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Monowa Guide to Acoustics

Sound insulation values are generally given as a Rw dB rating.  This is the laboratory test value under near perfect conditions and can vary significantly from the in-situ sound insulation performance.  The Rw dB rating should therefore only be used for initial specification purposes and must be complimented by the required in-situ sound insulation value; usually defined as the DnTw dB.

It is therefore important that the DnTw dB value or other relevant in-situ value is stated when ordering operable walls.  This will enable the supplier to assure the sound reduction performance from the completed installation as doors, service penetrations and glazed panels may significantly reduce the overall DnTw value.

Monowa can supply and install acoustic operable walls rated at Rw 38 dB to Rw 56 dB with on-site sound reduction values of up to DnTw 45 dB*.

*Subject to surrounding structure and flanking elements being approved by Monowa.


Below are some of the acoustic terms that are used in the industry (which often cause confusion) defined for simplicity.

dB = Decibel  (unit of noise measurement)

dBA = actual noise that the average human ear can hear

Rw dB = Laboratory test values under near perfect conditions, e.g with no noise leaks or structure- borne noise flanking. Typically the dB Rw value is at least 5 dB better than the relevant dB Dn Tw value and can be up to 15 dB better. For example, a partition with a value of Rw 52 dB in the laboratory can sometimes only achieve Dn Tw 45 dB on site and in a worst case might only achieve Dn Tw 37 dB due to noise  leaks and other acoustic weaknesses.

dB DnTw = Sound reduction value from on – site testing corrected for the reverberation time in the receiving room.

dB Dw = Sound reduction value from on – site  testing but not corrected for reverberation time, typically used for offices or other spaces where no specific acoustic parameter is stated.

Note that the value for schools is DnT (Tmf,max)w dB and is related to the reference reverberation time for the type of room being tested as identified in BB93 Acoustic Design of Schools.

DnTw + Ctr dB is the similar on- site value but is only used in residential premises, e.g. flats, houses and hotels etc.

There are many other types of decibel such as Dncw dB which is the sound loss between two adjacent rooms over and through the ceiling void andDnew dB which is the sound reduction of a small opening such as a vent or grille. Both of these might possibly have some effect on the actual room to room sound insulation.