Worked Example: Apartment Bedroom — NBR 15575 Brazilian Standard
30 m³ apartment bedroom with carpet, plasterboard walls, and curtains
A 30 m³ residential living designed to NBR-15575 requires RT60 ≤ 0.5s. With Painted plaster on the ceiling, the calculated RT60 is 0.43s — PASS.
Room Setup
Total surface area: 63.6 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling | Painted plaster | 15.0 | 0.04 |
| Floor | Heavy carpet | 15.0 | 0.29 |
| Walls — painted plaster | Painted plaster | 14.0 | 0.04 |
| Walls — plasterboard | Plasterboard on studs | 8.0 | 0.07 |
| Curtains | Curtains (medium weight) | 4.0 | 0.56 |
| Bed + furnishings | Upholstered seating | 3.5 | 0.55 |
| Window | Double glazing 6mm | 2.5 | 0.03 |
| 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 × 3 × 2 = 30 m³
- 2
Total Surface Area
Stotal = 15.0 + 15.0 + 14.0 + 8.0 + 4.0 + 3.5 + 2.5 + 1.6 = 63.6 m²
- 3
Absorption per Surface at 500 Hz
Ceiling: 15.0 m² × 0.04 = 0.60 Sabins
Floor: 15.0 m² × 0.14 = 2.10 Sabins
Walls — painted plaster: 14.0 m² × 0.04 = 0.56 Sabins
Walls — plasterboard: 8.0 m² × 0.05 = 0.40 Sabins
Curtains: 4.0 m² × 0.49 = 1.96 Sabins
Bed + furnishings: 3.5 m² × 0.56 = 1.96 Sabins
Window: 2.5 m² × 0.04 = 0.10 Sabins
Door: 1.6 m² × 0.08 = 0.13 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 0.60 + 2.10 + 0.56 + 0.40 + 1.96 + 1.96 + 0.10 + 0.13 = 7.81 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 30 / 7.81 = 0.62s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.43s. Target: 0.3--0.5s per NBR-15575. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 4.5 | 5.1 | 7.8 | 12.9 | 16.1 | 16.6 |
| RT60 (s) | 1.08 | 0.95 | 0.62 | 0.38 | 0.30 | 0.29 |
| Target (s) | — | — | 0.50 | 0.50 | 0.50 | — |
| Verdict | — | — | FAIL | PASS | PASS | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (5m × 3m × 2m) and RT60 target (0.5s).
Open CalculatorField Story
A residential tower in Sao Paulo advertises NBR 15575 "Superior" acoustic performance as a premium selling point. The 5 m by 3 m master bedroom relies on soft furnishings rather than dedicated acoustic treatment: heavy carpet absorbs mid and high frequencies, a king-size bed with upholstered headboard provides absorption equivalent to two acoustic panels, and blackout curtains across the window add variable mid-frequency absorption. Plasterboard partition walls to the adjacent bedroom ride on independent studs for sound insulation, with panel absorption at low frequencies. The painted plaster ceiling and remaining walls are reflective. NBR 15575 Part 6 sets reverberation targets for residential spaces; the calculation confirms typical furnished bedrooms naturally achieve the "Superior" tier without acoustic ceiling treatment.
Frequently Asked Questions
What RT60 does a Apartment Bedroom — NBR 15575 Brazilian Standard achieve?
With the specified materials and dimensions (5m x 3m x 2m, volume 30m3), the calculated mid-frequency RT60 is 0.43s using the Sabine equation. The target under NBR-15575 is 0.3--0.5s. The result is a PASS.
What materials are used in this residential acoustic example?
This example uses Painted plaster on the Ceiling (NRC 0.04), Heavy carpet on the Floor (NRC 0.29), Painted plaster on the Walls — painted plaster (NRC 0.04), Plasterboard on studs on the Walls — plasterboard (NRC 0.07), Curtains (medium weight) on the Curtains (NRC 0.56), Upholstered seating on the Bed + furnishings (NRC 0.55), Double glazing 6mm on the Window (NRC 0.03), Solid timber door on the Door (NRC 0.09). The total absorption at 500 Hz is 7.8 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.