Audio Engineering Assoc KU4
Unidirectional Ribbon Mic, Supercardioid


The KU4 celebrates the legendary RCA unidirectional KU3A, a highsensitivity microphone designed for the Hollywood movie studios.
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Audio Engineering Assoc KU4
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The KU4 celebrates the legendary RCA unidirectional KU3A, a highsensitivity microphone designed for the Hollywood movie studios. Also known as a M-10001 for its manufacturing number, it was RCA’s most expensive ribbon microphone. Fewer than 600 were ever manufactured. What made the KU3A special? It combined the smooth ribbon sound of a 44 with a unidirectional pattern, a wide sweet spot and less proximitybass boost. It expanded an engineer’s range of placement choices and became a standard at film studios around the world. Although condenser mics became the new standard by the end of the 1960s, ribbon mics are still appreciated today by experienced music recording engineers. However the KU3A is a rare microphone, a collector’s item, and few studios or rental houses own them. Opportunities to work with a good KU3A are limited.

The KU4’s supressed rear lobe is useful when the back of a figure-of-eight would pick up undesirable sounds. TheKU4’s reduced proximity bass boost facilitates closer micing and its low-tuned ribbon delivers solid, undistorted bass. These characteristics make the KU4 well suited for modern studio production. Its lightly-tensioned, ultra low mass ribbon has a frequency response out to 40 kHz and fast, accurate transients. There is no upper midrange ringing common to large condenser mics. The KU4’s ribbon is well protected and its field-tech replaceable pole piece and ribbon assembly is a real convenience if an accident occurs. The KU4 is your ticket to discovering why the KU3A has been part of high-end studio life for over 60 years. AEA is honored to play a part in its history, and invites you to listen to the KU4 and claim your part of this legacy.   


  • Supercardioid pattern for excellent rear rejection
  • Reduced proximity effect
  • Smooth, high-bandwidth frequency response
  • Authentic New Old Stock RCA ribbon material
  • High-quality anodized & nickel-plated finish
  • Custom AEA transformer, neodymium magnets
  • Consistent Quality
  • Field-tech replaceable ribbon assembly
  • Hand-crafted in Pasadena, California


Operating Principle: Velocity microphone

Frequency Response: Below 30 Hz to above 20 kHz

Maximum SPL: 140 + dB SPL above 200Hz for 1% third harmonic

Output Sensitivity: 2.8 mV/Pa into unloaded circuit

Output Impedance: 300 O nominal

Recommended Load: 1.2 KO or greater

Phantom power: Not required or recommended

Polarity: Pin 2 high for positive pressure at the front of the microphone.

Connector: XLR-3M wired to a 1.5 meter captive cable

Off Axis Response:

Polar Pattern: Supercardioid

Relative Output at 180° (dB): -12

Angle of Maximum Rejection: 135°

Transducer element

Ribbon Thickness: 1.8 microns ( .0000018 meter ) of pure aluminum

Ribbon Width: 0.082” (2.1 mm)

Ribbon Length: 1.25” (28.6 mm)


Included: Custom storage/shipping case, stand adapter, manual and

attached 1.5 meter microphone cable

Limited Warranty:

Three years parts and labor, shipping not included.


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