The indicator of the approximate sound insulation rating, taking into account the spectral adaptive indicator Ctr.

Professional Definition

The approximate sound insulation index, corrected for the spectral adaptation index Ctr, is a single-number parameter that determines the ability of a partition (usually external, e.g., a wall with a window) to attenuate noise, where low frequencies dominate.

In engineering practice, this parameter (often denoted as R'A,2 or the sum of R'w + Ctr) is crucial when designing facades of buildings exposed to transportation noise, such as urban, railway, or air traffic. "Approximate" insulation refers to the value obtained in field conditions (on-site), taking into account execution imperfections and lateral transmission, as opposed to ideal laboratory conditions.

Acoustics in Simple Words

Imagine that the sound insulation of your wall is a shield. A standard shield (Rw index) protects well against arrows (neighbor's conversations, dog barking – sounds of medium and high tones). However, street noise – the roar of diesel engines, the rumbling of bus wheels – is not arrows, but a heavy ram hitting at low frequency (bass).

The index with the suffix Ctr tells us how resilient this shield is to the impacts of a ram. Two windows may have the same overall level of insulation, but the one with the higher index accounting for Ctr will significantly more effectively mute the rumble of the street, even though it will let conversations through just as much as the other one.

Summary

This is a key parameter for living comfort in the city, determining real protection against low-frequency noise (bass). It takes into account the specifics of traffic and real installation conditions on site, providing a more reliable picture of silence in the apartment than standard laboratory indices.