Here’s a guide to using this free software tool. First, enter information about your cables, amplifier, and loudspeakers on the left side of the calculator. You will need to find out how the gauge (or diameter) of the conductors in your speaker cable is specified. You can find the gauge of the wire from packaging, the label on the wire spool or, in some cases, printed on the insulation. If you see the acronym AWG, this means American Wire Gauge, and you should select the “Imperial” System of Units from the drop-down list at the top left of the interface. If the wire gauge has digits after a decimal point, such as 2.08, select “Metric” as the System of Units. If the wire size is specified as IEC Gage, then click the IEC check box, which supersedes the drop-down selector.
Next, enter information about your amplifier. These specifications should be printed in the user manual or on a data sheet. Make certain you enter the correct output power and load impedance (Output rated into…). These two values are always specified in pairs. Then enter the amplifier damping factor. Next, enter the nominal impedance of your loudspeaker. Finally, select your wire gauge from the pull-down selector, enter the length of the cable between the amplifier and loudspeaker, and enter the capacitance per unit length in picofarads. You should be able to find the characteristic capacitance of the cable from the manufacturer’s literature.
The single most important piece of information on the right side of the calculator is the net power loss in the cable. This is a measure of how much of the amplifier power is dissipated in the cable, before it ever gets to the loudspeaker. The lower the power loss, the more power actually goes into making sound. For an 8-ohm loudspeaker connected to 40 feet of 18-gauge zip cord, the power loss is about ½ dB, which is neither audible nor significant, especially for an amplifier with high power output. So, from the standpoint of power transmission, 18-gauge wire is suitable for many home applications. But for longer cable runs, the losses can be greater and you should consider changing to a larger diameter cable.
Another result to note is that, for many cables, the roll-off frequency is well above 20 kHz, the upper limit of the audible frequency range. If the roll-off frequency is below 80 kHz, you might consider changing your cable to a larger diameter.