“A (UOM – unit of measure) used to show the proportion of one estimation of intensity or field amount to another on a logarithmic scale, the logarithmic amount being known as the force level or field level, individually.” The decibel’s scientific definition has its roots in the early 20 th century and is based on the measurement of power used in telephony back then in the US Bell System the decibel was initially used to quantify power losses during the transmission of telegraph and telephone signals sent via long cables. Source: Echo Barrier What are Decibels (dB)? Simply put, the greater the decibel level, the louder the sound. This scale is known as the decibel scale and uses units called decibels (dB). To help measure the different levels of sound and deem which ones are safe and harmful, experts use a nonlinear scale to describe the intensity of sound waves conveniently. While certain sounds may help protect us, others may prove to be damaging. In short, this astounding piece of natural machinery can detect the sound of a nearby pin hitting the floor, and can also shield itself against the roar of an engine not very far away. With its ingenious internal mechanisms and physiology, the human ear can adjust its sensitivity to increasing sound levels and handle a vast array of sound power levels. For example, ocean noise pollution produced by ships may be as great as 200 dB expressed in the sound pressure level, where the more familiar sound intensity level we use here would be something under 140 dB for the same sound.When looking at the most versatile and amazingly sound devices, nothing can compare to the human ear. It is beyond the scope of most introductory texts to treat this scale because it is not commonly used for sounds in air, but it is important to note that very different decibel levels may be encountered when sound pressure levels are quoted. This scale is used particularly in applications where sound travels in water. It should be noted at this point that there is another decibel scale in use, called the sound pressure level, based on the ratio of the pressure amplitude to a reference pressure. For example, a 56.0 dB sound is twice as intense as a 53.0 dB sound, a 97.0 dB sound is half as intense as a 100 dB sound, and so on. In equation form, intensity\boldsymbolis given (and not the actual intensities), this result is true for any intensities that differ by a factor of two. Power is the rate at which energy is transferred by the wave. Intensity is defined to be the power per unit area carried by a wave. The relevant physical quantity is sound intensity, a concept that is valid for all sounds whether or not they are in the audible range. High noise exposure is hazardous to hearing, and it is common for musicians to have hearing losses that are sufficiently severe that they interfere with the musicians’ abilities to perform. In cartoons depicting a screaming person (or an animal making a loud noise), the cartoonist often shows an open mouth with a vibrating uvula, the hanging tissue at the back of the mouth, to suggest a loud sound coming from the throat Figure 2. We are all very familiar with the loudness of sounds and aware that they are related to how energetically the source is vibrating. But when a passing motorist has his stereo turned up, you cannot even hear what the person next to you in your car is saying.
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After settling into bed, you may hear your blood pulsing through your ears.
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In a quiet forest, you can sometimes hear a single leaf fall to the ground. Noise on crowded roadways like this one in Delhi makes it hard to hear others unless they shout.