Any class or 种类 of 声波 which once existed but has since been replaced superseded or has otherwise ceased to be 听 except as a 博物馆 artifact 消失 声 are 通常 those 联合 with 社会 活动 although some 自然 species and their 声 have also become extinct When the 能量 形式 used in 社会 change many 直 and indirect acoustic changes result As travel by horse gave way to mechanized transport the 声 of shoed horsehooves reins sleighbells and wagonwheels disappeared but so did the 声波 of the blacksmith and wheelwright

In some cases an interesting 形态学 occurs if the characteristic 声波 undergoes a metamorphosis rather than simple extinction The 发展 of the hunting horn and post horn for instance through the 蒸汽 whistle and compressed air horn to the 现代 electrically driven 设备 is a typical such progression Sometimes changing 材料 形（曲）式 the 基础 of acoustic change earthenware to glass and then plastic for instance Road 表面 show another interesting progression with a strong acoustic 组成

Often 消失 声 become 声波 浪漫 and if recalled as for instance in earwitness accounts or through 录音 may 触发 extensive 内存（记忆） of the past In many cases the 声 involved did 不 seem 重要 to the 人 at the 时间 and their actual passing may have gone unnoticed One 重要 活动 of 声景观（声景） 研究 is the careful collection and archival 卷宗 of 消失 声

源 Barry Truax - Handbook for Acoustic 生态学 CD-ROM Edition Cambridge Street 出版 1999 - CSR-CDR 9901