Noise ---- A Necessary Evil?
Over
Noise Pollution
May
Have Abated,
But
It’s Not Forgotten.
Compressed Air
Magazine
January 1995
Two years ago, some residents of Taos, N. M., found themselves plagues by
a low-level irritating sound that began to drive them to distraction, even
out-of-towner. Scientists investigated,
but the mysterious “hum” has defied capture and categorization. This annoyance had a cousin of sorts in
Alabama where, in 192, citizens in Hueytown complained of an indeterminate
vibrating noise that some blamed on mining exhaust fans. A University of Alabama investigation proved
inconclusive as to the source. Less
puzzling, but sometimes as unsettling are thunder-claps, high winds, and
crashing waves … all powerful sounds of nature. Then there is the neighbor’s
dog.
In his book, The Unwanted Sounds,
David M. Lipscomb calls noise “the natural by-product of expanding human
technology.” In other words, disagreeable sounds, aka noise, are mostly fruits
of our own creation. Truck traffic,
chain saw, jet takeoffs, food blenders, raucous music, residential heat pumps,
untended car and burglar alarms—these more common sounds play havoc with our
hearing and sometimes our sanity. They
intrude like unwelcome guests. Because
the annoyance threshold is very subjective, measurement and control are
complex. At high enough levels over
long enough time any noise can create stress and cause physiological harm.
Noise has been an environmental
factor for ages. Ancient Romans
complained about chariots rattling on the pavement, and Renaissance
metal-smiths often lost their hearing.
As we know it, noise is more associated with the Industrial and
Technological Revolutions—looms and locomotives, presses and transformers,
motorcycles and leaf blowers, riveters and amplifiers, gunfire and garbage
cans. In an Atlanta neighborhood near a
hospital, sirens scream with some frequency.
In Tokyo, political campaigns literally assault the ears as sound trucks
prowl the streets incessantly blaring candidates’ names and slogans. In Sarajevo, artillery rounds rend the air.
Noise became a cause celebre in the
late 1960’s and early 1970’s. One
estimate then held that sound levels in some American cities were up20 dB over
levels 2 decades earlier, and some officials forecasted that noise in the
United States would double in another 2 decades. Numerous books and articles appeared about noise pollution, with
the more zealous observations predicting us
nation of the deaf before the turn of the century.
Federal legislation in the form of
the 1972 Noise Control Act aimed at controlling excessive noise emissions. Among other things, it was designed to
establish a means for effective coordination of federal research and activities
in noise control and establish federal noise emission standards for certain
products. An Office of Noise Abatement
& Control (ONAC) was instituted in the U.S. Environmental Protection Agency
(EPA). Many cities adopted noise
control ordinances. The 1971
Occupational Safety & Health Act, according to Lipscomb, extended
industrial hearing health activities to some 57,000,000 workers, mandating,
among other things, noise abatement, sound-level measurement, and hearing
conservation in the workplace.
In the 1990’s, noise seems less a
concern for journalists, environmentalists, industrialists, bureaucrats, and
politicians. The Reagan administration
silenced ONAC a decade ago by cutting it’s funding. Asbestos, water pollution, hazardous waste, and other issues
dominate the agendas. “Noise,” says one EPA official, “fell through the
crack.” Today, even the National Safety
Council has no noise-related policy or guidelines.
The sound and fury over noise
pollution may have abated, but there are several signs in the research
community, in industry, and in the general population that it’s far from
forgotten. Indeed, a Census Bureau
survey of 80,000 rural, suburban, and urban homes revealed noise to be
perceived as the number one environmental problem.
Prolonged exposure to sound levels
above 85 dB can impair one’s hearing; the greater the level and longer the
exposure the greater the risk. Different activities and devices generate
different levels of noise. For example, a rock music concert can run in the 110
dB range or higher; a jet takeoff, 140 dB; large firecrackers, 150 dB; and a
farm tractor, 100 dB. Even rush-hour
traffic can hit 90 dB or more. Pressure
waves from elevated levels of such noise permanently destroy specialized cells
in the inner ear, resulting in diminished hearing ability. Environmental noise can disturb sleep,
distract attention, and create anxiety.
In the early 1970’s, some 6,000,000
industrial workers were said to be in occupations where the noise level is
dangerously high. By 1992,, one
estimate puts the number at 20,000,000.
Hearing loss ranks near the top of occupational disorders in the United
States and remains a top priority of the Occupational Safety & Health
Administration (OSHA), according to an official of that agency. Studies have indicated that workplace noise
not only can impair hearing but also lower productivity, efficiency and morale,
and increase accidents, resulting in millions of dollars lost to industry.
Research also indicates that there
are non-auditory adverse effects of noise.
More than a decade ago, the University of Miami Medical School conducted
EPA-sponsored studies on rhesus monkeys.
The animals were subjected to daily exposures of “typical’ workday
sounds, from wake-up alarms and electric razors to commuter traffic and work
site noise to TV and overhead aircraft.
