The recording apparatus consists of a tuned bass-reflex port -- stopped similar to a organ diapason for tuning puposes, and to ensure a deficiency of upper partials. Attached to this port is a suction cup of a modified telephone pickup coil. A newer tuned-port bass reflex enclosure is being tested, but lately there has been no occurence of the HUM. A 10ft. cable was run from the trancducer to the recording machine which is a simple portable DC powered deck capable of running at different tape speeds. Tuning of the port was arrived at by formula and empirical experience. The pickup coil is modified with two neodymium-iron-boron magnets and a second coil attached to the rear of the unit.
The system was initially amplified in real time and different tape speeds were used to ensure the recording was picking up the HUM and not artifact from the recording apparatus. The sound on the recording is exactly as experienced.
Click HERE to hear a recording made with the above apparatus.
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