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So, for instance, if you have a sound that measures 70dB and it decreases to 60dB, it would sound about half as loud to the human ear. You can use any base, but base 10 or e will allow you to use the calculator easily. Since the variable t is an exponent, take logarithms of both sides. Every 10 decibels (dB) reduction in noise level is roughly perceived as a halving of the perceived loudness. Divide by 6.9 to get the exponential expression by itself.
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It approximates the ear at very high sound levels and has been used for traffic noise surveys in noisy areas. sound energy is decreased by a factor of 100. The C-contour does not filter out as much of the lows and highs as the other contours. The intermediate B-contour aproximates the ear for medium loud sounds. Measurements made in dBA approximate the loudness level in phons and are practical to make with a standard meter. A good practice in sound level surveys is to measure all levels in both dBA and in the flat-response mode where the intensity in decibels (dB) is measured directly. The unit dB implies that all frequencies in the audible frequency range are treated equally - something very different from what the ear does. When this filter, (which is one of the standard contour filters of most sound level meters) is used, the levels should be recorded as dBA rather than dB. This measurement is made with a sound level meter with an A contour filter which provides the best instrument match of the ear's equal loudness curves for soft sounds in the neighborhood of 40 dB. When making practical assessments of the sound level of a concert or as a part of a general survey of ambient sound levels, the type of measurement which is usually made is that of the level in dBA. It is very useful for eliminating inaudible low frequencies. The A-contour filters out significantly more bass than the others, and is designed to approximate the ear at around the 40 phon level. The C weighting is reasonably close to a flat decibel response. Most low-cost sound level meters cannot merit such certification, and typically have just two weightings, A and C. The logarithm base 10 (log10) is employed to express the relationship in decibels, which are a logarithmic unit of. In this formula, the factor of 20 is used to convert the ratio of distances to decibels. Consequently, we may say: G 10log10 G (10.2.2) (10.2. Decibel Distance (dB) 20 log10 (d1 / d2) Where: d1: Initial distance from the sound source. Our gain of 1.3 Bels is equivalent to 13 decibels. To convert to decibels, simply multiply the number of Bels by 10. The weighting marked 20kHz means that it has a certified flat response to 20kHz. The result is the decibel (one-tenth Bel). These rules allow you to move back and forth between intensity and sound intensity level without a calculator: Change in intensity. This is the Weighting control on a research-quality General Radio sound level meter. The key is the two simple rules of thumb shown below. The different contours were intended to match the ear at different sound intensities. Standard filter contours are used to make the instrument more nearly approximate the normal human ear. A, B, and C Contour Filters for Sound Measurement A,B, and C Contours