Microphones and cables are configured in lo-Z or hi-Z varieties to suit specific audio signal needs. The difference between lo-Z or hi-Z the cables is primarily physical, but an explanation of impedances, and the use of balanced and unbalanced audio signals is necessary to understand cable function and application. “Z” is the abbreviation for impedance as used in mathematical formulas, with “lo” and “hi” serving as shorthand for “low” and “high”.
Cable Impedance Basics
In electrical circuits, impedance is a capacitive and inductive reactance to voltage -- meaning the quality and efficiency of electrical current flow is subject to the physical properties of the cable wires. Voltage capacitance is the cable's ability to transfer sufficient voltage from the mic to sound equipment without loss. Inductive reactance is the cable's ability to react and recover voltage changes inherent in the reproduction of different sound frequencies. The manner in which cables transfer voltage directly affects sound quality.
Lo-Z Microphone Cables
Low-Z cables carry positive and negative voltages through dedicated wires in addition to a separate ground wire doubling as a shield against outside electrical noise interference. The shielded 2-wire configuration results in a "balanced" signal, splitting voltage equally between the two conductor wires resulting in improved capacitance and reactance over high-Z cables. This equates to longer mic cable lengths up to 400 feet without sound degradation or noise interference, and is why low-Z mics and cables are used exclusively for professional audio.
Hi-Z Microphone Cables
High-Z cables carry positive and negative voltage through a single wire, with a shielded ground wire employed for minimizing noise. This wire setup results in an "unbalanced" signal, with the lone wire sharing positive and negative voltage burdens. Higher microphone voltage requirements are necessary to compensate for potential signal loss due to compromised design efficiency and decreased ability for adequate capacitance and reactance with long cables. As hi-Z cable lengths exceed 20 feet, sound quality decreases and potential for outside noise interference and electrical hum increases. Hi-Z mics and cables are not used in professional situations for these reasons.
Lo-Z and Hi-Z Cable Connectors
Lo-Z microphone cables employ 3-pin XLR connectors at both ends. Pin 1 is used for the shielded ground wire, pin 2 for the positive wire and pin 3 for the negative. Hi-Z microphone cables use 1/4-inch TS (tip and sleeve) connectors at the mixer end and a 3-pin XLR cable at the mic end. The 3-pin XLR on hi-Z cables uses pin 1 for the ground, and pin 2 or 3 for the "hot" wire depending on mic manufacturer. Inexpensive hi-Z mics sometimes employ integrated cables with a 1/4-inch TS plug at the mixer end.
Impedance is measured in ohms and can vary widely depending on microphone design. High-impedance mics range from 10,000 to 100,000 ohms, with low-impedance mics ranging from 50 to 600 ohms. While higher mic impedances theoretically equate to stronger audio signals due to increased voltage, this is not always desirable due to the risk of noise as impedance rises. Quality low-impedance mics connected to pro-grade audio gear will compensate for any loss in power and provide the advantages of long cable lengths and quiet operation.