The rate at which sound energy is transmitted, called sound intensity, is proportional to the square of the SPL. SPLs decrease with distance from the source. The ambient SPL in a library is about 35 dB, while that inside a moving bus or subway train is roughly 85 dB building construction activities can generate SPLs as high as 105 dB at the source. The normal human ear can detect sounds that range between 0 dB (hearing threshold) and about 140 dB, with sounds between 120dB and 140 dB causing pain (pain threshold). Loudness (also called sound pressure level, or SPL) is measured in logarithmic units called decibels (dB). Sound is typically described in terms of the loudness ( amplitude) and the pitch ( frequency) of the wave. Sound waves are vibrations of air molecules carried from a noise source to the ear. Noise pollution is commonly generated inside many industrial facilities and some other workplaces, but it also comes from highway, railway, and airplane traffic and from outdoor construction activities. Noise pollution, unwanted or excessive sound that can have deleterious effects on human health, wildlife, and environmental quality. Study how underwater noise affects marine animals, particularly harbour porpoises See all videos for this article

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Noise pollution control