Audio Taper Vs. Linear Taper

Mechanism

• A variable resistor, also called a potentiometer, rheostat or simply a ̶0;pot,̶1; has a strip of resistive material on which a metal contact slides. It has an electrical connection at one end of the strip and another at the metal contact. As the contact moves back and forth across the strip, its location determines the resistance between the two connections. For a rotary potentiometer, the resistive strip is circular. In a linear potentiometer, the strip is straight. The contact moves in a straight line along its surface.

Audio Taper

• The resistance of an audio taper pot follows a logarithmic curve, remaining at a low resistance percentage until the final 30 percent of its travel, when the resistance increases to 100 percent. In other words, the curve of resistance versus movement is not straight; it remains lower than a straight curve for most of its length, after which it increases suddenly and catches up. Early examples of audio taper potentiometers had a true logarithmic curve, although these proved expensive to make. Engineers later found that two strips with linear resistance, carefully cut to approximate a logarithmic taper, worked well enough; they cost much less.

Linear Taper

• The resistive strip of a linear taper potentiometer has equal amounts of resistance along its whole length. At a quarter of its travel, it is at a quarter of its total resistance. At halfway, it has half its total resistance. A reasonably pure resistive material has a linear resistance along its length, so linear-taper potentiometers are easier to make.

Uses

• Many stereos and TVs used variable resistors as sound volume controls. This created a problem, however, as a linear potentiometer gives an odd volume response. For most of its rotation, the sound is too loud. Because the human ear responds to loudness in a logarithmic way, the answer to the problem was an audio-taper pot. This evened out the amount of loudness per amount of control movement, making the control easier to use. Linear potentiometers see use in other kinds of equipment, such as a lamp dimmer, a temperature control on a heater or a frequency knob on an oscillator.