Theater Calculators

Signal, cables & storage

Soundproofing STC Estimator

STC ≈ 13.5 log10(mass) + 13 + 5 log10(1 + gap/20). It is a speech-range single number. Subwoofer rumble is another fight.

Inputs

Units
kg/m²

One 13 mm drywall is ~10 kg/m²; lb/ft² × 4.88 = kg/m².

mm

1 in = 25.4 mm.

Results

Estimated STC
34

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

Example products

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Calculation method

Mass law plus a crude air-gap bonus. Use it to compare “one sheet vs two with a gap”, not to pass a lab.

Exact formula

STC ≈ 13.5 log10(m) + 13 + 5 log10(1+g/20). Limits: no flanking, no coincidence dip, no mass-air-mass resonance (a gap under ~25 mm can do worse than none), no cavity insulation, no doors/windows, speech band only.

Frequently asked questions

Is STC isolation?

It is a lab number for airborne speech. Impact and bass are different tests.

More gap always better?

Mostly: a wider cavity pushes the mass-air-mass resonance lower. A gap under about 25 mm can put that resonance in the bass or low speech range and do worse than no gap there; fibre insulation in the cavity damps it and usually adds several points.

Doors?

The leaky door sets the wall. Seal it or the STC is fiction.

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