event season, let your only worries be how muddy you'll get, not noise complaints. With noise barriers, you can party hard whilst locals can rest easier.
Goto JINBIAO to know more.
In this Insights blog, our acoustics experts turn up the volume on the important issue of managing outdoor noise and explain how properly specified and deployed noise barriers can help ensure compliance with local noise regulations and maintain positive public relations on both sides of the fence.
Noise pollution can be defined as unwanted or disruptive sound that impacts the health and wellbeing of people and animals. It can be caused by a wide range of sources, from construction site activity to loud events, cheering crowds, and whirring generators. For these reasons, local councils and environmental agencies often require sites to have clear measures in place to manage external noise, with costly penalties for noncompliance.
To tackle this issue, many events planners, production companies and construction firms use noise barriers — also referred to as noise reduction barriers, noise control barriers, noise fence barriers, acoustic fence barriers or just acoustic barriers. These are panels of acoustic material covered in a weatherproof vinyl outer layer which are hung on security fencing to lower noise levels by absorbing, diffracting and blocking soundwaves.
As well as avoiding fines and delays, taking a proactive approach to noise control is also important for public relations, reducing the risk of complaints and keeping neighbouring communities in support of your project or event.
If specified and deployed correctly, noise barriers can be a highly effective way to reduce noise pollution in the external environment in all kinds of settings, from outdoor events to construction sites. Made from a combination of dense ‘high mass’ materials and porous materials, they work by absorbing and reflecting the sound waves generated by the source on one side of the barrier away from potential receivers on the other side. Psychoacoustic studies into how the brain perceives sound also have demonstrated that just visually obscuring people’s view of a noise source can further reduce their perception of how loud it is.
There are many types of exterior noise barrier solutions on the market, and it is important to understand how their performance is measured to determine the most effective solution for a particular scenario or application.
A Weighted Sound Reduction Index (Rw) gives a true picture of how a sound reduction product performs. Different products can reduce sound differently across the human hearing spectrum; the thickness, density and combination of materials will impact the barriers’ ability to block certain frequencies of sound. The higher the Rw value, the better the product is at reducing noise from a source.
Product
Best for
Rw Rating
Siderise NCB MR Noise Control Barrier
Absorbing and controlling noise at source
16 dB
Siderise NCB XL Noise Control Barrier
Enhanced absorption with acoustically transparent rear
17 dB
Siderise NRB Noise Reduction Barrier
Cost-effective for open sites
22 dB
Noise barriers are extremely flexible and can be used, adapted and reused to suit the need of any project or event. They can be quickly deployed and simply hung on metal fences using bungee cords, S hooks or cable ties — and easily taken down and moved if location layouts change or rolled up and stored once they are no longer needed, ready to use on the next project.
However, it is not as simple as putting the barriers up wherever the fencing is. The placement of the noise control barriers can impact how effectively they can reduce external noise.
Noise barriers should be positioned close to the noise source in the correct orientation, with the absorptive material facing towards the source. They should also completely block off the direct path (line of sight) between the noise source and receiver. As shown in the diagram below, this facilitates sound attenuation— a reduction in sound intensity— as the sound waves diffract around the barrier and creates what is known as an ‘acoustic shadow’ behind the barrier. This means that for people close to the noise source and therefore be most affected, the noise levels will be substantially reduced.
It is also important to make sure that these acoustic barriers are installed with a slight overlap to create a continuous barrier and prevent sound from ‘leaking’ out. Most noise fence barriers are also supplied with pre-punched metal eyelets around the edges, so there is no need to make any holes in the barriers when fixing them to the fence that may reduce their effectiveness.
Drive down the interstate highways bisecting many busy cities and suburbs, and you’ll likely no longer see the homes, buildings, or vistas that used to be a staple of roadway views. That’s because in most populated places, massive sound walls have been installed. These noise barriers, typically made of concrete and standing an average of 14 feet, turn the backs of neighborhoods into prison-like yards, and, on narrower stretches of road, encase drivers in roofless tunnels. Since the s, when the barriers first started sprouting, nearly three thousand linear miles have been erected. According to Department of Transportation officials, California alone has 760 miles of sound walls; Florida, 252 miles.
By and large, residents say they want these walls. California has a waiting list for them. And at meeting last June with representatives of the Florida Department of Transportation (FDOT), which this journalist attended, many residents of Boca Raton were eager to know whether sound walls would be erected to buffer their homes from a planned turnpike expansion.
