# Acoustic Glass Performance
## How to Read Acoustic Performance Data for Laminated, Insulated & Composite Glass
**Key Specs Badge:** STC 39–55 ｜ TL Curve per ASTM E90 / ISO 10140 ｜ STC / Rw / OITC / NIC ｜ Lab vs Field ｜ JUMBO Glass Group
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## 01 – What This Page Covers
This page explains **how to interpret acoustic glass performance data** — what the numbers mean, how they are measured, where they come from, and what they **do not** tell you. It is written for procurement managers, specifiers, and acoustic consultants who need to evaluate glass performance claims without being misled by a single STC label.
Acoustic glass performance is not a single number. It is a **frequency-dependent transmission loss profile** expressed through a TL (Transmission Loss) curve, from which rating systems like STC and Rw are derived. Understanding the difference between the curve and the rating is the key to making informed procurement decisions
## 02 – The Transmission Loss (TL) Curve – The Foundation
Every acoustic glass performance value starts with a **Transmission Loss (TL) curve**.
TL is measured in decibels (dB) across **1/3-octave frequency bands** from 100 Hz to 5000 Hz (per ASTM E90 / EN ISO 10140). At each frequency, TL tells you how many decibels of sound the glass **blocks**.
Frequency (Hz) 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000
TL (dB) 20 22 24 26 28 30 32 34 36 38 40 42 44 45 45 44 43 42
**Key insight:** The TL curve reveals **everything**. A single STC number is just a simplified summary of this curve. Two glass builds can have the **same STC** but completely different TL curves — meaning one leaks speech while the other is private.
> **Procurement rule:** Always ask for the **TL curve**, not just the STC number.
## 03 – STC – Sound Transmission Class
**STC (Sound Transmission Class)** is the most widely used single-number rating for interior glass. It is calculated by fitting a standard contour to the TL curve per **ASTM E413** (USA) or derived from **EN ISO 717-1** (Europe, as Rw).
### What STC Measures
- Based on **16 frequency bands** from 125 Hz to 4000 Hz
- Weighted toward the **speech frequency range** (500–2000 Hz)
- Higher STC = better sound isolation
### STC Rating Guide (Glass-Only, Indicative)
| STC Range | Performance Level | Typical Application |
|-----------|------------------|---------------------|
| 25–30 | Poor – voices clearly audible | Not recommended for privacy |
| 30–35 | Fair – voices understandable but muffled | Basic partitions |
| 35–40 | Good – normal speech not intelligible | Phone booths, open offices |
| 40–45 | Very Good – loud speech barely audible | Office pods, meeting rooms |
| 45–50 | Excellent – raised voice inaudible | Executive, HR, boardrooms |
| 50+ | Superior – shouting barely audible | Recording booths, broadcast |
> **Critical note:** These are **glass-only indicative values**. Final system performance depends on frame, seals, door, and installation. STC is **not additive** — you cannot add glass STC + frame STC to get system STC.
---
## 04 – Rw – Weighted Sound Reduction Index
**Rw** is the European equivalent of STC, defined by **ISO 717-1**. While STC and Rw use similar contour-fitting methods, they are **not interchangeable**.
### STC vs Rw – Key Differences
| Parameter | STC (ASTM E413) | Rw (ISO 717-1) |
|-----------|----------------|----------------|
| Standard | ASTM E413 | ISO 717-1 |
| Frequency Range | 125–4000 Hz | 100–3150 Hz |
| Contour | STC reference contour | ISO reference contour |
| Adaptation Terms | None | **C** (pink noise) and **Ctr** (traffic noise) |
| Typical Use | North America | Europe, international |
### Rw + C / Rw + Ctr
- **Rw + C**: Adjusted for pink noise spectrum (typical indoor speech)
- **Rw + Ctr**: Adjusted for traffic noise (low-frequency weighted)
> **Procurement rule:** "STC 40 ≠ Rw 40" — even for the same glass. Always specify which standard your project requires.
