Impedance Basics
Impedance (Z) is measured in ohms and can be defined as “resistance” (opposition to the flow of electrical current representing the audio signals). The theory behind impedance can get very technical, so we will only go into enough detail to help you understand the basics. Although impedance is usually only associated with speakers (which is incorrect), impedance is also measured at equipment Outputs (Source) and Inputs (Loads). And then there are Cable Impedances as well (which are not covered on this Webpage).
a) Output Impedance: (also called “Source Impedance”) Is the impedance (resistance) that is “Inherent” in signal sources. Output Impedances include: Microphones, Mixers, Signal Processors, Electric Guitars / Bass Guitars, Amplifiers (Power Amplifiers / Guitar Amplifiers), Digital playback devices, etc.
Note: Electric guitars / basses usually have higher output impedances (typically up to 12,000 ohms) due to the nature of magnetic pickups. Many current guitar pickup designs are exhibiting lower output impedances.
b) Input Impedance: (also called “Load Impedance”) Is the impedance (resistance) that is “seen” by the signal source – Input Impedances include: Speakers, Mixers, Signal Processors, Amplifier Inputs, etc.
c) Impedance Matching: Is best described as the “appropriate” connection of Output and Input sources. When the output impedance of the source device is acceptable to the input impedance of another device.
Examples of Typical PA System and Electric Guitar Set-Up Below:
Notice that the Electric Guitar output and the Guitar Amplifier both indicate a “High Output Z.” This is due to the “Output Z” on the electric guitar being higher as compared to the “Output” Impedances on other audio equipment. Since the guitar’s “Output Z” is significantly lower when compared to the “Input Z” of the guitar amp – It is still considered a Low Output Impedance.
Notes on Cable Impedances: Shielded Instrument Cables are high impedance and low power. Speaker cables are the opposite – low impedance and high power. There is no advantage to using a Shielded cable as a speaker cable. One main reason is that smaller diameter cables will have more resistance to the signal flow and can waste an amplifier’s energy output. The large diameter of a speaker cable allows better signal flow from the amplifier to the speaker. Using a larger gauge, twisted pair cable for speaker cable is highly recommended. One cable does not fit all applications, which is why so many different cable types and uses exist!
Other Notes regarding Impedances:
- Outputs – Low Impedance (Typically, 600 ohms or lower, usually 10X lower than Input Impedances).
- Inputs – High Impedance (usually at least 10X higher than Output Impedance sources).
- Impedance matching (Low Z Outputs to High Z Inputs) allows for a Maximum transfer of Voltage.