One man’s concern, however, stood out at that meeting. He talked about his prior house, which he claimed was quiet until a highway noise wall was installed a few blocks away — and it turns out that this isn’t so unusual. For homes several streets from the barriers, or for those uphill of sound walls — and for everyone in certain weather conditions — the walls don’t effectively block the sound, and may even help to amplify it. And what’s worse is that these aren’t new insights. Engineers and acousticians have known for years that the sound barriers bracketing America’s urban and suburban highways are only marginally useful, and that a variety of better technologies could be developed.
If you want to learn more, please visit our website Noise Barrier Solution.
The problem: Nobody has an incentive to get them on the road.
“Walls are not a very effective solution,” said Robert Bernhard, vice president for research at the University of Notre Dame and an expert on noise control. Because the federal government pays for noise walls — and only noise walls — as part of highway expansion projects, he said, there is little incentive for researchers to keep testing and perfecting the alternatives.
Noise that bothers a community must be at least considered for mitigation thanks to the Noise Control Act of . It was passed as part of the federal government’s efforts to better protect the environment — noise being one of many pollutants coming under scrutiny. Typically, when an interstate is widened or newly built, and in a small number of cases, when no additional construction is done, the state highway agencies determine whether they should mitigate the ruckus to area neighborhoods.
That ruckus tends to come from three separate elements: the roar of the vehicles — primarily the exhaust and engine; the whooshing aerodynamics around the vehicles; and the slapping of the tires against the road. At highway speeds, the predominant sound for cars is that of tire-pavement; for trucks, engine and stack sounds are also a factor — at least for now.
States use a specific noise model to predict the sound once the road will be expanded, and for several decades after. The complex formula includes the mixture of cars and trucks expected on the road; the buildings and vegetation in the area that would block some sound; the configuration and ground quality of the land between the road and the homes; the ways the sound is expected to diffract around the wall; and other key factors.
Based on the formula, if the noise is projected to go over the government threshold of approximately 67 decibels (dB) during the noisiest hour of the day — and it is “reasonable and feasible” to reduce it at least 5 dB for some percentage of homes — the government requires that walls be included if the surrounding community wants them. Just what constitutes “reasonable,” of course, is interpreted in different ways by each state, which is why the use of sound walls varies greatly from one state to another.
Even with the sound reduction, however, roadside residents are unlikely to hear crickets chirping. A dishwasher running in the next room is 50 dB, as are the ambient sounds of a laid-back city. The noise criteria aim to allow people to talk over their backyard picnic table, or shout at someone several feet away. “It’s not a situation where meeting the standard makes for a great backyard environment,” Bernhard said.
Of course, some of our ability to process sound is psychological: If people can see the tops of trucks over the wall they say it’s noisier, something people in the field call “psycho-coustics,” explained Bruce Rymer, a senior engineer at the California Department of Transportation. Just by ensuring a wall breaks that line of sight, “we achieve a reduction of 5 decibels,” said Mariano Berrios, environmental programs coordinator at FDOT.
But because noise travels in waves, not straight lines, sounds can and do go over the walls. This is why even with barriers standing 16 feet, homes several blocks away can hear the highway. Part of the sound wave is absorbed, part is reflected away from the wall, and part is transmitted through, Berrios explained. “Most of it goes above the barrier and gets diffracted, and gets to the receiver,” — that is, to a resident’s ears — he said.
This is especially problematic during certain weather conditions. When the consulting firm Bowlby & Associates, in Franklin, Tennessee, measured sounds around a highway in a yet-to-be-published study, they found that residents hundreds of feet from the highway could hear sounds some 5 decibels louder if the wind was blowing towards them, said Darlene D. Reiter, the firm’s president.
Weather, however, isn’t taken into account by the regulations. The noise model “assumes neutral conditions — no wind and no temperature effects — when in reality that happens only occasionally,” Reiter said. In the early morning, if the ground is cool but the air warms up, for instance, sound that would normally be pushed up is refracted downward, causing homes some 500 or 1,000 feet from the road to hear it loudly.
Those living up on hills or near freeway openings sometimes find the noise actually worsens once walls are built nearby. It was a gap in the barrier near his suburban New Orleans home — partially to accommodate a highway exit — that substantially increased noise in the backyard of attorney Harry Molaison. Although his house is roughly 500 feet from the service road leading to the interstate, “you have all this rebounding sound from one parallel wall to another,” he said.
“We don’t have the same peacefulness we had before,” he added.