According to Dr. Ernest Peterson who led this pioneering study, all test
animals showed elevated blood pressure that persisted months after cessation of
the noise.
The irony, says Peterson, is that
the results were so uniformly good they evoked skepticism at EPA. A follow-up study was planned involving
baboons, but the funding vanished with ONAC.
“There have been no contradictory findings that I know of,” says
Peterson, adding that most of this type of noise research is now being done in
Europe. OSHA did look at non-auditory
effects of noise and considered establishing an overall permissible exposure,
not just one for hearing. However, the
agency faced many difficulties in identifying and factoring these effects and
did not conduct a review. It has no
plans to do so.
Turn
it Down!
Attenuating noise involves a variety
of methods and devices, from earplugs and mufflers to specially built rooms to
regulations. Public building and
mass-transit systems may ban noise-generating consumer electronics. In offices and homes, noise-masking machines
can cover an objectionable sound with one that is more acceptable and
pleasant. Noise exposure maps identify
an airport’s present and future noise levels and show noise contours I
decibels.
Experts say the optimal method is to
engineer quiet at the outset, whether it’s a project, a structure, or a
machine. But, they admit, that is not
always possible. In industrial
settings, noise abatement can be a matter of switching processes—say, from
riveting to welding—or materials—say, from metal to plastic or rubber. Close tolerances and proper lubrication play
important roles, too.
Ingersoll-Rand pioneered quieter
compressors in the 1960’s, developing a portable unit that lowered the sound
level from 110 dB to 85 dB. Mack Truck
designed a quieter assembly line.
General Motors worked on soundproofing elements on its vehicles, such as
truck engine shrouds and double-wall mufflers.
Other companies even found a niche specializing in noise control
equipment. Industrial Acoustic Company
in New York, for example, manufactures ventilation silencers for labs and
hospitals, jet aircraft “run-up” pens, noise-lock doors, silencers for industrial
fans and gas turbines, anechoic chambers, and even quiet correctional security
systems.
Noise barriers have become features
at man airports, along highways, and in neighborhood. Many are made of
preformed concrete; others include engineered wood products and brick. Such barriers are constantly being
refined. There are, for example,
specially coated sound-absorbing barriers to shield against highway noise and
eliminate reflection from opposite sides.
These come free-standing or can be retrofitted to existing walls.
On the cutting edge of noise
abatement is “active” control that, in contrast to “passive” mufflers and
barrier systems, fights noise with noise.
It is particularly effective against low-frequency tones. In this technique, a sensor picks up sound
pressure wave patterns and feeds the data to a digital computer, which creates
an “anti-noise” pattern equal, but exactly opposite, to the targeted offensive
noise, thereby canceling it out.
The theory has been understood for
years, but development of high-speed computer chips capable of rapid,
continuous, precise calculations has made active control feasible. Companies working in this field include
Toshiba, Hitachi, and at least one smaller firm, Noise Cancellation
Technologies of Stamford, Conn. It
designs active silencers and mufflers for generators, transformers, and
pipelines. Applications also include
fans in consumer appliances. Other
developments at the Connecticut firm consist of active mounts and active
panels. When SCX used the company’s
active controller (plus passive treatment for non-exhaust noise) on its vacuum system that unloads bulk material
from railcars to trucks, it reportedly realized a decrease of more than 25 dB
at the operator position. This allowed
employees to work 8-hour-per-day shifts; they had been working in half-hour-per
day stints.
The company also has developed a
consumer headset to cancel out noise; an industrial version should be available
in mid-1994. It can be “tuned” to a
specific piece of equipment, say a printing press. By interfering only with the objectionable noise, the headset
permits speech and warning sounds to be heard.
The firm claims users can expect a 10 dB noise reduction in the 50 to
1000 Hz range.
Noise Cancellation Technologies says
its active-control mufflers permit free flow of exhaust gases, thereby lowering
back pressure and reducing fuel consumption.
The New York City Transit Authority tested electronic mufflers on some
of its buses in 1993.
According to Dr. Gary Koopman, head of
PennState University’s Center for Acoustics & Vibration (CAV), active
technology is the wave in noise control. “That’s where the funding is right now,” he says. CAV is researching diverse aspects,
including eternal sound fields such as those generated by transformer noise and
military vehicles. Response parameters include sound pressure, intensity, and
energy density measured with optimally spaced microphones and sound pressure
gradient devices. Researchers also are
looking at “smart” materials to govern sound power radiated by a structure by
directly controlling its response—for example, engine parts. Here, passive control might entail tailoring
such material properties as thickness, density, or fiber orientation of a
composite. Active control might
minimize radiation efficiency by controlling stress fields with externally
mounted ferroelectric actuators.
Noise-related research is underway
in other areas, as well. For example,
high-speed civil transport—supersonic passenger and cargo aircraft—to be
acceptable must resolve the tremendous noise of takeoffs and landings and of
sonic booms. The National Aeronautic
& Space Administration (NASA) and industry partners, such as General
Electric, are exploring modifications of engine exhaust nozzle design to
determine ways of reducing noise from supersonic aircraft. One goal involves cutting engine exhaust
noise levels 20 dB below those of the Concorde, thus meeting U.S. Department of
Transportation (DOT) regulations for quieter airports.
