Groove Tubes: Understanding Microphone Polar Patterns

The term polar pattern is used to describe the response of a microphone to sound sources from various directions. Each type of polar pattern has its own place and usage in the recording process. Note that the classic polar pattern definitions apply most accurately when sounds hit the microphone on axis—that is to say, approaching perpendicular to the planar surface of the diaphragm. In general, microphones tend to become more directional in focus as frequencies increase. In other words, capsules are generally less sensitive to high frequencies off axis. This phenomenon is typically less significant in medium capsules than in large capsules.

Cardioid Pattern

The cardioid is the most common polar pattern found in microphones. The name derives from this pattern’s resemblance to a heart shape. Cardioids are unidirectional, meaning that they pick up sound primarily from the front of the capsule. The back of the capsule rejects sound, allowing the engineer to isolate the signal source from other performance elements or background noise. More noticeable in larger capsule designs, cardioid patterns typically exhibit a proximity effect—a boost in low-mid frequencies as the proximity between the source and mic increases. Proximity effect is also more prominent with both larger capsules and lower frequencies.

Omni Pattern

As the name implies, the omnidirectional or omni pattern picks up sounds equally well from all directions. Omni is used to capture room ambience and reflections along with the source, thereby yielding a more open sound compared to the more focused quality of cardioid. Omni is great for vocal groups, Foley sound effects, and realistic acoustic instruments—assuming that the acoustic space of the recording environment is desirable.

Omni also exhibits significantly less proximity effect than cardioids. One result is that omnis are somewhat less sensitive to the movements of an animated vocalist. Another is that omnis tend to have less need for EQ. As mentioned earlier, however, while omnis pick up 360 degrees of sound, they tend to be more directional as frequencies increase—especially in larger capsules.

Figure 8 or Bidirectional Pattern

The figure 8 or bidirectional pattern is equally sensitive on the two opposing faces of the microphone, yet rejects sound from the sides. This pattern does exhibit the proximity effect found in cardioid patterns.

The figure 8 is excellent for capturing a duet or face-to-face interviews with a single mic. The -40dB side rejection spec also makes it great for isolating an instrument like a snare from the rest of the drum kit. Figure 8 is also one of the key components to M/S (mid-side) miking—an advanced stereo recording technique we’ll look at in a subsequent installment.


Super-Cardioid Pattern

The super-cardioid pattern exhibits an even narrower area of sensitivity than the classic cardioid and is used for very sonically focused recording. Super-cardioid is great for zeroing in on that perfect sweet spot for instruments such as piano or drum. This pattern is also ideal for live recording sessions where isolation is important, including minimizing bleed between a vocalist and their own instrument.


Single Pattern vs. Multi-Pattern Mics

The most inexpensive way to make a microphone is with a single fixed pattern. Cardioids have openings in the backs of the capsules that produce the physics of a unidirectional pattern. This is inherently a fixed pattern design. An omnidirectional pickup pattern can be achieved by sealing the back of the capsule, resulting in another fixed pattern. Supercardioid employs yet a different design. In most cases, different back-end electronics are required for each pattern, thus making it difficult to make interchangeable capsules. Groove Tubes mid-sized mics—the GT33 and GT44—are designed in a unique way to allow interchangeable capsules. These mics ship with cardioid capsules, while omni and super-cardioid capsules are available as an option. Needless to say, this design approach is much less expensive than purchasing separate mics.

The secret to building a single mic with multiple pickup patterns is placing two cardioids back-to-back in combination with various electronic tricks. An omni-directional pattern can result by wiring two back-to-back cardioids in phase with each other. Similarly, those same two opposing cardioids wired out of phase yield a figure 8 or bi-directional pattern. Tweaks to the polarity and output level result in a super-cardioid. While the presence of two high-quality diaphragm/backplate assemblies increases the cost, this solution provides the best polar pattern performance and is still significantly less expensive than buying multiple microphones in order to have a choice of patterns at your disposal.


This approach to capsule design can be seen in large diaphragm mics from Groove Tubes. The Model 1B, Model 1B FET, GT55 and GT66 are fixed cardioids, each utilizing a single diaphragm/backplate assembly. The GT57 and GT67 employ an opposing pair of those same diaphragm/backplate assemblies, thus allowing for the selection of multiple patterns via switches on the body of the mics.

Tip: Note that the out-of-phase wiring of the two sides of a figure 8 capsule can deceive the uninitiated. One side will sound strange to a vocalist or speaker who is simultaneously monitoring the mic signal through headphones. That’s because one side of the mic is in phase with the performer (and therefore reinforcing their perception of their own sound) while the other side is not. Addressing the in-phase side while monitoring produces optimal monitoring results.

Top Address vs. Side Address

The orientation of the diaphragm within the head of the microphone determines if the microphone is addressed from the top or the side. While not an absolute rule, medium diaphragms are typically top-address while large diaphragms are usually side-address. As you might surmise from the previous discussion about design considerations in attaining various polar patterns, top-address mics typically have single pattern (at least without physically changing the capsule) while side-address mics lend themselves to the possibility of back-to-back capsules for switchable patterns. Note that on side-address mics, the side with the logo is the primary or cardioid side.

Polar patterns aside, the practicality of side-address versus top-address has to do with logistics as well. Top-address microphones can usually fit into tighter spots, such as between drums, than can side-address mics. As with many microphone features, this reflects yet another reason why pro engineers have various mics in their mic lockers.