Sound Pressure vs Sound Power: dB(A), Octave Bands and Logarithmic Addition

Published July 22, 2026 · Engineering coordination review by TransformerGrid · Project-specific requirements require manufacturer, utility and applicable-standard verification.

Decibels are logarithmic. Before comparing transformer acoustic results, identify whether the report states sound pressure or sound power.

Sound pressure level

L_p = 20 log₁₀(p/p₀), p₀ = 20 μPa

Sound pressure belongs to a location and is affected by distance, background and reflecting surfaces. A property-line or indoor reading is usually a sound-pressure assessment at a receiver.

Sound power level

L_W = 10 log₁₀(W/W₀), W₀ = 10⁻¹² W

Sound power characterizes total source radiation and is determined through a defined measurement surface and correction process. It is not the direct reading of a sound-level meter at an arbitrary point.

dB(A), bands and logarithmic addition

A-weighting reduces low-frequency contribution to approximate overall hearing response. Transformer tonal components near 100/120 Hz and harmonics may be clearer in octave or one-third-octave data. Equal A-weighted totals can therefore have different spectra and subjective character.

L_total = 10 log₁₀(Σ 10^L_i/10)

Two independent equal levels combine to about 3 dB above one source; 50 dB + 50 dB is not 100 dB. Background also cannot be removed by ordinary arithmetic subtraction.

Report review fields

quantity and reference value;
weighting, time response and frequency bands;
measurement contour, instrument and calibration;
operating condition, background correction and uncertainty;
scope of the conclusion.

Return to the engineering guide.

Procurement application: Apply this technical reference in how to state an acoustic metric in an RFQ.

Technical Questions and Engineering Discussion

For questions about sound pressure, sound power, dB(A) or band data, contact [email protected]. Technical exchanges are welcome.

Primary engineering references

IEC 60076-10:2016 — determination of transformer and reactor sound levels.
IEC 60076-10-1:2016 and Amendment 1:2020 — application guidance.
IEEE C57.136-2023 — sound and vibration guidance for liquid-immersed power transformers.
NEMA TP 80050-2013 (R2024) — audible sound levels for distribution transformers.

Standards must be applied within their stated scope and the edition incorporated into the project documents. This page is an engineering reference, not a substitute for the governing contract, utility specification or safety procedure.