Investigation On Maoshan Bugle Echoes And Analogous Phenomena

There is a peculiar acoustic phenomenon at Maoshan in Jurong, Jiangsu. When a firecracker is launched in the square in front of several large groups of steps, one can hear bugle-like echoes composed of clear 6 notes. According to preliminary study, the Maoshan bugle echoes are formed by explosive sound successively reflected on 6 groups of steps. In this paper, the reflection on the steps interface is studied in detail, we have revealed the acoustic principles of forming Maoshan bugle echoes and other analogous phenomena. A number of widespread peculiar echo phenomena was discovered.Theoretical methods used in this paper are plane-wave mode expansion, Kirchhoff tangent plane approximation in integral representation of reflected sound field and far-field approximation. Studies have shown that periodic steps have a special role on sound reflection. At any incident angle of sound, the reflected sound field is composed of modes propagating to different directions. There are a great many of frequency components of explosive sound. After reflection by steps, observer on the ground can only receive echo composed several specific frequencies whose certain reflection mode propagated to the observer. The spectrum of echo is discrete approximately, and each order overtone is an integer multiple of the fundamental frequency. This phenomenon is known as the space comb-like filter effects. In the medium-high frequency, there is a sharp directivity in a particular direction of reflected sound field, and this direction depends on the incident angle and the inclination angle of steps. In Maoshan echo experiment, reflected sound field appears maximum amplitude in the direction of observer on the ground. Since the incident sound and most of the reflected sound are on the same side of the normal to the steps interface, this phenomenon may be referred to the negative reflection of sound. Due to the negative reflection of high-frequency sound, there are amount of harmonics of echo which like the sound played by wind instrument, in spite of the weak high-frequency component of explosive sound.Experiment on steps was conducted in Mangdangshan, Yongcheng, Henan. The observer also heard bugle-like echoes, which validate the theoretical solutions. We predict there are analogous peculiar echoes phenomena elsewhere, such as steps of Sun Yat-sen Mausoleum in Nanjing and Hua Guofeng’s tomb in Jiaocheng, Shanxi. Another interesting phenomenon is related with Chinese ancient pagoda. At Yingying pagoda in Yongji, Shanxi and pagoda of Baolun temple in Sanmenxia, Henan, people heard the echoes which like frog calls in response to hitting stone or clapping in front of pagoda about 20 m far away. There are several layers of lamination of overhanging eave in each level of pagoda, generally concave inner, which is quasi-periodic. Frog calls is formed by sound of hitting stone reflected on lamination of overhanging eave, and have a similar acoustic principles with Maoshan bugle echoes. In addition, we found a lot many echo pagoda, such as pagoda of Songyue temple, pagoda of Fawang temple in Dengfeng, Henan. The echo of pagoda of Yongtai temple in Dengfeng is like duck’s quack but not frog calls.These peculiar echo phenomena, on the one hand as a demonstration experiment of popular science education, on the other hand have an important tourism value. The research of this paper provides a theoretical guidance for the design of similar acoustic landscape.