Technical Tip of the Day: “I see that Neumann just came out with an M50 microphone that is omnidirectional. I also notice that they have a KM183 that is an omni as well. On top of this, I see you guys have a lot of Earthworks omnis and also sell DPA (Bruel and Kjaer) who are known for omnidirectional mics. When and why do people buy these microphones? It seems that in a studio you’d want more isolation between all of the instruments than an omni can provide.”
For the answer to today’s inSync question we went to one of our in house experts on the subject, Sweetwater Sales Engineer, Nika Aldrich.
There are several applications for omnidirectional microphones, just like any other pattern.
One advantage of omnis is that, due to the capsule design, they have no proximity effect. This means that an omni directional microphone can be moved as close to the source as is comfortable with no change in the direct sound’s frequency response. Omni microphones also typically have very flat frequency response curves both on and off axis, and can handle very high SPL‘s.
Because of all of this, it is very common to use omnis in jazz and classical music where accuracy is of prime importance. The microphone can be as close as possible to the instruments with a very flat response to it. It is not uncommon to see omnis mounted less than 1″ from their source. When mics are put this close, they function very much like cardioid mics because the on axis sound is so prevalent over the off axis sound [Ed- due in part to the Inverse Square Law]. The difference is that with any microphone you’re going to get SOME off axis sound. With an omni it is often said that the off axis sound is more “musical” because it follows a flatter curve.
A general rule of thumb is that an omni mic and a cardioid mic will pick up the same amount of off axis sound when the cardioid mic is twice the distance from the source. Thus, if a cardioid mic is typically placed 6″ from the source, place the omni 3″ from the source for the same level, but a different type of sound.
Omnis are also used a lot on percussion, guitars, banjos, accordions, harps, upright basses, pianos, and even vocals. They are also commonly used in stereo pairs for room mics.