User guide

Hum Noise and Mic Orientation

All dynamic microphones, including ribbons, utilize powerful magnets in their motor

assemblies and matching transformers, and are, to some degree, susceptible to picking up

stray alternating magnetic fields. Power transformers (such as those found in guitar

amplifiers) and alternating current motors are the most likely sources of radiated noise.

Building wiring and electrical utility transformers are other likely sources. A well-

designed microphone provides shielding to minimize the effects of stray magnetic

radiation. In some cases complete isolation is impossible and the result is usually hum or

buzz. Ribbon microphones can potentially manifest this condition to a greater degree

because of their higher gain requirements. With vintage ribbon microphones, that employ

large bulky magnet structures, the problem can be worse. Royer SF-1 and SF-12

microphones are designed to minimize the effects of unwanted radiation by integrating the

transducer barrel as part of the magnetic return circuit. With this design, the barrel

housing the transducer serves to complete the North-South magnetic return and

neutralizes the effects of outside magnetic radiation. The SF-1 mono and SF-12 stereo

ribbon microphones go one step further by incorporating toroid impedance matching

transformers, which have a natural ability to repel magnetic radiation.

Dynamic and ribbon microphones are passive devices, meaning they incorporate no

external or internal power supplies and have no head amplifier and therefore cannot

produce hum on their own. Unwanted noise (hum) can only come from an external

source. Fortunately, there is a simple procedure that can be used to identify the source of

the noise and eliminate it. Repositioning a dynamic and ribbon microphone is the

number-one way to get rid of unwanted noise. If hum is detected, it means that the

microphone is in the proximity of an alternating magnetic field. While listening (preferably

with headphones) to the mic, move it around. The mic will “find” the noise source quite

easily. If you are miking a guitar amplifier and suspect the amplifier’s power transformer

may be the source of unwanted noise, move the mic around the amp. You will probably

find that the noise is louder as you approach the amplifier’s power supply and quieter

when you move it away. Eliminating the noise can be fairly simple and requires finding

the “null” point of the noise. The “null” point is the position that places the

microphone’s magnetic components away from the lines of radiation. Simply rotating the

microphone slightly is many times all that is required to cancel out the noise. This is

similar to the procedure guitarists use to eliminate noise from single coil guitar pickups.

There will be a “magic position” where the noise disappears completely. Finding the

exact position that also provides acceptable acoustic placement of requires a little

practice, but the results are well worth the time.

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Orientation of the SF-12 microphone is such that the “ROYER” logo should always face

the sound source to avoid inadvertent phase reversals.

When the microphone is aimed as described, the center stage is picked up equally (3dB

down) by both transducers. Their included angle of 90 degrees produces a continuous