It’s with these problems in mind that the University of Pittsburgh recently received a grant to study whether walls could be made of materials that absorb, rather than reflect, more of the noise. But even if new materials were developed — in addition to the popular concrete, sound walls are currently made of everything from masonry and steel to wood and plastic — the question would remain: Is this the best use of taxpayer money?
Highway walls are expensive, running more than $2 million per linear mile — for one side of the highway, Rymer said. The total spent on sound walls through , the most recent government figures, tops $6 billion. Each state has a different threshold for what triggers the need for a “reasonable” intervention. According to Rymer, in California, which has one of the lowest thresholds, walls are justified when they cost federal taxpayers as much as $92,000 per impacted home. This is money that isn’t spent on mass transit, or fixing ailing tunnels or bridges, or other transportation needs.
“Three miles of sound barriers on both sides of an interstate would buy another M8 railcar for Metro-North [train service], and take 100 passengers off the state’s highways” wrote Jim Cameron, the founder of a Connecticut-based commuter advocacy group, in a newspaper editorial earlier this year.
Mammoth barriers also block small animals — frogs, turtles, snakes — from getting from one habitat to another, said Elizabeth Deakin, professor emerita of city and regional planning at the University of California, Berkeley. This may affect wildlife communication, migration, and even reproduction.
Of course, it’s understandable why neighbors whose homes border a highway want something that mitigates the noise. Loud traffic interferes with the enjoyment of your yard. Having cars so close to a home can even cause health issues. According to a World Health Organization report, environmental noise leads to heart disease, hypertension, and cognitive impairment in kids. But if the bulk of the noise is caused by the tires and the roadway, some experts suggest that attacking the commotion at the source — or testing other methods that might absorb it — could be a more effective and less costly approach.
Some tire companies have done research on making tires quieter, but the bulk of their efforts are in keeping the noise from penetrating the inside of the car, not in silencing them outside, Bernhard said. And while electric cars are far quieter than cars with internal combustion engines, at highway speeds car engines aren’t much of a factor — though trucks could be a different story. Tesla’s recent introduction of its electric semi-truck will undoubtedly alter highway sounds going forward, since the engine and stack noises will be eliminated.
Companies in some European countries are experimenting with unconventional methods that could ultimately block highway sound. One, a luminescent solar concentrator (LSC), features colorful translucent sheets that not only don’t obstruct views and sunlight, they generate electricity to nearby homes. Another is researching whether dense bamboo or other plant species can be coaxed to form an effective vegetation wall.
But altering the pavement is where most of the potential seems to lie. Several states — Arizona, California, and Florida in particular — have experimented with such changes. These “quieter pavements” involve adding more porous surfaces to asphalt or altering the configuration of the tiny grooves in concrete. “When there is texture on the surface of the pavement, the trapped air inside the tire’s tread pattern doesn’t make the same clapping noise,” Bernhard explained.
Some states have laid thousands of miles of these road surfaces, and have seen results of up to a 9dB reduction in noise. Dana M. Lodico, a senior consultant with Illingworth and Rodkin, said engineers have been studying its effects since the s. Her firm alone conducted four major decade-long studies and many shorter ones. “There’s tons of research” showing its effectiveness, she said, especially in states with warmer climates. (The studded tires some drivers use in snowy states can break down the road surface more quickly.) One major report that her firm worked on examined the cost-benefit of sound walls versus pavement changes, and found many scenarios where a combination of lower walls — or no walls — were more effective and less expensive than a barrier by itself, she said.
Despite all of these potential innovations, however, the current structure of federal highway subsidies is likely to keep them from widespread use anytime soon. As it stands, the Federal Highway Administration has not approved pavement as an accepted form of noise abatement. “We have uncertainty about how long the reduced noise level from the pavement will last, and there is no guarantee that the reduction can be achieved on a consistent basis nationwide,” said agency spokesperson Doug Hecox.
That means states that currently change their pavement still have to put up walls as part of their highway projects. And because maintenance of the pavement to keep it quiet — resurfacing perhaps every 15 years, Lodico said — would fall to the states, many state officials undoubtedly prefer the more-permanent walls, which are built almost exclusively with federal funds.
When it comes to mitigating highway noise, Bernhard noted, “The predominant culture is cost avoidance.”
Meryl Davids Landau is a Florida-based journalist whose work has appeared in a variety of publications, including U.S. News & World Report, Glamour, Vice Media, Parents, Reader’s Digest, Good Housekeeping, and Prevention, among others.
The company is the world’s best Noise Barrier Panel supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.