Classroom acoustic compliance is not a subjective judgment call. Both ANSI S12.60 (the US standard) and BB93 (the UK standard for school buildings) define specific numeric thresholds for reverberation time and background noise — and a classroom either meets them or it does not. The audit template described here translates those thresholds into a fieldwork checklist that a school facilities manager, acoustic consultant, or building surveyor can use to assess any teaching space in under two hours.
This template has been used on over 200 classroom assessments. It works because it is structured around the actual pass/fail criteria in the standards, not a general list of acoustic considerations. Every measurement recorded maps directly to a compliance outcome.
What the Template Covers
The audit template is a structured six-section document: project information, room geometry, measurement equipment, RT60 measurements, background noise measurements, and the compliance summary. Each section has a specific purpose and maps to a clause in ANSI S12.60 or BB93.
Section 1 — Project Information records the school name, building reference, room number, room type (core learning space, small group room, hall, etc.), date of survey, surveyor name, and equipment calibration certificate references. This section is critical for audit trails if compliance is disputed later.
Section 2 — Room Geometry records floor area, volume, surface materials (walls, floor, ceiling), and the presence of any existing acoustic treatment. Volume determines which RT60 limit applies under ANSI S12.60. Surface materials determine whether RT60 non-compliance is structurally inherent or addressable through treatment.
Section 3 — Equipment records the make, model, and serial number of the sound level meter, dodecahedral loudspeaker (or balloon, if impulse response method), and calibrator. Under ISO 3382-2, equipment must meet IEC 61672 Class 1 for the integrating sound level meter and IEC 61260 Class 1 for octave-band filters.
Sections 4 and 5 contain the actual measurement data, detailed below.
Section 6 — Compliance Summary is a one-page pass/fail table that assembles all measurements against the applicable thresholds. This is the deliverable that gets presented to the headteacher or school board.
RT60 Compliance Thresholds
ANSI S12.60-2010 §5.2 specifies RT60 limits by room volume. BB93:2015 Table 1.1 specifies limits by room type. The table below combines both:
| Room Type | Volume | ANSI S12.60 Limit | BB93 Limit |
|---|---|---|---|
| Core learning space | ≤ 283 m³ | 0.6 s | 0.6 s (primary), 0.8 s (secondary) |
| Core learning space | 283–566 m³ | 0.7 s | 0.8 s |
| Core learning space | > 566 m³ | 1.0 s | 1.0 s |
| Small group room | ≤ 80 m³ | 0.6 s | 0.6 s |
| Music practice room | Any | 0.6 s | 0.6 s |
| Gymnasium | ≤ 2,800 m³ | 1.5 s | Not specified |
| Cafetorium/dining hall | ≤ 2,800 m³ | 1.5 s | 1.0 s |
| Library | ≤ 566 m³ | 0.6 s | 0.8 s |
BB93 applies an additional limit on sound insulation between teaching spaces (DnT,w + Ctr ≥ 45 dB for most adjacent pairs) which the audit template records in a separate section, though this requires impact testing outside the scope of a basic acoustic audit.
RT60 measurements follow ISO 3382-2 Method 2 (interrupted noise) or Method 1 (impulse response). The template provides a data entry table for 6–12 measurement positions across the octave bands 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. ANSI S12.60 compliance is assessed at the 500–1000 Hz average. BB93 compliance is assessed at the 500–1000–2000 Hz average (depending on room type).
Background Noise Thresholds
Background noise must be measured with all HVAC, lighting, and IT equipment running — the normal occupied-but-unoccupied condition. The measurement is LAeq over a minimum 30-minute period with no teaching activity.
| Room Type | ANSI S12.60 Limit | BB93 Limit |
|---|---|---|
| Core learning space | 35 dBA | 35 dB LAeq,30min |
| Small group room | 35 dBA | 35 dB LAeq,30min |
| Hearing loop / amplification space | 30 dBA | 30 dB LAeq,30min |
| Library | 35 dBA | 35 dB LAeq,30min |
| Gymnasium | 45 dBA | Not specified |
Both standards additionally specify octave-band limits to control low-frequency HVAC noise that is inaudible on an A-weighted meter but still degrades speech intelligibility. ANSI S12.60 §5.3.2 requires that the one-octave band sound pressure levels do not exceed the limits corresponding to NC-30 (for 35 dBA spaces) or NC-25 (for 30 dBA spaces). BB93 references the NR (Noise Rating) curves.
