Acoustic Calculator

Calculate sound transmission, absorption coefficients, and acoustic properties for various building materials including glass, concrete, wood, and more.

ASTM E413 · ISO 717-1 · ASTM C423

Select Material

glass

concrete

wood

metal

insulation

other

Material Properties

Typical range: 3-20mm

Default density for Standard Glass (Annealed): 2500 kg/m³

Quick Tip:

The calculator uses industry-standard formulas to compute STC ratings, transmission loss, and absorption coefficients across octave bands from 63Hz to 8kHz.

Configure inputs and calculate to see results

About Acoustic Calculator

The acoustic calculator estimates the sound transmission and absorption performance of building materials, returning the mass-law transmission loss, STC rating, NRC, and critical frequency. It is used by acousticians and building designers to compare glazing and partition options for noise control.

Pick a material and thickness (or configure a laminated or double-glazed build-up), and the tool computes the mass per unit area, the critical and resonance frequencies, an octave-band transmission loss and absorption response, and the summary STC and NRC ratings, all sanitized to remain finite even for degenerate inputs.

How It Works

  1. Compute the mass per unit area from material density and thickness.
  2. Evaluate the mass-law transmission loss TL = 20*log10(m*f) - 48 across the octave bands, with resonance and coincidence corrections.
  3. Find the critical frequency from the panel bending stiffness and mass, and the panel resonance frequency.
  4. Average the band transmission losses to a simplified STC rating and average the absorption coefficients (250 to 2000 Hz) to an NRC.

Worked Example

A 6 mm annealed glass pane with density 2500 kg/m3. Mass per unit area m = 2500 * 0.006 = 15 kg/m2. Mass-law TL at 500 Hz = 20*log10(15 * 500) - 48 = 20*log10(7500) - 48 = 20*3.875 - 48 = 29.5 dB. The critical frequency works out to about 2000 Hz.

Formulas

Mass per unit area
m = rho * h
Mass-law transmission loss
TL = 20 * log10(m * f) - 48
Critical frequency
fc = (c^2 / (2 * pi)) * sqrt(m / D)
NRC absorption rating
NRC = (a250 + a500 + a1000 + a2000) / 4

Standards & References

  • ASTM E413
  • ISO 717-1
  • ASTM C423

Frequently Asked Questions

What is the STC rating?

STC (Sound Transmission Class) is a single-number rating of how well a partition attenuates airborne sound, derived from the transmission loss across the speech-frequency bands per ASTM E413. Higher STC means better sound isolation.

What is the critical (coincidence) frequency?

The critical frequency is where the bending wavelength in the panel matches the airborne sound wavelength, causing a coincidence dip in transmission loss. It depends on the panel mass and bending stiffness, so thinner, stiffer panels have higher critical frequencies.

What is the difference between STC and NRC?

STC measures sound transmission through a partition (isolation between spaces), while NRC measures sound absorption at the surface (how much sound is absorbed rather than reflected within a room). They describe different acoustic problems.

Does the calculator handle laminated and double glazing?

Yes. It models single panes, laminated glass with a damping PVB interlayer, and double-glazed units with a mass-air-mass resonance, applying coincidence-dip and damping corrections for each configuration.