Decibels on equipment pages: when noise figures are comparable
A decibel figure expresses a logarithmic level relative to a reference. Equipment pages may report sound-pressure level or sound-power level; these describe different acoustic quantities even when both are written in dB. [1][2]
KEY TAKEAWAYS
Pressure and power
OSHA’s technical explanation distinguishes sound pressure at a location from acoustic power emitted by a source. Distance and room reflections affect pressure readings. A figure for sound power cannot simply be substituted for a sound-pressure figure in a comparison table. [2]
Why a few decibels are not a percentage
A logarithmic scale turns multiplication into a level difference. For acoustic power, ΔL = 10 log₁₀(W₂/W₁): twice the power is about +3 dB and ten times the power is +10 dB. For sound pressure, ΔL = 20 log₁₀(p₂/p₁): twice the pressure is about +6 dB. These follow NIST’s level formulas under the same reference and like-for-like conditions. They are not percentages or claims about perceived loudness. [1]
What the suffix means
A, C and Z designate frequency weightings. OSHA explains that A-weighting approximates the human ear’s frequency response, emphasising middle frequencies and reducing the contribution of low frequencies. A dBA value therefore describes a weighted measurement, not a percentage of perceived loudness. The weighting still does not identify microphone position or device speed. [2]
EPA also notes that an air cleaner’s fan speed can affect its noise; the operating mode belongs beside the acoustic figure. [3]
Which fields make two noise figures comparable?
Our reading: A comparable record identifies the acoustic quantity, weighting, distance or test geometry, operating mode and method. A bare quiet label answers none of these questions. This article explains ratings; it does not assess a worker’s exposure or translate a product figure into a hearing-safety conclusion.
Article Sources
- National Institute of Standards and Technology (NIST) — NIST Guide to the SI, Chapter 8
Primary source
Chapter 8: composition quantities in sections 8.6.6 and 8.6.10; logarithmic levels in section 8.7. Use the section matching the quantity discussed in the article.
Webpage updated:
- US Occupational Safety and Health Administration — OSHA Technical Manual, Section III Chapter 5: Noise
Primary source
Background, II.B.5–10: logarithmic decibels, sound fields, pressure versus power and A/C/Z weighting. Exposure thresholds and US compliance advice are excluded.
Webpage updated:
- US Environmental Protection Agency (EPA) — Guide to Air Cleaners in the Home
Primary source
Portable-air-cleaner section and Q&A: CADR covers particles at the highest speed, with pollutant categories and speed-related noise. Home air cleaning is not local nail-dust capture.
Webpage updated:
Written and reviewed with AI assistance using the linked sources. No hands-on product testing or independent specialist review was performed.
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