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Making a new boom cable

Updated: Oct 3, 2021

With a couple of film shoots and field recording trips in the pipeline, I decided to make a couple of new XLR cables.

I prefer to use star quad cable for microphone cables, especially when they are going to be used on location or out in the field. This is due to the noise-rejection properties that are inherent in its design. Star quad cable is constructed with four cores that are arranged in two pairs, which are helically wound around each other. The theory behind this construction is that any EMI (electromagnetic interference) that penetrates the outer sheath and is picked up by the inner cores, is picked up equally by both pairs - therefore being canceled out when the signal is phase-inverted across the + and - legs of the signal.

Normal two-core microphone cable can suffer from interference from things like fluorescent lights, power cables, and radio signals, because unlike star-quad cable, when the interference gets to the inner cores, the signal will be slightly stronger in the core that is closest to the source. When it is then phase inverted across the + and - legs, some audible interference will remain.

Although I have always had good results with star quad, with this cable I wanted to adopt a 'belt-and-braces' attitude, and take the opportunity to test a special XLR connector from Neutrik called the EMC, which is specifically designed for high EMI environments.

This connector has two pins for legs two and three, as normal, but the first pin is soldered to a PCB which connects the shield to a ring of capacitors. There is also a ferrite bead which filters out high frequency radio interference.

I have not had a chance to test the effectiveness of this combination of cable and connector, compared to the star quad cable with a standard connector, but am hoping that this solution will bring peace of mind when recording in high-interference areas, and that it will allow me to record in the field in some interesting locations.

I have detailed the process of terminating these types of connector below, as they are an unusual design and are wired pretty differently from the standard connectors.

Firstly, strip the shield back to expose the two pairs of signal cores. strip the insulation off the inner cables back to the inner core and twist each pair together. In most cable, the two cores of the same colour are the pairs, and like colours should be twisted together.

Then, solder the two pairs of inner cables to the correct pins, and clamp the two metal pieces together on top of the PCB. Once the strands from the shield have been spread out over the metal casing, slide the black plastic cable grip over, trapping the strands to the metal.

Trim back the excess strands of wire from the shield, and then insert it into the shell and screw the plastic piece on. Finished!



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