08/24/03
Infrasound: I'm all shook up!

By MALCOLM BRENNER
Staff Writer

Sound, that most intangible of sensations, can harm you.

Almost everyone will wince at painfully loud sounds: the crack of nearby thunder, a heavy-metal rock concert, the boom of a jet breaking the sound barrier or ... the gut-shaking bass of vehicle audio systems.

Audio manufacturers advertise the raw power of their vehicular products. Some boast of speakers that can handle up to 5,000 watts of electricity, more than a water heater or air conditioner draws.

Special speakers intended to win "boom car" competitions can blast out 170 decibels of sound that's literally ear-splitting. (The threshold for immediate deafness is 180 decibels. "You can hear -- and feel -- the difference," one manufacturer raves.

But the physical vibration so prized by car audio fanatics, and despised by their victims, is largely produced by sounds pitched too low to hear, called subsonic or infrasonic sounds. Medical research over the past four decades shows that exposure to infrasound can have devastating effects on the human body and mind that go far beyond mere hearing loss.

This controversial medical condition, vibroacoustic disease, has only been recognized since the 1970's, said Dr. Robert Fifer, Director of Audiology and Speech Language Pathology at the Mailman Center for Child Development at the University of Miami.
"You don't see it much outside an industrial or military environment," Fifer said. "You see it once in a while in a 'sick building,' but everybody in that building will show some type of stress-induced illness."

The culprit isn't so much the infrasound's frequency, or pitch, as it is its amplitude, or loudness, measured in a logarithmic unit called decibels.

"Whenever a sound is beyond 80-90 decibels, the body reacts to it by increasing its stress reaction," Fifer said. "When a human body is exposed to high intensity sound, it releases stress hormones, starting with adrenalin. The blood pressure shoots up, respiration becomes more rapid, the heart rate increases and the body in general is working much harder than it usually would. It's under a generalized stress situation."

In other words, the body's "fight or flight" response can be triggered by a sound you can't even hear. It's called "large pressure amplitude and low frequency" noise, or LPALF for short.
Long-term exposure to stress hormones can, in turn, cause unhealthy physical changes, including heart disease, ulcers, fatigue, back pain, headaches and joint pain, to name but a few.

If it's loud, as it often is in a boom car, a subsonic sound's frequency can affect a person physically and psychologically. The low end of the human hearing range is about 20 Hertz, or cycles per second. Loud infrasound in the range of 0.5 to 10 Hz is sufficient to activate the vestibular, or balance system, in the inner ear.

"It affects the 'sentry cells' in the vestibule of the inner ear," Fifer explained. "They produce our feeling of linear acceleration, of moving forward and back, up and down. It can have the same effect as spinning you without actually spinning."

Early symptoms of exposure to excessive infrasound can include mild to moderate mood disorders, increased aggressiveness and decreased cognitive function, repeated respiratory infections, bronchitis (even in non-smokers), gastrointestinal dysfunction, fatigue and chest pain, according to M. Alves-Pereira, a scientist with the New University of Lisbon in Portugal.

Alves-Pereira studied the effects of VAD on technicians working in a noisy aircraft manufacturing, maintenance and repair facility, where 10 percent of the work force had been diagnosed with late-onset epilepsy, a rate 50 times higher than expected. He tried to find an effective diagnostic tool for the condition, but failed. He did manage to develop a classification system for its effects, however.

Although its effects on the body's nervous system are well-documented, there's some suspicion that LPALF sounds can affect the body directly. Low frequencies carry more power than high frequencies, and at loud enough volumes they can literally shake an object to bits the same way a soprano's high notes can shatter a wine glass.
The French military tried to develop weapons using this property of infrasound in the early 1960's, but the weapons couldn't be aimed because their effects were indiscriminate.
Ear protection can reduce the volume of infrasound, but some researchers suspect that it can vibrate the body, causing cells in susceptible areas to rub against each other. This could account for the thickening of the heart membranes, lungs and other body systems observed in some infrasound victims, but so could the stress hormones produced.

"The preliminary consensus is, vibroacoustic disease is related to stress rather than noise," Fifer said. "It's still up for debate as to whether the direct cause of the damage is sound waves or stress hormones. If you are undergoing whole body stress and you've got these potent hormones going five or six days a week, for years, the body will show some kind of physical changes as a result of that stimulation."

From all data shown, cell wall thickening does not occur until after years of regular infrasound exposure, Fifer said. So hearing a "boom car," or even driving one occasionally, won't do it. The jury is out on whether continued daily exposure to the intense booming sounds of car audio systems will produce the serious medical conditions.

Fifer, 51, first encountered vibroacoustic disease when he served in the U.S. Air Force at Wilford-Hall Medical Center in San Antonio, Texas in the 1970's and '80's.

"We had some 'sick building' cases flown in for evaluation," Fifer recalled. "The problem was widespread enough that, through a process of elimination and deduction, we came down to the harmonics in the building, which produced tremendous low-frequency noise."

In one sick building case, a roof-mounted air conditioning unit came loose from its base and created low frequency vibrations that sickened everyone in the building. None of those affected were aware of "noise" the unit was creating.
Few occupations in Southwest Florida could create vibroacoustic disease, but aircraft maintenance is one of them.
"I haven't heard of it," said Ron Hill, vice president of Southwest Florida Aviation Inc., in Punta Gorda. The company restores and maintains Huey helicopters.

"I've been working around aircraft for 20 years with no problems, and my father has been for 40 years with no problems," Hill said.
A couple of years ago, Hill had some industrial safety inspectors monitor the noise in his shop, but their equipment couldn't measure below 20 Hz.

That lack reflects Alves-Pereira conclusion about why vibroacoustic disease so often goes undiagnosed and untreated: "The underlying reason for this state of affairs is the decades-old, but erroneous, assumption that noise only affects the ear."

You can e-mail mailto:mbrenner@sun-herald.comMalcolm Brenner at mbrenner@sun-herald.com