Making my soundfx archive...

[Noiz2]

...
For example, I once attached one to the side of my old microwave when I baked a potato, and the resulting freaky shimmering harmonics have been my go-to effect for a few sci-fi projects. Need a creepy screaching effect? Tape a pickup to one side of a cookie sheet and drag a brass-bristled brush across the other side....

The Hollywood Edge "Sounds of a Different Realm" set has a bunch of contact mic recordings done by Ann Kroeber. She and her husband Alan Splet did the sound for all of David Lynch's films (until Alan's death) and most of Carroll Ballard's films. The third disk in the set is all "FRAP" recordings. She uses a contact mic that was developed to have a very flat response (for recording violins etc). I think it stands for Flat Response Acoustic Pickup. Anyway the recordings have the FRAP on one channel and a Schoeps on the other so you get the contact and air recordings of the same event. Very cool stuff.

 

[sputnikslim]

Thanks Smuir!

 

[Brad S.]

You guys rock! Thanks for the tips and the link.

 

[SMuir]

My poss issue with the design is that you have a awfully stiff capsule and I would think this would have a serious impact on what it picks up.

Quite possibly, but that particular design is useably at some pretty serious depths. They seem pretty popular among cetacean researchers, and the Loughborough University of technology has provided some more detailed instructions: http://sonar-fs.lboro.ac.uk/uag/downloads/bender2.pdf

I did a bit of searching, and found this alternate design: http://users.tpg.com.au/users/adsl9dhg/hydro_dunking.htm

The author houses the bender element in a plastic 35mm film canister, adds a preamplifier, and fills it with vegetable oil. I imagine one could easily enough swap out the first-stage preamplifier with a ballanced P48 circuit.

Alternately, you could just pour "Goop" or epoxy resin all over the bender and seal it to the cable. I knew a guy who tried that, but complained that fish kept nibbling on it.

 

[Noiz2]

Great links. Sort of interesting, the thinking seems to be with the film can that your picking up on the sides of the canister rather than the bottom. Though again it probably doesn't make much difference because of the nature of water VS air. The 3 foot separation to discern stereo explains why I've never managed to get any useful stereo recordings :~)

Thanks for the links

 

[SMuir]

The 3 foot separation to discern stereo explains why I've never managed to get any useful stereo recordings

Theoretically, you could record a discerneable spaced omni stereo image if you quadrupled the distance between the hydrophones (to correct for the speed of sound through water), and rigged some sort of rigid spacer to keep the hydrophones from wanderring away from or closer to each other. Of course, I haven't tried that.

I have found that I could get some interesting stereo effects with widely spaced contact transducers, though.

 

[Noiz2]

It's the widely spaced that I haven't done. I tried using long thin strips at 180 deg but that didn't make a noticeable image. Hard surfaces are like water and vibrations travel very fast through them. Wide I think is the key. It's on my todo list for 2008.

 

[SMuir]

It's the widely spaced that I haven't done. I tried using long thin strips at 180 deg but that didn't make a noticeable image. Hard surfaces are like water and vibrations travel very fast through them. Wide I think is the key. It's on my todo list for 2008.

I crunched the numbers, and here are a few estimates regarding the distance between pickups for recording A-B stereo in various materials. I used an omni pair spaced 0.5m appart in a warm studio as a reference point:

Aumninum: 4.0m
Concrete: 3.4m
Copper (pure): 13.0m
Glass: 3.2m
Polystyrene: 1.5m
Steel: 11.5m
Wood: 0.8m
Salt Water (10m): 2.17m

I'm awfully curious to see whether this works or not, so I'll be slapping together a more-or-less matched pair of 2.5cm pickups this weekend. If I come up with anything worth hearing, I'll put it up on my website.