What do Rw, Ctr and NRC mean?

What do Rw, Ctr and NRC mean?   
Rw, Rw+Ctr and NRC values for different materials are carefully evaluated under controlled conditions.

How is soundproofing measured?

There are a number of different measurements for soundproofing, because of the number of different factors to consider. The most effective way to measure how effectively soundproofing works is by playing a series of sounds of varying frequency on one side of a wall or ceiling and using special equipment to measure how much sound carries through to the other side. The difference in the amount of decibels (db) is what's known as the 'sound transmission loss (STL) value'.

What does Rw mean?

The Weighted Sound Reduction Index (Rw) is a number used to rate the effectiveness of a soundproofing system or material. Increasing the Rw by one translates to a reduction of approximately 1db in noise level. Therefore, the higher the Rw number, the better a sound insulator it will be.



What does Rw+Ctr mean?

Ctr is an adjustment factor which is used to account for low frequency noise - typically the biggest problem with sound insulation. Ctr is always a negative number, so the Rw+Ctr will always be less than the Rw value. Many sound insulation types will represent how effective they are by displaying the Rw/Rw+Ctr values together.

What does NRC mean?

The Noise Reduction Coefficient (NRC) measures how much sound a given material will absorb. This is usually applied to structural materials and room finishes. Materials with a low NRC value, like tiles, will not absorb sound as readily as those with a higher NRC, like carpet.

How are these values applied to insulation and building products?

These values are tested in a lab to give an indication of acoustic resistance, and will not take into account real world factors. Because each individual use of a product will vary according to the situation it's used in, it's best to get an expert opinion on how much soundproofing you will need for a given application.

What should I look for?

The higher the Rw/Rw+Ctr values of a sound insulation product, the better the product will perform as soundproofing. NRC values on room finishes will contribute to the sound landscape too; higher values will ‘deaden’ the sound in a room, lessening the reverberation of echoes, meaning less airborne noise transmission.