---
## 05 – OITC & NIC – When STC / Rw Are Not Enough
For applications with **low-frequency noise** (HVAC, traffic, bass) or **field measurements**, STC and Rw may be insufficient.
| Metric | Full Name | Frequency Range | Use Case |
|--------|-----------|----------------|----------|
| **STC** | Sound Transmission Class | 125–4000 Hz | Lab glass performance, speech band |
| **Rw** | Weighted Sound Reduction Index | 100–3150 Hz | European lab glass performance |
| **OITC** | Outdoor-Indoor Transmission Class | 80–4000 Hz | Exterior walls, traffic noise |
| **NIC** | Noise Isolation Class | 125–4000 Hz | Field measurement (installed condition) |
### When to Use OITC
- Perimeter offices with highway traffic
- Facade glass exposed to low-frequency noise
- Any application where STC underestimates low-frequency transmission
### When to Use NIC
- Field verification after installation
- Comparing actual performance vs. lab prediction
- Troubleshooting complaints in completed projects
## 06 – The Coincidence Dip – Why STC Can Be Misleading
Every glass panel has a **coincidence frequency** — the frequency at which the bending wavelength of the glass matches the acoustic wavelength in air, causing a sharp **drop in TL**.
TL (dB)
50 | /\
45 | / \
40 | ________/ _
35 | /
30 |__/
100 250 500 1000 2000 4000 Frequency (Hz)
↑ Coincidence dip
**The problem:** If the coincidence dip falls in the **speech band (500–2000 Hz)**, the glass will leak conversation even if the STC is high.
**How acoustic glass solves this:**
- **Acoustic PVB interlayer** widens and flattens the dip
- **Asymmetric construction** (e.g., 6+8 mm) creates two different coincidence frequencies, preventing a single deep dip
> **This is why two glasses with identical STC can have completely different real-world privacy performance.** Always check the TL curve for coincidence dips in the speech band.
## 07 – Lab vs Field Performance – The 3–6 dB Rule
Laboratory STC is measured on a **bare glass sample** in a controlled acoustic chamber (ASTM E90 / ISO 10140). Field performance is measured on the **installed system** (ASTM E336 / ISO 16283).
### Why Field Performance Is Always Lower
| Factor | STC Penalty |
|--------|-------------|
| Frame flanking | -1 to -3 dB |
| Seal gaps | -1 to -2 dB |
| Ceiling plenum bypass | -2 to -4 dB |
| Door undercut | -3 to -6 dB |
| **Total system loss** | **-3 to -6 dB** |
> **Rule of thumb:** A glass with lab STC 47 will typically deliver **field STC 41–44** in a well-sealed partition system. A pod with lab STC 50 glass may achieve **ASTC 44–47** (ISO 23351) as a complete enclosure.
---
## 08 – Glass-Only vs System Performance
| Level | Rating | Standard | What It Measures |
|-------|--------|----------|------------------|
| Glass-only | STC / Rw | ASTM E90 / ISO 10140 | Single glass component |
| Wall assembly | FSTC / Field STC | ASTM E336 / ISO 16283 | Glass + frame + seals |
| Complete pod | ASTC (ISO 23351) | ISO 23351-1 | Entire enclosure |
> **ISO 23351** is a **complete booth/cabin system standard, not a glass certificate**. Glass contributes to but does not determine the final ASTC rating.
---
## 09 – Common Misinterpretations – Buyer Beware
| Myth | Reality |
|------|---------|
| "STC 50 glass means a silent pod" | STC 50 glass in a poor frame may yield ASTC 44. Glass is only one component. |
| "Higher STC is always better" | Not if the coincidence dip is in the speech band. Check the TL curve. |
| "STC values are additive" | False. You cannot add glass STC + frame STC. System performance requires calculation. |
| "Rw and STC are the same" | Similar but not interchangeable. Rw includes adaptation terms (C / Ctr). |
| "Lab STC = installed performance" | Field performance is typically 3–6 dB lower due to flanking paths. |
## 10 – How to Read a Test Report – 9-Point Checklist
When your supplier provides an acoustic test report, verify:
1. **Laboratory name** – Accredited third-party (e.g., SGS, Intertek, NVLAP)
2. **Standard cited** – ASTM E90 / ISO 10140 (not just "tested to STC")
3. **Glass build-up** – Exact thickness, PVB type, cavity width
4. **TL curve** – Full 1/3-octave data, not just a single number
5. **Frequency range** – Minimum 100–4000 Hz
6. **Sample size** – Must represent production capability
7. **Date of test** – Within 3 years (acoustic properties do not change, but standards evolve)
8. **Mounting condition** – Lab only (no frame/seal data)
9. **Disclaimer** – "Glass-only rating; system performance depends on installation"
> **Red flag:** If a supplier cannot provide a TL curve, only a stated STC number — request the full report or consider another supplier.
