Neumann KM88i Pencil Condenser Microphone #28392 (Vintage)

The Neumann KM88i is a small-diaphragm, multi-pattern FET condenser microphone--essentially the solid-state counterpart to the KM56. Both models, along with the SM2 and SM23 stereo microphones, shared a capsule design similar to the KM54's.

In the KM56 and KM88, a pair of small-diameter capsules were mounted back-to-back, separated by a gap. This design increased the time delay between low-frequency signals reaching the two diaphragms. Standard dual-diaphragm capsules typically have minimal spacing between the front and back membranes, resulting in nearly identical low-frequency phase alignment. When the rear diaphragm's polarity is reversed to achieve a figure-of-8 pattern, the low-frequency response is reduced because the signals, though inverted, effectively cancel each other out.

The diaphragms in the KM56/KM88 capsules were made of 0.7-micron nickel, far thinner than the typical 6-micron condenser diaphragm. However, their original loose tensioning made them prone to damage from high sound pressure levels (SPLs).

In 1982, Neumann adjusted the tensioning of the nickel diaphragm to enhance durability for close-miked vocal applications, such as those required in German broadcasting. This modification, however, impacted the microphone's frequency response. Specifically, the low-frequency response diminished—by 5 dB at 40 Hz in Cardioid mode and approximately 11dB at 40 Hz in figure-of-8 mode.

The microphone body featured a switch for selecting Cardioid, Omni, or Figure-of-8 polar patterns. In Cardioid mode, the rear capsule was disengaged from the circuit. Despite these adjustments, the amplifier circuit maintained consistent sensitivity and noise performance across all patterns.

Neumann's BV-107 transformer, also used in the KM83, KM84, and KM85 microphones, was incorporated into the KM88's output circuit.