to obtain the desired transmission loss and the installation of a ventilation system. Windows will probably have to be in heavy glass or even double-glazed with an intervening air space to provide added insulation.
Other Types of Accommodation:
In offices, retiring rooms, typing and general offices, and the main consideration is to provide conditions to facilitate the kind of work being done. Within the overall requirements of quietness and freedom from excessive reverberation, these rooms must be acoustically designed in the light of the specific activities to be carried on there.
Rooms intended for rest and relaxation (in this category, libraries and reading rooms can be included) will be characterised by quietness and the acoustical treatment must be designed with this aim in mind. On the other hand, the main problem in special plant rooms (boiler house, air-conditioning plant, lift motor-room, etc.), will be the control of incidental noise.
Many of the problems which arise under all these headings have since they are common to many different types of building. But there are certain basic considerations, applicable to judicial and administrative buildings generally. These can best be discussed under the headings of acoustical correction, acoustical transmission control and heating and ventilating systems.
Acoustical Correction:
In court rooms and council chambers, designing for good acoustical conditions involves the selection of suitable materials to provide accurate diffusion of sound; reinforcement of sound reaching the participant and the public and the attainment of a favourable ratio of direct to reflected sound in all parts of the room. Factors which determine these conditions include the shape and size of the room and the distribution of sound absorptive material.
Wall and ceiling surfaces should be treated in accordance with a properly designed acoustical scheme to provide the required degree of absorption and diffusion. Reverberation times relative to frequencies should approach optimum characteristics. This is determined by the value of acoustical absorbents, compatible with room size and desired or necessary finishes and furnishings.
Acoustical Transmission Control:
In planning noise control in a building where quietness and good hearing qualities are vitally necessary, it is desirable to take measurements of everyday normal noise activity at points adjacent to the site. Acceptable noise levels, based, perhaps, on known accepted noise levels for judicial and other public buildings, can be determined and these should form the references against which acoustical policies are formulated.
Attention must be paid to the propagation of noise through the free air, through openings and ducts and suitable attenuation measures applied. Data can be obtained by investigation and/or measurement against known values. It will also be necessary to obtain a reduction of sound and noise transmission and, in certain cases, to ensure speech privacy by means of suitable forms of partitioning. An obvious example is the case of probation offices, where sound-isolating partitions of high noise transmission loss must be installed. The jury retiring room can be quoted as another such special case.
Heating and Ventilating:
A well-designed heating, ventilating and air-conditioning system should operate quietly enough to be free from unwanted noise generated by and transmitted through the system. Nor should privacy be adversely affected by the transmission of conversations through pipes and ducting.
Steps which can be taken to reduce the amount of noise caused by the air-conditioning system include careful choice of motors, fans and grilles, the streamlining of the ducting so that turbulence at badly-designed points is prevented and the application of absorptive treatment in the equipment room (i.e., where the air-conditioning plant is sited) and in the duct system itself.
Where noise levels are quite low so that inter-room cross-talk interference occurs, it may be necessary to install suitable attenuators in the ducting. To undertake all this work in an existing building will clearly be difficult and may prove impracticable, even if the cost alone is not prohibitive.
5. How to Control Noise in Entertainment Industry?
Practically all forms of entertainment depend, in greater or lesser degree, on the transmission of sound from performers to audience, so that acoustical factors are all-important in buildings and rooms used for entertainment purposes, from theatres and concert halls to television and recording studios.
Only in the present century has a systematic approach been adopted towards this problem and even today, much remains to be done, especially in cinemas, dance halls and other locations where good acoustics are becoming increasingly recognised as an essential part of the amenities provided in view of its specialised application. This clearly opens up an extremely wide and complex field which will only be briefly reviewed here.
Auditoria:
Special problems have to be considered in the design and construction of all auditoria, where the participants sit and listen to sounds produced from specific areas, as in a concert hall, the ‘live’ theatre or cinema. As in the case of all buildings, if a completely new installation is under consideration, acoustical problems must be taken into consideration at the very earliest stage, namely, the selection of the site.
