Any cheap ways to record infra-sonics?

[finrot]

Does anyone know of a cheap way of recording infra-sonics?

By which I mean frequencies between 0 hz and 20 hz. I'm currently attempting to bodge some piezzo mikes, then into a pre amp and then into the sound input of a Mac. However rumour has it that I need a specialised sound card and pre-amp for these frequencies.

Contact with anyone whos messed around with this sort of stuff is appreciated as I'm blundering around in the dark at the moment.

Cheers.

 

[The Axis]

Many mikes, soundcards, and preamps would continue to work below 20 Hz, but they aren't calibrated there because of the lack of interest. A lot depends upon the accuracy that you can tolerate and how low you really need to go in frequency. You could test your existing (or prospective) equipment with a signal generator and osciloscope, but if you want calibrated laboratory grade instruments, you will end up spending a LOT of money. Even then, you will first have to answer the questions: how low and how accurate.

I know this isn't very helpful, sorry.
Good luck,
Rick