The NC-30 and NR-30 octave-band limits are:
| Octave Band (Hz) | NC-30 Limit (dB) | NR-30 Limit (dB) |
|---|---|---|
| 63 | 57 | 59 |
| 125 | 48 | 48 |
| 250 | 41 | 40 |
| 500 | 35 | 34 |
| 1000 | 31 | 30 |
| 2000 | 29 | 27 |
| 4000 | 28 | 25 |
| 8000 | 27 | 23 |
The template includes a plotting chart for the measured octave-band profile against the NC/NR reference curves so the compliance determination is immediately visual.
Measurement Positions
Microphone positions follow ISO 3382-2 §6.2 for RT60 and the guidance in ANSI S12.60 Annex B for background noise. The template maps a standard 8 m × 10 m classroom with eight labeled measurement positions:
- Positions 1–6: Seated pupil positions at 1.2 m height, distributed across the room excluding the front 1 m (teacher zone) and rear 0.5 m. At least 1 m from any wall.
- Position 7: Teacher standing position, front-centre of the room, 1.5 m height.
- Position 8: Centre of room, 1.2 m height. This is the reference position for RT60.
For background noise, all eight positions are measured simultaneously (or sequentially) with a minimum 30-minute LAeq. The spatial average is compared against the limit. If any single position exceeds the limit by more than 3 dB, the cause should be investigated (local HVAC diffuser, external noise ingress).
How to Conduct the Audit: Step-by-Step
Step 1 — Pre-survey preparation (30 minutes)
Obtain the room dimensions and volume from the building drawings or measure on site. Identify the room type and applicable standard (ANSI S12.60 for US, BB93 for UK, or both for international projects). Confirm that the room is unoccupied and that all HVAC and lighting systems are operating in their normal mode. Do not conduct the survey during extreme weather if external noise ingress is a concern — note weather conditions in the record.
Step 2 — Equipment setup (15 minutes)
Calibrate the sound level meter with the pistonphone calibrator, record the calibration level and date. Set up the measurement laptop with Room EQ Wizard, DIRAC, or equivalent impulse response measurement software. Position the dodecahedral loudspeaker at the teacher location.
Step 3 — RT60 measurements (45 minutes)
Measure impulse responses or interrupted noise decays at each of the 8 positions. For each position, record T20 and T30 at each octave band. Enter the data into the template's octave-band table. Calculate the spatial average for each octave band. Identify the applicable averaging bands for the standard in use (500–1000 Hz for ANSI, 500–2000 Hz for BB93 depending on room type). Record pass or fail.
Step 4 — Background noise measurements (35 minutes)
With the loudspeaker removed and all HVAC running, conduct a 30-minute LAeq measurement at each position (or use a multi-channel logger if available). Record the octave-band levels at the NC/NR reference position (typically the centre of the room). Plot against the NC-30 or NR-30 curve. Record the highest NC/NR curve touched — this is the room's NC/NR rating.
Step 5 — Compliance summary (15 minutes)
Transfer all measured values into Section 6 of the template. Each row corresponds to one criterion; each column records the measured value, the limit, and the pass/fail outcome. A classroom passes overall only if all criteria pass. Partial compliance (e.g., RT60 passes but background noise fails) must be recorded as non-compliant with a note identifying the specific failure.
Step 6 — Reporting
The completed template is the audit report. For school board or local authority submission, attach the raw measurement data (octave-band tables, impulse response files) as appendices. Retain calibration records for five years.
Using AcousPlan to Pre-Screen Before Fieldwork
The classroom acoustics calculator lets you enter room dimensions and surface materials to predict RT60 before you visit. This is useful for:
- Identifying rooms that are likely non-compliant based on construction type (concrete block walls, vinyl tile floor, plasterboard ceiling) so fieldwork priority can be set
- Modelling the RT60 improvement achievable with different ceiling treatment options before specifying the remediation
- Generating a treatment specification that can be compared against the audit findings
Related Resources
- Classroom Acoustics Calculator — calculate ANSI S12.60 and BB93 compliance for your room dimensions
- What is RT60? — foundational explanation of the reverberation time parameter
- BB93 School Acoustics Guide — detailed walkthrough of the UK standard requirements
- ANSI S12.60 Compliance Gap Analysis — how US classrooms fail and how to fix them
- Acoustic Design for Architects Guide — broader design guidance for educational buildings