Worked Example: Home Cinema — THX Reference Standard Design
40 m³ home cinema with acoustic foam ceiling, fabric panel walls, and heavy carpet
A 40 m³ cinema theatre designed to ISO-3382 requires RT60 ≤ 0.4s. With Acoustic foam 50mm on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.17s — MARGINAL.
Room Setup
Total surface area: 75.6 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling — acoustic foam | Acoustic foam 50mm | 20.0 | 0.63 |
| Floor | Heavy carpet | 20.0 | 0.29 |
| Walls — fabric panels | Fabric-wrapped panel 50mm | 14.0 | 0.78 |
| Rear wall — mineral wool | Mineral wool 50mm (wall) | 6.0 | 0.73 |
| Screen wall | Painted plaster | 8.0 | 0.04 |
| Walls — plasterboard | Plasterboard on studs | 6.0 | 0.07 |
| Door | Solid timber door | 1.6 | 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 = 5 × 4 × 2 = 40 m³
- 2
Total Surface Area
Stotal = 20.0 + 20.0 + 14.0 + 6.0 + 8.0 + 6.0 + 1.6 = 75.6 m²
- 3
Absorption per Surface at 500 Hz
Ceiling — acoustic foam: 20.0 m² × 0.55 = 11.00 Sabins
Floor: 20.0 m² × 0.14 = 2.80 Sabins
Walls — fabric panels: 14.0 m² × 0.78 = 10.92 Sabins
Rear wall — mineral wool: 6.0 m² × 0.70 = 4.20 Sabins
Screen wall: 8.0 m² × 0.04 = 0.32 Sabins
Walls — plasterboard: 6.0 m² × 0.05 = 0.30 Sabins
Door: 1.6 m² × 0.08 = 0.13 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 11.00 + 2.80 + 10.92 + 4.20 + 0.32 + 0.30 + 0.13 = 29.67 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 40 / 29.67 = 0.22s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.17s. Target: 0.2--0.4s per ISO-3382. Verdict: MARGINAL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 7.0 | 18.2 | 29.7 | 41.2 | 49.0 | 50.4 |
| RT60 (s) | 0.91 | 0.35 | 0.22 | 0.16 | 0.13 | 0.13 |
| Target (s) | — | — | 0.40 | 0.40 | 0.40 | — |
| Verdict | — | — | PASS | FAIL | FAIL | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (5m × 4m × 2m) and RT60 target (0.4s).
Open CalculatorField Story
An audiophile in Surrey is converting the double garage into a dedicated home cinema pursuing THX certification. The 5 m by 4 m space with 2 m ceilings is treated on every surface except the screen wall, which remains hard plaster as a reflective boundary for the acoustically transparent projection screen. Acoustic foam on the ceiling eliminates vertical flutter echo. Fabric-wrapped panels on both side walls absorb first lateral reflections from the 7.2.4 Dolby Atmos speaker array. Dense mineral wool on the rear wall prevents reflections reaching the listening position with a delay exceeding 20 ms. A section of plasterboard remains for mounting rear speakers. THX specifications require RT60 below 0.4 s for rooms under 60 m³ — ensuring precise phantom image positioning and clean bass response.
Frequently Asked Questions
What RT60 does a Home Cinema — THX Reference Standard Design achieve?
With the specified materials and dimensions (5m x 4m x 2m, volume 40m3), the calculated mid-frequency RT60 is 0.17s using the Sabine equation. The target under ISO-3382 is 0.2--0.4s. The result is a MARGINAL.
What materials are used in this residential acoustic example?
This example uses Acoustic foam 50mm on the Ceiling — acoustic foam (NRC 0.63), Heavy carpet on the Floor (NRC 0.29), Fabric-wrapped panel 50mm on the Walls — fabric panels (NRC 0.78), Mineral wool 50mm (wall) on the Rear wall — mineral wool (NRC 0.73), Painted plaster on the Screen wall (NRC 0.04), Plasterboard on studs on the Walls — plasterboard (NRC 0.07), Solid timber door on the Door (NRC 0.09). The total absorption at 500 Hz is 29.7 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.