---
title: "A Server Noise Number Needs a Physical Quantity Before It Can Rank an Offer"
description: "Leviathan Systems — Technical content Published 2026-10-20; updated 2026-10-20."
canonical: "https://www.leviathansystems.co/articles/server-acoustic-sound-power-pressure-declarations"
last-updated: "2026-10-20"
---

# A Server Noise Number Needs a Physical Quantity Before It Can Rank an Offer

Leviathan Systems — Technical content
Published 2026-10-20; updated 2026-10-20.

An offer saying 70 dB and another saying 55 dB cannot be ranked until their physical quantities and declared conditions are known. Sound power describes acoustic energy emitted by a source per unit time; sound pressure describes pressure fluctuations at a position. Compare matching quantities, references, weighting, declaration statistics, configurations and modes. A comparable equipment declaration is an input to site planning, not a prediction of occupied-room noise.

## Identify what the number describes

A server quotation with a single noise column can conceal two different questions: how much acoustic energy does the equipment emit, and what pressure fluctuation does that sound produce at a particular position? A lower numeral answers neither question until the column identifies its quantity.

Sound power is the rate at which a source radiates acoustic energy, expressed in watts. Its level uses a reference of 1 picowatt, written 1 pW or 10⁻¹² W. This acoustic power is distinct from the server's electrical input power.

Sound pressure is the fluctuating part of pressure at a location. Its level in air uses a reference of 20 micropascals, written 20 μPa. The reference therefore belongs to a different physical quantity. Two entries sharing the unit dB are not automatically comparable.

The useful distinction is source versus position. A sound-power declaration characterizes the stated equipment under its declared conditions. An emission sound-pressure declaration also identifies a position near that equipment under specified test conditions. Neither is simply a free-standing description of how loud a populated room will be.

References: [E74](https://ecma-international.org/wp-content/uploads/ECMA-74_22nd_edition_december_2025.pdf), [B1](https://www.bksv.com/doc/br1626.pdf)

## Keep A-weighting, units and edition attached

A-weighting applies a frequency-dependent weighting related approximately to human hearing sensitivity. It can be applied to either quantity. The notation dB(A) therefore identifies weighting without resolving whether the entry is sound power or sound pressure; retain the full quantity name and symbol.

ECMA-109, 11th edition, June 2025, uses dB for declared sound power and permits optional emission sound-pressure declarations at operator positions, bystander positions or both. Do not assume that power must be in bels and pressure in decibels.

Historical declarations may use bels, symbol B. One bel equals ten decibels. Preserve the original entry and show any unit conversion explicitly, without changing its quantity or statistic. Converting a unit does not convert sound power into sound pressure. Retain the declaration's actual standard and edition alongside the value.

References: [E109](https://ecma-international.org/wp-content/uploads/ECMA-109_11th_edition_june_2025.pdf), [B1](https://www.bksv.com/doc/br1626.pdf), [N1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)

## Compare the same statistic and operating condition

In ECMA-109, LWA,m denotes the declared mean A-weighted sound-power level for a batch. LWA,c denotes a statistical upper limit; Kv is the statistical adder used with the mean to obtain that limit. A mean and an upper limit are different comparison fields, not interchangeable labels.

Keep idle and operating modes separate too. An idle declaration cannot stand in for an operating condition that has not been declared. ECMA-109 requires configuration and mode information and, where relevant to varying emissions, ambient temperature and altitude or equivalent ambient pressure.

A buyer should return mismatched fields for clarification before awarding a quieter-equipment preference. A higher upper-limit entry beside a lower mean does not establish which offer has the lower mean. An idle entry beside a different operating mode leaves the intended operating comparison unanswered.

References: [E109](https://ecma-international.org/wp-content/uploads/ECMA-109_11th_edition_june_2025.pdf)

## AC-245: clarify the quantity before comparing the offers

AC-245 is an entirely fictional quotation example. Offer A declares a mean A-weighted sound-power level of 70 dB. Offer B initially supplies an A-weighted emission sound-pressure level of 55 dB at its stipulated operator position. The fifteen-unit numerical difference is not measured attenuation, a receiver-level difference or a ranking of their emitted powers.

The buyer asks B for the matching sound-power declaration. In the revised fictional response, B supplies a mean A-weighted sound-power level of 73 dB. For this second comparison only, stipulate the same equipment configuration and operating condition, and matching declaration method, edition, reference, weighting and statistic for A and B.

The revised pair supports a nominal comparison of the declared means: A's 70 dB is 3 dB below B's 73 dB. B's original 55 dB pressure entry can remain in its own correctly labelled field; it has not been contradicted or replaced by the power entry. The clarification has supplied the previously missing quantity.

This example determines no statistical significance, actual room pressure, annoyance, hearing exposure or suitability. All values are invented to explain the comparison; none describes a named product or an actual test.

References: [E74](https://ecma-international.org/wp-content/uploads/ECMA-74_22nd_edition_december_2025.pdf), [E109](https://ecma-international.org/wp-content/uploads/ECMA-109_11th_edition_june_2025.pdf)

Fictional AC-245: unlike quantities first, matched declarations second
| Comparison stage | Offer A | Offer B | Permitted conclusion | Source |
| --- | --- | --- | --- | --- |
| Initial: quantities differ | Mean A-weighted sound-power level: 70 dB re 1 pW | A-weighted emission sound-pressure level: 55 dB re 20 μPa at its stipulated operator position | No ranking of emitted powers; the numerical gap is not attenuation. | Planning analysis |
| Revised: matched declaration basis | Mean A-weighted sound-power level: 70 dB re 1 pW | Mean A-weighted sound-power level: 73 dB re 1 pW | A has the lower nominal declared mean sound-power level under the stipulated common conditions. | Planning analysis |
Only the revised row stipulates matching configuration, operating condition, method, edition, reference, weighting and statistic. These are illustrative declaration entries, not complete conformity statements or measured results.

