Potentiometers: Audio vs. Linear Tapers

What's the difference between linear and audio taper potentiometer?

By Megan Tung

Rotary Potentiometer A potentiometer is a three-terminal resistor with a sliding or rotating contact which forms an adjustable voltage divider. Two terminals (GND and +Vcc) are connected to a fixed resistance strip and one terminal (output) is connected to a sliding contact called the wiper. The wiper can be moved along the resistive strip either by a linear sliding control or a rotary contact. In a rotary potentiometer, rotating a knob or dial attached to the shaft causes the internal wiper to sweep across a curved resistive strip. Slider potentiometers change the value of their contact resistance by means of a linear motion.

Potentiometer taper is the relationship between the position and resistance of the pot. Linear TaperIn a linear taper the relative position is equal to the resistance ratio. For example, rotating the potentiometer to 50% will cause the pot to function at 50% of the maximum resistance. Linear tapers can be good for adjusting lighting through light dimmers or for motion control. Non-linear tapers are often referred to as a logarithmic or audio taper. These are most commonly used for audio volume control. The human ear is sensitive to sound intensity in a logarithmic fashion, meaning at low sound intensities a small change in intensity is perceived as a big change in loudness, while at high intensities a large change in intensity is required for the same change in perceived loudness. When adjusting the volume an audio taper is used (rather than a linear taper) to obtain a more natural ‘linear’ perception in sound intensity change.

Applications

Potentiometers are used to adjust levels of analog signals and as control inputs for electronic circuits. The uses of potentiometers can be separated into two categories: null instruments and electronic components.

When used as a null instrument, pots permit precision measurement by adjusting a value of a circuit element until a meter reads zero. Situations where potentiometers are used as null instruments are when it compares the emf of a battery cell with a standard cell, measuring the internal resistance of a battery cell, or measuring the voltage across a branch of a circuit.

When used as an electronic component, the potentiometer varies the resistance in the circuit. Pots were formerly used in televisions to control the brightness, contrast, and color response. High precision pots were used in analog computers to scale intermediate results by the desired constant factors, or to set initial conditions of a calculation. Although pots are no longer used in modern televisions and computers, these applications demonstrate how potentiometers vary the resistance to alter the outputs. Linear pots are used for motion control as position feedback devices in order to create a “closed loop” control. Potentiometers are widely used as transducers to measure displacement. As the body moves, the position of the slider changes accordingly so the resistance between the fixed point and the slider changes. The change in resistance is proportional to the change in displacement of the body; therefore, the voltage change indicates the displacement of the body. As mentioned above, log tapers are used for audio control, such as to control audio equipment, change loudness, and frequency attenuation.

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Megan Tung is an intern at Jameco Electronics. Megan is a rising junior at University of California, Santa Barbara. She is interested in photography, music, business, and engineering.