Balmorhea is a band composed entirely of strings with the exception of a drum set for percussion, and for whatever reason when I listen to Balmorhea, it instantly takes me back to what I’ve learned about the movement of sound. For the sake of this post, we’ll discuss Huygen’s Principle. It is this principle that defines and explains how sound moves, the behavior of sound waves as they travel through some medium or reflect off of something.
This principle states that each point on an advancing wave front may be considered to be a new point source generating spherical Huygens’ wavelets. If you know the location of a wave front at x time, you can use that information to figure out the location of the wave front at a slightly later time by drawing spherical arcs centered at points along the wave front. It is important to note that each spherical arc is a Huygens’ wavelet. The radius of each of these arcs is given by the distance that sound travels in that relatively small amount of time.
In the figure below, the initial wave front is labeled “A”. If the sound speed is c (340 meters/second), then therefore in a small time increment, delta t (seconds), sound travels a distance c*delta t (meters). The new wave front, labeled “B,” is the convergence of these wavelets with a radius c*delta t, and is made by drawing the line tangent to the leading edges of the wavelets.
With each strike of the xylophone I envision a sound wave being generated, invisible to the eye yet visible to the ears. I can imagine the sound widening due to the new points being generated and new wavelets being created.
Not really sure if ‘Untitled’ is a new track, but I haven’t heard it yet and like all Balmorhea songs it sounds amazing. I have always been a huge fan of Balmorhea, and I’m still kicking myself for missing their show at a really small local venue in Providence a few years back by about a hair. Nevertheless, they did this totally epic session for Daytrotter, you can download all the tracks there.