Noise Sound Level Measurement Original Record: Contents, Standards, and Best Practices

A noise sound level measurement original record is the primary technical document that captures raw acoustic readings, instrument settings, calibration checks, and environmental conditions at the moment a sound level determination is performed. In accredited third-party laboratories, this record underpins traceability, reproducibility, and compliance with ISO/IEC 17025 and international acoustic test standards. This article explains what a complete original record must contain, how noise measurements are executed, and how the resulting data supports product certification and regulatory compliance.

Technical Overview

The noise sound level measurement original record (often called a raw data sheet or bench record) is the first-hand, contemporaneous documentation produced while a sound pressure or sound power level determination is being carried out. Unlike the polished test report delivered to a client, the original record preserves exactly what the technician observed: uncorrected meter readings, microphone positions, ambient conditions, instrument identifiers, and any deviations from the test standard. It constitutes the technical evidence from which every reported decibel value can later be reconstructed and defended.

Sound levels are expressed in decibels (dB) referenced to 20 µPa. Measurements are taken with a sound level meter conforming to IEC 61672-1 (or its Chinese equivalent GB/T 3785.1), applying frequency weightings (A-weighting for most measurements, C-weighting for peak and low-frequency assessment) and time weightings (Fast, Slow, or equivalent continuous integration). The original record must state these settings explicitly, because identical equipment can produce different results under different weighting and averaging conditions.

• Contemporaneity: entries are made at the time of measurement, not reconstructed afterward.
• Completeness: all raw values, settings, and conditions are recorded, including apparent anomalies.
• Traceability: instrument identification, calibration status, personnel, date, and location are documented.
• Integrity: corrections follow controlled rules such as a single strike-through that is initialed and dated; records are never erased or overwritten.

The governing framework combines product or environmental test standards, such as ISO 3744, ISO 3746, ISO 11201, ISO 7779, ISO 9612, ISO 1996, IEC 60704, GB 12348, and GB 3096, with the laboratory quality requirements of ISO/IEC 17025, particularly clause 7.5 on technical records and clause 8.4 on the control of records.

Testing Samples

Original records for noise determination are generated for a wide range of test objects. Typical sample categories include the following.

Information Technology and Telecommunications Equipment

Servers, desktop computers, printers, storage enclosures, power supplies, and network hardware are tested under ISO 7779. Microphone positions include the operator position and defined bystander positions, often supplemented by tone and impulsive noise detection, with declared noise values established per ISO 9296.

Household and Similar Electrical Appliances

Washing machines, refrigerators, range hoods, vacuum cleaners, air conditioners, and kitchen machines are tested according to the IEC 60704-1 and IEC 60704-2 series, with declared values for labeling purposes established under IEC 60704-3.

Industrial Machinery, Power Tools, and Generators

Motors, pumps, compressors, machine tools, generator sets, hand-held power tools, and outdoor equipment are measured per ISO 3744 (engineering grade), ISO 3746 (survey grade), or the ISO 11201 series for emission sound pressure level at the work station, with declaration of noise emission values per ISO 4871.

HVAC, Fans, and Ventilation Equipment

Air handling units, axial and centrifugal fans, chillers, and terminal units are measured in semi-anechoic, reverberation, or in-duct configurations, commonly using ISO 3744, ISO 3741, or ISO 5136 depending on the installation condition being simulated.

Environmental, Boundary, and Occupational Noise Sources

Factory boundary noise is assessed against GB 12348, community and area noise against ISO 1996 and GB 3096, and worker noise exposure against ISO 9612. For these in-situ measurements, the original record additionally captures site sketches, measurement coordinates, wind conditions, and relevant traffic or process circumstances.

Testing Items

Depending on the applied standard and client requirements, the following quantities are determined and logged in the original record.

• A-weighted equivalent continuous sound pressure level (LAeq,T) over a defined measurement interval.
• A-weighted time-weighted sound pressure levels (LpAF, LpAS) for steady or fluctuating sources.
• Emission sound pressure level at the operator position or specified bystander positions per the ISO 11201 series.
• A-weighted sound power level (LWA), calculated from the surface-averaged pressure level with area and environmental corrections per ISO 3744 or ISO 3746.
• C-weighted peak sound pressure level (LpCpeak) for impulsive noise and hearing-damage assessment.
• Statistical levels (L5, L10, L50, L90, L95) for environmental noise characterization.
• Octave or one-third-octave band spectra for tonal component identification.
• Background noise level, the difference between source-on and background levels, and applied corrections (K1A, K2A).
• Repeatability of repeated readings and the estimated measurement uncertainty.

Testing Methods

Measurement execution directly determines record content. The workflow below reflects common practice in laboratory-grade determinations.

Instrumentation and Verification

A Class 1 (or Class 2 where the standard permits) integrating sound level meter meeting IEC 61672-1 is used together with an acoustic calibrator meeting IEC 60942. The record lists each instrument's name, model, serial number, equipment ID, and calibration due date. A field verification at a reference level (typically 94 dB or 114 dB at 1 kHz) is performed immediately before and after the measurement series; the recorded drift is commonly limited to ±0.5 dB, and periodic verification of the measurement chain against IEC 61672 is also documented.

