New Age Science: Magic Crystals and Whale Songs

It is unclear if these people

have a permit, but their lack

of clothing is very clear

Whale song - almost everyone's heard it somewhere.  It's especially prevalent on new-age CDs, usually combined with the sounds of the pan flute.  Scientists don't generally play wind instruments to whales: it's actually illegal to play sounds to whales without a permit in the United States.  Recording whale song is not illegal, as long as you don't get closer to the whale than 100 yards.  But how does the whale's song get from the whale into your iphone?

I've already talked a little about how dolphins produce sound.  The method of sound production for whales is less well understood, so let's just start with the sound once it leaves the whale's body and enters the water.

A humpback whale and
hydrophone, photo by
Flip Nicklin

Like most sound, the sounds of whale songs are a result of vibrations.  These vibrations compress and expand molecules in the the water around the whale, so the molecules are squeezed together and then spread apart.  What we think of as "sound waves" are really a measure of the amount of pressure on the molecules in the water.  This is similar to what happens when you hum: as the vocal chords in your throat move back and forth, they create changes in pressure in the air around you. Here's a little video showing how molecules are moving when you hear a sound:



The applause for "Sound and Pressure" in this video is particularly poignant.

We can't usually feel the pressure of sound waves anywhere but our ears, unless the sound is really loud, like when you stand too close to the speakers at a rock concert.

Quartz, topaz, salt, sucrose (table sugar),

bone, and even silk have piezoelectric

properties. Smashing raw quartz against
the head not recommended to activate
these properties.

Now we know that sound is made of pressure waves, but how can we convert those pressure waves into the electrical signal we need for our recorder?  This is where the new-age folks would really get excited: we're going to use some "magic" crystals.  In 1881, a man named Gabriel Lippmann came up with the idea that if we squeeze certain types of "charged" crystals, we can create an electrical current.  This theory was later demonstrated by the famous Curie family, of radioactive fame.

Charged crystals are made up of thousands of molecules, each of which has a positive and negative charge.  When the molecules are "relaxed" (when you're not squeezing them), the charges balance out.  However, when the crystal is squeezed or bent, the charges are forced together or apart, creating an electronic charge on one side of the crystal.  Modern piezoelectrics are generally made of ceramic, which are coated on either side with a thin layer of metal.  You can see a modern piezoelectric crystal if you dissect the earpiece on your headphones or a singing card from the grocery store.

Note: I found an almost identical figure on a creationism site, as evidence of creationism.  They claimed as evidence that quartz is the only natural piezoelectric material.  As we see above, this just isn't true.

Compression of the crystal
results in a change in electrical
charge, measured in volts (V).

The whale sound increases the pressure in the water.  This compresses the crystal, which creates an electronic charge on each side.  Wires attached to the crystal lead up to the computer on your boat, usually via a pre-amplifier.  A pre-amplifier is just what it sounds like - it makes things louder (amplifies them) before (pre) they go up the wire and into your computer.  Pre-amplifiers are sometimes necessary because the change in charge created by the crystal is too small to travel up a long wire.

Even when the electrical charge has gone all the way up the cable, and into the boat, it isn't done yet.  It still needs to be changed from an analog to a digital signal.  Today, we generally use computers and other digital devices (ipods, hard drives, etc) to store our data and music.  Analog data is continuous, like a sound wave.  Digital data is not continuous - it takes many many samples along a sound wave. In the figure below, we can see the analog sound (in blue) with the digital samples (red).  This is probably why many hipsters people think that records are better than digital sound - because digital recordings don't keep track of most of the sound wave.

A great example of analog recording is the vinyl record.  If you don't know what a record is, you're either very young or not a hipster.  When you play a vinyl record, a needle runs down a continuous groove in the record.  As the needle moves down the groove, it vibrates up and down.  These vibrations travel up the arm of the record player, and eventually to a piezoelectric crystal (you know this one already!).  The crystal converts the vibrations to an electric signal and sends them on to your speakers.

Scanning Electron microscope photograph of the groove

 in a record, by Chris Supranowitz.

In contrast, the data on a CD is stored digitally.  Each CD is engraved with millions of tiny dots and dashes, which your computer reads with a laser and translates into music.

Scanning Electron microscope photograph of a CD, 

by Chris Supranowitz.

After an analog to digital converter has changed our electrical signal into thousands of data points, we can finally listen (and look) at the recordings we've made. As it turns out, physics, chemistry, materials and electrical engineering, and biology have all been necessary to get the sound from the whale and into the computer.  Whether you're doing yoga (like my friend Sheldon) or desperately trying to finish your thesis, there's a lot of science behind those sounds!

Bottlenose dolphin recordings from my acoustic research.

Tweet