Sound is then added to a third sound and so on. In using the Chart, two sounds are added together first. Let us try adding the three sounds of 60 dB, 65 dB and 70 dB by To use the formula to add the three sounds together.Īddition of sound levels can also be done simply using the following Please click on the demo button to learn how One can use the above formula to add three sounds together - 60ĭB, 65 dB and 70 dB. Please click on the demo button to see the details. The followingįormula explains the general principle of adding sounds on the decibel Inįact, adding 60 decibels to 60 decibels gives 63 decibels. Not the case with sounds when they are expressed in decibels. the addition of sounds.Īdding 60 apples to 60 apples results in 120 apples. One may be interested to know what results when one sound In real life, several sources of sounds often occur at the same This is because human ear responds to the logarithmicĬhange in level, which corresponds to the decibel scale.Īdding Sounds or Noises together on the Decibel Scale One useful aspect of the decibel scale is that it gives a muchīetter approximation to the human perception of relative loudness [Chart illustrates relation between sound pressure in micropascal Scale helps us to handle numbers on a wide scale much more easily. In the following chart, some sounds are expressed both linearly You can click on the demo button to learn the formula.
In decibels (dB), can then be obtained using the following formula. Sound pressure level, which is often abbreviated as SPL or L p, The scale uses the hearing threshold of 20 μPa or 20 x 10 -6 Involve some unmanageable numbers, the decibel or dB scale is used. To avoid expressing sound or noise in terms of Pa, which could [Animation illustrates relationship between linear and logarithmic Introduction of the common logarithm to the base 10.Ĭlick on the demo button, you may learn more about the relationship The following table illustrates sound pressure level of the above events expressed in Pa and µPa.Ī simpler way is to use a logarithmic scale for the loudness On the other hand, the sound pressure close to some very noisy events such as launching of the space shuttle can produce a large pressure variation at a short distance of approximately 2000 Pa or 2 x 10 9 µPa. The softest sound a normal human ear can detect has a pressure variation of 20 micro Pascals, abbreviated as µPa, which is 20 x 10 -6 Pa ("20 millionth of a Pascal") and is called the Threshold of Hearing. Human ear can perceive a very wide range of sound pressure. In Pascal, abbreviated as Pa, which is defined as N/m 2(Newton Pressure and pressure variations are expressed Usually has a larger pressure variation and a weak one has smaller PleaseĬlick on the demo button to hear their sounds and the differenceĪnother property of sound or noise is its loudness. Produced by a whistle, as shown in the following diagrams. The sounds produced by drums have much lower frequencies than those
The higher the frequency, the more high-pitched a sound is perceived. Is called the frequency of sound, and is measured in Hertz (Hz)
The number of pressure variations per second When sound travels through air, the atmospheric pressure Sound is the quickly varying pressure wave travelling through a
There are two important characteristics of sound or noise - frequency