Worked Example: Brazilian University Auditorium — NBR 15575
RT60 calculation for a Brazilian university auditorium under NBR 15575 acoustic requirements. Perforated metal ceiling with mineral wool backing and fabric wall panels address the challenges of a concrete block building in a tropical climate.
A 640 m³ classroom designed to NBR-15575 requires RT60 ≤ 1s. With Perforated metal ceiling on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.52s — PASS.
Room Setup
Total surface area: 560.0 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Perforated metal ceiling | 160.0 | 0.75 |
| walls-main | Painted concrete block | 152.0 | 0.07 |
| walls-treatment | Fabric-wrapped panel 50mm | 56.0 | 0.80 |
| floor | Vinyl/linoleum floor | 160.0 | 0.03 |
| windows | Single glazing | 24.0 | 0.15 |
| door | Solid timber door | 8.0 | 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 = 16 × 10 × 4 = 640 m³
- 2
Total Surface Area
Stotal = 160.0 + 152.0 + 56.0 + 160.0 + 24.0 + 8.0 = 560.0 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 160.0 m² × 0.80 = 128.00 Sabins
walls-main: 152.0 m² × 0.06 = 9.12 Sabins
walls-treatment: 56.0 m² × 0.78 = 43.68 Sabins
floor: 160.0 m² × 0.03 = 4.80 Sabins
windows: 24.0 m² × 0.18 = 4.32 Sabins
door: 8.0 m² × 0.08 = 0.64 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 128.00 + 9.12 + 43.68 + 4.80 + 4.32 + 0.64 = 190.56 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 640 / 190.56 = 0.54s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.52s. Target: ≤ 1s per NBR-15575. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 100.3 | 164.8 | 190.6 | 204.2 | 192.8 | 173.4 |
| RT60 (s) | 1.03 | 0.63 | 0.54 | 0.50 | 0.53 | 0.59 |
| Target (s) | — | — | 1.00 | 1.00 | 1.00 | — |
| Verdict | — | — | PASS | PASS | PASS | — |
Compliance Verdict
Reference: NBR 15575:2021 Part 6, §14
NBR 15575:2021 Part 6 establishes acoustic performance requirements for Brazilian buildings. University auditoria should target RT60 of 0.8-1.0s for a balance between speech clarity and room envelopment.
STI result: 0.63 (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 (16m × 10m × 4m) and RT60 target (1s).
Open CalculatorField Story
A federal university in São Paulo is renovating its 1980s auditorium, a concrete block structure typical of Brazilian institutional buildings. Students frequently record lectures on their phones but the recordings are unusable due to excessive reverberation. The original RT60 exceeds 3 seconds. Budget constraints preclude replacing the concrete block walls, so the engineering team focuses on a new perforated metal ceiling system with 100mm mineral wool backing — providing high absorption at a cost point suitable for a public institution — supplemented by strategically placed fabric panels on the rear and side walls where they have maximum acoustic impact.
Frequently Asked Questions
What RT60 does a Brazilian University Auditorium — NBR 15575 achieve?
With the specified materials and dimensions (16m x 10m x 4m, volume 640m3), the calculated mid-frequency RT60 is 0.52s using the Sabine equation. The target under NBR-15575 is 1s or less. The result is a PASS.
What materials are used in this education acoustic example?
This example uses Perforated metal ceiling on the ceiling (NRC 0.75), Painted concrete block on the walls-main (NRC 0.07), Fabric-wrapped panel 50mm on the walls-treatment (NRC 0.8), Vinyl/linoleum floor on the floor (NRC 0.03), Single glazing on the windows (NRC 0.15), Solid timber door on the door (NRC 0.08). The total absorption at 500 Hz is 190.6 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is R$7,560 for 216 m2 of absorptive material at approximately R$35/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.