[rickcr42]

From the Rane Library :

Quote:

infrasonic filter (aka rumble filter) A high-pass filter used with phonograph turntables to reduce the effects of low frequency noise and vibration, called rumble, caused by imperfections in turntable performance and warped records. Often mistakenly called subsonic filter. Since typical rumble frequencies occur in the 3-10 Hz area, most infrasonic filters have a corner frequency of around 15 Hz, with a steep slope, or rolloff rate, of 18 dB/octave, and a Butterworth response.

Not the full story but close.They left out the part about turntable "tuning" where every single turnatable ever made to my knowledge has a self resonance point where it will peak and then fall off rapidly to each side of the peak and why we have what is called a turntable "set up" which is the balance between the tonearm/turntable/cartridge that allows the best combination of bass and tracking (so the damn cartridge does not jump right out of the groove !!!).
even a totally flat "non warped" disc will have a resonance and why the vinyl playback is called a "system" and not a "source"

**edit***


looks like benz chose a low pole and a shallow slope

http://www.dreamaudio.kiev.ua/benzmicro.htm

 

[Garbz]

hmmm ok i have a DC blocking cap in my design. It's on the output. 1uf. The input stage following has a 330k input impednace. So currently the filter has an Fc of 0.5hz

.

Other then noticable flutter in speakers I don't think this is doing any damage, however I assume that when I finally get around to building a subwoofer this could get quite anoying.

Btw since I'm here is there any easy mathematical way to calculate a 2 pole filter? When adding a second RC combination the Fc changes so I'm wondering what the mathematical relationship between 1RC and 2RC filters is.

Anyway putting 12k to ground after the 1uf cap, and a 56nf in series after it along with the 330k input stage gives a plesant 20db down at 1hz (from reference 1khz so 40db down from 20hz) at 12db/octave.

/edit: Before you say it one could really make it resistant to changes in input impedance of the following stage but I sooo could not be bothered

 

[Garbz]

Hmmm ok this didn't work. It noticably cut out a lot of the bass output of the source. I tried several combinations of caps and resistors and I simply can't get anything like I simulated. So in the end I decided a single RC combo with the 1uf cap and a 22k resistor. Corner frequency is about 8hz once paralleled with the input stage of the receiver.

simulations show 4db down from 1khz @1hz, and 22db down from 20hz. Rolloff is 6db/octave.