Choice is bound to be restricted, for obvious commercial reasons, to town centres, with the disadvantages of considerable environmental noise. Nevertheless, if there is an element of choice in respect of the site, the acoustician will naturally recommend a site where the problem of noise entrainment is likely to be less serious, having first taken the necessary noise level readings as evidence.
Careful consideration must also be given to the shape of the auditorium, since the geometrical acoustics are of very great importance. The shape of the auditorium must, necessarily, be closely related to its use, but close collaboration between the acoustic consultant and others concerned, should make it possible to arrive at a reasonable compromise between the optimum shape from the acoustical point of view and the requirements of the function the room is to perform.
Because it is necessary for everyone in the auditorium to be able to hear everything from the stage with the utmost clarity, it is particularly important that the elevational cross-section should be carefully considered. The possibility of architectural reinforcement, by which sound is reflected from specially designed parts of the structure, can also be considered.
The design of ceilings in relation to actors or musicians on a stage is of particular significance in this connection. By the use of such forms of architectural reinforcement, it is possible to distribute the sound from its source around the auditorium without distortion. It may also be necessary to allow for changes in the source of sounds as, for example, when actors move about a stage.
In theatre design, special attention will also have to be paid to the stage and full use made of its geometries and such ancillary equipment as flats (scenery) to produce the best results. When full advantage has been taken of architectural reinforcement, it will then be possible to discover what electronic reinforcement, if any, is needed to produce the desired results in all parts of the auditorium.
Consideration must also be given to the fabric of the building, with regard to the possible entrainment of outside noise. It will be advisable to work to a noise criterion of NC25 as the upper limit and this objective, under normal conditions, can usually be achieved by the use of general standard construction techniques, employing steel and concrete with substantial infill.
A good modern auditorium will also require first-class air conditioning and ventilation arrangements and the usual precautions must be taken in selecting the site for the primary source of noise and in installation of attenuators at appropriate points.
When the shape of the auditorium has been determined, it is next necessary to consider its acoustical problems in greater detail, including the selection and installation of acoustical absorbent materials. This will be based on the results of a careful acoustical analysis, bearing in mind that very high musical fidelity and speech definition will be required.
In the case of auditoria to be used exclusively for music, as with concert halls, it will be necessary to extend the analysis over a wide range of frequency bands, in order to ensure faithful reproduction of the various musical instruments and voices. In auditoria where speech definition is the chief criterion, the level of syllable articulation will demand particular attention.
Standard tests for syllable articulation can be carried out by persons in various parts of the auditorium, the results being based on an agreed formula. The desirable level of speech definition, according to the prescribed test, is in the region of 98-99 per cent.
On the basis of the acoustical analysis, the selection and orientation of absorbent materials is considered. It is most likely that these will be required on the side and rear walls to give the precise absorption performance needed, according to the results of the analysis.
Depending on the geometrical considerations, the ceiling may have to be of sound-reflective materials or at least, of materials with very low coefficients. In some cases, however, it may be necessary to employ the ceiling as a low-frequency absorbent unit, by utilising very special ceiling design techniques.
Where a ceiling is to have an absorbent function, it may take the form of a suspended ceiling with gaps and with absorbent materials behind it. It may also have to be specially designed to provide acoustical correction in relation to specific frequency bands.
When taking out an acoustical analysis, particular care must be exercised to include every amenity in the auditorium, including carpets, seats and the occupants, all of which have their absorbent coefficients. With regard to the audience, it is usual to work on the basis of a half-filled auditorium, making allowance for seasonal differences (e.g., heavier clothing in winter).
If all these steps are taken, it will be possible to build-in an acoustical performance which will be as near the perfect level as calculations can attain. Good predicted control of sound obtained in this way is of great importance but may not always attain the desired level of performance when actual tests are taken in the completed auditorium.
