Excerpted from our “Home Studio Series” Volume 4, The Home Studio Microphone Guide.
Different types of mics are categorized by the type of element used. The most common mics used in an audio recording situation are condenser, electret (condenser), ribbon, and dynamic. Differnt mics also have various pickup patterns (or polar patterns), which refers to breadth of a microphone’s area of concentration. In other words, it refers to how sensitive the microphone is to picking up a sound source relative to it’s central axis. Most mics have a fixed pattern, though many studio mics include a range of pickup pattern choices, typically by way of a switch on the mic.
(Polar Pattern images © Galak76) • click on the images to enlarge
Omnidirectional
An omnidirectional pattern will pick up 360 degrees around its element. While it picks up sound sources equally from every angle, you may find that there is a slight flattening of the response from sources coming in from the back of the microphone. But if you have one mic and you want to pick up everything going on in the room, like a choir or a circle of singers or strings, an omni mic setting is the one to use.
Bi-directional (Figure-8)
A bi-directional (or Figure-8) mic will pick up sound sources equally from the front and back of the mic. A bi-directional mic has two elements, one is negatively charged and the other positive. Most ribbon microphones have a bi-directional pattern, which is useful if you have two sound sources you want to record, like a duet of singers or instruments.
Cardioid
Cardioid is a tighter pickup pattern, and gets its name from the heart-shaped pattern seen in the diagram. The most popular mic pickup pattern, cardioid mics will pick up sound sources in a fairly wide range from the front of the mic, will taper out sources not directly in front, and have almost no sensitivity to sounds coming directly from the rear of the mic. This helps reduce feedback and focuses on the sound source.
Hyper-Cardioid
Compared to a Cardioid pattern, a hyper-cardioid microphone has a tighter area of front sensitivity plus a small area of rear sensitivity. A hyper-cardioid microphone is not unlike a bi-directional, but with a larger area of concentration in the front and a smaller area in the back.
Super-Cardioid
A super-cardioid pattern is similar to a hyper-cardioid, with a slightly larger area of concentration in the front and a thinner area in the rear.
Unidirectional
A unidirectional pattern has extreme off-axis rejection, meaning it will only pick up sound sources that are directly in front of the microphone.
Shotgun
A shotgun mic is a unidirectional mic designed to pick up things that are far away, with a high degree of focus, so as not to pick up sources it isn’t directly pointed at. They’re typically electret condensers, and are often used for TV and field recording, though they can be used to isolate instruments in a studio setting, like a bass drum or piano.
Pressure Zone Microphone (PZM)
PZMs have a very specific place, and are not typically used in studio recordings (of course, there are exceptions). Most often, a PZM is an omni-directional mic mounted to a plate, so that the mic picks up all the reflections of the sound in an awkward space (e.g. inside a closed piano).
{ 3 comments… read them below or add one }
It looks to me like the author is not too familiar with the subject matter. Most glaring error–”unidirectional” is normally understood as a synonym for “cardioid” when it comes to microphone polar patterns. In each case, the microphone’s primary sensitivity is in one direction (hence the “uni”). Also, a cardioid pattern is not “tighter” than a bidirectional pattern–the bidirectional pattern actually has a narrower angle of sensitivity over its front axis than a cardioid does. However, the cardioid will pick up slightly less ambient sound due to its having no rear pickup lobe.
The author does not make clear what they mean by a “slight flattening of the response” of sound approaching from the rear of omnidirectional microphones. It is more accurate to say that omnidirectional mikes become less omnidirectional at high frequencies, where the body of the microphone tends to block smaller wavelengths. At lower frequencies, omni mikes really do pick up all sound uniformly.”Area of concentration” is not a term normally used when describing microphone polar patterns. It is usual to say that a microphone is more sensitive to sound in a particular direction (or directions) from its axis, and less sensitive in other directions. Further, most microphones still pick up sound from the less sensitive parts of their polar patterns, but with reduced level–for example, a typical cardioid will pick up sound from the rear axis (the null point of the pattern) about 15 to 20 dB down from the front axis level. Finally, in real rooms, sound rejected by the null axis of a microphone can still bounce off a wall or other boundary and enter the primary (most sensitive) axis. Therefore, in real rooms, even the most directional microphones achieve only partial rejection of off-axis sound.PZM stands for “pressure zone microphone”. This particular type of microphone uses an omnidirectional element facing a mounting plate from a very short distance (a small fraction of an inch). The PZM is typically placed on a boundary (a floor, a wall, taped to the lid of a grand piano). This places the microphone element within the pressure zone acoustically present at the boundary. A reflection is sound that occurs at a point in time after the arrival of direct sound. As direct sound and the boundary reflection arrive at the same time for a PZM mike, the boundary reflections are eliminated, which can result in clearer sound in many situations.
A shotgun mike uses an interference tube (a long tube with slots along its length and a front opening) in front of a hyper-cardioid element. At high and mid frequencies, the interference tube rejects sound from all but a narrow angle in front of the microphone. At lower frequencies (how low depends on the length of the interference tube–longer equals lower) the interference tube is no longer effective, and the shotgun mike becomes a hyper-cardioid. Interference tubes do a good job of rejecting direct sound waves but have no effect on reverberant sound (sound approaching from random directions). Therefore, shotgun mikes are quite effective outdoors but do not work well indoors, especially in very reverberant rooms.
OK guys… you’ve got to step up to the plate and put actual sound recordings behind this info. Same place, different sounds. To much reading and not enough audio/visual…. Please..would be great! Thanks!
Totally agree with Robert
this article doesn’t match what I know to be common knowledge practiced by Live and Recording Engineers I’ve work with or just what I’ve picked up in playing music for 25 years.