Room materials’ absorption coefficient varies with frequency

Evidence

Equation 6.16 gives us the time between surface interactions, and at each of these interactions, α is the proportion of the energy absorbed, where α is the average absorption coefficient discussed earlier. If α of the energy absorbed at the surface, then (1 − α) is the proportion of the energy reflected back to interact with further surfaces. At each surface a further proportion, α, of energy will be removed, so the proportion of the original sound energy that is reflected will reduce exponentially. The combination of the time between reflections and the exponential decay of the sound energy, through progressive interactions with the surfaces of the room, can be used to derive an expression for the length of time that it would take for the initial energy to decay by a given ratio. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830 (#expands, via linked claim)

Categorization

• XREF: connects to: Room absorption shrinks mode bandwidth and flattens standing wave peaks; Room sound energy decays exponentially through repeated surface absorptions — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830; At high frequencies rooms act as irregular interference fields rather than standing-wave patterns (+2 more)

Related

• Room sound energy decays exponentially through repeated surface absorptions (similarity 0.91)
• The diffuse field assumption underpins room acoustics predictions but fails at low frequencies (similarity 0.89)
• Room sound homogeneous decay holds for typical rooms but can be engineered away (similarity 0.88)
• Reflected sound obeys an inverse square law in addition to surface absorption losses (similarity 0.87)
• Total surface area determines a material’s acoustic dominance more than its absorption coefficient alone (similarity 0.86)
• Reflected sound intensity is reduced in proportion to the absorption coefficient (similarity 0.86)
• An audience’s breathing and perspiration dynamically alter a hall’s high-frequency acoustics (similarity 0.86)
• Absorption at each reflection governs how fast reverberation decays (similarity 0.85)
• Absorption coefficients reduce reflected intensity by their proportion (similarity 0.85)
• Room acoustical behavior changes across a broad transition region, not at one frequency (similarity 0.85)
• Higher absorption reduces the first-reflection energy that feeds the reverberant field (similarity 0.85)
• Reverberation time depends on room volume and surface area, not absorption alone. (similarity 0.85)
• Room acoustics shift from standing waves to irregular interference as frequency rises (similarity 0.84)
• Reverberation time depends on both surface absorption and time between reflections (similarity 0.84)
• Room reverberation time varies with frequency, altering perceived timbre (similarity 0.84)

Broader Connections

• Room absorption shrinks mode bandwidth and flattens standing wave peaks #expands (0.95)
• Room sound energy decays exponentially through repeated surface absorptions #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830
• At high frequencies rooms act as irregular interference fields rather than standing-wave patterns #complicates (0.75)