Sound Recording, Mechanical

a system of recording sound in which the shape of the medium is mechanically altered; the first practical method of recording sound.

Physicists began recording the vibrations of certain sound sources in studying acoustic signals as early as the beginning of the 19th century. These recordings were intended for visual study only and could not be reproduced. In 1877 the French scientist C. Cros scientifically substantiated the principles of recording sound on a drum or disk and then reproducing it.

The first apparatus for recording and reproducing sound mechanically was the phonograph invented by the American T. A. Edison (patent application, 1877). His phonograph, which played wax cylinders, was not widely used. Copying the record was complicated, the cylinders wore down quickly, and the quality of reproduction was poor. In 1888 the German engineer E. Berliner suggested using a disk as a recording medium. After making a recording, a master disk could be made from the disk by electroplating. The master disk could be used, in turn, for pressing phonograph records.

Mechanical sound recording was monophonic until the 1950’s, when stereophonic recording, which provided better sound quality, became popular. Quadraphonic recording, using acoustic signals transmitted through four independent channels in a single groove of the disk, was proposed in the early 1970’s. Playback makes use of four speakers placed in four corners of the room.

There are three stages in mechanical sound recording: rerecording from a magnetic tape to a lacquer disk, making a master, and pressing records. The apparatus used for rerecording on the lacquer disk comprises a tape recorder, electronic equipment for amplifying and correcting the electric signals, and a disk-recording apparatus (a drive mechanism, a recorder, and monitors). The electric signals are converted to mechanical vibrations by the recorder, whose cutter carves out a groove, modulated by the acoustic signal, on the lacquer disk. A stereophonic recorder has two independent dynamic systems (according to the number of channels) linked to a single cutter. The signals of each channel are recorded separately on the left and right walls of the groove. In order to obtain the metal masters and the dies from which the records will be made, the recording is transferred by electroplating from the lacquer disk to metal disks. To do this, the lacquer disk is coated with a thin layer of silver, to which a nickel film and then a layer of copper is added. The first metal master is left when the lacquer disk is removed. The second master, from which nickel dies are made, is produced in the same way. The dies are fastened to heated compression molds; the phonograph records are molded from synthetic materials on hydraulic presses.

Mechanical sound recordings are reproduced on electric record players. The advantages of this system of recording are that the records can be mass-produced at a relatively low cost. In addition, they are easy to handle, and recordings can be kept for a long time on the metal masters. The chief disadvantages of the system are that phonograph records wear down relatively rapidly as a result of direct mechanical contact with the phonograph needle. It is also impossible to edit and erase the recordings.