Worked Example: Cinema Auditorium — BS 8233 Low Reverberation Design
2000 m³ cinema with mineral wool ceiling, fabric walls, and 250 upholstered seats
A 2000 m³ cinema theatre designed to BS-8233 requires RT60 ≤ 0.5s. With Mineral wool 50mm (wall) on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.44s — PASS.
Room Setup
Total surface area: 1323.0 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling — mineral wool | Mineral wool 50mm (wall) | 400.0 | 0.73 |
| Floor | Heavy carpet | 400.0 | 0.29 |
| Walls — fabric panels | Fabric-wrapped panel 50mm | 200.0 | 0.78 |
| Walls — painted plaster (screen) | Painted plaster | 60.0 | 0.04 |
| Seating (250 seats) | Upholstered seating | 125.0 | 0.55 |
| Rear wall — acoustic foam | Acoustic foam 50mm | 30.0 | 0.63 |
| Walls — plaster (upper sides) | Painted plaster | 100.0 | 0.04 |
| Doors | Solid timber door | 8.0 | 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 = 20 × 20 × 5 = 2000 m³
- 2
Total Surface Area
Stotal = 400.0 + 400.0 + 200.0 + 60.0 + 125.0 + 30.0 + 100.0 + 8.0 = 1323.0 m²
- 3
Absorption per Surface at 500 Hz
Ceiling — mineral wool: 400.0 m² × 0.70 = 280.00 Sabins
Floor: 400.0 m² × 0.14 = 56.00 Sabins
Walls — fabric panels: 200.0 m² × 0.78 = 156.00 Sabins
Walls — painted plaster (screen): 60.0 m² × 0.04 = 2.40 Sabins
Seating (250 seats): 125.0 m² × 0.56 = 70.00 Sabins
Rear wall — acoustic foam: 30.0 m² × 0.55 = 16.50 Sabins
Walls — plaster (upper sides): 100.0 m² × 0.04 = 4.00 Sabins
Doors: 8.0 m² × 0.08 = 0.64 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 280.00 + 56.00 + 156.00 + 2.40 + 70.00 + 16.50 + 4.00 + 0.64 = 585.54 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 2000 / 585.54 = 0.55s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.44s. Target: 0.3--0.5s per BS-8233. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 126.9 | 381.8 | 585.5 | 774.4 | 891.9 | 900.9 |
| RT60 (s) | 2.54 | 0.84 | 0.55 | 0.42 | 0.36 | 0.36 |
| Target (s) | — | — | 0.50 | 0.50 | 0.50 | — |
| Verdict | — | — | MARGINAL | PASS | PASS | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (20m × 20m × 5m) and RT60 target (0.5s).
Open CalculatorField Story
A boutique cinema chain is building a premium 250-seat auditorium in London targeting Dolby Atmos certification, demanding RT60 below 0.5 seconds. Every surface except the screen wall is heavily treated: mineral wool panels behind perforated fabric cover the entire ceiling, fabric-wrapped panels line both side walls at lower levels, and acoustic foam on the rear wall prevents delayed reflections reaching back rows. The upper side walls remain as painted plaster to manage cost. Heavy carpet eliminates footfall noise during quiet scenes. The 250 fully upholstered seats each contain 50 mm foam. BS 8233 and the Dolby standards converge: a cinema must be acoustically "dead" so the multi-channel sound system has total control over spatial audio imaging.
Frequently Asked Questions
What RT60 does a Cinema Auditorium — BS 8233 Low Reverberation Design achieve?
With the specified materials and dimensions (20m x 20m x 5m, volume 2000m3), the calculated mid-frequency RT60 is 0.44s using the Sabine equation. The target under BS-8233 is 0.3--0.5s. The result is a PASS.
What materials are used in this performance acoustic example?
This example uses Mineral wool 50mm (wall) on the Ceiling — mineral wool (NRC 0.73), Heavy carpet on the Floor (NRC 0.29), Fabric-wrapped panel 50mm on the Walls — fabric panels (NRC 0.78), Painted plaster on the Walls — painted plaster (screen) (NRC 0.04), Upholstered seating on the Seating (250 seats) (NRC 0.55), Acoustic foam 50mm on the Rear wall — acoustic foam (NRC 0.63), Painted plaster on the Walls — plaster (upper sides) (NRC 0.04), Solid timber door on the Doors (NRC 0.09). The total absorption at 500 Hz is 585.5 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.