In these days of integration of audio and video, we responded to the need of small, relatively invisible, yet ultra high quality microphones. Next to the CCM-65, compact omni-directional microphone, Sonodore also introduced this 'boundary layer' microphone, which also makes use of the same renowned capsule of the RCM-402. This microphone is suited for placement on the floor or on the wall. Due to the boundary layer principle, the noise level is even 6dB lower than the RCM-402, and the microphone has a very distinctive and unique polar pattern. We found this pattern, which can most easily be described as a large circle laying on the ground around the microphone, in the shape of a thick 'sausage', to be very suitable for surround 'back' channels. The frequency response rolls gradually of from 14kHz, also due to the principle of a microphone membrane close to a large surface, and the polar pattern of two BLM channels gives a rather unique, diffuse 'stereo' image, which proves to be ideal for acoustic surround channels. Also for placement on stages at live performances the BLM-21 will be very useful.

The result of recording voices and back-ground noises in radio plays is stunningly transparent and natural. The fact that all sounds from all directions are picked up, and accumulated at one point on the floor or the wall, and thus no first early delayed reflection from floor or wall are to apparent like placing the membrane in the air, creates a high suggestion of actual presence of the sound source.

We believe to have created the best boundary layer microphone to date by using the un-compromised high quality pressure capsule from the RCM-402 and we also found that the capabilities of the principle are highly underestimated...

Capsule type:  prepolarised condenser microphone capsule

Principle of operation: pressure

Directional pattern: hemisperical

Frequency response: 5 Hz(-3dB) to 20kHz (-7dB), (14kHz 0dB)

Sensitivity at 1 kHz:  75mV/Pa

Equivalent noise level: A-weighted typically 13 dB

Maximum sound pressure level: 136 dB SPL peak

Amplifier THD at 124dB SPL:  0,0004% at 1kHz, 0,0013% at 10kHz

Temperature coefficient:  +0.005 dB/ºC

Output impedance: 39 Ohms

Cable drive capability: > 100m

Powering: via separate power supply PS-402

Weight: 650g

Dimensions:  18cm x 21cm x 7,2cm (7.1" x 8.3" x 2.8")

Capsule diameter: 12.8mm (0.5”)

Connection: fixed cable (diameter 3mm) with 4-pin XLR male

As an option, capsules with different frequency responses can be supplied for use in various recording situations.