Schoeps MK-21
A capsule that sits between omni and cardioid. Engineers reach for it when nothing else will do.
Overview
The MK-21 is a subcardioid capsule in Schoeps' Colette series. Trade advertising repeatedly described that lineup as offering interchangeable capsules for a variety of applications (Studio Sound, March 1990, p.107). The MK-21 was pitched at engineers working with spaced omnis who needed something the omnis couldn't give them: low-frequency performance in omni territory, but enough directionality to solve problems the omnis created. Schoeps' own launch material, as reported in the trade press at the time, billed it as uniquely suited to pickup situations where spaced omnis fall short, with low-end comparable to an omni and off-axis behavior that keeps the rear pickup in check.
The number to remember is the rear attenuation. The MK-21 attenuates sound arriving from behind by about 10 dB. That is not a cardioid's deep rear null and not an omni's complete indifference. The pattern sits roughly halfway between omni and cardioid. It mates with the CMC amplifier bodies, and it joined the Colette range as one of a family of interchangeable capsules - fifteen at the time of its introduction, a count that grew to sixteen as the line expanded.
In practice the MK-21 blends. A subcardioid's off-axis response is smoother than a cardioid's, and because it still picks up a healthy amount of room, it sits in a mix of omni and directional mics without fighting either. Engineers who work with it describe using it as a spot mic that doesn't sound like a spot mic, or as a section mic that keeps some of the hall in the picture.
One orchestral engineer, describing a Philharmonic session, put the MK-21 on string sections - first violins, second violins, cellos - one mic per section. The same engineer also used it as a solo spot because, in that engineer's words, it works on everything: violin, voices, all of it. The reasoning given was that the subcardioid pattern blends with the omni main pair rather than sticking out of it. The engineer also noted a working method of moving from less directional mics at the front of the orchestra to more directional ones upstage, and the MK-21 fits that graduated approach.
It shows up in less rarefied work too. A 1996 orchestral and jazz session had horns, woodwinds, and brass largely covered by U87s and Schoeps with MK-21 capsules. A 1994 piano session used a pair of MK-21s in XY, placed as high as possible over the hammers, for direct sound. A 2000 multi-piano broadcast project standardized on Schoeps across eighteen pianos, with most instruments miked by a CCM 4 in the crotch of the piano and an MK-21 on a Colette system at the tail piece, pointed back toward the keys. The engineer described that second position as giving a warmer, easier sound. A 2012 television production listed the MK-21 among its interior boom mics alongside Sennheiser MKH 60 and MKH 50.
Anyone reading old session notes should know about one wrinkle. One account of the 2000 piano project describes the MK-21 as being fitted with a cardioid capsule. That is either a transcription error or a writer's confusion, because the MK-21 is itself the capsule. The Colette system is modular: the capsule is the MK-21, the body is a CMC amplifier, and the two are not interchangeable in the way that sentence implies. Treat that description with caution.
For collectors, the MK-21 is a capsule rather than a complete microphone, which changes the math. Buying one means either already owning a CMC body or budgeting for one, and the capsule alone is a small, precision-machined object that lives or dies by its diaphragm. The Colette series' interchangeability helps here, since a single body can host a range of patterns, and the MK-21 is the one many owners keep mounted because it covers so much ground. It is not a collector's trophy the way a rare tube mic is. It is a working tool, and the market treats it accordingly.
It is not a cardioid with the rear rejection turned down, and it is not an omni with a baffle. The 10 dB rear attenuation is a specific design choice, and engineers who expect cardioid-like isolation will be disappointed. The MK-21 is meant to be part of a blend, not the whole picture.
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