Sound Fields
What field is very close to a sound source?
Near field
What happens when sound reflects?
It bounces from a surface
What is sound bending around an obstacle called?
Diffraction
What does a diffuser do to reflected sound?
Scatters it in many directions.
What happens when two sound waves meet?
Interference.
In a free field, what happens to the sound level when distance from a point source doubles?
It falls by about 6 dB
From which reference line are the angles of incidence and reflection measured?
The normal, a line perpendicular to the surface.
During refraction, which property stays the same: speed, wavelength, or frequency?
Frequency
Which shape tends to spread reflections across a wider area: concave or convex?
Convex.
What type of interference makes the pressure variation larger?
Constructive interference.
In which field does reflected sound become strong compared with direct sound?
Reverberant field
A sound wave strikes a flat wall at 30° from the normal. What is its reflection angle?
30° from the normal
Why does bass bend around a barrier more easily than high-frequency sound?
Its longer wavelength produces stronger diffraction around the same barrier.
What repeated sound effect can occur between flat parallel walls?
Flutter echo.
Two tones are 440 Hz and 444 Hz. What is their beat frequency?
4 Hz.
Why can a sound-level reading change sharply when taken very close to a source?
Levels can vary over short distances in the near field
Why might a concave rear wall create a loud hot spot?
It focuses reflections toward one area
Sound travels from warm air toward cooler air. Toward which layer does its path tend to bend?
Toward the cooler, slower layer.
What is the difference between absorption and diffusion?
Absorption removes some sound energy; diffusion scatters reflected sound.
Two tones are 256 Hz and 260 Hz. How many beats occur per second?
4 beats per second.
A student claims every room has a fixed distance where the near field ends. Why is that claim unreliable?
The boundary depends on the source, frequency, direction, and room conditions
A lecturer is hard to hear under a balcony. Name one design measure that could help.
Add a ceiling reflector or a carefully placed loudspeaker to cover the acoustic shadow.
A solid wall blocks traffic noise, but a gap remains under its door. Why can the gap weaken sound isolation?
Sound passes through the opening and spreads beyond it, bypassing the wall.
Why might decorative texture fail to diffuse low-frequency sound?
Its features may be too small compared with the long wavelengths.
Why might one seat have weak bass while a nearby seat has strong bass?
Direct and reflected waves can interfere differently at each position, creating pressure minima and maxima.