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Recording Kite Line Scream

Posted by Tom Benedict on 28/09/2015

Anyone who’s flown a kite and held the line to their ear knows the sound of wind screaming over a kite line. The big plastic hoop winders many kiters use for larger kites are perfect for this. Just barely touch the line to the side of the winder, and the whole thing acts like a loudspeaker. But how to go about recording it?

A couple of weeks ago I built a contact microphone using tips from Zach Poff’s page. The mic consists of a piezo disk, a 6′ length of Mogami microphone cable, an Alex Rice piezo preamp, and an XLR connector. I salvaged the connector from a cable in the to-go pile at work. (Neutrik connectors are still on order.) The cable is the same stuff I’ve been using for my EM172 mics. I ordered the preamp boards from OSH Park, and the components (the list of which can be found on Zach Poff’s page) from Mouser. I got some piezo disks from Mouser as well, but I wound up using one I’d salvaged from a piezo buzzer ages ago.

The only trick when building one of these is that shielding is important. No, let me put that another way: Shielding is IMPORTANT! The first time I tested it, I picked up horrendous 60Hz buzz. I fixed it by insulating the preamp and the piezo disk, then covering each one with copper tape, which I connected to the shield in the cable. Once it was shielded from the XLR to the piezo disk the buzzing went away.

I’d describe all the rigorous tests I performed on it, but mostly I just played. I recorded sound from the supply and return lines on a CTI cryocooler, the sound of a PCC cooler (which is totally different), and the sound of pasta sauce simmering by attaching the contact mic to the end of a spatula and sinking the other end in the sauce. It worked great!

So today I took it out with me while I was doing KAP (and KAV and KAS).

Not much to the setup: Tascam DR-70D, headphones, contact mic, and blue sticky stuff. And a kite and line, of course. (And my hat to cushion everything, ’cause those rocks are like razors!)

Contact Mic Recording

I tried attaching the mic to the line two ways. The first was to stick it on the line itself using Blu Tak (the sticky stuff you get for sticking posters to walls.) This worked great, but braided Dacron likes to stick to the sticky stuff a little too well. When I removed the mic, I was left with gooey bits I had to pick off the line.

Contact Mic on Line

So for my second attempt I stuck it to the carabiner on my ground anchor strap. This worked as well. The mass of the carabiner helped damp some of the higher frequency sounds, leaving more of the bass notes. Unfortunately it also picked up the twisting/creaking/grinding sound of the ground strap.

Contact Mic on Carabiner

I think suspending a carabiner midway along the line would provide the best of both worlds: more bass notes, but better isolation from the ground strap. Unfortunately I didn’t try this. I also didn’t try just sticking the contact mic directly to the winder! Things to do next time.

Still not happy with how Soundcloud embeds in WordPress documents, but in case you’ve never heard kite line scream, here ya go!

Attached to the kite line:

Attached to the carabiner:

Both are mono recordings. (Hey, now I need to do this on a two-line sport kite so I can record in stereo!

On a whim I took a look at the spectrogram of the recording with the mic stuck directly to the kite line.

Line Scream Spectrum

Talk about harmonics! The primary is somewhere between 500Hz and 1kHz depending on the line tension, and the 2x, 3x, and 4x harmonics show up quite strongly.

Fun stuff…

(Told you I wasn’t testing this with any kind of rigor!)

– Tom

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