Why does 1% open area destroy so much performance?

Transmission adds by area, not decibels. An opening passes essentially all the sound that hits it, so 1% open area passes 1% of the energy whatever the other 99% is made of. That caps the assembly at 20 dB.

Is the mass law optimistic or pessimistic?

Optimistic in almost every real case. It assumes a limp panel with no stiffness, ignores the coincidence dip and flanking, and laboratory ratings already come in below it. Treat the result as a ceiling.

Why does doubling the barrier weight only add 6 dB?

The relationship is logarithmic: 20 times the log of twice a number is about 6 more than 20 times the log of the number. That is why removing a 2% opening can beat doubling the material.

Can I use this for a partition wall?

Only as a first check. Partition performance depends on decoupling between layers more than total mass. Use a tested STC or laboratory rating for the assembly, and this page only to see how leakage pulls it down.

Acoustic, Noise, Vibration & NVH Products calculator

Barrier Decibel Reduction Calculator (Mass Law With Leakage)

Find what a mass barrier achieves at the frequency that matters, including the penalty its openings impose. Enter surface density, frequency, open area and the target; the page returns the sealed and composite transmission loss.

What this calculator does

Estimate the reduction a mass barrier delivers once its openings are counted, using the field-incidence mass law and an area-weighted composite.

Formula used

Sealed barrier TL = 20 × log10(surface density × frequency) − 33.5, floored at zero
Barrier transmission coefficient = 10^(−barrier TL ÷ 10)
Composite coefficient = (1 − open fraction) × barrier coefficient + open fraction
Composite TL = 10 × log10(1 ÷ composite coefficient)
Constant 33.5 is the field-incidence imperial form; normal incidence would read about 5 dB higher

Inputs explained

Barrier Surface Density: Weight per square foot of the barrier layer, from the datasheet.
Frequency of Interest: Octave-band centre frequency driving the complaint.
Open or Untreated Area: Share that is gap, duct, pass-through or unsealed seam.
Target Reduction: Reduction the specification or complaint requires at this frequency.

How to use the result

Best suited to checking a proposed enclosure against a dB target, deciding between adding mass and sealing gaps, explaining why heavier curtains will not fix leaks.
Not a measurement or laboratory rating: real assemblies underperform this figure. Ignores the coincidence dip, panel resonance and stiffness effects that matter for rigid sheets. Ignores flanking through structure or ductwork, which often dominates in practice.

Common questions

Why does 1% open area destroy so much performance? Transmission adds by area, not decibels. An opening passes essentially all the sound that hits it, so 1% open area passes 1% of the energy whatever the other 99% is made of. That caps the assembly at 20 dB.
Is the mass law optimistic or pessimistic? Optimistic in almost every real case. It assumes a limp panel with no stiffness, ignores the coincidence dip and flanking, and laboratory ratings already come in below it. Treat the result as a ceiling.
Why does doubling the barrier weight only add 6 dB? The relationship is logarithmic: 20 times the log of twice a number is about 6 more than 20 times the log of the number. That is why removing a 2% opening can beat doubling the material.
Can I use this for a partition wall? Only as a first check. Partition performance depends on decoupling between layers more than total mass. Use a tested STC or laboratory rating for the assembly, and this page only to see how leakage pulls it down.

Last reviewed 2026-10-01.