Though they often take tremendous abuse in daily use, microphones are the most delicate and important part of the pro audio chain. To keep microphones working properly, there are a few things the audio engineer can do.
Sweetwater Sound in Fort Wayne, Indiana compiled microphone care and maintenance advice from engineers at Shure on dynamics mics, Klaus Heyne of German Masterworks on condenser mics and Royer Microphones on ribbon mics. Also, some additional advice came from ProAudioNet. Most is simple to achieve in routine equipment maintenance.
Dynamic microphones are the most rugged and reliable of all mics, which accounts for their extreme popularity — especially by music groups on location. Depending on the aggressiveness of the user, these mics get spun around by the cord, spit on and usually accumulate lots of muck, including lipstick, beer and dirt.
Though the old saying goes that you can drive a nail with Shure’s SM58, that doesn’t keep the microphone clean or even hygienic for a rotating cast of users. The most important maintenance function with dynamic mics is to clean them after use.
This begins by unscrewing the grille and rinsing it with water. A mild detergent can eliminate odors. If the grime is really dense and caked on, use a toothbrush with soft bristles to clean the grille.
After cleaning, let the grille dry before placing it back on the microphone. Air dry it with a hair dryer on low heat if you’ve removed the internal foam windscreen. Avoid high heat, which can melt the windscreen.
If the dynamic mic doesn’t have a removable grille, hold it upside down and gently scrub it with a damp toothbrush. This prevents moisture from leaking into the mic’s cartridge. The foam that covers a SM58’s diaphragm can be cleaned the same way.
If the microphone has a bad odor, scrub it with a toothbrush soaked in a diluted solution of mouthwash and water. Be sure to hold the mic upside down while doing this. Never spray disinfectant or any cleaning agent at the head of the mic, since that will penetrate the grille and possibly damage the mic.
If someone wearing lipstick used a mic, it can be smeared all over the grille. Lipstick was designed to stay on, not come off. However, there are makeup wipes that are designed to remove lipstick. These can be used to wipe the outside of the grille and keep the next person using the mic from getting second-hand lipstick.
Condenser microphones are more fragile than dynamics. They should never be dropped or abused, and should not be exposed to excessive heat or extreme cold. Condensers like a temperature of 78 degrees. Avoid subjecting condensers to excessive vibration and keep ambient relative humidity down (30 to 40 percent is the goal).
It is a good practice to use a plastic bag to cover the mics when they are not in use. These bags will stop airborne dust and foam particles from windscreens and storage boxes from settling on the mic’s capsule. Always bag the mic before storing it in its case.
Use a pop filter when recording vocals. It will intercept the mist from a singer’s saliva and keep it from gumming up the mic’s diaphragm. The filter will also keep the electrically charged capsule from turning into a flypaper for airborne particles.
A contaminated capsule will eventually affect high frequencies. This can cause discharge noise or the microphone to shut down completely. It is also advisable to keep a minimum distance of six inches between mouth and mic to prevent plosives from damaging the capsule.
Always connect the cable from the power supply to a tube condenser mic before turning the power supply on. Voltage shock from a live power supply, or “hot plugging,” can damage or kill a microphone’s tube. Also, provide surge-protected AC power to your audio system. A lightning strike or the surge after a power outage can fry condenser mics.
Use a rule of thumb about your own hearing to protect a condenser microphone. If a sound hurts your ears, it probably will hurt the microphone too. Condenser mics are very sensitive instruments that respond to minute sound pressure changes. Excessive sound pressure level (SPL) will eventually degrade the capsule’s diaphragm the same way prolonged exposure will damage your hearing.
Klaus Heyne of German Masterworks, who provided the information on condensers, is one of the world’s foremost authorities on microphone repair and modification. He restores and customizes recording mics for Disney, Apple, Lucasfilm and many studios, artists and producers. Info also provided by ProAudioNet.
While modern ribbon mics are more durable than vintage models, they still need to be handled with care. Treat all ribbon microphones with the respect you would give a fine precision instrument.
While not as delicate as a Stradivarius, most ribbon mics won’t tolerate being tossed into a crate like a dynamic mic. So make sure stage hands and crews know the difference between ribbons and other types of microphones and handle them accordingly.
Rule #1 is never put a ribbon microphone down — especially on the floor — without covering it first. The powerful magnets in a ribbon mic will attract small metallic particles that can result in distorted recordings. Don’t underestimate the strength of the magnetic force that extends around your ribbon microphone.
Don’t hand a ribbon microphone to a novice user. Most people, including some audio technicians, don’t understand the proper methods for the care and handling of ribbon mics. If a ribbon mic is treated like a dynamic mic, it will likely be rendered unusable. Just one person blowing into the ribbon mic to check the sound level can send it back to the factory for repair.
Always position a ribbon microphone slightly off-axis when close-miking high energy sources. This will protect it from excessively loud sources. Ribbon mics have a fairly even pickup pattern, so moving it slightly off-axis won’t have an adverse effect on the recording. Also, always use good quality mic cables with ribbon mics. High resistance or high capacitance "economy" cables greatly degrade the performance of ribbon mics.
When using a ribbon on a kick drum or any other instrument with a strong directional blast of air, angle the length of the ribbon at 45 degrees to the source — not parallel to the drumhead. This will lessen the stress on the ribbon, allowing it to pick up the sound without the entire acoustic pulse hitting the ribbon all at the same time.
Always use a pop filter on ribbons when close-miking loud plosive sound sources. The concentrated blast of air from loud sources is extremely hard on the mic’s delicate ribbon. When capturing guitar or bass cabs, kick drums or vocalists, a pop filter is recommended. The rule of thumb is, "If you can feel a breeze, use a pop-screen!"
While it’s possible to connect some ribbon mics to a phantom-powered mic input without damaging it, it’s always advisable to turn off phantom power before connecting a ribbon mic. Many modern ribbons need phantom power and other models can be damaged by it. Know the power requirements or limitations of each ribbon mic.
Ribbon microphones employ magnetic components as a basis for their operation. All microphones that utilize magnets are somewhat susceptible to induced magnetic radiation, especially from alternating magnetic fields such as those found in motors, transformers and video monitors.
These fields can be strong enough to induce an alternating electric current in microphones that in turn gets amplified by the preamplifier. This is the same effect that plagues electric guitars, especially those with single coil pick-ups. If you experience this phenomenon, locate the source of the radiated field and move it away, shut it off or simply move the mic away from the offending device.
When traveling, the cargo hold of an airplane changes pressure with altitude and can affect ribbon microphones stored in sealed containers. Watertight containers or relief-valve type cases, such as Pelican camera cases, will often come out of cargo hold in a vacuum condition.
When opened, pressure is released and a significant "whoosh" of air blows through the case, which can put stress on the ribbon element. Before putting your ribbon mics in cargo hold, prevent against the vacuum condition by loosening the relief valve on such cases or providing a small vent hole on watertight containers.
Don't worry about the low temperatures in cargo hold. Fluctuations in temperate and humidity do not affect ribbon microphones.
Treating and maintaining microphones properly is a key to good sound. Follow the rules of the pros, and users will be rewarded with good performance over the long run.
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