Making Hospitals Quieter - Inside Science

Reported May 2006

BACKGROUND: A new study by researchers at Johns Hopkins University reveals that hospital noise levels around the world have increased steadily over the past 50 years. In fact, it is among the top complaints of both patients and hospital staff members. To date, scientific studies have been scarce, and were conducted by medical personnel, not acoustical experts. The Hopkins researchers were also able to test two techniques that helped reduce noise in some patient areas.

THE PROBLEM: Since 1960, hospital sound levels have raised from 57 decibels --about the noise level of a normal conversation -- to 72 decibels -- about the noise level of a freeway. This exceeds the World Health Organization's 1995 guidelines for hospital noise. Among other concerns, high noise levels disturb patients and staff members, raise the risk of medical errors, and hinder efforts to modernize hospitals with speech recognition systems. Noise levels even remain high at night because of hospital ventilation settings. Many spaces use acoustical ceiling tiles to absorb sound, but these are often absent from patient areas because they can house infectious organisms.

POSSIBLE SOLUTIONS: Two small changes made in the study helped reduce noise by modest amounts. First, in the pediatric intensive care ward, outfitting staff with small hands-free personal communicators that operate much like cell phones enabled them to be signaled quietly and directly. It cut the frequency of loudspeaker announcements from an average of one every five minutes to about once an hour. By wrapping fiberglass insulation inside antibacterial fabric and attaching them as sound absorbers to the ceiling of a cancer unit, they were able to reduce the amount of sound bouncing around a room by a factor of three. Unfortunately, noise from air handling systems is much more difficult to address in existing facilities. In the future, acoustics experts and architects could work together to reduce noise problems in new hospitals.

HOW NOISE CANCELLATION WORKS: Unlike ear plugs and sound dampeners, noise cancellation tries to block the unwanted sound at its source, rather than merely trying to prevent it from entering our ears. If we add two sound waves together and the peaks of one line up with the valleys of the other they will cancel each other out. Digital signal processors (DSPs) are microelectronic devices that determine which sound wave is required to cancel the unwanted sound wave (noise). It then creates that sound and amplifies it through speakers or headphones. The end result is near silence. Most cell phones, CD players, and hearing aids now contain one or more DSP devices.

The Acoustical Society of America contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Ilene Busch-Vishniac
Professor, Mechanical Engineering Department
Johns Hopkins University
Baltimore, MD 21218
(410) 516-8777

For more on hospital noise and other acoustical issues:

The Acoustical Society of America
2 Huntington Quadrangle
Melville, NY 11747-4502
(516) 576-2360
asa@aip.org
http://asa.aip.org

DID YOU KNOW...

The word noise comes from the Latin word nausea, meaning seasickness.