Enter Third-Octave Transmission Loss Data
Use laboratory or design-stage TL values from 125 Hz through 4000 Hz.
Example Data Table
The sample below uses a steadily improving TL curve to demonstrate the contour fit and resulting rating.
| Frequency (Hz) | 125 | 160 | 200 | 250 | 315 | 400 | 500 | 630 | 800 | 1000 | 1250 | 1600 | 2000 | 2500 | 3150 | 4000 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Example TL (dB) | 32.0 | 35.0 | 38.0 | 41.0 | 44.0 | 47.0 | 50.0 | 52.0 | 54.0 | 56.0 | 58.0 | 60.0 | 62.0 | 64.0 | 66.0 | 68.0 |
| Shifted Contour (dB) | 36.0 | 39.0 | 42.0 | 45.0 | 48.0 | 51.0 | 52.0 | 53.0 | 54.0 | 55.0 | 56.0 | 57.0 | 58.0 | 59.0 | 60.0 | 61.0 |
| Deficiency (dB) | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 | 2.0 | 1.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Example STC | 52 | Total deficiency: 27.0 dB | Maximum single deficiency: 4.0 dB | |||||||||||||||
Formula Used
This calculator applies a common STC contour-shift method across the 16 standard third-octave bands from 125 Hz to 4000 Hz.
The default limits are 32 dB total deficiency and 8 dB maximum single-band deficiency. These settings support practical contour fitting and quick engineering comparisons.
How to Use This Calculator
- Enter transmission loss values for all 16 third-octave bands.
- Set the total deficiency and optional single-band limits.
- Choose an assembly name and type for reporting clarity.
- Press Calculate STC Rating to fit the highest valid contour.
- Review the result cards, graph, and band-by-band deficiencies.
- Download CSV or PDF files for documentation or comparison work.
FAQs
1) What does STC measure?
STC estimates how well a building element reduces airborne sound, especially speech-related frequencies. Higher ratings usually mean better indoor privacy and less sound transfer.
2) Which frequencies are used here?
This calculator uses the standard 16 third-octave bands from 125 Hz through 4000 Hz, which are commonly used when fitting an STC reference contour.
3) Why do low-frequency bands matter?
Weak low-frequency performance can create large contour deficiencies. Even if high-frequency TL looks strong, poor bass isolation may lower the overall fitted rating.
4) Is this result equal to a certified laboratory rating?
No. It is a design and checking tool. Certified ratings still depend on formal test procedures, specimen conditions, mounting details, and the governing standard edition.
5) Why can the single-band check be disabled?
Some teams use flexible internal screening during early design. Disabling the extra check helps compare options quickly, though standard reporting should keep stricter criteria.
6) What inputs should I enter?
Use measured or predicted transmission loss values in decibels for each listed frequency band. Keep values consistent with the same assembly, source, and test basis.
7) What does the critical frequency card show?
It identifies the band with the largest contour deficiency. That band often reveals where the assembly is acoustically weakest and where design improvements may help most.
8) Can I compare walls, doors, and floor systems?
Yes. Any assembly with consistent third-octave TL data can be checked here. Always compare like-for-like datasets and confirm the applicable rating method for final reporting.