Aviscom Network

Radio frequency interference (RFI) can bleed into sound systems from nearby radio stations, or C.B. radio transmitters. Electro-magnetic frequency (EMF) interference can also come from other electrical devices such as electrical transformers, fluorescent lights, computers, electric motors, or switches.

High impedance microphones and equipment are much more sensitive to these types of interference. In some cases, interference in such systems can be reduced by using shielded microphone and input cables, and reducing their lengths.

If possible, the best solution is to convert to low impedance, balanced mics and equipment, making certain that all mic and input cables and connections are well shielded. Low impedance systems are more resistant to interference. If interference is detected, it’s often due to some defect in a shielded cable or connection somewhere in the input side of the system which can be traced and repaired.

Grounding problems can be another common cause for PA interference. If your control board and amps are equipped with a three pronged, grounded AC plug, make sure that the electrical outlet is properly wired with a good ground connection. If electrical “buzz” still occurs, some amps or mixer boards have polarity switches that can be reversed, which by experimentation may help reduce or eliminate some electrical noise. If problems persist, consider that the problem may originate in one of the components in your system. Remove individual components (such as equalizer, limiter, etc.) one at a time, and see if their removal eliminates the problem. If no success, try temporarily lifting the ground at the electrical source to see if the “buzz” disappears. If so, this will usually confirm that it is a grounding problem somewhere in the system.

Removing the ground to a system or certain devices is a common method that some technicians use to eliminate grounding buzzes, but it is dangerous and not recommended to leave a system ungrounded. A ground is there for human safety, to provide shut-down of an electrical circuit in the event that live voltage comes in contact with the chassis or a user handled area. Even though most audio equipment will be powered by 110 volts, this is more than enough to kill a human being under the right circumstances. For this reason, all sound operators or technicians should always wear rubber-soled shoes.

For temporary testing purposes, a ground fault interrupter (GFI) can be substituted in absence of a ground, which can provide an operator some limited protection from electric shock. But the advisable method of dealing with grounding problems is to have an electrician seek out and eliminate any possible “floating ground” or “ground loop” in your electrical source. When possible, have an “isolated” dedicated ground installed to the outlets which supply power to all PA related equipment. All inter-related audio devices such as tape recorders, film projectors, VCR’s or TV broadcast equipment must share the same common ground.

Obviously, there may be times that you experience a problem that only can be remedied by a trained technician. But these suggestions may help in many situations, and hopefully, save you time and money for the Lord’s work.