TABLE OF CONTENT
1.0 INTRODUCTION
2.0 ESTABLISHING EFFICACY OF IMPROVEMENTS IN CLASSROOM ACOUSTICS
3.0 NOISE CONTROL
3.1 CHOOSING A SITE
3.2 RECOMMENDATIONS FOR EXTERNAL NOISE LEVELS OUTSIDE SCHOOL BUILDINGS
3.3 NOISE SURVEY
3.4 NOISE BARRIERS
3.5 NOISE FROM SCHOOLS TO SURROUNDING AREAS
3.6 PLANNING AND LAYOUT
3.7 LIMITING INDOOR AMBIENT NOISE LEVELS
3.8 IMPACT NOISE
3.9 CORRIDORS, ENTRANCE HALLS AND STAIRWELLS
3.10 MASKING NOISE
3.11 LOW FREQUENCY NOISE AND HEARING IMPAIRED PUPILS
4.0 GENERAL PRINCIPLES OF SOUND INSULATION AND TYPICAL CONSTRUCTIONS
4.1 ROOFS
4.2 EXTERNAL WALLS
4.3 VENTILATION
4.4 EXTERNAL WINDOWS
4.5 EXTERNAL DOORS
4.6 SOUND INSULATION OF THE BUILDING ENVELOPE
4.7 INTERNAL WALLS AND PARTITIONS
4.7.1 GENERAL PRINCIPLES
4.7.2 CORRIDOR WALLS AND DOORS
4.8 INTERNAL DOORS, GLAZING, WINDOWS AND FOLDING PARTITIONS
4.9 BUILDING UNITS SOUND INSULATION
4.9.1 DOORS
4.9.2 LOBBIES
4.10 FLOORS AND CEILINGS
4.11 IMPACT SOUND INSULATION
4.11.1 VOIDS ABOVE SUSPENDED CEILINGS
4.11.2 CONCRETE FLOORS
4.12 OPEN-PLAN TEACHING AND LEARNING AREAS
4.13 MULTI-PURPOSE HALLS
4.14 OTHER LARGE SPACES
4.15 DINING AREAS
5.0 CONCUSION
6.0 REFERENCES
1.0 INTRODUCTION
In order to improve learning, productivity, concentration, and teacher – student communication, you need to control the background noise and reverberation level within the classroom. ANSI Standard S 12.60-2002 American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools now recommends maximum background noise at 35 decibels and reverberation at 0.6 to 0.7 for unoccupied classrooms. No matter how hard students try to concentrate on the teacher's instructions, they can't help but be distracted by noise. Their concentration levels are affected by sounds that come from inside and outside the classrooms. Thus stressing the importance of materials that will reduce the background noise and absorb the echo and reverberation within school classrooms, gymnasiums, auditoriums, cafeterias, or anywhere a noise problem is encountered.
The goal of noise reduction in large open rooms is to add sound absorption materials to reduce reverb within the room. Typically these large rooms have hard reflective walls and floors such as concrete block and there is a need for noise reduction. Adding noise control products such as hanging baffles or wall panels will increase speech intelligibility and reduce ambient noise during events for greater usage of the room. These sound absorption materials should be planned into the design of the gym or multipurpose room, however they can be added as a retrofit application as the need for noise reduction within the facility is addressed.
www.noisecontrolproducts.com
Like elementary schools, the challenge in secondary school design is to incorporate high-performance design features and technology cost-effectively. But high schools and junior colleges have even more sophisticated technology needs.
Proposed standards for classroom acoustics are being developed. A work group of the Acoustical Society of America (ASA) in conjunction with the American National Standards Institute (ANSI) recommends that classroom noise not exceed 35 decibels. Many American class- rooms today can be as loud as 50 decibels, For satisfactory communication, speech should be 15 decibels above background noise. The group also recommends that reverberation time not exceed O.6 seconds.
Joint-use facilities are more common. Opening schools to the community dramatically decreases the development footprint because communities are constructing and maintaining fewer buildings and parking. This conserves land, building materials, energy and other resources, and enhances the value of civic life.
