Acoustic insulation of a wall
The R index, the calculation of which has been harmonised by standard EN ISO 717-1, relates to the acoustic quality of a wall. This refers to the difficulty it has in transmitting airborne noise. It is measured solely in the laboratory and only takes into account direct transmission (ignoring lateral transmission!). R is expressed in dB(A). It is measured across the whole spectrum from 100 to 4000 Hz.
The basic curve (in blue) is shifted dB by dB until the sum of the unfavourable values (pink dots beneath the green curve) is as high as possible, but lower than 10 dB across five octave bands (32 across 16 third octaves).
The Rw value of the wall is 500 Hz on the shifted curve (green).
In the example shown in the graph opposite, the Rw value = 40 dB(A).
Two Rw adaptation indexes have been created to take into account the properties of the noise source:
- C This is the adjustment for noise sources containing few low frequencies (fast road traffic, children playing, daily activities, etc.).
- CtrThis is the adjustment for noise sources containing many low frequencies (urban traffic, long-haul aircraft, discotheques, etc.)
The sound reduction index R of a partition / door therefore in fact comprises three terms and is expressed as follows: Rw (C; Ctr)
Example: a partition is assessed at Rw (C; Ctr) = 37(-1; -3)
This means that the weighted reduction index is 37.
For purposes of insulation against the noise of urban traffic, Ctr adjusts the sound insulation downwards to 34dB and in the case of fast motorway traffic, C adjusts the sound insulation downwards to 36dB.
If the type of noise is known from the outset (noise analysis), Heinen can adapt a door to ensure that the downward C or Ctr adjustment is minimal. For example, doors for a discotheque with a lot of low frequencies.