The differences between predicted and actual results are not likely to be large, however and correction by, for example, the reorientation of acoustical materials, will be relatively easy and certainly much easier than if the building had been constructed without any attention to acoustical analysis in the first place.
Studios:
Increasing sophistication in the techniques of radio and television broadcasting and sound recording has led to demands for much closer attention to the acoustics of studios. In addition to the entertainment aspect of the problem, the increasing use of recording and cine-photography techniques in industry gives the problem a far wider application.
Two sets of problems arise here: the treatment of the studio to enable it to perform its particular function with the best possible results and treatment to prevent the activities of the occupants of the studio being a nuisance to other people.
Treatment of studios internally to provide the best possible conditions for the users is a complex subject. General points to be considered, however, include the usual strict control of noise from associated equipment, such as ventilation and air-conditioning plant and careful consideration of the acoustical treatment given to the room, which will probably require saturation with absorbent materials.
Since studios tend to be small rooms in larger buildings, the most urgent problems are often those related to the transmission of noise to people in other parts of the building. Even if these other rooms are occupied by people employed by the organisation which operates the studio, their work, as scriptwriters, music arrangers, etc., will suffer if excessive noise is transmitted from the studio.
In an extreme case, it may be necessary for the studio to be constructed as a ‘room within a room’, the gap between the two rooms being draped with absorbent materials. In all cases, it will be necessary to control structure borne noise from musical instruments, especially percussive instruments such as piano and drums. These instruments can be fairly readily isolated from the structure, but this procedure is complicated if, as is usually the case, it is desired to move the instruments around the studio in order to suit recording requirements.
Though the problems of studio acoustical treatment are difficult, consultants, including some who specialise in this type of work, are rapidly building up a fund of experience which enables them to devise procedures to meet most difficulties, whether they are ones which affect the user of the accommodation or people living and working adjacent to the source of noise.
6. How to Control Noise in Flats and Apartments?
It is probably true to say that only in comparatively recent times has any scientific consideration been given to the acoustical problems of large blocks of flats and apartments, where noise was formerly regarded as a necessary evil which had to be endured. More recently, however, with the rapid increase in the number of flat dwellers in all income groups, the very real acoustical problems of this type of residential accommodation have been more fully considered.
General Considerations:
Many problems arise when planning the control of noise in blocks of flats, but they may be said to fall into three main divisions: the insulation of the accommodation against outside noise: the insulation of partitions between rooms; and the control of entrainment of noise from plant and equipment within the building into adjacent apartments.
Assuming that the usual consideration has been given to the selection of the site with respect to surrounding noise and that the fabric of the building has been chosen and erected with due regard to the control of outside noise, the next problem to be considered is the design of floors. If practicable, the best solution will probably be the laying of discontinuous or ‘floating’ floors throughout the building, preferably on mineral wool quilt of specified density and compliance.
This should be laid down in such a way that impact noise on floors in any particular room is not transmitted to the structure of the building and so carried to other rooms, to the discomfort of their occupants. In addition to controlling structure-borne noise, the additional weight of the isolated floating screed, in combination with a quilt of this kind, will also increase the transmission loss of airborne noise between floors.
Partitions between flats and between single rooms in each flat must also be selected with care, particularly where bedrooms are adjacent to living-rooms. All partitions should achieve high transmission loss and some form of discontinuous construction may well have to be considered, using either wet or dry construction, as required. Bedrooms and other rooms should be ventilated from the quiet side of the building or, if this is not possible, double glazing for the windows and internal air conditioning should be considered.
Certain rooms and areas demand special attention. These include bathrooms and toilet accommodation, which must be carefully insulated acoustically from other parts of the buildings. Much can be achieved here by careful selection of equipment and fittings.
