Free Noise Level Measurement Log — ISO 1996 Compliant Field Sheet (PDF)

A noise measurement log is not merely an administrative formality. It is the document that converts raw meter readings into legally defensible evidence. In planning appeals, enforcement proceedings, and environmental impact assessments, the difference between a successful and unsuccessful case often comes down to whether the measurement record demonstrates that ISO 1996 requirements were followed: appropriate equipment, correct calibration, documented weather conditions, and a measurement programme that genuinely represents the noise climate.

The log described here was developed against the requirements of ISO 1996-1:2016 (Quantities and Procedures) and ISO 1996-2:2017 (Determination of Sound Pressure Levels). It works for attended and unattended measurements, road traffic noise, industrial noise, entertainment noise, and mixed-source assessments.

What ISO 1996 Requires

ISO 1996-1:2016 defines the quantities to be measured and the assessment methods. ISO 1996-2:2017 specifies the measurement procedures. Together, they require:

• A-weighted LAeq for the assessment period (typically 1 hour, 8 hours, or long-term annual average)
• Frequency analysis (octave or 1/3-octave bands) for tonal source assessment
• LA90 for background noise characterisation
• Measurement height ≥ 1.5 m above ground (facade measurements at 0.5–2.0 m from the building face)
• Calibration before and after each measurement session
• Wind speed ≤ 5 m/s during measurement (or use windscreen and document wind conditions)
• Minimum 10-minute measurement duration for attended surveys; 24-hour periods for unattended

Log Structure: Section by Section

Section 1 — Project Header

Section 2 — Equipment Record

Every instrument used must be documented with its serial number, current calibration certificate reference, and the applicable IEC standard. ISO 1996-2 requires that the sound level meter meets IEC 61672-1 Class 1 for environmental noise surveys. Class 2 is permitted for preliminary screening only.

Calibration log: Record calibration level before and after each session. If the before/after difference exceeds 0.5 dB, the data from that session is suspect and should be noted in the report. If it exceeds 1.0 dB, the session data should be discarded.

Section 3 — Measurement Position Record

For each measurement position, record:

Include a site plan with positions marked. Photographs of each measurement position are not required by ISO 1996 but are strongly recommended for dispute resolution.

Section 4 — Attended Measurement Record

This is the core field data sheet. One row per measurement interval:

The "Notes" column is critical. Events that are audible but not representative of the typical noise climate (emergency sirens, one-off construction events, aircraft) should be noted so they can be excluded from the assessment LAeq calculation if appropriate. ISO 1996-2 §7.3 permits exclusion of isolated sound events that are not part of the noise source being assessed, provided the basis for exclusion is documented.

Section 5 — Octave-Band Data Table

For tonal assessments, planning conditions involving low-frequency noise, or industrial source characterisation, octave-band data is required. The log provides an octave-band table for each attended measurement:

Octave-band data is used to assess tonal content (ISO 1996-2 Annex D), to calculate noise rating (NR) curves, and to verify that measured levels are consistent with the expected spectral signature of the source.

Section 6 — Unattended Measurement Summary

For 24-hour unattended measurements, the logger generates a statistical summary. The log template provides a transfer sheet for the key statistics per hour, from which Lden is calculated:

Lden Calculation Step by Step

The formula written out:

Lden = 10 × log { (12/24) × 10^(62.3/10) + (4/24) × 10^((58.1+5)/10) + (8/24) × 10^((51.4+10)/10) }

Step 1: Convert each term:

• Day: (12/24) × 10^(6.23) = 0.50 × 1,698,244 = 849,122
• Evening: (4/24) × 10^(6.31) = 0.167 × 2,041,738 = 340,970
• Night: (8/24) × 10^(6.14) = 0.333 × 1,380,384 = 459,668

Step 3: Lden = 10 × log(1,649,760) = 10 × 6.217 = 62.2 dB

The template performs this calculation automatically in a formula cell once you enter Ld, Le, and Ln.

WHO and EU Noise Limit Context

The WHO Environmental Noise Guidelines for the European Region (2018) recommend:

The EU Environmental Noise Directive (2002/49/EC) uses Lden and Lnight as its primary indicators with action thresholds at Lden 55 dB and Lnight 50 dB for urban agglomerations. Local planning authorities typically set more restrictive conditions for new residential development, often requiring the LAeq at the facade to remain below these thresholds with windows open.

Completing the Log in the Field

Three practical tips from experienced noise surveyors that the template is designed to accommodate:

Document everything, not just the measurements. The measurement context matters as much as the numbers. Note the presence of leaf litter on trees (affects low-frequency background levels), construction activities in the vicinity, whether the day was a school holiday (affects traffic patterns), and any anomalies in the meter performance.

Take photographs at every position. Not required by ISO 1996, but invaluable when writing the report three weeks later and essential if the data is challenged in a planning inquiry.

Record rejected measurements explicitly. Do not simply delete measurements that were affected by anomalous events. Record them with a note explaining why they are excluded from the assessment. This demonstrates rigour; deletion looks like data manipulation.

Related Resources

• Acoustic Simulator — model room acoustic performance and noise criteria compliance
• How to Measure Room Acoustics — practical guide to RT60 measurement methodology
• Noise Criteria NR/NC/RC Explained — understanding NC, NR, and RC curves for indoor noise assessment
• Acoustic Design for Architects — how noise data feeds into design decisions