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The temperature in the room is obviously dependent on the room itself, the insulation, and whether other sources of heat are present. Temperature is also the physical quantity that makes us feel hot or cold. Consider the following example: an electric heater radiates heat into a room and temperature is the effect. This curve shows that sounds at 50 Hz would have to be amplified by 30 dB to be perceived equally as loud as a sound at 1000 Hz at normal sound levels.Ī sound source radiates power and this results in a sound pressure. The A-weighting curve has been widely adopted for environmental noise measurement, and is standard in most sound level meters. Noise with high frequencies such as mosquitoes buzzing are heard as high-pitched noise.Ī-weighting is applied to instrument-measured sound levels in effort to account for the relative loudness perceived by the human ear, as the ear is less sensitive to low audio frequencies. Noises with low frequencies such as thunder are heard as low-pitched noise. The ear interprets the frequency of a sound as pitch. The human ear is able to hear frequencies ranging from 20 Hz to 20,000 Hz. The number of cycles per second, for example if an object vibrates 500 times per second, the frequency of the noise it produces is 500 cycles per second or 500 Hertz (Hz). Each octave comprises three one-third octave values. The octave increments are obtained by doubling the previous frequency. For room acoustics the relevant octave frequencies are 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The decibel scale is ideal for acoustics because of the large range of sound levels the human ear is able to hear and the comparatively large numbers we would otherwise have to use had this system not been adopted.Īcoustic parameters such as the sound pressure level or the sound absorption coefficient are usually expressed in increments of octaves and one-third octaves. For example, a noise level recorded at 10 dB which then increases to 40 dB has multiplied by a factor of 10,000 (10 x 10 x 10 x 10 or 104). The decibel scale is used to calculate noise levels and counts ratios in powers of ten. The term decibel was developed by Graham Alexander Bell to simplify the calculations involved when measuring the resistance of a piece of wire. The standard unit of measurement of noise is the decibel (dB).