The Physical Ripple Tank

Published On: July 10, 2020Tags:

Synesthesia: a sense impression experienced by one sense through stimulation of another sense

Have you ever seemed to see a flash of red at the instant the violin section hits fortissimo? Or a haze of deep blue across your vision as the bassoons begin to harmonize? These experiences would be classic synesthesia, and few people can truly claim to possess it.

The rest of us can find ways of mechanically or electronically generating analogous representations of the sound waves into visual movement and color or hue shift. In practical terms, we find ways of seeing what the bass is really doing in our audio rooms.

Get ready for a snippet of an important thesis paper, one that launched the career path of a certain acoustical engineer (hint: he invented the TubeTrap!)

The Ripple Tank, ca.1975

The ripple tank is an optical device by which the ripple wave action of a transparent liquid becomes visible via shadows and bright spots cast upon a viewing screen. See figure 1.

The Physical Ripple Tank illustration

Light is passed through a glass bottomed pan and is refracted by the sloping water surfaces of the ripple wave, leaving a shadow directly above on the viewing screen. The wave peaks and troughs have a flat surface and impinging light is not refracted but passes directly through to create bright spots on the screen.

Making Waves

A pneumatic wave drive was developed, shown in figure 2, which provides a clean frequency response from 1 to 40 Hz. The driver is a hollow chamber whose open end is set just below the surface of the water, thereby entrapping a quantity of air. As the air pressure is varied, it raises or lowers the water level inside the chamber which changes the local water level just outside the walls of the chamber, creating ripples.

The Physical Ripple Tank, illustration part 2

Ripple Tank Simulator

Let’s demonstrate a typical event in a listening room. Here we have two point sources located in typical speaker locations in a reflective end of a room. In the subwoofer/bass range, sound is usually omnidirectional and acts like a point source. This image shows the wavefront a few milliseconds after the sonic event.

Head End Ringing In Plain Sight

Now, a mere 50 milliseconds later, we see the entire front end of the room aglow with chaotic bass waves, thunderous in level and smeared in time. Cancellations, reverberation, and booming are just a few of the byproducts. Not good!

The Physical Ripple Tank

Click here to visit the simulator with these settings and play around with it.

Damping Wave Motion [comments added]

Once a water ripple [bass sound] has served its viewing [listening] purpose, it continues to travel about the tank [room] by reflecting off the walls. In a short time, the view screen would be full of these reflecting waves if not for the ripple damping system [TubeTraps] which is installed around the perimeter of the tank [room].  A sectional view of the tank wall and damping system is illustrated in figure 3.

Sheets of 1/4″ industrial scouring material [resistive/capacitive tubular devices] is glued onto the slope [placed at the room boundaries] to provide the necessary energy dissipation of the wave.

See the FULL TEXT here.

Head End Ringing: the uncontrolled buildup of early reverberation in the plane of the speakers

…and the scourge of musical fidelity and articulation. A veritable wall of sloppy sound comes barreling down the room at you at the snail’s pace of 1-2 feet per second. Talk about smearing!

The solution? Why, TubeTraps of course. Start with the front corners, then move to the front wall and to positions flanking your speakers, and listen to your system clean up while musicality improves across the entire audible spectrum.

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