The Difference Between Rw and Dw
TYPES OF SOUND INSULATION IN
There are two main types of noise that are of concern
when it comes to sound insulation in buildings.
Music from a loudspeaker
Sound from a television
Airborne noise is any unwanted noise that travels or
transfers through the air. It is most relevant when
constructing partitions between rooms.
This is defined as a variant of either Rw or Dw, and is
usually specified as a minimum value of insulation which
must be achieved.
Impact noise occurs when energy passes into a partition
from an impact, and re-radiates as noise on the other
side. The example of this you will likely be most familiar
with is footsteps on a floor that can be heard in the room
below - especially concerning in domestic situations.
Impact is a form of structure-borne noise, which many of
us have also experienced when neighbours decided to get
the drill out and do some DIY too early on a Sunday
morning! This is specified as a variant of Lw and, in
contrast to airborne sound insulation, is specified as an
upper limit which must not be exceeded.
Avoiding Flanking and The Difference Between Rw and Dw
Ductwork passing from room
to room may also prove an
issue, but cross-talk
sections of ductwork with
acoustic lining) can be used to
stop ducting acting like a
“speaking tube”, and allowing
speech to transfer from room
Flanking is sound that transfers from Room A to B through a
route other than directly through the partition. This might
include junctions of walls with ceilings or floors, if the partition
isn’t properly detailed and sealed. It's also common for a hole to
be drilled through the partition, for example for cables, then not
be properly sealed, leading to excessive flanking.
Products like expanding foam won't stop noise from passing
through; in any case, the key to sound insulation is mass. To stop
sound flanking, small openings need to be properly stopped up
with mineral wool and mastic. Larger openings may require a
cover plate to perform as intended.
Rw and Dw
THE DIFFERENCE BETWEEN
The laboratory stated value of
the sound reduction index of
a building. It can, for example,
apply to walls, ceilings, floors,
doors, windows, etc.
The on-site measured values
of the sound insulation. This is
the target used to measure
against in pre-completion
Both Rw and Dw are ways of rating the
performance of a partition in terms of Sound
Insulation which must be achieved.
SO, YOU WANT TO ACHIEVE DECENT
FOLLOW THE "GOLDEN RULES"
Get some help on specification from an acoustic
consultant - it's not just about the wall / floor
Build it properly - sound can be like water, it'll trickle
through any holes you leave
Throw that expanding foam in the bin... Please?
WE'D BE HAPPY TO HELP