Royer Manual

Hum, Noise & Mic Orientation

All ribbon microphones are susceptible to picking up stray alternating magnetic ﬁelds, which

show up in the audio signal as hum. Power transformers (such as those found in guitar

ampliﬁers) and alternating current motors are the most likely sources of hum. In-wall wiring,

solid-state light dimmers, and electrical utility transformers are other likely sources.

A well designed microphone provides shielding to minimize the effects of such stray magnetic

radiation. Complete isolation is not possible however and unpowered ribbon microphones can

manifest this condition to a greater degree because of their higher gain requirements. With

vintage ribbon microphones that often employ large, bulky magnet structures and are often

poorly shielded, the problem can be even worse.

The SF-2 reduces induced hum in three ways. Because the essential gain is provided at the

microphone, there is no need to push the preampliﬁer for excessive (hum producing) gain. Royer

SF microphones (SF-2, SF-12, SF-24 and SF-24V) are also designed to minimize the effects of

stray radiation by integrating the transducer barrel as part of the magnetic return circuit, further

reducing hum potential. Lastly, all SF-series ribbon microphones incorporate toroidal impedance

matching transformers, which repel magnetic radiation.

Hum can only come from external sources and simply repositioning a ribbon microphone is the

best way to control it. If hum is detected, the microphone is in the proximity of an alternating

magnetic ﬁeld.

While listening to the mic’s output (preferably with headphones), move the mic around. It will

“ﬁnd” the noise source quite easily. For example, if you are miking a guitar ampliﬁer and suspect

the ampliﬁer’s power transformer to be the source of hum, move the mic around the ampliﬁer.

You will probably ﬁnd that the hum is louder as you approach the ampliﬁer’s power supply and

quieter when you move it away. Eliminating the hum can be fairly simple and requires using the

“null” point of the microphone. The null point is the position that places the microphone’s

magnetic components away from the lines of the noise's radiation. Slightly rotating the

microphone is usually all that is required to cancel out the hum. This is similar to the procedure

guitarists use to eliminate hum from single-coil guitar pickups, turning around slowly while

listening for the hum to cancel. There will be a position where the hum disappears from the mic’s

output. Hum and other noise can even be picked up by microphone cables. Since the output of

Royer Active Series mics is 15 dB to 25 dB higher than with traditional ribbon microphones, any

noise picked up in the mic cables will be at a corresponding lower level and thus less likely to be

objectionable.