Frequency check

Frequency-based methods can improve noise-control laws

By Smita Pandey
Published: Saturday 04 July 2015

imageTRAFFIC noise is more than just a nuisance. It is a health hazard that can lead to several health problems over a period of time. Different nations have set different legal standards for monitoring noise pollution. But one thing is common: all these standards are based on noise intensity, measured in decibels (dB). Most countries, including India, nations of the European Union and the US, have legal noise limits between 40-75 dB depending on the type of area, vehicle and time.

A team of researchers from Indian Institute of Technology, Kanpur, and Rajiv Gandhi Institute of Petroleum Technology, Raebareli, has now proposed a frequency-based approach to map noise pollution. While noise intensity is an indicator of the loudness, frequency indicates the number of sound waves produced per second and is measured in hertz (Hz). “Intensity of sounds is important to characterise noise. But for developing a holistic noise map, we also need to take other parameters of noise, like frequency, duration and distance from a noise source, into account, ” says one of the researchers, Susham Biswas, assistant professor at Rajiv Gandhi Institute of Petroleum Technology. “Even sounds falling within the safe limit of below 75dB can have health effects if they have very high or low frequency,” he says.

Although healthy young adults can hear frequencies between 20-20,000 Hz, prolonged exposure to both very high and very low frequency noises is hazardous. “Very high-frequency noise can make people prone to hearing impairments, hypertension, high blood pressure, speech interference and annoyance. Extremely low-frequency noise, on the other hand, can cause sleep deprivation and physiological disorders,” says Avishek Dutta, an audiologist who runs Bengal Speech and Hearing Private Limited in Kolkata. “Taking sound frequencies into consideration can definitely lead to better noise control regulations.”

For the study, published in Current Science on November 25, the researchers analysed traffic noise at a road-crossing adjacent to a railway track in Kanpur during different times of the day. They found that hazardously high levels of high frequency sounds of 1kHz and low frequency sounds of 63 Hz contributed significantly to the traffic noise in the area.

Biswas says only a handful of detailed studies are available on traffic noise in an Indian scenario where commercial and residential areas conspicuously overlap and a large number of people live in close vicinity to roads and highways. He stresses the need for noise maps, like the ones used in some western countries, and frequency-based methodologies to monitor and analyse ever-increasing traffic noise.

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