In sound recording, the acoustical era is from the 1890s until 1925. During this time, all sound recordings were made by mechanical means without the use of microphones or electrical amplification.
To make a sound recording prior to 1925, instrumentalists, singers, and speakers performed in front of a flared metal horn which gathered and funneled sound waves toward a thin diaphragm at the small end of the horn. The energy of the sound waves caused the diaphragm to vibrate. The vibrating diaphragm caused an attached stylus to etch the sound waves onto a blank wax rotating cylinder or disc. There were no electronic tone controls. All adjustments to the sound were made by altering the performer's position relative to the horn or by trying horns of differing sizes or diaphragms of varied thickness.
To play back an acoustic recording, a mechanical reproducing machine reversed the process. A reproducing point-usually a steel needle, or a sapphire for cylinders-was affixed to an encased diaphragm (called a sound box or reproducer) that was attached to a tapering tube known as a tonearm. The needle running over a cylinder or disc caused the diaphragm to vibrate and create sound waves conducted through the tonearm.
A performer used a great deal of ingenuity to create a successful acoustically recorded performance. The artist manipulated the voice and stance before the horn, moving away from the horn for louder and higher notes to prevent distortion, and moving toward the horn to prevent under-recording soft sounds. Consequently these movements could distort the dynamics intended by the composer of a musical selection.
The acoustical recording process could capture only a limited range of audio frequencies-approximately 100 to 2500 Hz. In the acoustic era, banjo, xylophone, trumpet, trombone, and tenor and baritone voices reproduced better than others. This constraint influenced the repertoire of early recordings. When acoustic recording improved later, the repertoire was expanded.
While the recording range for acoustics was very limited, a wider range of frequencies could be achieved by any of the following: a thinner, more sensitive diaphragm, the sharpness of the cutting point, the characteristics of the recording horn (most companies kept many on hand of varying sizes, flare, thickness, etc.) and the pliability of the wax. Softer wax could capture more sonic highs than harder wax.
The sound of an acoustic record may give the impression of an echo more than the impression of live performance we are used hearing in later recordings. Depending on the company, some acoustic recordings produced surprisingly lifelike sounds. For instance, Victor discs made during the 1900-1903 period are known for their bright sound and strong bass presence.