Water is visible, so we can see how it travels. It takes the path of least resistance, surrenders to gravity's downwards tugs and heat's upwards pulls. At first, it moves around obstructions, but given enough time it erodes whatever is in its path.
W a v e s
Sound does not travel visibly over and around surfaces like water. Sound waves travel invisibly through molecules - quickly through the tightly packed molecules of solid objects, fluidly through the loose molecules of liquids, and more slowly through the spaciously arranged molecules of air and other gases. Sound waves travel similarly to light waves - bouncing off of reflective surfaces, and getting subsumed into absorbent surfaces.
T h r e e f o l d E f f e c t
Our experience of sound is thus a combination of the sound source, the space in which that sound travels, and our own physical and mental receptivity to the sound.
W o n d e r
We hear rather than see how sound travels, and this subtler level of perception lends an enigmatic quality to the experience of the acoustics of unusual spaces. I recently had the opportunity to wander around a giant former refrigerator - the size of a giant warehouse - sounding, listening, and wondering.
The moment I stepped inside, I heard my footsteps reverberate noticeably louder and longer than usual, but there was something peculiar about what I was hearing.
I explored the length of the reverberations by singing chords. I sang one note, paused to let it fill the space, and then sang another note in harmony with the previous note I had sung. If I sang quickly, I could hear a four-note chord fade into a three note chord, and on down into silence. As engrossing as this activity was, I was distracted by an irregularity in the way sound traveled through the space.
I walked slowly and carefully, trying not to overwhelm the sonically sensitive space with an endless stream of footstep reverberations. I stopped, made a few isolated sounds - sang a note briefly, clapped my hands once, made a tongue click - and then followed the sonic trajectories with my ears.
E c h o
Sound was not reverberating evenly throughout the space, creating the kind of uniform reverberant wash we hear in halls and rotundas. The room had highly reflective surfaces that created a strong reverberation effect, and was also large enough to have an echo that enriched and lengthened the reverberation effect.
M y s t e r y
What mystified me was that no matter where in the room sound originated from, it echoed only on one side of the room. I had entered through a giant and thick doorway on one end of the rectangle. That doorway was the only irregularity in the walls. I shut the door as much as I could without locking myself in, but the sound continued to bounce about wildly only in the far side of the space.
I wondered how sound would travel when that door was entirely shut, but that is an experience that only the refrigerated items of the past know.