What to Check in a Reference Sound Source Calibration Certificate for Sound Power Comparison Measurements

If a laboratory plans to use a reference sound source for sound power comparison measurements, procurement acceptance should check the instrument identity, band calibration data, installation and operating conditions, uncertainty, and intended method together. “Calibration certificate included” alone does not establish suitability for the planned tests.

Define the measurement capability first

A comparison method uses a source with known sound power to relate sound pressure measurements in the same environment to the sound power of the source under test. Before purchasing, define the product test method, required frequency bands and test environment, then specify the calibration service accordingly. Choosing equipment first and looking for a method afterwards reverses that process. ISO 6926:2016 public introduction and definitions (https://www.iso.org/obp/ui?_escaped_fragment_=iso%3Astd%3Aiso%3A6926%3Aed-3%3Av1%3Aen)

ISO 6926:2016 addresses reference source stability, spectrum, directivity and sound power calibration. Check whether ISO 6926:2016/Amd 1:2020 is included and reconcile the stated basis with the edition adopted for the project. A standard number in a product brochure does not establish that the delivered certificate covers every project requirement. ISO base standard catalogue (https://www.iso.org/standard/42873.html); 2020 amendment catalogue (https://www.iso.org/standard/74022.html)

The document checks and handover arrangements below are engineering recommendations, not additional standard clauses or universal acceptance limits.

Check results and uncertainty band by band

The published scope of ISO 6926 includes octave-band, one-third-octave-band and A-weighted sound power calibration data and uncertainty under reference meteorological conditions. ISO 6926:2016 scope (https://www.iso.org/standard/42873.html)

For a project that processes results by frequency band, match each required band to the certificate. Advertised broadband output, a typical spectrum or a single A-weighted overall level cannot directly replace the required band calibration values for the individual source. Clarify whether missing bands can be supplied before ordering the calibration service. Do not fill gaps yourself and treat the resulting values as calibrated data.

Also check whether a table reports sound power level or sound pressure level, whether the unit and reference quantity are stated, and which results and conditions the uncertainty applies to. If expanded uncertainty is reported, check that its coverage factor and associated explanation are clear. Verify the model, serial number, calibration date and attachments to avoid applying another unit’s results or a sample table to the purchased source.

Match installation conditions relative to boundaries

The distance between a reference source and nearby reflecting planes can affect its output, with particular attention needed at low frequencies. Here, installation position concerns the source’s configuration relative to the floor, support and nearby reflecting boundaries. It should not be read as restricting the certificate to an absolute coordinate in the original room. ISO 6926:2016 public introduction (https://www.iso.org/obp/ui?_escaped_fragment_=iso%3Astd%3Aiso%3A6926%3Aed-3%3Av1%3Aen)

Establish whether calibration used a floor-mounted or elevated source and what placement the intended test requires. If changing from floor mounting to a stand, first establish whether the existing data remain applicable rather than carrying them over automatically. Moving to another laboratory is not, by itself, a reason to declare the certificate invalid. Check installation compatibility and the target environment’s suitability for the test method separately.

Operating and environmental records should explain how to use the data

As a model-specific example, Brüel & Kjær’s Type 4204 product data describes individual calibration tables recording the supply conditions, temperature, barometric pressure, humidity and rotational speed. It also explains that supply and environmental changes can affect output. Its treatment should not be generalized to every reference source. Manufacturer product data BP 0263–20, 2013-04 (https://www.bksv.com/-/media/literature/Product-Data/bp0263.ashx)

When ordering, request an explanation of the operating state associated with the calibration values, whether they have been converted to reference conditions, and which corrections apply during use. If both the certificate and software address the same correction, establish where it is applied and retain a record to avoid applying it twice. Following maintenance or abnormal operation, use the instrument instructions and laboratory procedures to determine whether checks or recalibration are needed. A model-specific interval should not become a universal rule.

Assess source evidence separately from laboratory capability

Source calibration establishes data for the individual source under stated conditions. Comparison measurements must also satisfy the environmental and measurement requirements of the selected method; a source certificate cannot replace validation of the complete method. The public introduction to ISO 6926 notes that applications such as environmental qualification can involve additional requirements. ISO 6926:2016 public introduction (https://www.iso.org/obp/ui?_escaped_fragment_=iso%3Astd%3Aiso%3A6926%3Aed-3%3Av1%3Aen)

If procurement requires a service within an accredited scope, separately verify that the issuing organization’s relevant scope matches the deliverable. “In accordance with ISO 6926” should not be treated as proof of accreditation.

Assemble a checkable handover package: unit identification and certificate; required band data and uncertainty statements; calibration installation, operating and environmental conditions; the applicable basis for corrections and records of their treatment; and arrangements for subsequent checks, maintenance and recalibration. Identify any uncovered bands or use configurations separately. This makes it possible to distinguish established capability from conditions still to be addressed before comparison measurements begin.

Sources

1. ISO 6926:2016, Acoustics — Requirements for the performance and calibration of reference sound sources used for the determination of sound power levels, edition 3. References are limited to the official catalogue and public introduction, scope and definitions. Catalogue (https://www.iso.org/standard/42873.html); public preview (https://www.iso.org/obp/ui?_escaped_fragment_=iso%3Astd%3Aiso%3A6926%3Aed-3%3Av1%3Aen).
2. ISO 6926:2016/Amd 1:2020, Amendment 1, 2020-11. Official catalogue (https://www.iso.org/standard/74022.html). Used only to establish the amendment’s identity, not to infer its revised provisions.
3. Brüel & Kjær, Product Data: Reference Sound Source Type 4204, BP 0263–20, 2013-04, page 2. Manufacturer PDF (https://www.bksv.com/-/media/literature/Product-Data/bp0263.ashx). Used only as a model-specific example of calibration records and influencing factors, not as a current procurement specification.

Sources checked: 2026-10-22.