Quiet-operating electrical switches should be selected and this applies particularly to the ceiling poppet types which are most liable to transmit noise. Data should be collected on the noise produced by different types of lavatory-flushing equipment and the most silent type selected.
Pipes supplying water to baths and washbasins should be large enough to allow relatively low speeds of water flow, so avoiding the noise created by a turbulent flow of water. Where a relatively noisy water pipe is unavoidable, it should be wrapped with mineral wool and insulated from the building structure by means of flexible connections.
Halls, corridors and stairways are often reverberant: this is not only annoying to people walking through them but such areas also convey noise between various parts of the building, especially, as is often the case, if they incorporate surface finishes such as hard plaster walls and ceilings and wood block floors. The situation can be improved, both for those using these facilities and for those in other parts of the building affected by structure-borne noise, if suitable absorptive materials are applied, in accordance with the results of an acoustical analysis.
Other rooms which may require special attention include dining-rooms and living-rooms. These will normally contain large areas of absorptive materials in the form of furnishings, but if they are absent, transmission loss problems can result. Kitchens should be treated with absorptive materials and any power-driven domestic appliances, such as refrigerators and washing-up machines, must be suitably isolated from walls and floors.
The sink waste-disposal units which are being increasingly installed in many present-day blocks of flats pose particularly difficult noise problems and before installing such equipment careful investigation should be made into suitable mounting and isolating techniques.
All this equipment will normally be installed as part of the facilities of the building and the problem of noise can be considered before installation and proper remedial measures undertaken beforehand. Problems which cannot be so readily foreseen arise from the personal equipment and appliances which tenants may install in the flats, such as pianos, high-fidelity radio and gramophone equipment and the like, all of which can cause considerable nuisance to other occupants. To provide overall protection throughout the building will probably be too expensive and tenants may have to be given individual advice on the precautions necessary if their personal equipment is not to cause annoyance to neighbours.
Some of the problems which affect other large buildings, such as noise from lifts and air-conditioning equipment, will also have to be solved in blocks of flats. A great deal of work has already been done on providing quiet-running lifts and it is becoming standard practice to treat the inner walls of lift shafts with sound-absorbing materials.
Pipes and ductings for heating and ventilating systems should be suitably isolated from the partitions and the solid fabric of the building and mechanical equipment, such as fans, motors, pumps, fuel injectors, main and secondary chokes, transformers, coolers, switchgear and ancillary equipment should also be isolated form the building structure.
Waste-disposal chutes are a great convenience to flat dwellers but they can produce unwanted noise. They can be isolated from the building structure by fitting suitable mountings at appropriate levels and if possible, by constructing the chutes of material other than the conventional concrete.
Hygienic but compliant materials, such as heavy duty PVC mouldings, are suitable as further advantages will be obtained from an acoustical point of view if design methods can be employed to reduce the velocity of travel of the rubbish at the terminal disposal points.
Acoustical Design Procedure:
When planning a new block of flats, three main categories of acoustical consideration must be considered. These are – acoustical transmission control, acoustical correction and noise control of the various services. Preliminary steps necessary in respect of acoustical transmission control will include an analysis of the magnitude, nature and distribution of noise, which can be predicted from the plans and on-site measurements and subsequently verified by acoustical measurement.
Decision will be taken as to acceptable noise levels in the various apartments and areas, both with respect to each other or as individual rooms contained within each apartment. These can be determined by known and accepted levels, as experienced in other similar locations. Other information which must be assembled relates to the movement of sound through the free air, through opening and ducts for example and these levels can be determined by investigation, measurement, known values or prediction.
Further factors to be considered under the heading of acoustical transmission control include the reduction of sound or noise transmission and the attainment of speech privacy by selection and design of suitable partitioning, the reduction of machinery or other noise at source by careful selection of equipment and the reduction of noise in plant rooms by the use of sound absorbing treatment and insulation. In some cases, known data will be available in respect of some equipment.