## 11 – Performance by Glass Type (Indicative Reference)
| Glass Type | Typical Build | Indicative STC* |
|------------|--------------|-----------------|
| Acoustic Laminated | 6+1.14PVB+6 | 41–43 |
| Acoustic Laminated | 8+1.52PVB+8 | 43–45 |
| Acoustic Insulated (IGU) | 6+16Ar+8 | 45–47 |
| Acoustic Laminated Insulated | 6+PVB+6 + 16Ar + 8 | 49–52 |
| Triple Glazing | 6+12Ar+6+12Ar+6 | 50–54 |
*\*Indicative glass-only values. Final system STC depends on frame, seals, and installation. Tested per ASTM E90 / ISO 10140.*
## 12 – Selection Guide – Which Metric for Your Project?
| Your Priority | Primary Metric | Secondary |
|---------------|---------------|-----------|
| Speech privacy (office pod) | STC / Rw | TL curve review |
| Traffic noise (perimeter office) | OITC | Rw + Ctr |
| Field verification | NIC | FSTC |
| Complete pod specification | ASTC (ISO 23351) | Glass STC + system calculation |
---
## 13 – Manufacturing & Quality – JUMBO Glass Group
- **20+ years** acoustic glass production
- **Dedicated acoustic line** – humidity-controlled PVB laminating, argon-filled IGU chamber
- **Jumbo capability** – flat tempered 3300×20000mm, laminated 3300×18000mm, IGU 3300×13000mm
- **CNC machining** – hinge/lock cut-outs, ±0.5 mm tolerance
- **QC** – 100% spark test, dimensional laser scan, TL curve on request
- **Certifications** – EN 14449, EN 12150, EN 14179, ANSI Z97.1, AS/NZS 2208, ISO 9001:2015
- **Third-party testing** – SGS / Intertek on request
- **Lead time** – samples 10–14 days; bulk 25–35 days FOB
---
## 14 – FAQ
**1. What is the difference between STC and Rw?**
STC is the North American standard (ASTM E413), Rw is the international/European standard (ISO 717-1). They use different contours and frequency ranges. "STC 40 ≠ Rw 40."
**2. Why is the TL curve more important than STC?**
STC is a single-number summary of the TL curve. Two glasses with identical STC can have very different TL curves — one may leak speech while the other is private.
**3. What is a coincidence dip?**
The frequency at which the glass panel resonates and transmission loss drops sharply. If it falls in the speech band, privacy is compromised regardless of STC.
**4. Can I add STC values?**
No. STC is not additive. System performance requires calculation considering all flanking paths.
**5. What is the difference between lab STC and field STC?**
Lab STC is measured on bare glass (ASTM E90). Field STC is measured on the installed system (ASTM E336). Field is typically 3–6 dB lower.
**6. What is ISO 23351?**
A standard for measuring acoustic attenuation of complete office pods/cabins. It is a **system standard, not a glass certificate**.
**7. When should I use OITC instead of STC?**
When low-frequency noise (traffic, HVAC bass) is the primary concern. OITC covers 80–4000 Hz vs. STC's 125–4000 Hz.
**8. How do I verify a supplier's test report?**
Check lab accreditation, standard cited, glass build-up, TL curve data, and date. See our 9-point checklist above.
**9. Does argon fill improve acoustic performance?**
Slightly — argon adds 1–2 STC points via higher density. Its main benefit is thermal (U-value).
**10. How do I request a quote?**
Send your glass build-up, target STC/Rw, dimensions, and project details to sales@jumbotemperedglass.com.
---
## 15 – Final CTA
### Need Help Interpreting Acoustic Performance Data?
Send us your specification or competitor's test report. Our engineering team will review the TL curve, identify coincidence dips, and recommend the optimal glass build for your target performance.
[Request a Quote] [Download Performance Guide] [Send Your Drawing]
- 📩 Email: tomron1688@gmail.com
- [Request a Quote] [Download Datasheet]
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