Worked Example: Theatre Auditorium — BS 8233 Speech Optimised
1500 m³ theatre with acoustic plaster, 350 upholstered seats, and stage curtains
A 1500 m³ cinema theatre designed to BS-8233 requires RT60 ≤ 1s. With Acoustic plaster 15mm on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.61s — MARGINAL.
Room Setup
Total surface area: 1171.0 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling — acoustic plaster | Acoustic plaster 15mm | 180.0 | 0.66 |
| Ceiling — painted plaster | Painted plaster | 195.0 | 0.04 |
| Floor — carpet | Heavy carpet | 300.0 | 0.29 |
| Floor — timber stage | Timber floor (sealed) | 75.0 | 0.09 |
| Walls — plaster | Painted plaster | 200.0 | 0.04 |
| Walls — fabric panels | Fabric-wrapped panel 50mm | 24.0 | 0.78 |
| Seating (350 seats) | Upholstered seating | 175.0 | 0.55 |
| Curtains (stage) | Curtains (medium weight) | 16.0 | 0.56 |
| Doors | Solid timber door | 6.0 | 0.09 |
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 = 25 × 15 × 4 = 1500 m³
- 2
Total Surface Area
Stotal = 180.0 + 195.0 + 300.0 + 75.0 + 200.0 + 24.0 + 175.0 + 16.0 + 6.0 = 1171.0 m²
- 3
Absorption per Surface at 500 Hz
Ceiling — acoustic plaster: 180.0 m² × 0.65 = 117.00 Sabins
Ceiling — painted plaster: 195.0 m² × 0.04 = 7.80 Sabins
Floor — carpet: 300.0 m² × 0.14 = 42.00 Sabins
Floor — timber stage: 75.0 m² × 0.10 = 7.50 Sabins
Walls — plaster: 200.0 m² × 0.04 = 8.00 Sabins
Walls — fabric panels: 24.0 m² × 0.78 = 18.72 Sabins
Seating (350 seats): 175.0 m² × 0.56 = 98.00 Sabins
Curtains (stage): 16.0 m² × 0.49 = 7.84 Sabins
Doors: 6.0 m² × 0.08 = 0.48 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 117.00 + 7.80 + 42.00 + 7.50 + 8.00 + 18.72 + 98.00 + 7.84 + 0.48 = 307.34 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 1500 / 307.34 = 0.79s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.61s. Target: 0.7--1s per BS-8233. Verdict: MARGINAL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 78.0 | 181.9 | 307.3 | 430.1 | 497.3 | 488.7 |
| RT60 (s) | 3.10 | 1.33 | 0.79 | 0.56 | 0.49 | 0.49 |
| Target (s) | — | — | 1.00 | 1.00 | 1.00 | — |
| Verdict | — | — | PASS | FAIL | FAIL | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (25m × 15m × 4m) and RT60 target (1s).
Open CalculatorField Story
A regional repertory theatre in Bristol is building a 350-seat auditorium prioritising speech intelligibility — unamplified actors must be heard from the back row. Acoustic plaster covers just under half the ceiling, providing broadband absorption without the visual presence of suspended tiles that would compromise the theatrical atmosphere. Fabric-wrapped panels on the side walls absorb first reflections that would create comb filtering. The 350 upholstered seats are the dominant absorber, matched to average audience occupancy. The timber stage floor is intentionally reflective to project actors voices. Heavy carpet in all audience circulation areas damps footfall noise. BS 8233 recommends 0.7-1.0 s for drama theatres — short enough for speech clarity but with sufficient early reflections to support acoustic projection without amplification.
Frequently Asked Questions
What RT60 does a Theatre Auditorium — BS 8233 Speech Optimised achieve?
With the specified materials and dimensions (25m x 15m x 4m, volume 1500m3), the calculated mid-frequency RT60 is 0.61s using the Sabine equation. The target under BS-8233 is 0.7--1s. The result is a MARGINAL.
What materials are used in this performance acoustic example?
This example uses Acoustic plaster 15mm on the Ceiling — acoustic plaster (NRC 0.66), Painted plaster on the Ceiling — painted plaster (NRC 0.04), Heavy carpet on the Floor — carpet (NRC 0.29), Timber floor (sealed) on the Floor — timber stage (NRC 0.09), Painted plaster on the Walls — plaster (NRC 0.04), Fabric-wrapped panel 50mm on the Walls — fabric panels (NRC 0.78), Upholstered seating on the Seating (350 seats) (NRC 0.55), Curtains (medium weight) on the Curtains (stage) (NRC 0.56), Solid timber door on the Doors (NRC 0.09). The total absorption at 500 Hz is 307.3 Sabins.
How much does acoustic treatment cost for this room?
Cost data is not available for this example. Use the AcousPlan calculator to estimate treatment costs for your specific room configuration.
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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.