M 250b

Common name: Neumann M 250b

Production Status: Discontinued / Vintage

The Neumann M 250b is a special version of the M 50b microphone with a RF-shielded 7-pin Tuchel connector produced between 1961 and 1964 when it was replaced by the M 250 c. Although connectors are different there is no difference in powering. In 1951 Georg Neumann GmbH launched a special microphone derived from the M 49 that was developed in partnership with NWDR – Nordwestdeutscher Rundfunk (Northwest German Broadcasting) with the headquarters located in Hamburg. The M 50 has the same body of the M 49, the same amplifier following M 49 subsequent upgrades (b and c versions). The first version was recognizable by the absence of the Neumann logo replaced by a red “jewel”for the M 49 and white one for the M 50. The M 50 is a pressure microphone (omnidirectional) featuring a 21 mm small diaphragm capsule installed on a spherical body whose diaphragm is aligned with the surface of the plexiglass sphere. For physical reasons the flush mounted diaphragm exhibits particular behavior, depending on the diffraction sphere diameter. The transducer has a very smooth response up to the frequency in which the wave length becomes comparable with the sphere diameter, then, for higher frequencies with smaller wave lengths, the frequency response is boosted. In the M 50 this limit is around 1 kHz, thereafter the frequency response rises gradually with an overall +6 dB boost in the 8000 to 16000 Hz range. The polar response is at the same  omnidirectional for lower frequencies and directional for higher ones. The transducer practically works like a pressure one for low-end and like pressure gradient for higher frequencies. These features make the microphone the perfect choice for high distance environmental orchestra recordings, as high frequencies are more prone to long distance attenuation than low frequencies. Upon first release in 1951 the K 50 capsule employed a PVC gold sputtered diaphragms, then aluminum diaphragms with the K 53 in 1954,  Nickel diaphragms with the K 53 in 1958 and finally gold-sputtered polyester foil (MCF) diaphragms with the K 63 / K 83 in 1965. To achieve high sensitivity and low equivalent noise level, the distance between the moving diaphragm and the back electrode is narrow (10 µm) and the diaphragm is highly tensioned. Decca records Ltd. used these microphones extensively for classical “FFSS” (Full Frequencies Stereophonic Sound” productions in their “Decca tree” arrangements (three microphones) as “out-riggers” microphones (side microphones). RCA Victor Living Stereo (LSC series) often used M 50s with A-B center-fill techniques. The M 50 was also popular as spot (close distance) microphones for woodwinds and strings. The “white Jewel” M 50 initially used a MSC 2 metal tube made by Hiller, although most of them were later upgraded to Telefunken AC 701 k “b” or “c” circuits either by the Neumann factory or by recording studios maintenance laboratories. M 50s are quite rare and high value microphones. In recent times Neumann manufactured the TLM 50, M 150 and KK 133, all working with the same transducer principles.

Electrical Characteristics

Frequency Response
35Hz - 15 kHz
Output Sensitivity
1 mV/Pa
Self Noise (CCIR)
Self Noise (DIN/IEC)
Output Impedance
50 or 200Ω
Recommended Load
Proprietary unit
Supply Current
Alternative Powering
Tube Model
Telefunken AC 701

Switchable Options


Physical Characteristics

Tuchel 7 pin
Connector notes
Available Colours
Satin nickel
800 g
163 mm
Min diameter width
Max diameter
80 mm