Reflected sound fields dominate at low frequencies for almost all sources

Evidence

The audible spectrum, 20 Hz to 20 kHz, has wavelengths ranging from about 57 ft (17 m) to 0.6 in (17 mm). As a result, the dispersion of radiated sounds changes with frequency depending on the size of the sound-radiating surface. It matters not whether we are considering voices, musical instruments or loudspeakers. Low frequencies from most sources radiate essentially omnidirectionally because the wavelengths are long compared to the size of the source—the directivity index (DI) is near zero. … Therefore, as a rule, humans are exposed to more energetic reflected sound fields at low frequencies than at high frequencies, whether we are at a live concert performance, carrying on a conversation in a corridor or listening to loudspeakers in a room. — , Toole, Floyd E - Sound reproduction-…, 1213

Categorization

• XREF: Bears directly on the reader’s silence/soundscape library — why low-frequency ‘bass boom’ is a general condition of indoor listening and presumably part of why rooms feel sonically different outdoors vs. indoors. — connects to: Surface reflection reduces total sound power and favors high frequencies; A critical distance exists where reverberant sound begins to dominate the direct field; A single sound source near a reflecting surface creates interference via an image source (+7 more)

Related

• Free-field radiation requires the source to be far from reflecting surfaces (similarity 0.91)
• ASW depends most on mid-frequency reflections within the first 80 ms (similarity 0.87)
• Lower frequencies diffract more around obstacles than higher frequencies do (similarity 0.86)
• Reflected sound obeys an inverse square law in addition to surface absorption losses (similarity 0.86)
• In small rooms reflections arrive early and never form a diffuse field (similarity 0.85)
• Higher absorption reduces the first-reflection energy that feeds the reverberant field (similarity 0.85)
• Absorption coefficients reduce reflected intensity by their proportion (similarity 0.85)
• Absorbing first reflections cascades to attenuate the whole reflected sound field (similarity 0.84)
• Room boundary reflections are the second loudest sounds a listener hears (similarity 0.84)
• Reverberant field dominates home hi-fi listening from just 2 meters away (similarity 0.84)
• Reverberant sound level stays constant with listener position because reflections arrive from all directions (similarity 0.84)
• Reflection and diffraction of sound both depend on object size relative to wavelength (similarity 0.84)
• Surface absorption weakens early reflections below inverse-square-law predictions (similarity 0.84)
• Reflected sounds physically dominate what reaches listeners’ ears (similarity 0.84)
• Diffuse-field regions sound best because modes are minimal and level is even (similarity 0.84)

Broader Connections

• Surface reflection reduces total sound power and favors high frequencies #complicates (0.85)
• A critical distance exists where reverberant sound begins to dominate the direct field #expands (0.80)
• Reflection and diffraction of sound both depend on object size relative to wavelength #expands (0.80)
• A single sound source near a reflecting surface creates interference via an image source #expands (0.75)
• Reflected sound obeys an inverse square law in addition to surface absorption losses #expands (0.75)
• Low absorber rooms raise overall sound level because reverberant energy persists longer #expands (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1756
• Nearby reflecting surfaces constructively pile up wave reflections to amplify sound #expands (0.75)
• Higher absorption reduces the first-reflection energy that feeds the reverberant field #contradicts (0.70) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1763