Hydrophone, version 3

Another hydrophone design
A successful hydrophone design?

After a few failed attempts, I’m feeling pretty good about this hydrophone design.  Though this would probably work with a glass jar, Nalgene bottle, or similar but my plan is to use a water-tight aluminum cylinder.  It might need some weights in the bottom, but I think the thin aluminum will pick up sounds really well.

I’m especially excited about the easily replaceable cable without soldering, meaning it can even be switched in the field.

I would think best used with a DI box to isolate the hydrophone just in case of leaks, though with some recent and unrelated tests I’ve been doing on the conductivity of water, even a small leak probably wouldn’t zap anything.

Hopefully I can finish up a final prototype in the next few weeks and get them on ContactMics.com for sale very soon.

Walter Murch on blinking

In preparing excerpts for my video students, I found this lovely passage from “In the Blink of an Eye” by Walter Murch.

… It would be fascinating to take an infrared film of an audience and find out when and in what patterns people blink when they are watching a movie.  My hunch is that if an audience is really in the grip of a film, they are going to be thinking (and therefore blinking) with the rhythm of the film.

There is a wonderful effect that you can produce if you shine infrared light directly out in line with the lens of a camera.  All animal eyes (including human eyes) will bounce a portion of that light directly back into the camera, and you will see bright glowing dots where the eyes are: It is a version of the “red-eye” effect in family snapshots taken with flashbulbs.

If you took a high-contrast infrared motion picture of an audience watching a film… you would see a galaxy of these dots against a field of black.  And when someone in the audience blinked, you would see a momentary interruption in a pair of those dots. (pg. 70)

Accelerometer close-up

A very close view of an accelerometer chip

While researching the possibilities for using accelerometers for recording sound (struck out on Google, anyone know how this works?) I found this image of an extreme close-up of an accelerometer chip. The chip itself is only 5mm square.

Here’s a wider shot (click on image for much larger version):

Via: Sensor Mag


iStethoscope Pro screenshot
iStethoscope Pro screenshot

Probably unecessary to buy, since the voice recorder in the iPhone (in my experience at least) is quite good.  Instructions from the site:

For best results:
– Use good quality headphones (heart sounds are often too deep to hear using the white earphones).
– Press the microphone in the bottom of an iphone 3G to your chest. A good place is the apex of your heart (below your left nipple).
– Place the microphone directly against the skin, not through a shirt.
– Take the iphone out of its protective case if you use one.

Via: iStethoscope Pro

Sound and light

A sort of brainwave today, realizing that the difference between sound and light is that sound is energy moving through matter and light is matter (photons) moving through matter.

Our ears make sounds

The cilia of the inner ear - downloaded long ago, no source
The cilia of the inner ear - downloaded long ago, no source

According to this interesting article in New Scientist, our ears make sounds.  Called otoacoustic emissions or OAE’s, the tiny hairs in the ears (above) make very quiet sounds that are unique to an individual.

That’s because “hearing is an active process – the ear actually puts energy into the incoming sound waves to replace energy lost as sound is absorbed by the ear’s structure”, says Stephen Beeby, an engineer at the University of Southampton, UK, who is leading the research. “This process helps us hear things we otherwise would not, but as a result some of the energy added by the hair cells escapes as OAEs.”

Jacob Kirkegaard recording "Labyrithitis"

These sounds are between 0-5kHz and are thought to maybe be a kind of biometric password to be used over the phone.  A quick search found no recordings of OAE’s but did turn up the work “Labyrinthitis” by Jacob Kirkegaard.  The work is complicated, but Kirkegaard essentially recorded the frequencies his ear produced, synthesized and arranged a composition with them, and output them in a large performance/installation at the Medical Museion in Copenhagen.  The description of this work goes into more detail of how the piece was constructed and well worth the read.  An excerpt of a recording is below:

“Incomprehensible commentaries”

In his liner notes and broadcasts, [pianist Glenn] Gould created more than two dozen alter egos for satirical, humorous, or didactic purposes, permitting him to write hostile reviews or incomprehensible commentaries on his own performances. Probably the best-known are the German musicologist “Karlheinz Klopweisser”, the English conductor “Sir Nigel Twitt-Thornwaite”, and the American critic “Theodore Slutz”.

From the liner notes to Bach Partitas, Preludes and Fugues, p. 14: Sony CD SM2K-52597.

Via: Wikipedia