Weighted sound insulation rating (Rw)

Professional Definition

The weighted sound insulation index (Rw) is a method of assessment provided by the standard PN-EN ISO 717-1. This standard adjusts the reference curve to the measured sound insulation index curve.

It is a laboratory parameter, expressed in decibels (dB), which determines the ability of a partition (e.g., wall, window) to attenuate airborne sounds. Since insulation varies with frequency, the ISO 717-1 standard allows the entire frequency characteristic to be reduced to one number, facilitating product comparisons. This value pertains only to direct transmission through the partition, without the involvement of flanking paths.

Acoustics in Simple Terms

Think of this index like the “fuel consumption” stated in a car catalog. It is the result obtained under ideal laboratory conditions, where the wall is perfectly sealed, and the sound has no other escape route (e.g., through ventilation or the floor).

If a manufacturer declares an Rw of 50 dB, it indicates the theoretical potential of that barrier. It’s like the thickness of a knight's shield - the higher the number, the stronger the shield, but this index does not tell us whether the knight might be hit in an unprotected foot (what we call flanking transmission in acoustics).

Summary

The Rw index is the basic standard for comparing building materials at the purchasing stage. However, it should be noted that this is a laboratory value, which in a real building will almost always be higher than the actual achieved insulation.