Sound insulation performance must be substantiated and based on UKAS accredited laboratories test reports, tested to BS EN ISO 717-1:1997 and BS EN ISO 10140-2:2010.

The quoted figures on this website are laboratory tested measured as the Weighted Sound Reduction Index (Rw) measured in decibels (dB), hence all values are RwdB figures.

All sound insulation data is based on laboratory evaluation of the building element in isolation and cannot reproduce your installed local conditions.  It is important that flanking transmission is considered at design stage.

On site testing is measured using a different scale. It uses DnT,w Standardised Level Difference.  Values on site are approximately 7 to 8 decibels lower than achieved in the laboratory.  One of the primary reasons for this difference will be the downgrading due to flanking transmission.  This highlights the importance for good design and flanking details to help minimise these reductions.  Deflection head details, if used, can also be expected to impact negatively on the decibel rating achieved on site.


  1. Duty Grade BS 5234-2:1992 Annexes A-F
  2. Calculated on a maximum limiting deflection of L/240 at 200 Pa at 600mm stud centres, greater heights can be achieved by reducing centres
  3. Excluding finishes
  4. BS 476:1987:Part 22 in minutes
  5. BS EN ISO 10140-2:2010
Speedline c studs incorporating British Gypsum Acoustic Boards
One layer of British Gypsum 12.5mm Gyproc Soundbloc each side of Speedline C stud at 600mm centres. 25mm APR in cavity. Size of C stud as per table.
1 x 12.5mm British Gypsum Gyproc Soundbloc (25mm APR)Duty Grade (1)Max Height m (2)Nominal Thickness (3)Fire Resistance (4)Sound Insulation RwdB (5)System Reference
50mm C studMD2.577304450-B-53 (25)
70mm C studMD3.697304670-B-53 (25)
92mm C studMD3.9119304692-B-53 (25)
146mm C studMD6.21733046146-B-53 (25)
AS70 Acoustic C studMD3.6973047AS70-B-153 (25)

Example - Speedline when tested in a UKAS accredited laboratory achieved Rw46 dB Ref. 70-B-53 (25) with 25mm APR insulation.

Residential requirements

Party walls, under Building Regulations Approved Document Part ‘E’ are measured as DnTw+Ctr.  Within this website we display the C and Ctr figures in brackets as (C,Ctr).  For example Twin I stud wall TWPI50-B-60 (50) shown below has an acoustic value of 67 (-4;-10).

Twin 50mm I stud utilising british gypsum boardsduty grade (1)HeightMax Width (2)Fire Resistance (3)Sound Installation*Test Reference w/ 50mm APR
Twin PI 50 Clad width 2 x 15mm British Gypsum Gyproc Soundbloc and 1 x 50mm APRSD2.7 (m)200 (mm)90 (min)67 (-3:-10)TWPI50-B-60 (50)

* Using 1 x 50mm APR infil RwDB (C, Ctr)


The actual tests carried out are used to offer an order of magnitude comparison for the  performance of the various systems.  Sound insulation on site is a function of the partition chosen and the associated structures in which it is installed.  Speedline take no responsibility for overall design and we would advise that specialist advice is sought at an early stage.  It is essential that consideration is given to blocking all air paths and flanking sound.

For further information on the information on the individual tests or to see where the test or assessment was carried out please quote the system references.

All test data and system specifications are for systems constructed with materials and components as shown.  The inclusion of other components without prior approval or constructed on site contrary to these documents will invalidate test certification and system performance.

All acoustic values are based on studs at 600mm centres.  If the stud centres are reduced to either 400mm or 300mm, this could impact negatively on acoustic performance.  Please refer to page 24 of the Speedline Drywall Manual for further details.

Flanking Noise

Flanking transmission occurs when sound travels along elements shared by adjacent structures.  Sound does not always travel straight through the building element.  If the wall, floor or partition concerned has good sound-reducing capabilities, the sound will travel from A to B by the easiest route, often around the sides or over the top.

Please note that flanking transmission can exceed direct transmission and damage the overall capabilities of the construction if flanking constructions are not correctly specified and constructed.

To over come this problem of flanking, any gaps in the installation must be filled with Speedline Fire Rated Acoustic Sealant on all edges and on both sides of the partition.

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