The speed of a wave depends on the elastic and inertia properties of the medium through which it travels. When a wave encounters different medium where the wave speed is different, the wave will change directions. Most often refraction is encountered in a study of optics, with a ray of light incident upon a boundary between two media (air and glass, or air and water, or glass and water). Snell’s law relates the directions of the wave before and after it crosses the boundary between the two media.
Sin 01/ C1 = Sin 02/C2
The wavefronts cross the boundary the wavelength changes, but the frequency remains constant.
In acoustics, however, sound waves usually don’t encounter an abrupt change in medium properties. Instead the wave speed changes gradually over a given distance. The speed of a sound wave in air depends on the temperature (c=331 + 0.6 T) where T is the temperature in oC. Often the change in the wave speed, and the resulting refraction, is due to a change in the local temperature of the air
For example, during the day the air is warmest right next to the ground and grows cooler above the ground. This is called a temperature lapse. Since the temperature decreases with height, the speed of sound also decreases with height. This means that for a sound wave traveling close to the ground, the part of the wave closest to the ground is traveling the fastest, and the part of the wave farthest above the ground is traveling the slowest. As a result, the wave changes direction and bends upwards. This can create a “shadow zone” region into which the sound wave cannot penetrate. A person standing in the shadow zone will not hear the sound even though he/she might be able to see the source. The sound waves are being refracted upwards and will never reach the observer.
Our goal will be to find an adequate technique to produce effectively a shadow zone in an existing sound environment, a sound ramp that will bend sound with a specific sculptural character.
There exist different heating techniques that can be tested to increase temperature in air. In this area directionality and efficiency are the more important requirements to have in consideration.
At the moment Industrial incandescent light bulbs seems to be appropriate for consideration since they do not produce any sort of gas and transfer heat directly into air as opposite infra red light heating which irradiate electromagnetic radiation which does not need a medium to transfer heat.
Detailed research on refraction by temperature changes and wind velocity
Research on heating systems candidates
Heating system tests (decibel difference of sound propagated before and after the heated media)
Design proposal considering electrical design, power consumption, heat dissipation and insulation.
Re-design and final proposal considering installation and transportation.
Generate budget for realization
Springer handbook of acoustics
By Thomas D. Rossing
Handbook of Acoustics
By Malcolm J. Crocker
Acoustics and psychoacoustics
By David Martin Howard, James A. S. Angus, Jamie Angu
Refraction of Sound Waves
By Daniel A. Russell, Ph.D.