The human ear’s sensitivity to different frequencies is not equal, with the most sensitive range being between 2 kHz and 5 kHz. A sound pressure level of 100 dB is perceived as very noisy, while anything greater than 120 dB is intolerable. A range of 0 to 40 dB is considered quiet to very quiet, while 60 to 80 dB is generally described as noisy. Sound pressure level (SPL) can be described subjectively based on the decibel (dB) scale. The smallest change humans can hear is about 3 dB. Although doubling the sound pressure corresponds to an increase of 6 dB, it takes about 10 dB of increase for the sound to subjectively appear twice as loud. In the decibel scale, audible sounds range from 0 dB, the threshold of hearing, to over 130 dB, the threshold of pain. Doubling the sound pressure in pascals increases the sound pressure level in decibels by 6 dB. This formula expresses the sound pressure level as a logarithmic function of the ratio of the sound pressure to the reference pressure. Using the formula Lp=10lg (p/p 0) 2, where p is the sound pressure in pascals, and p 0 is the reference sound pressure of 20 μPa. For example, 200 µPa corresponds to 20 dB (re 20 µPa), while 2000 µPa corresponds to 40 dB.īecause of large sound pressure amplitude changes, the sound pressure level in decibels (Lp) is used rather than Pascal units. When measuring sound pressure in Pa, adding 20 dB to the dB level is equivalent to multiplying the sound pressure by 10. At an SPL of 120 dB, the sound is considered to be at the threshold of pain, and any sound louder than this can cause permanent hearing loss. This is much louder than the threshold of hearing, but still relatively quiet.Īs the sound pressure increases, so does the SPL. Taking the logarithm (base 10) of this ratio gives you 1, and multiplying by 20 gives you an SPL of 20 dB. On the other hand, if the sound pressure is 200 µPa, then the ratio of the RMS sound pressure to the reference level of sound pressure is 200/20 = 10. This is the lowest possible SPL, which corresponds to the threshold of hearing. Taking the logarithm (base 10) of this ratio gives you 0, and multiplying by 20 gives you an SPL of 0 dB. This gives you the SPL in decibels (dB).įor example, if the sound pressure is 20 µPa, then the ratio of the RMS sound pressure to the reference level of sound pressure is 20/20 = 1. The sound intensity in the car will be approximately 57.8 dB.To calculate SPL, you take the ratio of the sound pressure to the reference level of sound pressure and then take the logarithm (base 10) of that ratio, and then multiply by 20. \( Sound \ Intensity in Decibels = (10 \ decibels) \times logarithm \ of (\frac) \) Mathematically, we can represent it as below: The unit of the scale is termed as the decibel, dB. The decibel scale uses the logarithmic function for representing a large range of intensities easily. We express it as Watts per square meter.Īnother more common way to express sound intensity is the decibel scale. It is equivalent to the average power per unit area. The intensity of a sound wave is measured as the rate at which it transports energy per unit area. This scale is referred to as the decibel scale. It is on 10 as the base, rather than a linear one. So, to express levels of sound meaningfully in numbers in a more manageable form, a logarithmic scale is used. If we think about it, then it would be very difficult to manufacture a sound level meter having linear performance. Thus the upper range rather than the quiet part. A sound meter uses a display with a decibel range and its resolution is further approximate to the ear’s range. When we measure the noise levels with a sound level meter, we measure the intensity of noise called decibel units (dB). The human ear can hear the sound of a pin dropping as well as the roar of a jet engine far away. It also has a remarkable ability to handle the enormous range of sound power levels. It has a clever in-built mechanism that reduces its own sensitivity with the rise of sound level. The human ear is a versatile and amazing hearing device. Source:en. Decibel Formula What is Decibel? In this topic, we will discuss the Decibel Formula with some examples. The dB is a logarithmic way of describing some ratios. Also, it is widely used in electronics, signals, and communication. The decibel (dB) is a logarithmic unit used to measure the level of sound. Also used for measuring the relative loudness of the sounds. dB is the unit for expressing the ratio between two physical quantities, generally acoustic or electric power.
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