Stereo Shotgun Microphone

RSM 191

A stereo shotgun microphone for broadcast, film, and on-location applications. Like its predecessor the RSM 191 A operates in mid/side technique; the corresponding new MTX 191 A matrix box offered significantly enhanced features.

  • Variable stereo shotgun microphone with shotgun and figure-8 patterns
  • Interference/pressure-gradient transducer
  • MS-stereo microphone, switchable to XY-stereophony
RSM 191
RSM 191

The Stereo Shotgun Microphone RSM 191 A Set

The RSM 191 is a stereo microphone system consisting of the microphone and the MTX 191 A matrix amplifier. It has an adjustable pick-up angle and high directivity.

The microphone has two separate capsule systems, a hypercardioid element and a figure-8, both in a short shotgun. Together they generate the mid and the side signals. The matrix amplifier controls the width of the stereo image by changing the gain of the side signal relative to the middle signal in six 3 dB steps.

The output signals of the matrix amplifier are either mid-side (MS) or left/right (XY). The signals are converted through transformerless sum-and-difference circuitry. The balanced, transformerless technology permits the use of long cables between the microphone, the matrix amplifier and the following mic input of other signal processing equipment.


The RSM 191 system is an ideal microphone system for:

  • Outdoor stereophonic news coverage, even in extremely noisy surroundings;
  • Stereo recordings for film and television where the actors are recorded simultaneously with acoustic ambiance, or an orchestra;
  • Stereophonic motion picture sound where the width of the sound image must match the camera viewing angle.


The RSM 191 consists of a capsule head containing two separate transducer systems and an amplifier section with two independent transformerless microphone amplifiers. An interference tube system with a hypercardioid characteristic generates the middle signal, while a horizontal figure-8 assembly provides the side signal.

Acoustic features

The RSM 191 achieves its high directivity and special acoustic features through a unique construction. The microphone capsule assembly is mounted inside a housing tube that is acoustically open but has a high flow resistance. This results in a high driving force for the diaphragm, even with a low pressure gradient factor of the capsule. Therefore, the microphone can suppress unwanted off-axis interference to a considerably higher degree than other microphones without such an interference tube. The middle system (M-signal) combines high attenuation of lateral sound incidence, similar to a hypercardioid characteristic (which is about 10 dB), with the large front-to back ratio of the super-cardioid characteristic. Therefore, sound from the rear is likewise attenuated by approximately 10 dB. This design approach makes the microphone less sensitive to wind or pop noise than other shotgun microphones. The side system (S-signal) consists of two single capsules arranged back to back, closely behind the interference tube (M-signal) capsule. Arrows engraved on the microphone housing show their orientation. The uniform and balanced performance characteristic of the microphone system is achieved without resorting to corrective resonance effects. Therefore, the microphone maintains an excellent impulse response, reproducing all transient phenomena in music and speech without coloration. The entire internal construction is decoupled from the housing to avoid structure borne and handling noise.

Electrical features

The output signals of the included matrix amplifier are in either MS or XY format. The small capsules are mounted in close proximity to ensure transparent and coloration-free stereo sound with excellent mono-compatibility. The stereo acceptance angle is variable and controlled remotely.

Filter and attenuation

For the handling of very high sound pressure levels, a 10 dB attenuation can be switched ON to avoid overloading of the following equipment. To suppress structure borne noise, a high-pass filter in the matrix box provides cutoff frequencies of 40 Hz, 80 Hz, and 200 Hz.

Battery supply

The RSM 191 system is fed from either 2 x P 48 phantom power or from a 9 V battery inside the matrix box. One alkaline battery provides 8 hours of operation.

Delivery range

The complete miocrophone system comes in a robust aluminum carrying case.   Along with the microphone and the matrix amplifier the case contains a windscreen, the special interconnecting cable and an adapter cable that splits the 5-pin XLR output of the matrix amplifier into two 3-pin XLR connectors for channels I and II to connect with the following equipment.

Diameter 30 mm
Length 212 mm
Weight 170 g
Current consumption (P48, IEC 61938) 2 x 1.9 mA
Directional Pattern M: Lobe-shaped, S: Figure-8
Frequency Range 20 Hz ... 20 kHz
Matching connector 2 x XLR 3 F
Rated Impedance 50 Ohms
Supply voltage (P48, IEC 61938) 2 x 48 V ± 4 V
Acoustical operating principle M: Pressure gradient/interference transducer, S: Pressure gradient transducer
Maximum output voltage 2540 mV
Rated load impedance 1000 Ohms
Equivalent noise level, CCIR 25/31 dB
Maximum SPL for THD 0.5% 134 dB
Equivalent noise level, A-weighted 16/22 dB-A
Sensitivity at 1 kHz into 1 kohm 23 mV/Pa
Maximum SPL for THD 0.5% with preattenuation 144 dB
Signal-to-noise ratio, CCIR (re. 94 dB SPL) 69/63 dB
Signal-to-noise ratio, A-weighted (re. 94 dB SPL) 78/72 dB
Signal-to-noise ratio, CCIR (re. 94 dB SPL) 69/63 dB

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