* The softest sound most people can hear is 0 decibels. A soft whisper is 30 decibels; rainfall is 50, normal conversation is 60; thunder is 120
* 70 decibels can directly affect health and school performance
* The noise level in many classes is about 72 decibels - as loud as a busy road junction
* In London primary schools, increases in external noise levels of 10 to 40 decibels - such as from road traffic and aircraft - can cut Sats scores by 30 per cent
* Noise in classrooms means staff constantly have to shout. Teachers form a disproportionate percentage of those attending voice treatment clinics in the UK
* In Hounslow, near Heathrow airport, lessons in some schools are planned around aircraft noise
Listen to that racket. How can anyone be expected to impart knowledge with all that row going on? Schools have never been the quietest of places, but it's an unfortunate fact that some are a lot noisier than others. Research has shown that a surfeit of decibels in class puts pupils at an unfair disadvantage, while making teachers stressed and frustrated. Which is why new school buildings have to meet strict acoustic design standards.
Increased awareness of the noise problem also means local education authorities will face pressure to bring existing premises up to standard.
It won't be easy, though. Because there's more to achieving a quieter life than simply signing up for double glazing.
Common sense says people have difficulty focusing their minds in noisy surroundings. But when Professor Bridget Shield of South Bank University, and Professor Julie Dockrell of London University's Institute of Education, set about quantifying the relationship between decibels and academic performance in London primary schools, the figures were little short of sensational. Even allowing for social and economic factors, they calculated that increases in external noise levels of between 10 and 40 decibels led to a 30 per cent fall in Sats scores.
External noise can come from many sources, but the most common are undoubtedly road traffic and aircraft. The researchers looked at schools in three London boroughs and found external noise levels in unoccupied classrooms were far in excess of government and World Health Organisation recommendations. (Measuring in an empty classroom gives accurate external levels as there is no background babble.) Most disturbing of all, it was clear that the greater the level of social deprivation in an area, the higher the external noise level, making deprived children doubly disadvantaged, said the researchers.
Schools in England have average noise levels of 72 decibels - that's as loud as a busy road junction. A Canadian study found schools in Ottawa had levels of about 55 decibels, equal to the noise in a shopping centre. The best spoken communication is believed to happen when speech exceeds background noise by about 15 decibels. As the strength of the human voice is limited, ideal conditions are achieved by reducing background noise. A Swedish standard says an "acoustically satisfactory" classroom should have an unoccupied noise level of no more than 30 decibels - the equivalent of a soft whisper.
Jet lag is no joke
In a recent survey by the London borough of Hounslow, which includes Heathrow airport, 90 per cent of teachers said aircraft noise affected children's literacy and numeracy skills, and 77 per cent said pupils had difficulty hearing lessons when planes were passing. In some cases, the noise was so loud that lessons had to be planned around it, while even playtime was disrupted by the din of jet engines. While the Hounslow survey was carried out in the context of local opposition to a third runway at Heathrow, its findings were consistent with earlier research. Studies have shown that aircraft noise can have a detrimental effect on long-term memory and blood pressure, and that the after-effects of sudden aircraft noise continue to disrupt teaching for some time.
In 2001, a detailed analysis of cognitive performance and stress responses among children at 20 west London primary schools found that aircraft noise was associated with poor reading performance, and in pupils, parents and teachers alike, it was responsible for increased levels of annoyance. That same year, the US Federal Aviation Administration and the port of Seattle agreed to divert airport revenues to a $200million project to insulate, and in some cases replace, 15 schools worst affected by noise from Sea-Tac Airport. The Seattle project, which is expected to take several years, started with the tearing down of an entire elementary school. In Hounslow, the council has put the cost of insulating its 37 worst affected schools at around pound;26m.
While aircraft noise makes loud headlines, most of the external noise nuisance in schools has a more mundane source. More than 85 per cent of children questioned in the London primary school survey had to endure disruptive traffic noise. And it's not just inner cities where road racket gets on people's nerves. Kent, once known as the Garden of England, is now criss-crossed by motorways carrying heavy lorries to and from Dover and the Channel Tunnel at Folkestone. When Maidstone Borough Council conducted a seven-month investigation into the effects of traffic noise on school life, it found that sound levels were far in excess of what was considered acceptable.