Environmental Condition Logging

Ambient temperature, relative humidity, barometric pressure, and wind speed are recorded because microphone sensitivity and acoustic propagation depend on them. Outdoor measurements generally use a windscreen and are suspended when wind exceeds approximately 5 m/s per ISO 1996-2. The record also documents the acoustic environment: semi-anechoic room, reverberation room, or in-situ conditions, including floor type and nearby reflecting surfaces.

Sample Mounting and Operating Conditions

The record describes how the test object was installed, its operating mode or load condition, supply voltage and frequency, speed settings, stabilization time, and any accessory operating cycles such as spin speeds or fan stages. For appliances tested under IEC 60704, the exact standard operating cycle is identified.

Microphone Positions and Measurement Surface

For sound power determination per ISO 3744, microphones are distributed over a hemispherical or parallelepiped measurement surface at a defined distance (commonly 1 m) from the reference box; the number and coordinates of positions, the measurement surface area, and the environmental correction K2A (limited to 4 dB for engineering grade and 7 dB for survey grade) are recorded. For operator-position measurements per ISO 11201, the microphone is placed at the operator's ear position or a defined reference point. Environmental surveys per ISO 1996-2 typically place microphones 1.2 m to 1.5 m above the ground and away from vertical reflecting planes. Position diagrams or sketches are attached or referenced.

Background Noise and Corrections

Background noise is measured with the source off. When the difference between the source-on level and the background level exceeds approximately 10 dB (or 15 dB under certain standards), the correction is negligible; when the difference lies between 3 dB and 10 dB, a background correction is mandatory; when the difference falls below 3 dB, the source level cannot be reliably determined and this limitation must be documented. All applied corrections, energy-averaged results, and rounding steps are shown in the record so the calculation can be independently repeated.

Record Completion, Review, and Control

Each page carries the record number, sample identification, client name, applicable standards, date, location, operator signature, and reviewer signature. Corrections follow the strike-through rule: a single line through the original entry, the correct value written adjacent, initialed and dated. Electronic records require audit trails, access control, and validated software in accordance with ISO/IEC 17025 clauses 7.5 and 8.4. Retention periods follow contractual and regulatory requirements, commonly six years for laboratory technical records.

Applications

Original records of noise determination serve multiple downstream purposes across industries.

• Noise declaration and labeling of machinery and IT equipment per ISO 4871 and ISO 9296, including eco-label and energy-efficiency submissions.
• Regulatory compliance evidence for factory boundary noise (GB 12348), environmental quality (GB 3096, ISO 1996), and occupational exposure limits (ISO 9612).
• Supporting data for product certification schemes handled by accredited third-party laboratories and market-access documentation.
• Engineering evaluation, including design verification, competitive benchmarking, and validation of noise-reduction modifications.
• Acceptance testing at commissioning to verify that delivered HVAC or production equipment meets contractual noise limits.
• Legal evidence in neighborhood disputes, environmental enforcement actions, occupational claims, and arbitration.

FAQ

What is the difference between an original record and a test report?

The original record contains raw, unprocessed observations and the full measurement context, created at the bench during testing. The test report is a formatted deliverable that presents evaluated, corrected, and rounded results together with conclusions and uncertainty statements. Every value in the report must be traceable back to the original record.

What information must an original record include as a minimum?

At minimum: unique record identification; sample name, model, and serial number; the standards and procedures applied with revision status; instrument and calibrator identifiers with calibration status; environmental conditions; microphone positions and setup sketches; operating conditions; all raw readings; background levels; corrections and calculations; deviations; date and location; and signatures of the operator and reviewer.

Why are calibration checks performed both before and after measurement?

Pre- and post-measurement verification with an acoustic calibrator demonstrates that the measurement chain remained within tolerance throughout the test. The recorded drift, commonly required not to exceed ±0.5 dB, protects the validity of the data; if the drift is exceeded, the results are invalidated and the measurement is repeated after instrument checks.

When is a background noise correction applied?

When the difference between the source-on level and the background level is small (typically below 10 dB, and mandatorily between 3 dB and 10 dB), the measured level overstates the source emission and a background correction is subtracted according to the standard's table or formula. If the difference is below 3 dB, the source level cannot be determined reliably and this limitation must be documented in the record.

Are handwritten original records acceptable?

Yes. Handwritten records on controlled forms remain fully acceptable provided entries are legible, indelible, dated, signed, and corrected only by controlled strike-through with initials. Electronic records are equally valid when supported by audit trails, secure access, and validated software, as required by ISO/IEC 17025.

How long must original records be retained?

Retention is governed by laboratory quality policy, contractual terms, and applicable regulations; six years is a common practice for technical records in accredited laboratories. Records must remain retrievable, legible, and protected against deterioration or unauthorized modification throughout the retention period.