a stereo floor (boundary) microphone using standard electrets microphone capsules
In each 120degr corner, a 6mm omni electrets capsule is facing down, at 0,5mm distance from the floor plate.
The mass-connected ALU tape at the underside of the floor plate screens the electrets capsules against static hum.
(better should be a matt painted and grounded ALU floor plate).
The ALU box contains two line-driver-PCB's.
AND but not seen here : near the capsules,at the front and the back of the perspec planes, there must be metal mesh connected to "ground". This prevents static hum-pickup.
For principles and usage of if the L2floorarray, see
Crown publication .
This publication is not available from Crown (now AKG) anymore.
This PDF therefore now is at my server.
This circuit is perfect for most ELECTRETS capsules with one mass connection and one signal-out connection (open drain),
which first should be modified.
Initial setting of total value (R8+R11) : 7k9.
R3 value is for 48V phantom power via 2x 6k81.
For 24V phantom power via 6k81, change R3 to 560 ohms.
What is so special about this design and the floor array principle?
Special componet demands
Modification of the OMNI electret capsule
Simple method for impedance balancing adjustment.
Precise measuring method.
Properties of the L2floorarray + pa0nhc line driver :
- Excellent STEREO imaging.
Listen to "photo2". The performers were here at 1 - 1,5m distance.
- Natural, UNcolored sound
Listen "photo 3". This microphone is (here invisible) placed near the feet of the musical director.
The performers were further away here, the distance varied.
- Wide and very flat acoustical frequency response (photo 3).
- Good suppression of reflected (indirect received) sound (photo 1).
- Fully class-A circuitry.
- Thanks to a special electronics design, the modified (cheap) electrets capsules used, and the L2floorarray
construction - low microphone noise level, little distortion and fairly high max. SPL.
- Vast suppression of phantom supply noise, cable induced noises and hum.
Over the full acoustic range between 50Hz and 20 kHz, the suppression is better than 40dB (100-1000 times !).
Never a problem with hum or switch-ticks. (!! See the earthed screening ALU-tape at the underside of the array !!).
- Therefore always enjoying a high Signal-to-Noise-Ratio, even in difficult recording circumstances such as
when cables from stage lighting run near your microphone cables.
- Good HF-immunity (against broadcast and communication transmitters).
Electronics and capsule modification also apply able to uni-directional back-elektret capsules .
Please listen recordings below using a good headphone, neutral EQ, and ample volume.