The theory of sound barrier
The indoor sound field is a semi-reverberation field. Set the source of the directivity of Q, room constant R, then the barrier of the insertion loss:
For the rectangular barrier, z is the direct distance between the sound source and the measuring point connection, Q is the directivity of the sound source,
, Δi is the difference between the shortest distance and the direct distance between the sound source and the receiver to the i-th side of the barrier. For the reverberation field, and the receiving point is in the far field range of the sound source, IL = 0, then the barrier has no noise reduction effect. Therefore, when the indoor noise barrier is provided, it is required that the room has a high sound absorption.
Sound insulation barrier location, as shown. Assuming that there is no diffraction phenomenon, the barrier can block all the sound. In fact, due to the diffraction of sound waves, the sound barrier effect of the barrier is related to the wavelength of the sound wave, the distance between the sound source and the receiver, and the sound insulation performance of the barrier material. The theory of barrier sound insulation is based on the diffraction theory of light waves. The difference between the shortest distance between the sound source and the receiving point is δ = (α + b) - (δ + b) - where the distance between the source and the receiver is the barrier, R + d); λ is the acoustic wavelength. Outdoor open (equivalent to semi-free field) sound insulation barrier noise reduction △ L and N relationship see table:
When N is negative, it indicates that the barrier does not block the direct sound between the sound source and the receiving point, and the maximum noise reduction effect is 5 dB. N value increases, the noise reduction increases, but the measured maximum noise reduction is 24 dB. The barrier material used shall be such that the sound insulation of each frequency is 6 dB above the sound barrier of the infinite barrier.
If both the sound source and the receiver are on the ground plane, the distance between the sound source and the barrier is r, the distance between the receiver and the barrier is d, the height of the barrier is h, and satisfies d >> r ≥ h Barrier noise reduction or insertion loss IL (see enclosure):
Where λ is the wavelength of the acoustic wave. For high frequency sound when to meet 10h / rλ >> 3,
