What is Rw Value?

October 12th, 2021

In addition to controlling heat, insulation can be used to reduce sound transmission in your home. Acoustic insulation is generally found in walls, ceilings and floors. There are a variety of values that are tested to give an indication of acoustic resistance. If you aren’t too sure what they are or how they are measured this blog is for you! 

What is Rw?

The ‘Rw’ value, or Weighted Sound Reduction Index, is a number used to rate the effectiveness of building materials as a noise insulator. The rating is measured in decibels, therefore increasing the Rw by one translates to a reduction of approximately 1db in noise level. Airborne sound insulation ratings can range from as low as Rw 10-15 up to values of Rw 75 and greater. 

Sometimes the Rw value includes an adjustment factor called the Ctr rating. This is used to account for low frequency noise like trucks and stereo subwoofers. Ctr is always a negative number and values typically range from -4 to around -12. Many sound insulation types will represent their effectiveness by displaying the Rw and Rw+Ctr values together. 

Did you know? Every 10db reduction in noise is perceived by the human ear as being half as loud, so that a 20db noise reduction would reduce the perceived noise by 75%.

How is it measured?

The most effective way to measure sound insulation is by playing a series of sounds of varying frequencies on one side of the 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 is known as the ‘sound transmissible loss or STL value. 

Image from Soundstop.co.uk

What is NRC? 

The NRC, or Noise Reduction Coefficient, refers to how much sound a material will absorb. This is usually applied to structural materials and room finishes. Materials with a low NRC value, such as tiles, will not absorb sound as easily as those with a higher NRC like carpet. 

What should you look for in soundproofing?

The higher the Rw/Rw + Ctr values the better the product will be at performing soundproofing. NRC values on room finishes will contribute to sound transmission too, higher values will lessen the reverberation of echoes meaning less airborne noise transmission. 

It is important to choose the right insulation for your project. The soundproofing strength of a product will vary according to the situation it is used in, so it is best to get an expert opinion on how much soundproofing you will need for a given application. Our team are wall system specialists so please give us a call on 03 9308 8800 to discuss your requirements! 

Just need some expert advice?

Proud stockists of the following leading brands

  • HEBEL
  • GTEK
  • INNOVA
  • WEATHERTEX
  • NRG
  • RONDO
  • INTEX
  • WALLBOARD TOOLS
  • GTPRO
  • TREMCO