One facet of this effort has
entailed a study at the Georgia Institute of Technology to assess human
responses to sonic booms that can rattle windows and dishes, disturb sleep,
crack walls, and set off burglar alarms.
Utilizing a giant boom box—an array of custom-built speakers measuring 8
X 5 X 20 feet—Georgia Tech researchers randomly broadcast sonic booms(as well
as truck, helicopter, and airplane noise) at a small house. After each experiment, data are collected on
the subjects’ reactions. The shape and
duration of a sonic boon “are extremely important in determining how
objectionable the boom will be,” says acoustics specialist Dr. Krishan Ahuja,
and those are determined by the shape, size and weight of the aircraft.
Recently, the political environment
has seemed less conducive to federally centered noise control than it has
been. In 1991, Congressional hearings
were held on noise and its effect. The
American Speech-Language-Hearing Association helped sponsor a national
symposium on federal legislation needs in noise abatement. In 1992, Representative Richard J. Durbin
(D-Ill.) Tried, unsuccessfully, to re-establish ONAC in EPA. According to an aid, he has not reintroduced
such legislation.
In 1992, The Administrative
Conference of the United States studied noise regulations and recommended that
Congress either repeal the 1972 Noise Control Act or give specific noise
control responsibilities to EPA, with funding for them. (Although the EPA paid for the study, it did
not try to influence it, says the agency’s Ken Feith.) The report, Feith notes, came in a year
later than expected, and that proved untimely because no action would be taken
with a new administration in the offing. The EPA has received no inquiries from
Congress regarding the report.
The EPA continues to enforce regulations
issued 2 decades ago, such as those concerning trucks and motorcycles, and
recently fined a manufacturer of hearing protections devices $900,000 for false
labeling. Today, says Feith, it’s a
matter of priorities and funding. Noise
doesn’t kill, there are not “blood and guts” associated with it. At the same time, Feith gets several
hundred calls and letters each year from citizens complaining about various
types of noise—leaf blowers, general traffic, grain dryers, auto racetracks,
and industrial exhaust systems, to name a few.
One issue raised by martin
Hirschorn, president of Industrial Acoustics, involves the arena of global
trade. In an effort to produce some
economic harmony, the European Community has proceeded with steps to standardize
specifications, regulations, and directives concerning a whole host of
products, from toys and dental instruments to pressure valves and
appliances. To export to Europe,
American manufacturers will undoubtedly have to make their products conform to
EC standards.
Hirschorn suggests lack of federal
guidance here could harm the nation’s exporters; if the United States doesn’t
meet EC noise standards it may be regulated out of competition in Europe. He cites “a lack of government interest in
noise pollution control” and advocates re-establishment of ONAC in EPA. Feith claims that EPA maintains contact with
various organizations on the subject of foreign noise-control objectives and
that domestic industry “has not been blindsided.” The agency will go to bat for an industry—for example,
lawn-and-garden-equipment manufacturers—if it is informed that certain
regulation appear too onerous.
On another plane, DOT wants quieter
airports by the end of the decade. Some 3,200,000 people are believed affected
by airport noise in this country.
Essentially, this effort means that aircraft must tone it down, and
that, in turn, means companies must acquire new, quieter aircraft, replace
engines, or install muffler systems (or “hush kits”) on existing fleets. In this “Stage 3” modernization, a gradual
phase-in is supposed to soften the impact on cargo and passenger airlines.
Of course, all this is not to say
noise lacks utility—emergency vehicles’ sirens come to mind. Then there’s the system developed by some Denver-based
environmental engineers to keep water-fowl away from potentially harmful
industrial ponds. The system’s radar,
on detecting incoming birds, triggers a barrage of random, unpredictable
noised—propane cannons, fire alarms, horrifying music, and high-pitched
firecracker-like blasts.
An, of course, a considerable amount
of noise abatement is under an individual’s control. Quieter products are available, but often people don’t buy them
because they equate noise with power and power with efficiency. Sometimes they erroneously believe quieter
implements are much more expensive.
Some striving for silence is
market-driven. Georgia Tech researchers
have undertaken work sponsored by Ford Motor Company to predict noise levels
that drivers hear inside their vehicles, particularly wind. One test involved placing hearing-aid
microphones in 41 locations in a car, including the driver’s eyeglass
frames. According to one Ford manager,
noise reduction is “value-added engineering.”
Improving quality meets customer expectations and helps sell cars.
In the end, it may come down to
education , on the part of the public, politician, and professionals. Robert M. Hoover, writing in a 1993 issue of
Noise Control Engineering Journal, calls for educational material for
use by Acoustical Society of American members in presentations to lay audiences
and says there’s a need to persuade college faculties to include courses in
noise control for engineering students.
Whatever the perspective, one thing comes through loud and clear—turning
a deaf ear to the issue will do nothing to bring peace and quiet.