By MARK HARTSELL
The recordings of the acoustical era—the 1890s to 1925—were created by mechanical means without the use of microphones or electrical amplification.
Musicians, singers and speakers performed in front of a flared metal horn that gathered sound waves and funneled them to a thin diaphragm at the small end of the horn. The energy of the sound waves caused the diaphragm to vibrate, and the vibrations caused an attached stylus to etch the waves onto a wax rotating cylinder or disc.
Record makers had no electronic tone controls to alter the sound—all adjustments were made by changing the performer’s position relative to the horn or by trying horns of different sizes or diaphragms of different thickness.
To play back the recording, the process was reversed. A steel needle or, for cylinders, a sapphire was affixed to an encased diaphragm—called a sound box or reproducer—attached to a tapering tube known as a tone arm.
The motion of the needle moving over a cylinder or disc caused the diaphragm to vibrate and create sound waves that were conducted through the tone arm.
Performers used a great deal of ingenuity to create a successful recording, moving away from the horn for louder and higher notes to prevent distortion and toward the horn to prevent under-recording of soft sounds. Such movements, however, could distort the dynamics intended by the composer.
The acoustical recording process could capture only a limited range of audio frequencies—about 100 to 2,500 Hz.
Banjos, trumpets, trombones and tenor and baritone voices reproduced best—a constraint that influenced the repertoire of early recordings. When acoustic recording improved later on, the repertoire expanded.