Scientists who study the "neuroscience of learning" are finding that certain lighting, acoustics, and spatial relationships support or hinder the learning process.
www.wbdg.org
2.0 ESTABLISHING EFFICACY OF IMPROVEMENTS IN CLASSROOM ACOUSTICS
Assuming that a survey with recommendations is conducted and that recommendations are effectively implemented, there should be an improvement in acoustic conditions and in the students' ability to perceive the speech of the teacher and other students. This improvement should lead, in turn, to improvements in functional classroom performance. The modifications and improvements, however, must be demonstrated in order to validate the process. If an acoustic consultant has been involved, physical measurements made before and after changes to the acoustic environment serve as physical measures of efficacy. If an acoustic consultant was not involved, the audiologist should complete the pre- and post-physical measurements. In addition to the physical measurements, behavioral measurements in the form of speech recognition scores, teacher or student report forms, changes in student behavior such as “on task behavior,” or changes in achievement test scores serve as measures of efficacy. Use of the Speech Transmission Index or other measures of predicted speech recognition might also be employed (Houtgast, T., & Steeneken, 1978). Above all, the audiologist must document that improvements have occurred and that the improvements persist over time.
For classrooms, the consulting process includes evaluating the design for the interior room acoustics, interior and exterior acoustical isolation, and mechanical system noise control. As a rule, acoustical consultants are not asked to design sound reinforcement systems (i.e., sound field amplification) for classrooms.
Interior Room Acoustics: In order to assure appropriate interior room acoustics, acoustical consultants work with the architects to select acceptable wall, ceiling, and floor materials or finishes for the classroom so that the reverberation time of the room meets or exceeds the reverberation design goal specified in the ANSI standard.
Background Sound Levels: To determine background sound levels in a room, various types of design calculations can be performed, supported, whenever necessary, with noise measurements to determine if the ANSI specified background noise level design goal of 35 dBA criteria could be met.
Mechanical Noise: Mechanical system noise accounts for the highest percentage of noise complaints in the United States (ANSI, 2002). An acoustical consultant can calculate sound levels in a classroom using the design documents provided by the mechanical engineers working on the project. If the 35 dBA design criteria is exceeded, sound attenuation devices can be recommended so that the design goal is met. Mechanical systems for classrooms fall into two categories:
Individual Units: It is easy and inexpensive to install unit ventilators in a classroom. A unit ventilator is a stand-alone unit that contains a fan and may also contain a compressor. Discharged air comes out the top and the intake is usually at the bottom. The best way to minimize sound from stand alone units is to build a closet around them. The supply air would be ducted out of the top to ceiling diffusers. The return air back to the unit would be through a lined shaft inside the closet. The walls and doors must be adequately sealed. This may increase the installed cost of each unit, but will significantly reduce sound levels.
Central System: A central mechanical system supplies air to a classroom through ductwork from a large air handling unit that serves many rooms. If designed carefully (i.e., locating units properly and using attenuation devices such as duct liners or sound attenuators) the sound in the classroom will be minimal. This method can make it easier to control noise since the units are not in the rooms themselves.
Exterior Noise: Exterior noise also contributes to the background sound in a classroom. If the building is in a high noise level area, such as close to an airport or major highway, noise isolation or performance of exterior windows and wall sections can be examined to ensure that the maximum background sound level is met inside the room. This may also require measuring sound levels at the potential site of a new school. More important, correct sound insulation design of the external walls and roof assembly needs to be assured.
Partition Design: Partitions between the classroom and adjacent areas should be designed or upgraded to achieve Sound Transmission Class (STC) ratings as recommended by the ANSI standard. The STC is a single number rating derived from sound transmission loss values and provides a measure of the sound insulation performance of a partition with a defined design configuration. The higher the value, the more the partition attenuates sound. The ANSI standard recommends a rating of 50 STC between classrooms, 45 STC between classrooms and corridors, and 60 STC between classrooms and high noise level rooms, like mechanical rooms or music rehearsal rooms. To achieve these ratings, the walls must be sealed to the underside of the structure above. Walls that stop just past acoustic tile ceilings will not achieve these ratings because the sound will travel through the acoustic tile ceiling, over the wall, and through the acoustic tile ceiling on the other side.
The information on the interior finishes, partitions and window details, and mechanical system modifications should be given to the design team so that they can be incorporated into the final design documents for the building.
www.asha.org
3.0 NOISE CONTROL
This section gives recommendations and guidance concerning noise control,
starting with the choice of a site and the control of external noise. Local
government planning policy will be influenced by the recommendations on
maximum external noise levels in playing fields and other external areas used
by the school. Also includes discussion of the means of controlling
indoor ambient noise.