## The room introduces paths, other sources and receivers

Sound leaving equipment propagates through the space. Room surfaces can reflect or absorb it, so pressure at a receiver depends on the paths between source and receiver as well as the source emission. An equipment emission sound-pressure declaration concerns its defined test position and environment; it does not include the customer's complete room.

The installed population matters as well. A room may contain several servers and other sound sources in different locations and operating states. A source declaration cannot identify that population or say where a person will be. Moving the receiver or changing the room leaves a different question even if the equipment declaration is unchanged.

Ecma's ECMA TR/27 landing page identifies its second edition as June 1995. Its stated prediction scope explicitly separates room acoustical properties, equipment locations and emission levels, and locations of interest. That historical scope explains the missing inputs; it supplies no current room prediction or numerical correction here.

The purchase consequence is to carry the declarations into a site-specific review with those inputs identified. Subtracting a universal distance allowance from the power number would skip the actual propagation and room question.

References: [B1](https://www.bksv.com/doc/br1626.pdf), [E74](https://ecma-international.org/wp-content/uploads/ECMA-74_22nd_edition_december_2025.pdf), [T27](https://ecma-international.org/publications-and-standards/technical-reports/ecma-tr-27/)

## Keep the acoustic evidence with the offered configuration

Retain the supplier's full declaration and its revision with the equipment line it supports. The comparison record should make the quantity, reference, units, weighting and statistic visible, together with the offered configuration and declared mode. For a pressure entry, retain the stated position. Keep any applicable environmental conditions and the cited measurement and declaration editions attached.

If the offered component population or mode changes, ask the supplier which declaration applies to the revised offer. A general model-family figure leaves that relationship unresolved. The aim is a traceable comparison, rather than a single noise numeral copied into a purchasing summary.

Use the existing server-fan article for the separate airflow and operating-point decision. Fan airflow evidence does not fill a missing acoustic declaration, and this acoustic comparison does not establish chassis airflow. The selected equipment package needs each relevant claim supported at its own boundary.

References: [E109](https://ecma-international.org/wp-content/uploads/ECMA-109_11th_edition_june_2025.pdf), [E74](https://ecma-international.org/wp-content/uploads/ECMA-74_22nd_edition_december_2025.pdf)

## Bring the resolved equipment decision into physical planning

For the resulting rack-layout and installation-document package, use Leviathan's Physical Infrastructure Planning & CAD service and the linked project inquiry. Share a nonconfidential equipment schedule, proposed positions, site constraints, requested outputs and the decisions returned by the customer's appointed specialists. Authoring capability, formats and review responsibilities are confirmed for the engagement.

The customer appoints the acoustic planning specialist separately. Acoustic consulting, workplace exposure assessment and noise guarantees are outside this Leviathan scope. The useful handoff retains the offered configuration, mode, physical quantity and declaration basis so that specialist can evaluate the actual site and return requirements for the physical package.

## Primary sources

- [E109 — Ecma International: ECMA-109, 11th edition, June 2025](https://ecma-international.org/wp-content/uploads/ECMA-109_11th_edition_june_2025.pdf). Checked 2026-10-20. Declaration quantities, statistics, positions and conditions for IT and telecommunications equipment; supports comparing supplier evidence.
- [E74 — Ecma International: ECMA-74, 22nd edition, December 2025](https://ecma-international.org/wp-content/uploads/ECMA-74_22nd_edition_december_2025.pdf). Checked 2026-10-20. Acoustical definitions and the distinction between equipment emission and installed noise. Definitions do not establish compliance with a supplier's cited measurement edition.
- [B1 — Brüel & Kjær: Environmental Noise, BR1626](https://www.bksv.com/doc/br1626.pdf). Checked 2026-10-20. Explains A-weighting and source power versus receiver pressure. Used for physical concepts, without adopting outdoor prediction equations or distance corrections.
- [N1 — NIST Guide to the SI, Chapter 8, section 8.7: Logarithmic quantities and units](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8). Checked 2026-10-20. Establishes the bel/decibel relationship and the need to retain the reference quantity when reporting a level.
- [T27 — Ecma International: ECMA TR/27, Method for the prediction of installation noise levels](https://ecma-international.org/publications-and-standards/technical-reports/ecma-tr-27/). Checked 2026-10-20. June 1995 second-edition scope identifies room, source and receiver inputs. Historical context for a planning question, without a site model or numerical rule.

## Related Leviathan resources

- [Physical Infrastructure Planning & CAD: define the installation package](/services/engineering-design)
- [Discuss the physical planning project](/contact?service=engineering-design&from=/articles/server-acoustic-sound-power-pressure-declarations)
- [Server fans: free-air CFM and the operating point](/articles/server-fan-airflow-static-pressure-operating-point)
- [Air-cooled and liquid-cooled servers: compare both interfaces](/articles/air-cooled-vs-liquid-cooled-platform-choice)
- [CXL Memory Expansion: Which Memory Does the GPU Server Offer Actually Add?](/articles/cxl-host-memory-expansion-gpu-hbm-boundary)

## Discuss the physical planning package for your selected equipment

Share the equipment schedule, proposed rack positions, site constraints, requested documents and specialist decisions so we can discuss scope, requirements and availability.

[Discuss the scope](/contact?service=engineering-design&from=/articles/server-acoustic-sound-power-pressure-declarations)