The graph above depicts the scale of various potentiometers as they are rotated. The x axis represents the amount of rotation of the potentiometer, with the y axis showing the resulting resistance of a sample 500kΩ potentiometer. Each line on the graph represents a different potentiometer scale, which you can read about below. Rotating the potentiometer above will show you the resulting resistance values at that point when you hover over the graph. Give it a try! Note that you can show and hide the potentiometer types by clicking on them in the legend above.
Linear vs. Logarithmic
Potentiometers come in multiple types. The differences in these types of potentionemeters is in the amount of resistance they affect depending on the rotation. In the simplest form of potentiometer, the linear (represented above in blue), for example, rotating the potentiometer to 50% will cause the potentiometer to function at 50% of the maximum resistance. If the potentiometer is a 500kΩ linear potentiometer, for example, a 50% rotation will output 50% of the 500kΩ, or 250kΩ. Likewise, an 80% rotation will output 80% of the maximum resistance - 400kΩ.
There are many cases in which a straight linear potentiometer is very functional and appropriate. For example, if you are adjusting the lighting in a room, you would use a linear potentiometer to control the output. If a lightbulb is capable of producing a certain amount of light, turning the potentiometer down to the halfway point would make the lighbulb half as bright. Your eyes observe lighting on a linear scale - half as much light appears half as bright, just as you would expect.
For audio applications, however, this is not the case. The human ear does not hear in a linear scale - a decibel (dB), the common unit of measurement for volume, is a logarithmic unit of measurement. This is because the human ear actually perceives sound on a logarithmic scale. In a lightbulb, if you double the power, you double the brightness. For sound, if you double the power, you only slightly increase the perceived loudness. To double the loudness, you would actually need to increase the power by ten times as much.
As a result of this method of perceiving volume, linear potentiometers are not ideal for audio applications - turning a linear volume-control potentiometer to the halfway point would not produce half of the volume. Instead, we use logarithmic-scale potentiometers for audio applications to better approximate the scale in which the human ear perceives sound. These types of logarithmic potentiometers are often referred to as "audio taper".
Ideal vs. Actual
An ideal audio taper potentiometer would perform on a perfectly logarithmic scale. This is represented above by the "Ideal Audio Taper" (orange) and "Ideal Reverse Audio Taper" (green). In reality, these perfectly logarithmic scales do not exist. Often, a potentiometer will be manufactured to simulate the logarithmic scale. One of the most common ways in which this is done is through the use of two linear scales combined to approximate the logarithmic scale. By combining these two different linear scales, the progression of the potentiometer gets much closer to the production of a logarithmic scale while greatly reducing the complexity of the potentiometer. This is why many manufacturers choose to create potentiometers this way. These "simulated" logarithmic scales are shown on the graph above as "Actual Audio Taper" (red) and "Actual Reverse Audio Taper" (purple). You can see that these types of simulated logarithmic scales stay very close to the "ideal" logarithmic scale at low and high values, but differ by a moderate margin near the middle values.
Often, you will find other variations on these scales which will approximate the ideal logarithmic as well. Potentiometer data sheets will provide graphs of their own to show the behavior of the potentiometers. The graph "5% @ 50 Audio Taper" above is a single example of one of these variations, pulled from an actual manufacturer specification. This scale approximates the logarithmic but with the midpoint of rotation producing only 5% of the output (thus 5% @ 50). You can see that this scale approximates the ideal logarithmic scale even more closely than the "Actual Audio Taper" linear scales.
In the end, your selection of potentiometer will often come down to preference when they are used for audio applications. The "feel" of the changes in volume based on the way you rotate your potentiometer is dependent on how these scales are implemented. You should now be better equipped to analyze and determine what potentiometer is best for you. At the very least, you should now know what these graphs mean on the potentiometer data sheets!
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