Preliminary work on acoustical correction will include the selection of suitable materials and their installation to obtain the correct amount of diffusion and absorption for each room and area. A particularly important aspect is the effective control of airborne noise through entrance halls, corridors, access ways and stairways to various parts of the building.
The distribution of absorptive materials is largely controlled by the nature, function, environment and shape of the rooms. Walls and ceilings should be treated in accordance with the results of acoustical calculations, taking due account of the minimum amount of soft furnishings likely to be introduced by the tenants.
In all rooms, reverberation time in relation to frequency should approach the optimum values previously determined and the acoustical correction scheme designed for each room, taken in conjunction with finishes and furnishings should be applied to this end. It must be remembered, of course, that reverberation time characteristics have a strong subjective element and it may even happen that tenants will eventually complain that a room is too quiet.
Much can be done at the preliminary planning stage to ensure that the heating, ventilating and other plant, together with domestic appliances, operate quietly enough to be free from unnecessary noise generated by and transmitted through the system. The amount of noise contributed to a room by mechanical ventilation, for example, should be reduced to a level which is negligible compared to other noises within the room.
Marine Acoustics:
In the diaries and biographies of travellers in the early days of mechanical propulsion at sea, there are frequent references to the comforting throb of the engines, which assured the voyager that at least these capricious machines had not broken down, with attendant fears of being isolated at sea, far from human aid.
Today’s travellers by sea, sped on their way by much more powerful engines, to say nothing of air-conditioning and ventilating plant, auxiliary plant for electric power generation and so forth, cherish less romantic ideas about shipboard noise and though comparatively little attention has yet been paid to acoustics on board ship, there have been signs, over the past year or two, that this position is changing.
Ideally, an acoustic consultant should be employed whenever a new ship is being designed and built, because so many of the most difficult acoustic problems are built in during the construction of the vessel and it is even more difficult in a ship to make the subsequent alteration than in a building.
Because so little has yet been done in the marine acoustics field, it is possible here to do no more than briefly indicate some of the directions in which developments may be expected to take place in the future.
Marine main propulsion machinery poses particularly severe problems. Not only are these necessarily of high capacity, but the method of propulsion demands that the drive arrangements and particularly the thrust blocks must be rigid. Thrust blocks, for instance, must be firmly bolted to the keel, whence all vibration is inevitably transmitted throughout the entire vessel.
There is a strong case for a close investigation of the acoustical performance of marine prime-movers, with a view to reducing excessive vibration at source through appropriate design changes and the possible utilisation of alternative materials. Similar considerations apply to other shipboard machinery and equipment, such as burners for oil-fired vessels, fuel and water pumps, donkey engines and air-conditioning plant.
Isolation techniques can be applied to all this equipment and attenuators fitted in all ducting and ventilation channels. And even when all due attention has been paid to the reduction of noise at source in the engine-room and other machinery areas, further control measures will be necessary in the form of acoustical treatment of these areas.
All partitions within the ship require much thought during the design stage and this is a very big subject to which comparatively little attention has been paid up to the present. Much can be done, by careful design and the selection of appropriate materials, to raise noise transmission losses through all partitions, from the main bulkheads to the partitions between cabins. High transmission-loss partitions are particularly necessary between cabins and crosstalk attenuators will generally be required to ensure the desired degree of privacy.
It is also necessary to pay attention to the acoustical treatment of cabins which are near particularly noisy areas. These include cabins adjacent to kitchens and other service areas and those which lie immediately below much-used decks, such as the sun deck on cruise liners.
Finally, the same careful attention which should be paid to all public rooms ashore should be given, in no less measure, to equivalent shipyard accommodation. Such rooms should include dancing and other recreational areas, restaurants and indeed, all rooms intended for the social relaxation of passengers.
This reference to marine acoustics, though necessarily brief, should suffice to indicate the extent of the problem, which is one that may be expected to exercise the minds of acousticians to an increasing extent in the future.