Earlier research found that noise levels of 40-55 decibels are annoying, up to 60 decibels disturbs sleep and 70 decibels can directly affect health and school performance. The Maidstone tests showed that noise levels of 60 to 70 decibels are commonplace in residential areas close to the county's motorways. The inevitable disturbance of home life for many families means many children and teachers start the school day feeling tired and irritable.
Sealing the envelope
In an ideal world, no schools would be built close to busy roads or on approaches to major airports. But in reality there is often little alternative, and in existing schools it may be a case of making the best of a bad site. Landscape features can make a difference, and recent work at the University of Hull has shown that certain species of tree, as well as other vegetation, can form useful noise barriers. But the main task is to ensure that what architects call "the building envelope" offers maximum resistance to sound waves. Fortunately, modern materials can shut out almost anything.
When did you last hear the deafening roar of jet engines as you sipped coffee in an airport lounge? And in the war on noise, every part of a school building has a part to play. Rain beating on a sheet-metal roof can cause noise levels of up 70 decibels inside a school assembly hall, while timber-framed walls with wooden cladding do little to keep low frequency noise such as traffic rumble out of a classroom.
But when it comes to the structure of a classroom, windows represent by far the weakest link. The solution is double-glazing, and even old buildings can be fitted with secondary units inside existing windows. Effectiveness depends not only on the thickness of the glass and the space between layers, but also on design and construction of the frame and the accuracy with which the units are fitted. An airtight seal is essential.
But hermetically sealing the classroom brings a fresh problem - ventilation.
Regulations in the UK require that at least eight litres of fresh air per person enter a classroom every second. But when external noise is a problem, throwing open the windows isn't an option. Nor is it then simply a case of sucking in air from the outside, as ventilators that penetrate walls or windows can themselves let in noise.
In these circumstances, devising an adequate ventilation system begins to resemble a branch of rocket science. And there is a further complicating factor: the noise of the mechanical ventilators themselves. For while good double glazing can keep out the rumble of traffic and even the roar of aircraft, it does nothing to damp down internal noise. The clatter of steel-framed furniture, the background babble of conversation, the stamp of feet in the room above, the school orchestra tuning up next door and, behind all this, the constant, all-blurring drone of ventilation units - every one of these sounds comes from inside the building. As an impediment to concentration and comprehension, they cannot be underestimated.
The inside story
When Bridget Shield and Julie Dockrell investigated the effects of noise in London primary schools, they confirmed that children were disturbed and distracted by road and air traffic noise. But it was internal noise that seemed to have the biggest negative effects on Sats results. Language-based tasks such as reading and spelling were particularly affected by background babble, and children with special educational or linguistic needs, and those with a hearing impairment, were especially vulnerable. The researchers noted that staff constantly had to shout, leading to sore throats for them (teachers form a disproportionate percentage of those attending voice treatment clinics in the UK) and aural confusion for pupils. Summing up their findings, Professor Shield said: "Classrooms can be noisy places, and that noise can be detrimental to children's performance at school. But appropriate acoustic design reduces noise levels, so it is essential that acoustics is given a high priority when new schools are being built or older schools refurbished."
Laying down the law
Recent guidelines for the acoustic design of schools (Department for Education and Skills: Building Bulletin 93) highlight the problems of teaching and learning when ambient noise levels are high - problems that have been brought into sharp relief by the new statutory requirement to increase the integration of special needs children into mainstream schools.
The guidelines, co-edited by Bridget Shield, were drawn up in response to new legislation, under which - for the first time - LEA-maintained schools in England and Wales are covered by Part E of the building regulations, which deals with noise.
From July last year, new schools and extensions to existing premises have to be built so that teaching and study areas meet stringent acoustic requirements. As well as stipulating effective insulation from external sound, they set out to limit the extent to which sound carries from room to room through walls, floors and doors. At the same time, the guidelines should be used as a benchmark for the refurbishment of existing buildings.
