Sound Transmission Loss Calculator
How many decibels a solid wall or panel blocks, from its surface mass and the frequency — the mass law of acoustics — with the level that gets through and what doubling the mass or the frequency does.
For a solid partition well above its resonance, transmission loss depends on one product: mass per square meter times frequency.
How the sound transmission loss calculator works
For a solid partition well above its resonance, transmission loss depends on one product: mass per square meter times frequency. Each doubling of either adds about 6 dB. That is why low frequencies leak through walls that stop speech, and why the cure for a noisy neighbour is mass, not foam.
The mass law is an idealization — real panels dip at the coincidence frequency and gain from double-leaf construction — but it is the right first estimate for any single solid layer.
Formula: TL ≈ 20 log₁₀(m × f) − 47 dB (m in kg/m², f in Hz)
Worked examples
| Inputs | Transmission loss (dB) | Note |
|---|---|---|
| 100 mm concrete at 500 Hz | 54.21 | about 54 dB |
| Plasterboard | 26.16 | about 26 dB |
| Bass | 36.22 | 18 dB less |
FAQFrequently asked questions
What is the mass law?
The rule that a solid partition's transmission loss rises 6 dB for each doubling of its mass per unit area or of the frequency. It is the baseline of every sound-insulation design.
Why do walls block bass so badly?
Because the loss falls 6 dB per halving of frequency. A wall giving 50 dB at 500 Hz gives about 32 at 63 Hz, which is why the neighbour's music arrives as thumping.
Does foam help?
Acoustic foam absorbs reflections inside a room; it adds almost no mass and does almost nothing for transmission. Blocking sound takes mass or an air gap between two leaves.
Where does the mass law fail?
At the coincidence frequency, where bending waves in the panel match the sound wavelength and the loss dips sharply — often 1 to 3 kHz for plasterboard. Real panels are rated by measurement.
What about double walls?
Two leaves with an air gap and absorption can beat the mass law by 10 to 20 dB above the gap's resonance. That is how lightweight partitions reach concrete-like ratings.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.