Sound Transmission Loss Calculator Formula
Understand the math behind the sound transmission loss calculator. Each variable explained with a worked example.
Formulas Used
Transmission Loss
tl = 20 * log10(frequency * surface_mass) - 47.3Variables
| Variable | Description | Default |
|---|---|---|
frequency | Frequency(Hz) | 500 |
surface_mass | Surface Mass Density(kg/m2) | 20 |
How It Works
Mass Law for Sound Transmission Loss
The mass law gives the theoretical TL of a single homogeneous panel.
Formula
TL = 20 log10(f m) - 47.3 dB
Doubling the mass or frequency increases TL by about 6 dB. This is the field-incidence mass law, valid below the coincidence frequency.
Worked Example
20 kg/m2 concrete panel at 500 Hz.
- 01TL = 20 log10(500 * 20) - 47.3
- 02TL = 20 log10(10000) - 47.3
- 03TL = 20 * 4 - 47.3
- 04TL = 80 - 47.3 = 32.7 dB
Frequently Asked Questions
Why does the mass law fail at certain frequencies?
At the coincidence frequency, bending waves in the panel match the airborne sound wavelength, causing a dip in TL. This frequency depends on panel stiffness and thickness.
How can I exceed the mass law?
Use double-leaf constructions (two panels with an air gap), add damping, or use different-thickness panels to avoid common coincidence frequencies.
Is thicker always better?
Heavier is better within the mass-law regime. Very thick panels of the same material are also stiffer, which can lower the coincidence frequency and reduce TL at mid frequencies.
Ready to run the numbers?
Open Sound Transmission Loss Calculator