Calculate STC / Rw ratings, compare glazing systems, and find the right specification for your noise environment.
ISO 717-1 / ASTM E413SGU · DGU · Laminated PVB · SGPVerified Manufacturer DataMass Law · Coincidence Dip
Glass System Builder
What is STC?
ASTM E413
—
Sound Transmission Class
US standard. Higher = better. Each +10 STC = sound perceived as roughly half as loud. STC 35 = conversational speech audible; STC 50 = loud speech inaudible.
What is Rw?
ISO 717-1
—
Weighted Sound Reduction Index
European/Indian standard. Rw+Ctr is most relevant for road traffic in Indian cities — accounts for dominant low-frequency content (buses, trucks, trains).
Coincidence Frequency
Physics
—
Critical Frequency (Hz)
At this frequency, glass resonates with sound waves — causing a performance dip. Thin glass (4-6mm) dips at 2000–3150 Hz — exactly human speech range. Lamination damps this.
Loss Factor η
Damping
—
Internal Damping Ratio
Monolithic glass η ≈ 0.002. Standard PVB η ≈ 0.04. Acoustic PVB η ≈ 0.10–0.20. Higher η suppresses the coincidence dip and improves broadband performance.
Single Glazing Unit (SGU) — All Thicknesses
Data per ISO 717-1 and ASTM E413. Verified against manufacturer published data. All values ±1 dB typical laboratory variance. Coincidence fc ≈ 12,000/d Hz.
Thickness
Weight kg/m²
STC
Rw
Rw+C
Rw+Ctr (traffic)
fc (Hz)
Rating
Mass Law vs Actual Performance
Mass Law predicts Rw ≈ 20·log₁₀(m·f) − 47 dB. Measured values can differ by ±3 dB near coincidence. Increasing thickness gives diminishing returns above 12mm due to coincidence dip migration.
Thickness
Mass kg/m²
Mass Law Rw
Actual Rw
Speech band
Traffic band
Best use
DGU — Symmetric Configurations
Symmetric DGU: cavity resonance near 150–200 Hz. Asymmetric panes stagger coincidence dips for 2–4 dB gain. Argon fill +1–2 dB Rw.
Configuration (mm)
Total mm
Mass kg/m²
STC
Rw
Rw+C
Rw+Ctr
OITC
DGU — Asymmetric Configurations
Configuration (mm)
Total mm
Mass kg/m²
STC
Rw
Rw+C
Rw+Ctr
OITC
Laminated PVB — Standard 0.38mm Interlayer
Standard PVB loss factor η ≈ 0.04. Primarily provides safety/security. Modest acoustic improvement over monolithic due to mass and slight damping. Source: Eastman Saflex® / Trosifol® data.
Configuration
Total mm
PVB mm
Mass kg/m²
STC
Rw
Rw+C
Rw+Ctr
η
Laminated PVB — Acoustic Grade 0.76mm+
Acoustic PVB: 3-layer co-extruded (stiff/soft/stiff). Loss factor η ≈ 0.10–0.20. Suppresses coincidence dip by 4–6 dB. Brands: Eastman Saflex® Q, Trosifol® Ultra Acoustic. Source: manufacturer datasheets.
Configuration
Total mm
PVB mm
Mass kg/m²
STC
Rw
Rw+C
Rw+Ctr
η
SGP Ionoplast — SentryGlas® Type
SGP is ~100× stiffer than PVB. η ≈ 0.07–0.10. Primary advantage: structural (blast, hurricane). Acoustic gain vs std PVB ≈ 1–2 dB. NOT a substitute for acoustic PVB if noise is the primary concern.
Configuration
Total mm
SGP mm
Mass kg/m²
STC
Rw
Rw+Ctr
η
Stiffness vs PVB
PVB vs SGP — Direct Comparison (same glass)
Comparing interlayer types for 6+6 and 8+8 laminated glass. SGP excels structurally; acoustic PVB excels acoustically.