Worked Example: University Lecture Theatre — BS 8233 Design
RT60 calculation for a 200-seat university lecture theatre under BS 8233:2014. Uses partial Armstrong ceiling coverage and targeted wall treatment to balance speech clarity with appropriate room liveliness.
A 810 m³ classroom designed to BS-8233 requires RT60 ≤ 1s. With Armstrong Ultima+ on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.68s — PASS.
Room Setup
Total surface area: 570.2 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Armstrong Ultima+ | 120.0 | 0.80 |
| walls-main | Painted plaster | 223.0 | 0.04 |
| walls-treatment | Fabric-wrapped panel 50mm | 20.0 | 0.80 |
| floor | Carpet (heavy) | 180.0 | 0.30 |
| windows | Double glazing 6mm | 20.0 | 0.04 |
| door | Solid timber door | 7.2 | 0.08 |
Absorption coefficients sourced from manufacturer datasheets and ISO 354 test reports. Browse the full acoustic materials database.
Step-by-Step Calculation
- 1
Room Volume
V = L × W × H = 15 × 12 × 4.5 = 810 m³
- 2
Total Surface Area
Stotal = 120.0 + 223.0 + 20.0 + 180.0 + 20.0 + 7.2 = 570.2 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 120.0 m² × 0.85 = 102.00 Sabins
walls-main: 223.0 m² × 0.04 = 8.92 Sabins
walls-treatment: 20.0 m² × 0.78 = 15.60 Sabins
floor: 180.0 m² × 0.14 = 25.20 Sabins
windows: 20.0 m² × 0.04 = 0.80 Sabins
door: 7.2 m² × 0.08 = 0.58 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 102.00 + 8.92 + 15.60 + 25.20 + 0.80 + 0.58 = 153.10 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 810 / 153.10 = 0.85s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.68s. Target: 0.6--1s per BS-8233. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 42.8 | 101.0 | 153.1 | 203.9 | 240.1 | 242.1 |
| RT60 (s) | 3.04 | 1.29 | 0.85 | 0.64 | 0.54 | 0.54 |
| Target (s) | — | — | 1.00 | 1.00 | 1.00 | — |
| Verdict | — | — | PASS | PASS | FAIL | — |
Compliance Verdict
Reference: BS 8233:2014 Table 4
BS 8233 recommends RT60 of 0.6-1.0s for lecture theatres depending on volume. This 810 m³ room needs balanced absorption to maintain speech clarity without sounding dead.
STI result: 0.68 (per IEC 60268-16:2020)
Cost Estimate
Costs are indicative and vary by region, supplier, and installation complexity. For a detailed cost breakdown, use the AcousPlan calculator.
Open the AcousPlan calculator pre-loaded with the exact room dimensions (15m × 12m × 4.5m) and RT60 target (1s).
Open CalculatorField Story
Students in a 1960s university lecture theatre consistently rate the room poorly on satisfaction surveys, citing inability to hear the lecturer from beyond row 8. The original brutalist design features exposed concrete on all surfaces. A refurbishment budget is allocated, but the heritage officer insists the concrete walls remain visible from the front. The acoustic consultant devises a scheme with partial Armstrong ceiling coverage and carpet throughout, supplemented by fabric panels on the upper rear and side walls where they are less architecturally prominent — achieving compliance while respecting the building's character.
Frequently Asked Questions
What RT60 does a University Lecture Theatre — BS 8233 Design achieve?
With the specified materials and dimensions (15m x 12m x 4.5m, volume 810m3), the calculated mid-frequency RT60 is 0.68s using the Sabine equation. The target under BS-8233 is 0.6--1s. The result is a PASS.
What materials are used in this education acoustic example?
This example uses Armstrong Ultima+ on the ceiling (NRC 0.8), Painted plaster on the walls-main (NRC 0.04), Fabric-wrapped panel 50mm on the walls-treatment (NRC 0.8), Carpet (heavy) on the floor (NRC 0.3), Double glazing 6mm on the windows (NRC 0.04), Solid timber door on the door (NRC 0.08). The total absorption at 500 Hz is 153.1 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is £20,800 for 320 m2 of absorptive material at approximately £65/m2. Actual costs vary by region, supplier, and installation complexity.
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All calculations are advisory and based on the Sabine equation (ISO 3382-2:2008 Annex A). Results require professional verification for compliance submissions. Absorption coefficients are sourced from manufacturer datasheets and ISO 354 test reports.