Reducing very low frequency rubble with Pleiades filters

Best to cut it at source.


For example isolating to the structure of low frequency vibrating equipment, motors, air conditioning etc or stopping them.


If it is not possible and the isolated microphone is pickup up all this coupled vibration to air waves, a Pleiades filter may be very useful.


It consists of just a coil inductor connected in parallel with the output of the microphone. That is at pins 2 and 3. It is a gentle 6dB per octave filter.


Any cutof frequency and be made by adjusting the number of wound turns on a tape wound core such as the Nanocrystalinne Nanoperm cores by Magnetec.


The lower the turnover cutoff frequency, say 20Hz, the more turns are needed.


For male voice 100Hz may be excellent if an omnidirectional mic is used. Or 200Hz or more may be even better as this compensates for the Fletcher Munson and voice effort curves that increase bass
perception to our brain.


If directional microphones are used then a Pleiadss filter of even more than 500Hz may be needed for
flat frequency response from vocal chords of singer-actor to listener's brain as the proximity effect needs to compensated too. The right cutoff frequency will depend on the distance of the mic to the source.


So far the Beyer M55 and the Philips N8 207 are two mics tested not to need any of the above. They can make a soft singing voice sound as natural as possible even at loud reproducing intensity.


Of course how voices sound in the room itself is very important. Panel bass absorbers are very useful as they convert bass reverberating sound to heat. An example are the panels by Bill Putnam on the studio later named Ocean Way. Such panels can be seen on the back CD cover of Pet Sounds - The Beach Boys. Or on a photo of the Mamas and Papas singing. Were they singing California Dreaming?


Pleiades schematics and concepts are open source.


Reference:
Acoustics of Radio and Television Studios - Gilford - BBC