Unheralded Problem Solver: The Microphone Splitter

A microphone splitter is an item in the sound engineer’s kit that is appreciated only when it is needed. But when a microphone must be simultaneously fed to a second mixer, a professional-quality splitter is worth its weight in gold.

Splitters are used in virtually every kind of pro audio — including broadcast, recording studios, live applications and complex audio monitoring. The splitter’s function is basic. It takes a single input and provides two or more isolated outputs. But like all audio issues, there is more to know about the subject.

Radial JS-2 mic splitter

Radial JS-2 mic splitter

Splitter boxes, such as the Whirlwind IMP Splitter 1×2 ($98.00) or the Radial JS2/JS3 (beginning at $219.99), feature a direct output and at least one isolated output. These small boxes are best when you only need to share a feed or two with the main mix.

However, for larger broadcast and media productions, devices like the Radial OX8 eight-channel splitter ($849.99) are often used. Because most mic splitters are passive, you can expect a small amount of signal loss.

Radial OX8

Radial OX8

Line splitters work in a way similar to mic splitters, but they are for line-level signals. They often include trim pots instead of the pad switches likely to be found on mic splitters.

In a white paper by Whirlwind on passive splitters, the company notes that signal flow in audio systems has low impedance outputs (microphones) feeding high impedance inputs (mixers). When a signal is split to be sent to more than one mixer, the input impedances of those consoles provide additional paths for the electrical current.

This split actually increases the overall load presented to the mic signal and limits how many times it can be split without degrading tone or introducing distortion.

Microphones can usually be split to up to three, and in some cases even four, destinations without the use of electronics. The number of splits that can be accomplished depends on the application, impedances present in the system, length of the cables and the quality of the components used in the splitter. This is called passive splitting, since no power is required.

Klark Teknik DN1248 Plus Active Splitter

Klark Teknik DN1248 Plus Active Splitter

Active electronic splitters will most likely be required when splitting microphones to four or more consoles. These are normally used in large broadcast or recording installations. Manufacturers of these rack-mounted devices, which are considerably more expensive, includes ARX, Klark Teknik and Midas.

There are two types of passive splitters: parallel and transformer isolated.

The simplest is the parallel splitter. It involves taking a mic cable and simply “Y” connecting the plus, minus and ground wires to two other cables. It’s cheap, but can cause a series of problems. Professionals typically avoid parallel splitters.

A transformer splitter is the safest solution for trouble free operation. In this case, the microphone is wired straight through to a “Direct Out” and also to the input of a splitting transformer. This transformer’s output side is connected to the second or “Isolated” split output.

Whirlwind TRSP-1F transformer with dual Faraday shields

Whirlwind TRSP-1F transformer with dual Faraday shields

Usually one of the splitter’s outputs is allowed to pass phantom power to the input. This solves any multiple phantom power-source problems. All but one of the outputs are usually floating, removing the risk of ground-loop problems. Pro units will also have multiple Faraday shields to minimize any risk of interference.

Grounding issues can always occur. Any time two pieces of audio gear are plugged in, their actual resistance to earth ground can vary quite a bit — even when the outlets are on the same circuit. Even when using a transformer split, a problem can arise when the consoles' grounds are connected directly to each other through a splitter.

If console A sees a lower resistance to ground through its connection through the splitter to console B, then part of its AC ground return current will take the path of least resistance. In this case, a ground loop occurs.

If that happens, never use a three-prong ground lifter on the AC power cable of either console. It’s not safe and can present an electrical shock danger to the people using the system. A better solution to this problem is to break the ground connection of one or more channels between the consoles.

This is accomplished by disconnecting each offending ground connection at one end (usually the splitter) and leaving it connected at the opposite end. The shield for that channel will continue to work because it is still grounded at one end.

Radial has ground lift switches

Radial has ground lift switches

It is best to install ground lift switches for each channel or use lift adapters when necessary. Many splitters, including the Whirlwind and Radial models described, have ground lift switches on them. With these switches, the ground can normally be left connected but lifted if there's a problem.

Passive mic splitters come at various price points, but as with most pro audio gear, you get what you pay for. Radial’s JS2/JS3 models, for example, are built like a tank and come in a rugged 14-gauge steel case with a Jensen transformer. Other far less expensive models are much lighter and use various quality levels of transformers and circuitry.

Every sound operator should carry at least two or three passive transformer splitters in a well equipped kit. These are essential devices.

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