Academic journal article The Science Teacher

Focus on Physics

Academic journal article The Science Teacher

Focus on Physics

Article excerpt

When What You See Is What You Hear

Acoustic engineers work and consult with construction engineers and architects to achieve good-quality sound in a variety of buildings, especially concert halls. It's not easy. For example, in a concert hall, as in any room, absorption of sound can be accomplished with drapes and carpets. But people are also sound absorbers, which is evident in the differences in sounds in an empty hall versus a fully occupied hall. Acoustic engineers must plan for concerts with a small audience as well as for a full house, and for orchestras of different sizes.

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Reflection of sound also affects sound quality (Figure 1). Sounds emitted by an orchestra are reflected from walls and ceilings, creating standing waves that produce natural resonances heard as pleasant sensations or annoying ones. At concert halls such as the Louise M. Davies Symphony Hall in San Francisco (left), control over part of the reflection is accomplished with acrylic panels suspended above the orchestra. The orientation of each panel is computer controlled to steer reflections and enhance sounds from the orchestra.

The law of reflection

In physics, the law of reflection applies to both sound and light: The angle of incidence equals the angle of reflection. The law of reflection is illustrated with arrows representing light rays in Figure 2. The angles of the incident and reflected rays are customarily measured from a line called the normal that is perpendicular to the reflecting surface. The incident ray, the reflected ray, and the normal all lie in the same plane.

The law of reflection applies both to rays of light and "rays" of sound. Like a ball bouncing from a floor, sunlight reflecting from the surface of water, or sound echoing from a hard surface, incoming and outgoing directions of motion follow this rule. …

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