对道路声屏障声学设计公式的讨论

一些行业标准推荐的声屏障绕射声衰减量计算公式含有严格的适用条件，从而限定公式的使用范围，可能不宜直接应用于道路声屏障的工程设计。为此，提出几点改进建议：（1）对存在反射地面的情况，建议采用虚声源和虚受声点的普适计算方法；（2）对声源和受声点都接近刚性地面的情况，介绍相应的绕射声衰减计算公式；并在点声源公式中对大菲涅尔数区段另行表述，以明确反映实际屏障存在的绕射声衰减限值；（3）应用虚声源概念计算双屏障的反射声修正量。计算实例不仅佐证这些建议的合理性，同时得到一些规律性的结果：（1）地面反射将增加受声点的声压级，减小屏障的绕射声衰减量；当声源和受声点都接近刚性地面时，受声点的声压级在无屏障时增加3 dB，有屏障时增加6 dB，屏障的绕射声衰减量减小3 dB。（2）对于点声源和线声源，不论是否存在地面反射，双屏障的反射声修正量基本相同，且随着屏障内壁吸声系数的增加而同步减小。

Discussion on Acoustical Prediction Formulas of Road Sound Barrier

There is some strict boundedness in acoustical prediction formulas of sound barrier recommended by some documents. The boundedness will limit applicable range of these formulas. Therefore some suggestion was proposed to improve acoustical prediction formulas of road sound barrier. The suggestion includes: (1) A universal method was introduced using the image source and image receiver when a reflect ground was considered; (2) Several corresponding prediction formulas were made when the source and receiver all are near a rigid ground, and for pulse point source, the attenuation formula was represented separately to express attenuation limiting value in an actual barrier when Fresnel number N>10; (3) The reflect sound reformation of a double barrier also can be calculated using the image source method.The examples discussed in this paper not only prove that the suggestion is reasonable, but also provide some interested conclusion, such as (1) The reflect ground will increase sound pressure at a receiver, and decrease attenuation of barrier. When the source and receiver all are near a rigid ground, sound pressure at a receiver will increase 3 dB without a barrier, and 6 dB with a barrier, the attenuation of barrier will decrease 3 dB; (2) The reflect sound reformation of a double barrier almost are same with or without the reflect ground, and the reformation will decrease with increase of the absorption of barrier surface toward source.