User guide

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. In-wall wiring and electrical utility

transformers are other likely sources. A well-designed microphone provides shielding to

minimize the effects of such stray magnetic radiation. In some cases complete isolation is

impossible and the result is usually hum or buzz. 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 worse.

The SF-24 reduces this condition because the essential gain is provided at the microphone,

negating the need for additional gain to be supplied by the preampliﬁer. In addition, the Royer

SF-1, SF-12 and SF-24 family of microphones are designed to minimize the effects of unwanted

radiation by integrating the transducer barrel as part of the magnetic return circuit. Royer’s SF-

series ribbon microphones go one step further by incorporating toroidal impedance matching

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

Unwanted noise (hum) can only come from external sources. Fortunately, simply repositioning a

ribbon microphone is the best way to get rid of unwanted noise. If hum is detected, 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. For example, if you are miking a guitar ampliﬁer and suspect the

ampliﬁer’s power transformer may be the source of unwanted hum, move the mic around the

amp. 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

ﬁnding the “null” point of the hum. 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. There will be a position where the hum disappears completely.

Hum and other noise is often picked up in microphone cables. Since the output of Royer Active

Series mics is 15 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 hence less likely to be

objectionable.

12