Ripple Tank Story Reflection

Published On: September 15, 2023Tags: , , , , , ,
Enjoy this week’s inSIGHTful story from Art relating to the Ripple Tank project.
Link to full thesis paper by ASC president and TubeTrap inventor, Art Noxon, PE Acoustical

Blinded, had to listen

During the summer of ‘72 while working on my master’s degree project, a high-end ripple tank, I temporarily blinded myself. During the next two weeks I discovered that I could hear the space and objects around me. The blind call it echolocation, sensing the reflections of sound. This perception of one’s immediate environment is also involved in setting up microphones when making a recording.

Back Story

It was basically a glass bottomed shallow tray of water in which ripples are made, light is beamed off a mirror through the bottom, casting bright and shadow images of the waves onto the ceiling of a classroom. I was near the end of the project but still needed to make a beach, a wave absorbing edge to the tank, so the viewing screen wouldn’t be obscured by reflected waves. Scotch scouring pads were glued with rubber cement to a sloped surface that ran around the edge of the wave tank, similar to a sloped beach, bringing my work-day to an end. Next day, I would fill it with water and test if the ripple tank was an anechoic ripple tank.

In the middle of the night, I had an idea, sat up in bed and rubbed my eyes. That was a big mistake, my eyes instantly felt as if they were on fire. Went to ER right away. The doctor applied a salve to my eyes and covered both eyes with pads and a large head wrap. Everything was feeling much better. The doc said to come back in two weeks when he’d take the bandages off. But to not get my hopes up, it is very possible I may not be able to see any more. I may have chemically burned the eye so badly, and he couldn’t tell how it would turn out. I was sent home.

Slept great and late in the morning woke up to a new reality, and possibly a permanent reality. I couldn’t see anything. Lacking sight I was afraid to even try to move around. I didn’t know where to go or how to get there. How far or where anything was. I recollected the location of the bed in the room and the layout of the small house. I practiced, moving along a wall, finding doorways, going around the door sill to the next wall and down it until I hit a couch or chair and so on. Slowly I figured out how to grope my way around the house.

After a while I got some help to try to walk outside. It was similar to moving inside the house, touching a fence I knew and passing a gate I knew and so on. I got a stick and used that instead of my hands. I was acclimating to being blind. I was blind for at least 2 weeks and might not ever get my sight back. Being blind had a side effect, my sense of hearing changed. Here I am, working on a master’s thesis on acoustics and suddenly I’m hearing sound as I never heard it before, because I had lost my sight.

I began to notice that I heard the sound of where I was change as I passed by. I could hear the rustle of my clothes and footfall creating an ambience that followed me around, It was due to the reflections of my sound off nearby surfaces. I wasn’t making little sounds or tapping a cane or stick or anything, the noise source was the rustle of my own movement. It seemed to begin as I passed through a doorway. The big or dramatic change was how the air sounded between the two rooms. And then something even more surprising, I could hear the doorway as I passed through it. Not the door, although I could hear a door’s position if it had the right angle, but here I could hear the 6” molding that created the flat sides and top of the door opening. So, the change in sound between 2 rooms was woosh-sis-Weesh and the doorway was the higher frequency sis sound. These sounds all came from my own movement, they were the reflections of my movement returning to me, back to my ears.

I couldn’t see space but I could illuminate the space with the slight sounds from my movement and hear what was reflected back. I didn’t hear an echo. It was as if I had a sound space around me and I could hear what it touched. It wasn’t separated from me, it was part of me. Outside was particularly adventurous. I could sense that I was passing by a tree as I walked down the sidewalk. A picket fence was amazing, sh-sh-sh-sh on a regular pattern depending how fast I was moving. A solid cedar fence was a steady shish. A tree in the planter strip didn’t have a steady presence, it changed tone and direction as I passed by shuesh. Walking towards the step up of a curb is very loud probably because it was so close to my feet. It had a higher frequency, kinda hollow and sharp at the same time, shoiss, as I approached it. One of the best feelings was passing an opening in a fence, where the ambience would drop out and then return.

Later I learned about early reflections and sound fusion, which is what I had been experiencing. At that time however, I was only studying the mechanics of sound, not the psychoacoustics part which is how people hear sound.

Sound Fusion Effect

This experience wasn’t active listening, using echo location, where a click is made and we listen to the echo to determine where something reflective is located, a wall or a parked car for example. It wasn’t passive listening, where we would listen to the sound field created by other things making sounds, getting a sense of what was where. Another version of passive listening is to notice the shadows of sound moving across you or as you pass by them.

It was related to echo location in that I was listening to the sound caused by my movement. Definitely an experience of hearing changes in the nearfield ambience caused by the noise from rustling and shuffling of my movement.

Doing some research on how blind people use sound to see the world around them, the word echolocation is not two words but one word. It means to the blind the making sound and hearing how it reflects off of an object. It includes the traditional farfield echo recognition, those with a delay time of over 40ms. It also includes sounds in the midfield and nearfield, with delays as quick as 1 ms.

In acoustics and recording, an echo is a distinct sound reflection that returns to the listener 40ms or later after it was created. Sound reflections that return inside of 30 ms are not heard as a distinct sound but heard as a change in the ambience or nature of the sound we are listening to. This listening experience is considered part of the sound fusion, precedence or Haas effect which is when the reflection joins with the direct and becomes a single perceived sound that is different than the direct sound.

In the world of blind, echolocation is not the distinct echo off a distant wall, it is what is heard when any sound is heard, regardless of time delay. The emphasis tends to be on location, the direction the reflected sound is coming from. But getting closer to an object and making clicking noises allows the blind to determine its shape and surface materials.

Reflecting upon my early experience with blindness and the echolocation blind people use to learn about their environment seems to resemble aspects of the QSF recording experience. The QSF technique involves recording a plethora of early reflections.

it's a bat shooting sonic waves out of its face. pew pew!

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