AEA KU4 is a passive supercardioid ribbon microphone — the only ribbon microphone with a supercardioid polar pattern in current serial production. It is based on the RCA KU3A (catalog number M-10001), a unidirectional ribbon microphone from the 1950s designed for overhead boom use in Hollywood motion picture studios, of which fewer than 600 units were ever built. The KU4 achieves its supercardioid pattern through a precision-milled aluminum acoustic labyrinth that delays rear-arriving sound to produce phase cancellation of the rear lobe — no English cow hair as in the original RCA. The 1.8-micron ribbon at 28,6 mm × 2.1 mm from NOS RCA material is substantially shorter and narrower than the Big Ribbon used across the R44 series — closer in size to the RCA 77 family, but with a fixed pattern and a more natural-sounding unidirectional response.
Supercardioid Ribbon — Upper-Mid Presence, No Resonances, No Bleed
The shorter ribbon element produces a pronounced upper-midrange accent — the KU4 is the brightest microphone in the AEA lineup. That midrange presence makes vocals, strings, and woodwinds read clearly in a mix without EQ, delivering ribbon smoothness without condenser harshness. Reduced proximity effect compared to the Big Ribbon designs allows close miking at 1–18 inches without the low-frequency buildup that makes most ribbon microphones unpredictable at this range. The suppressed rear lobe eliminates lateral bleed from adjacent instruments and early reflections off low ceilings, making the KU4 the practical ribbon choice for live tracking sessions and acoustically untreated spaces. Frequency response extends above 40 kHz with no upper-midrange resonances that are typical of large-diaphragm condenser capsules. The pole piece and ribbon assembly are field-tech replaceable without sending the unit to a service center.
Passive Circuit and Preamp Requirements
The KU4 requires no phantom power — 48 V is not recommended. Sensitivity of 2.8 mV/Pa (–51 dBV) and 300 Ω nominal output impedance require a preamp with at least 60 dB of gain and input impedance above 1.2 kΩ — the same requirements as the passive R84 and R44 series. The grille basket and yoke are interchangeable with an original RCA KU3A. The microphone ships with a 1.5-meter captive cable, a custom storage/shipping case, and a stand adapter; the cushion mount yoke is derived from the R44 series design.
KEY FEATURES
- The only passive supercardioid ribbon microphone in serial production
- Polar pattern: supercardioid — precision-milled aluminum acoustic labyrinth suppresses rear lobe
- Based on RCA KU3A — fewer than 600 original units ever built
- 1.8-micron aluminum ribbon — 28.6 mm × 2.1 mm (NOS RCA material)
- Shorter ribbon: more upper-mid presence and brighter tonal character than Big Ribbon designs
- Reduced proximity effect — close miking at 1–18 inches without low-end excess
- Response to above 40 kHz, no upper-midrange resonances
- Max SPL: 140+ dB (1% THD harmonic distortion >200 Hz)
- Sensitivity: 2.8 mV/Pa (–51 dBV) into unloaded circuit
- Output impedance: 300 Ω nominal
- Recommended load impedance: ≥1.2 kΩ
- Phantom power: not required or recommended
- Field-tech replaceable pole piece and ribbon assembly
- Grille basket and yoke interchangeable with original RCA KU3A
- 1.5 m captive cable, XLR-3M; storage case and stand adapter included
- Dimensions: 324 mm (H) × 117 mm (W) × 95 mm (D); weight: 2.15 kg with cable
- Handmade in Pasadena, California, USA
TECHNICAL SPECIFICATIONS
- Operating principle: pressure gradient transducer (passive)
- Polar pattern: supercardioid
- Frequency range: <30 Hz – >20 kHz (extended to >40 kHz)
- Max SPL: 140+ dB (1% THD >200 Hz)
- Sensitivity: 2.8 mV/Pa (–51 dBV) into unloaded circuit
- Output impedance: 300 Ω nominal
- Recommended load impedance: ≥1.2 kΩ
- Phantom power: not required or recommended
- Polarity: Pin 2 + for positive pressure at front
- Ribbon thickness: 1.8 µm; width: 2.1 mm; length: 28.6 mm
- Ribbon material: corrugated aluminum (NOS RCA material)
- Connector: XLR-3M on 1.5 m captive cable
- Dimensions: 324 mm (H) × 117 mm (W) × 95 mm (D)
- Weight: 2.15 kg (with cable)
- Made in: USA (Pasadena, CA)
