Any class or type of sound which once existed, but has since been replaced, superseded, or has otherwise ceased to be heard except as a museum artifact. Disappearing sounds are generally those associated with social activity, although some natural species and their sounds have also become extinct. When the energy forms used in society change, many direct and indirect acoustic changes result. As travel by horse gave way to mechanized transport, the sounds of shoed horsehooves, reins, sleighbells, and wagonwheels disappeared, but so did the sound of the blacksmith and wheelwright.
Road surfaces show another interesting progression with a strong acoustic component.
In many cases, the sounds involved did not seem important to the person at the time, and their actual passing may have gone unnoticed. Carding wool and grandfather clock, Nova Scotia. Spinning wheel, Nova Scotia. Three foghorns, each of which has replaced its predecessor at Point Atkinson, West Vancouver, B.C., the last being an electronic horn.