3.1 CHOOSING A SITE
The acoustic design of a school starts with the selection of the site, a noise survey of the site and planning the layout of the school buildings.
Economic sites for new schools with easy access to transport often suffer from traffic noise and pollution. In the past, schools have sometimes been built on sites which would not normally have been
considered suitable for housing. This has been in part because schools have not always been recognised as requiring particularly high environmental standards, and in part because there has been less formal control or regulation of noise levels in schools than for housing.
Where school sites are adjacent to busy roads they will require the use of intelligent design, zoning, noise screening
and, if necessary, sound insulating building envelopes together with mechanical ventilation or acoustically designed passive ventilation.
Many of the acoustic problems in existing schools derive directly from the school’s location in a noisy area. For existing schools, noise from road traffic is a common problem, but in some areas noise from railways and aircraft is intrusive. Noise from industrial and leisure sources is a less frequent problem
and can normally be dealt with at source by the Local Authority using their powers under the Environmental Pollution Act.
3.2 RECOMMENDATIONS FOR EXTERNAL NOISE LEVELS OUTSIDE SCHOOL BUILDINGS
Although Requirement E4 does not apply to external noise, the following recommendations are considered good practice for providing good acoustic conditions outside school buildings.
For new schools, 60 dB LAeq,30min should be regarded as an upper limit for external noise at the boundary of external premises used for formal and informal outdoor teaching, and recreational areas.
Under some circumstances it is possible to meet the specified indoor ambient
noise levels on sites where external noise levels are as high as 70 dB LAeq,30min but
this will require considerable building envelope sound insulation, screening or
barriers.
Noise levels in unoccupied playgrounds, playing fields and other outdoor areas should not exceed 55 dB LAeq,30min and there should be at least one area suitable for outdoor teaching activities where noise levels are below 50 dB LAeq,30min. If this is not possible due to a lack of suitably quiet sites, acoustic screening should be used to reduce noise levels in these areas as much as practicable, and an assessment of predicted noise levels and of options for reducing these should be carried out.
Playgrounds, outdoor recreation areas and playing fields are generally considered to be of relatively low sensitivity to noise, and indeed playing fields may be used as buffer zones to separate school buildings from busy roads where necessary.
However, where used for teaching, for example sports lessons, outdoor ambient noise levels have a significant impact on communication in an environment which is already acoustically less favourable than most classrooms. Ideally, noise levels on unoccupied playing fields used for teaching sport should not exceed 50 dB LAeq,30min. If this is not possible at all locations, there should be at least one area at which noise levels are below 50 dB LAeq,30min so that some outdoor teaching is possible.
Acoustic screening from fences, walls or buildings may be used to protect playgrounds from noise. At positions near the screen, traffic noise can be reduced by up to 10 dB(A).
All external noise levels in this section apply to measurements made at approximately head height and at least 3 m from any reflecting surface other than the ground.
3.3 NOISE SURVEY
Figure 3.1 shows typical external and internal sources of noise which can affect noise levels inside a school.
In order to satisfy the limits for the indoor ambient noise levels, it is necessary to know the external noise level so that the building envelope can be designed with the appropriate sound insulation.
The external noise level should be established by carrying out a noise measurement survey. (Note that a brief survey is advisable even if the site appears to be quiet, in case there are noisy events at certain times of the day.) The typical school hours and include noisy events (eg road traffic at peak hours, worst case runway usage in the case of airports, etc). The measurements must also take account of the weather conditions. For long-distance propagation of noise, the measured level is affected by wind gradients, temperature gradients and turbulence. With wind, the noise level is generally increased downwind or reduced upwind. (Note that temperature inversions can radically change noise propagation, but tend to occur only at night-time, outside school hours.)
A noise measurement survey must include octave or one-third octave frequency band levels. This is because the attenuation of sound, for example by a sound insulating wall or noise barrier, depends upon the frequency of sound. In general materials and barriers are less effective at controlling low frequency
noise than mid and high frequency noise.
Although overall noise levels and performance standards can be quoted as overall A-weighted levels, calculations must be carried out in octave or one-third octave bands and the results converted into overall A-weighted levels.