Lately I’ve been thinking that it might be handy to get hold of some omni–pattern dynamic mics. I can imagine they’d provide an interesting alternative in roles such as drum overheads, and the lack of proximity effect should make them useful for close–miking. Do you think they could be useful, and what models would you recommend if so?
SOS Technical Editor Hugh Robjohns replies: Omnidirectional microphones are (and always have been) excellent for music recording, and are the mainstay of most classical recordings for a variety of good technical and sonic reasons. However, dynamic omnis are relatively rare, and of those that do exist, most professional types seem to be intended for hand-held radio or TV interview applications. This is primarily because of their reduced susceptibility to handling and wind noise (compared to directional dynamic mics), and the fact that dynamic mics are inherently cheaper to make than electrostatic types. Most budget recording and all live-sound applications also place the rejection of unwanted sound as a high priority, so there is little call for dynamic omnis. High-quality recording mics tend to be capacitor or electret types — and there are plenty of omnis in that category, of course.
Using omnis in live-sound applications is not for the faint-hearted, but it’s not impossible. The rejection of spill (and room reflections) from the PA is the major challenge, but if the mics and PA can be well separated, and if the PA has a tightly controlled radiation pattern (with minimal reflections getting back to the stage) across the entire frequency range, then omnis can be used.
Music recording with omnis is not without its own problems, of course, the most obvious being the additional room sound (ambience/acoustic) and spill from other sound sources that they will capture compared to a directional mic at the same position. So achieving the required perspectives, separation and control are the main issues of concern.
Thankfully, given a good acoustic venue (large, high and relatively dry sounding) this isn’t always a problem and can actually be beneficial in helping to glue everything together in the mix, although the ability to control the mix balance purely through manipulation of the channel faders is greatly reduced. You really have to get it right by moving the mics around to set the desired acoustic balance.
As you say, there is no proximity effect to worry about, so you can place omni mics much closer to sources than you could cardioid mics without being overpowered by excessive bass — and that obviously reduces the proportional amount of room sound and/or spill — although close miking does also inherently restrict the amount of the instrument that the microphone can ‘see’ and usually affects the tonality as a result.
For me, the greatest advantage of using omni mics is the extended and open bass response, and the lack of the inherent phase shifts that affect directional mics. The latter is a subtle characteristic, but directly compare a cardioid to an omni at the same location and (independent of the differing amount of room sound), the omni will always sound more natural and open, especially on critical instruments such as pianos, violins and voices.
If you really must have a dynamic omni mic (as opposed to an electret or capacitor omni, of which there are a great many), your best bet is to use the search function of the www.microphone-data.com web site. It came up with just 19 options when I tried it, several of which are minor model variations. For instrumental and drum miking applications, I’d suggest the Beyerdynamic M101 or Sennheiser MD211, but the Electrovoice RE50 or 635, Microtech Gefell MD120 and AKG D230 are also good all-rounders.