The point sound source radiates according to the spherical wave, and the change of sound pressure can be calculated according to the surface area of the spherical wave radiated: the calculation formula of spherical surface area: S0 sphere = 4 π R 2 (R is the radius of the sphere, that is, the radiation distance). When R is twice the original, that is, the radiation distance is 2R, the surface area of the sphere is: S1 sphere = 4 π (2R) 2 = 4s0 sphere, as shown in the figure below：

That is: when the radiation distance becomes two times of the original, the spherical surface area becomes four times of the original, and the sound intensity becomes one fourth of the original; when converted into decibels, it is 10lg1 / 4 = - 6dB; that is to say, the radiation distance of the point sound source is doubled, and the sound pressure level attenuation is 6dB.

The linear sound source radiates according to the cylindrical wave, and the change of sound pressure can be calculated according to the surface area of the radiated cylindrical wave: the calculation formula of the surface area of the cylindrical surface: S0 cylindrical surface = 2 π Rh (R is the radius of the spherical surface, that is, the radiation distance). When R is twice the original, that is, the radiation distance is 2R, the surface area of the cylindrical surface is: S1 cylindrical surface = 2 π (2R) H = 2s0 cylindrical surface, as shown in the figure below:

That is: when the radiation distance becomes twice of the original, the cylindrical surface area becomes twice of the original, and the sound intensity becomes 1 / 2 of the original; when converted into decibels, it is 10lg1 / 2 = - 3dB; that is, the radiation distance of the line source is doubled, and the sound pressure level is attenuated by 3dB.

According to the above calculation results, we can draw a conclusion: the sound attenuation caused by the distance of the line sound source is obviously smaller than that of the point sound source. Under the same sound power condition, the transmission distance of the line sound source is twice larger, and the power consumption is twice less under the same transmission distance condition!

Sound attenuation is a key technical point that the sound industry practitioners must master, especially in our design work, it is one of the important reference calculation basis for our speaker configuration. In our daily work, we often encounter some colleagues who are puzzled by the sound attenuation calculation of line array. Some people calculate according to the way of point sound source, while others calculate according to the way of line sound source. The line array with limited length that we usually use is not a real line sound source. Within its critical distance, we should calculate according to the attenuation of line sound source, while outside the critical distance, we should calculate according to the attenuation of line sound source The calculation is based on the point source attenuation.