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Sound Advice

Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suits, & Other Compact Audio Installations Part by Neil A. Muncy

Earth “ground” connections were first implemented well over 100 years ago as a defense against lightning entering buildings on early power lines, and to minimize peak voltage in industrial electrical equipment, which were often located many miles from generating plants. Improving electrical “people safety” was the name of the game back then, and things haven’t changed since.

Nineteenth century electrical engineers used the word “ground” to describe a deliberate connection to the earth to minimize the risk of damage from lightning and power surges entering a building on the power lines. In North America the concept of earth ground connections has been refined for the principal purpose of making electrical equipment as safe as possible for the masses.

Ground has taken on a vast number of often confusing, contradictory, and/or misleading meanings, especially in the audio world. For the purposes of this discussion, lets just use Ott’s definition #2 [1]: “A ground is a low-impedance path for current to return to the source.”

Note: In North America, the means and procedures required to ensure adequate electrical safety in buildings are specified in the US National Electric Code (NEC) and the Canadian Electrical (CE) Code. These specifications are legally enforceable.

“Ground wire” is a contradiction in terms. The word wire is just another term for describing an antenna. Mother Nature does not read labels. You say, “… 5′ cable,” Mother Nature says, “… ½ wavelength antenna in the middle of the FM broadcast band.”

All conductors have inductance directly proportional to their length. Wind a conductor into a coil, and/or make it longer, and you get more inductance. Inductors oppose the flow of AC current. Increase the frequency, and there is more opposition to current flow.
Therefore, realize that a long ground wire from point A to point B is only really a useful ground conductor at very low frequencies, but there are a lot of folks who never considered, and/or believed, and/or understood this basic fact of physics. When electrical equipment is bonded together with ground wires, and there is more than one conductive path between any two pieces of equipment, a ground loop is formed.

Be sure to pick up the August issue of PS for an in-depth look at star grounding and loops.

References:
[1] OTT, Henry W., Noise Reduction Techniques in Electronic Systems, (2nd Ed., John Wiley & Sons, 1988) ISBN 0-471-85068-3

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

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