In their introduction, the authors point out that many Victorian school buildings are unsuitable for modern teaching methods, while more recent open-plan layouts, designed to accommodate several activities, are prone to high levels of background noise. "The pressure on finances has meant in the past that acoustics came low on the list of design priorities," say the authors. "The acoustic design will now have a higher priority as it will be subject to building control approval procedures."
The listening brain
How do various noises interfere with specific mental tasks? Are children, whose cognitive skills are still developing, more susceptible than adults to auditory disruption? Ecophon, a firm that makes acoustic ceilings, is paying a team of psychologists at Cardiff University to come up with answers to these questions. Led by Professor Dylan Jones, they will spend the next three years testing various theories at schools in south Wales.
"It seems that the process of ordering is the one that is really vulnerable to background sound," says Professor Jones. "The brain is good at ordering things, whether we want it to or not. We may be trying to do a sum or a comprehension test, but at the same time our brain will be ordering and sequencing events we are hearing, even if we are trying to ignore them.
Then there are two ordering processes going on simultaneously, and that is probably what causes the disruption." In three years' time, the team hopes to be in a position to provide detailed advice on school design. But Professor Jones says they are unlikely to advocate silent classrooms. "It may be important that children are exposed to background babble because that's part of how we acquire language. But we need to be aware that some tasks are very disrupted by certain kinds of irrelevant sound, so there should be quiet times for doing certain things."
Echoes of confusion
As if external and internal nuisance noise isn't enough of a handicap, teaching and learning are frequently hampered by a further factor: reverberation. When sound waves leave a teacher's mouth, only some of them find their way directly into the ears of their eager pupils. Most bounce off hard surfaces around the room, dividing as they ricochet so that each sound arrives as a sequence of echoes. In a room with poor acoustic characteristics - with what is termed a "long reverberation time" - the dying echoes of one sound overlap the arrival of the next, so the listener must strain to distinguish individual words. Add this distortion to a melange of clashing chair legs, background babble, traffic rumble and the occasional jet engine roar, and it's easy to see how poor acoustics can affect Sats results. Replacing hard, reflective surfaces with porous, absorbent materials can reduce the echo effect in a room. A false ceiling made of acoustic tiles with an air space above will have a dramatic effect on reverberation time - the time it takes for each sound to stop echoing.
Speech intelligibility increases accordingly, and with it, the ability of children to concentrate.
Music to their ears
While short reverberation times provide the best environment for speech, music lessons benefit from a degree of echo (think of King's College Chapel). The DfES guidelines for new school buildings spell out the acoustic requirements for various types of activity, differentiating between spaces used for quiet study and performance or recital areas.
But unfortunately for music teachers, there is little acoustic designers can do to protect them from one serious occupational hazard: permanent damage to their hearing. The 1989 Noise at Work Regulations outline the responsibilities of employers and employees to monitor and limit noise exposure and provide protection (ear plugs, muffs or caps), and European regulations to be introduced in 2006 are expected to reduce by up to two-thirds the noise levels to which workers can be exposed.
Ten years ago, the Somerset Music Service conducted its own survey of instrument tutors and found that peripatetic teachers, particularly those working with percussion and brass instruments, were most at risk. It drew up a health and safety code of practice, pointing out that the authority was duty-bound to protect employees, even though "tutors and pupils playing instruments will not consider their efforts as noise and, as such, may gain pleasure from high sound levels".
This point is echoed in A Sound Ear, an overview of health and safety issues commissioned in 1999 by the Association of British Orchestras. "The idea that music is not harmful is partly an instinctive belief, and partly based on science," writes the author, Alison Wright Reid. "It does, indeed, appear that pleasing noise causes less hearing damage than random noise, so musicians may be at less risk than is supposed. However, the studies also show that music which is disliked, or just plain boring, causes more harm than random noise. Furthermore, the nicenasty risk modification is related to levels of stress in the listener." This distinction between welcome and unwelcome noise, and the relative potential of each to distract, annoy or injure, may well have implications far beyond the music department.
The ninth annual international noise awareness day was on April 28. For details, visit www.lhh.orgnoise
Main text: David Newnham
Photographs: Alamy; National GeographicGetty
Additional research: Sarah Jenkins
Next week: sex education