Why does 1% open area destroy so much performance?

Because transmission adds by area, not by decibels. An opening transmits essentially all the sound that hits it, so 1% open area passes 1% of the incident energy no matter what the other 99% is made of. Ten times log ten of one over 0.01 is 20 dB, and that is the ceiling for the whole assembly. A heavier barrier cannot buy back energy that is going straight through a hole.

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 where performance collapses over a band of frequencies, and takes no account of flanking through the structure. Laboratory ratings measured to ASTM E90 already come in below it, and field performance comes in below the laboratory rating. Treat the number here as a ceiling.

Which mass-law constant does this use, and does it matter?

It uses the field-incidence imperial constant of 38.5. The normal-incidence value is roughly 5 dB more favourable, and quoting it for a real partition overstates the barrier by that margin. Five decibels is the difference between an enclosure that satisfies a specification and one that gets torn out and rebuilt, so the page states which convention it applied rather than leaving you to guess.

Why does doubling the barrier weight only add 6 dB?

Because the relationship is logarithmic: twenty times the log of twice a number is about six more than twenty times the log of the number. That is the fundamental economics of mass barriers. It is also why sealing wins so often, since removing a 2% opening can be worth more than doubling the material you hang.

Can I use this for a partition wall rather than an enclosure?

Only as a first sanity check. Partition walls are usually multi-layer assemblies with studs, cavities and insulation, and their performance depends on the decoupling between layers far more than on total mass. Use a tested STC or laboratory TL rating for the actual assembly instead, and use this calculator to understand why leaks and flanking will still pull the field result below it.

What does the blocking warning about the leakage ceiling mean?

It means the open area alone caps the assembly below your target, so no barrier specification can reach it. The calculator blocks rather than quietly returning a shortfall because the natural next move, add mass, cannot work, and following it wastes both money and the chance to fix the real problem. Seal first, then come back and size the barrier.

Acoustic, Noise, Vibration & NVH Products calculator

Barrier Decibel Reduction Calculator (Mass Law with Leakage)

Estimate what a mass barrier will really achieve at the frequency that matters, including the penalty its openings impose. Enter the barrier's surface density, the frequency of interest, the percentage of the area that is gap or pass-through, and the reduction you need. The calculator applies the field-incidence mass law to the sealed barrier, then combines barrier and openings by area-weighted transmission coefficient to produce the composite figure a measurement would actually show. It exists because the sealed number is the one people quote and the composite number is the one they get, and the gap between them decides whether an enclosure works.

What this calculator does

Estimate the reduction a mass barrier will actually deliver once its openings are counted, using the field-incidence mass law and an area-weighted composite.
Use it for checking whether a proposed enclosure can meet a dB target before quoting it, deciding between adding barrier mass and sealing existing gaps, sizing barrier weight for a specific octave band complaint, explaining to a customer why a heavier curtain will not fix a leaking enclosure.
Estimate the reduction a mass barrier will actually deliver 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) − 38.5, 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 38.5 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. Mass-loaded vinyl is commonly 0.5–2 lb/ft²; 18 ga steel is about 2 lb/ft².
Frequency of interest: The octave-band centre frequency driving the complaint. Mass barriers perform far worse low down.
Open or untreated area: Share of the barrier area that is gap, duct, cable pass-through or unsealed seam. This usually decides the answer.
Target reduction: The reduction the specification or the complaint requires at this frequency.

How to use the result

Best suited to checking whether a proposed enclosure can meet a dB target before quoting it, deciding between adding barrier mass and sealing existing gaps, sizing barrier weight for a specific octave band complaint, explaining to a customer why a heavier curtain will not fix a leaking enclosure.
Not a measurement and not a laboratory rating: real assemblies underperform this figure. Ignores the coincidence dip, panel resonance and any stiffness effect, all of which matter for rigid sheets. Ignores flanking through the floor, structure or connected ductwork, which often dominates in practice. Below roughly 125 Hz it is optimistic, because the required mass becomes impractical and resonance takes over.

Common questions

Why does 1% open area destroy so much performance? Because transmission adds by area, not by decibels. An opening transmits essentially all the sound that hits it, so 1% open area passes 1% of the incident energy no matter what the other 99% is made of. Ten times log ten of one over 0.01 is 20 dB, and that is the ceiling for the whole assembly. A heavier barrier cannot buy back energy that is going straight through a hole.
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 where performance collapses over a band of frequencies, and takes no account of flanking through the structure. Laboratory ratings measured to ASTM E90 already come in below it, and field performance comes in below the laboratory rating. Treat the number here as a ceiling.
Which mass-law constant does this use, and does it matter? It uses the field-incidence imperial constant of 38.5. The normal-incidence value is roughly 5 dB more favourable, and quoting it for a real partition overstates the barrier by that margin. Five decibels is the difference between an enclosure that satisfies a specification and one that gets torn out and rebuilt, so the page states which convention it applied rather than leaving you to guess.
Why does doubling the barrier weight only add 6 dB? Because the relationship is logarithmic: twenty times the log of twice a number is about six more than twenty times the log of the number. That is the fundamental economics of mass barriers. It is also why sealing wins so often, since removing a 2% opening can be worth more than doubling the material you hang.
Can I use this for a partition wall rather than an enclosure? Only as a first sanity check. Partition walls are usually multi-layer assemblies with studs, cavities and insulation, and their performance depends on the decoupling between layers far more than on total mass. Use a tested STC or laboratory TL rating for the actual assembly instead, and use this calculator to understand why leaks and flanking will still pull the field result below it.

Last reviewed 2026-08-25.