Free-field radiation requires the source to be far from reflecting surfaces

Evidence

Equation 1.30 describes the reduction in sound intensity for a source which radiates in all directions. However, this is only possible when the sound source is well away from any surfaces that might reflect the prop­ agating wave. Sound radiation in this type of propagating environment is often called the free field radiation, because there are no boundaries to restrict wave propagation. — David Howard, Jamie Angus, coustics and Psychoacoustics, 304

Categorization

• DEFINE: Defines the free field condition that pure spherical spreading assumes.
• corroborated: 3 independent passages support this claim — David Howard, Jamie Angus, coustics and Psychoacoustics, 304
• XREF: connects to: A finite source-to-wall distance creates a destructive interference null at the half-wavelength frequency; A single sound source near a reflecting surface creates interference via an image source — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 366; Reflected sound fields dominate at low frequencies for almost all sources — , Toole, Floyd E - Sound reproduction-…, 1213 (+1 more)

Broader Connections

• A single sound source near a reflecting surface creates interference via an image source #expands (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 366
• A finite source-to-wall distance creates a destructive interference null at the half-wavelength frequency #complicates (0.80)
• Reflected sound fields dominate at low frequencies for almost all sources #complicates (0.75) — , Toole, Floyd E - Sound reproduction-…, 1213
• Surface reflection reduces total sound power and favors high frequencies #qualifies (0.72)