Second, the total sound level produced by two sounds of different levels is usually only slightly more than the higher of the two. For example:Ħ0 dB + 60 dB = 63 dB, and 80 dB + 80 dB = 83 dB First, if a sound's intensity is doubled, the sound level increases by 3 dB, regardless of the initial sound level. However, some simple rules are useful in dealing with sound levels. Sound levels between 130 to 140 dB are felt as pain (Berglund and Lindvall 1995).īecause of the logarithmic nature of the decibel unit, sound levels cannot be arithmetically added or subtracted and are somewhat cumbersome to handle mathematically. Normal speech has a sound level of approximately 60 dB sound levels above 120 dB begin to be felt inside the human ear as discomfort.

A sound level of 0 dB is approximately the threshold of human hearing and is barely audible under extremely quiet listening conditions. Such a representation is called a sound level. As a result, a logarithmic unit known as the decibel (abbreviated dB) is used to represent the intensity of a sound. Because of this vast range, using a linear scale to represent the intensity of sound becomes very unwieldy. The loudest sounds that can be detected comfortably by the human ear have intensities that are a trillion times higher than those of sounds that can barely be detected. Sound intensity or level is measured by a unit called a decibel. Video Link:įor more on the basics of sound, check out this NASA Video How is Sound Measured? The third important characteristic of sound is duration or the length of time the sound can be detected. Low-frequency sounds are characterized as rumbles or roars, while high-frequency sounds are typified by sirens or screeches. The second important physical characteristic of sound is frequency, which is the number of times per second the air vibrates or oscillates.

The greater the sound pressure, the more energy carried by the sound and the louder the perception of that sound. First, intensity is a measure of the acoustic energy of the sound vibrations and is expressed in terms of sound pressure. The measurement and human perception of sound involves three basic physical characteristics: intensity, frequency, and duration. Whether that sound is interpreted as pleasant (e.g., music) or unpleasant (e.g., jackhammers) depends largely on the listener's current activity, past experience, and attitude toward the source of that sound. Sound is a physical phenomenon consisting of minute vibrations that travel through a medium, such as air, and are sensed by the human ear. Sound is all around us sound becomes noise when it interferes with normal activities, such as sleep or conversation. How does Noise affect Domestic Animals and Wildlife?.How does Weather affect Aviation Operations?.What are the Federal Aviation Regulations that deal with Aircraft Noise?.

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Decibel exposure chart