A decibel value is meaningless without an attached reference level
Evidence
A value in decibels has no meaning if there is no reference measure. In some cases the reference measure is implicit; for example, the sound pressure level (SPL) has a reference level defined worldwide as 2 105 N/m2 (20 μPa). Often a symbol is added after dB (V, u, v, m, A) that means a reference level: dBV: 1 V dBu: 0. — Almo Farina, Soundscape Ecology, 1943
Categorization
- DEFINE: Suffixes dBV, dBu, dBm, dBA each pin the measurement to a different reference, so bare dB reports are under-specified.
- XREF: connects to: Loudness, measured in sones, depends inherently on frequency content — Almo Farina, Soundscape Ecology: Principles,…, 982; Decibel sound levels cannot be added directly because sound powers combine, not levels — David Howard, Jamie Angus, coustics and Psychoacoustics, 278; Decibels cannot be summed directly because they are logarithmic power ratios — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 275 (+4 more)
Broader Connections
- A plus or minus 5 dB loudspeaker deviation goes unnoticed without a direct reference
#exemplifies(0.85) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 504 - Decibels cannot be summed directly because they are logarithmic power ratios
#expands(0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 275 - Sound level references implicitly mean sound pressure level
#exemplifies(0.80) - Amount of masking is expressed as a decibel difference, not an absolute SPL level
#exemplifies(0.78) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 460 - Decibel sound levels cannot be added directly because sound powers combine, not levels
#expands(0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 278 - Zero decibels is a perceptual threshold, not a true physical absence of sound
#exemplifies(0.75) — George Michelsen Foy, Zero Decibels, 473