What Is the Attenuation Coefficient?

The attenuation coefficient is also called the attenuation constant. Is the real part of the propagation coefficient. It includes two parts: classical absorption and molecular absorption. Classical absorption is due to the acoustical energy dissipation caused by the viscosity of the air, the heat conduction effect, and the rotation of air molecules. Its size is proportional to the square of the frequency of the sound wave, and it is related to the air temperature and pressure. This absorption can generally be ignored. . The molecular absorption is mainly caused by the vibrational relaxation effects of oxygen and nitrogen molecules in the air. It is closely related to the temperature and humidity of the air and also changes with the increase and decrease of the sound wave frequency, but the change law is more complicated. ^[1]

The attenuation coefficient is the real part of the propagation coefficient. It consists of two parts: classical absorption and molecular absorption. Classical absorption is due to the acoustic energy dissipation due to the viscosity of the air, the heat conduction effect, and the rotation of air molecules. Its size is proportional to the square of the frequency of the sound wave, and it is related to the air temperature and pressure, but not to the air humidity. Unless the frequency of the sound wave is high, such absorption is generally not considered. The molecular absorption is mainly caused by the vibrational relaxation effects of oxygen and nitrogen molecules in the air. It is closely related to the temperature and humidity of the air and also changes with the increase and decrease of the sound wave frequency, but the change law is more complicated. The sound attenuation due to absorption in the atmosphere, such as the summer when it is hot and relatively dry, the relative humidity can be as low as 24%, the sound attenuation at 3kHz is 0.14dB / m, and the sound attenuation at 10Hz is 0.48dB / m.

The sign is ; if a quantity F (x) as a function of distance x is F (x) = Ae-axcos [ (xx ₀ )], then is the attenuation coefficient, is the phase coefficient, and the propagation coefficient = + j. Period and its related phenomena and the amount of acoustics. SI unit: m (per meter, minus one square meter). The amount 1 / is called the attenuation length. The quantity (xx ₀ ) is called the phase. The units of and are Np / m and rad / m, respectively. ^[2]