Through the years the design of the electromagnetic system has been continuously improved. In the most common type of receiver, introduced in the Bell system in 1951, the diaphragm, consisting of a central cone attached to a ring-shaped armature, is driven as a piston to obtain efficient response over a wide frequency range. Telephone receivers are designed to have an accurate response to tones with frequencies of 350 to 3,500 hertz—a dynamic range that is narrower than the capabilities of the human ear but sufficient to reproduce normal speech.
Through the years the design of the electromagnetic system has been continuously improved. In the most common type of receiver, introduced in the Bell system in 1951, the diaphragm, consisting of a central cone attached to a ring-shaped armature, is driven as a piston to obtain efficient response over a wide frequency range. Telephone receivers are designed to have an accurate response to tones with frequencies of 350 to 3,500 hertz—a dynamic range that is narrower than the capabilities of the human ear but sufficient to reproduce normal speech.
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