Royer Labs SF-12 - Manual (Page 7)

The reason that ribbon mics take EQ so well is their inherent low self-noise, unusually smooth
frequency response characteristics and freedom from off-axis coloration. Dialing in high
amounts of equalization on condenser or dynamic microphones also means dialing in extra
amounts of the microphone’s distortion products and self noise; garbage that contributes to an
unnatural, unpleasant sound. Because distortion and self-noise are almost non-existent in ribbon
microphones, high levels of EQ can be used without adding harshness or excessive noise.
Hum, Noise and Mic Orientation
All dynamic microphones, including ribbons, are 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 hum. 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 that houses 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 and buzz) can only come from an external source. Repositioning a
dynamic or ribbon microphone is the easiest way to identify and eliminate 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 using the ‘null’
point of the microphone. The null point is the position where the microphone’s pick-up of stray
magnetic radiation is at its lowest. Slightly rotating the microphone is usually 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 position where the noise is greatly reduced or
disappears completely.
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