Isolation Calculator — Sound Transmission Loss

According to the mass law, doubling the mass of a wall increases sound isolation by approximately 6 dB. The ideal field-incidence mass law gives a single-leaf brick wall (200 kg/m²) about 53 dB at 500 Hz (20·log10(200×500) − 47 = 53 dB), matching this calculator. Real measured Rw is typically 5-8 dB lower (around 45-50 dB) because coincidence and panel stiffness reduce performance near and above the critical frequency. Adding mass is still the most predictable way to increase isolation.

Home studio: STC 45-55 (reduces loud music to faint background). Professional recording studio: STC 55-65. Broadcast studio: STC 60+. Drum room isolation: STC 65+. Each 10 STC increase roughly halves the perceived loudness transmission.

No. Decoupled double-wall construction (two separate walls with an air gap) can far exceed mass law predictions. The air gap acts as a spring, and adding absorption inside the cavity further improves performance. Flanking paths through floors, ceilings and ducts often limit real-world performance.

The mass law shows that isolation decreases by 6 dB per octave as frequency drops. Going from 500 Hz down to 50 Hz is one full decade (20·log10(50/500) = −20 dB), so a wall providing 50 dB at 500 Hz drops to about 30 dB at 50 Hz. Bass wavelengths are also longer and can more easily diffract around barriers and travel through structural paths.