Constructional measures - sound insulation

  The levels of desired sound insulation for different types of building and between the individual rooms or apartment of a building can be achieved by the following constructional measures of noise control and sound insulation.

Wall & partitions •  These wall construction should act as vertical barriers in the

transmission of air borne sound or noise .To achieve this objective the following methods of wall construction can be adopted depending upon the extent of sound insulation required .Rigid and massive homogeneous partition

•  The sound insulation of a partition increases with the increase in its thickness .But the increase in insulation value of a solid wall construction is slow in proportion to the increase in its thickness. •  Hence it is not economical to increase the thickness of a solid wall beyond a certain limit.

Partition of porous material The sound insulation increase about 10% higher than the non-porous variety of the same weight due to the absorptive property of the material but partition of flexible porous material, such as felt mineral wool, quilt etc offer very low sound insulation as compared to rigid materials.

Hollow and composite partition It is established that a cavity wall or double wall construction is better for sound insulation than a solid wall construction .A composite partition of cavity wall type construction by filling the cavity or leaving the air space with some resilient material is best for increasing insulation value or sound proofing rooms .

This consist of two leaves of wall made of light material ,such as metal lath and plaster fiber boards, plaster boards, plywood etc fixed on studs with an air space in between the air space of about 10 to 12 is kept between the leaves of wall and staggered wooden studs are provided as supports.

Cavity wall type construction: This is an ideal construction for sound proofing. The gap between the two walls may be left air – filled or else filled with some resilient material, like quilt, etc., well suspended in the gap. The two faces of the wall may be fixed with insulating board. The width of cavity should be at least 5cm and the two wall leaves should be tied by use of only light wall ties.

Wall Insulation: (Vertical barriers) – “Sound Insulation in walls”. Walls & partition are the vertical barriers to noise. Their construction for desired sound insulation are of three types. •  Rigid homogeneous walls •  Partitions of porous materials •  Double wall partition •  Cavity wall type construction.

Rigid homogeneous walls: A rigid wall consists of stone, brick or consulate masonry construction, well plastered on one or both the sides. The sound insulation offered by these rigid walls depends upon their weight per unit area. The sound insulation thus increases with the increase in the thickness of the wall.

Partitions walls of porous materials: Porous materials may be rigid or non – rigid. Rigid porous materials (such as process concrete masonry cinder concrete etc.,) the insulation increases about 10% higher than the non porous rigid materials. However partition walls of non – rigid porous materials (felt, mineral wool, etc.,) offer very low sound insulation, though they can be used in combination with rigid materials with added advantage. Double wall partition: It consists of plaster boards or fiber board’s with sound absorbing blanket in between. Staggered wooden stud is provided as support, though their number should be a minimum. A double wall construction is thus a partition wall of rigid & non – rigid porous materials.

Floor & ceiling These floors and ceiling are required to act as horizontal barriers in the transmission of both air borne and impact sounds or noises . In most of cases where the ceilings and floors construction is of solid type like R.C.C floors they offer adequate insulation against air borne sounds because of rigid and heavy construction but offer poor insulation for structure borne or impact sounds .This objective can be met by the following constructional measures, Use of resilient surface material on floors.In this method over the massive and rigid construction of floors slabs ,a surface layer of resilient materials such as linoleum insulation boards ,cork, asphalt mastic and carpet etc are employed.

Providing  a  floa,ng  floor  construc,on  The  principal  underlying  the  construc3on  of  a  floa3ng  floor  is    its  insula3on  from  any  other  part  of  structure.  To  achieve  this    an  addi3onal  floa3ng  floor  is  made  to  rest  or  float  over  the    exis3ng  floor  by  means  of  a  resilient  like  glass  wool  ,material    wool  ,quilt,  hair  felt  ,cork  ,rubber  etc,  so  that  impact  sounds    and  consequent  vibra3on  are  not  transmi<ed  to  the  room    below  it  also  improves  insula3on  against  air  borne  sounds.    Floa3ng  floor  construc3on  can  be  adopted  for  both  concrete    as  well  as  wooden  floor  and  is  described  below.  

Concrete floor In case of concrete floor ,the resilient layer on which the floating floor is intended to rest, is turned up at all edges which about the wall partition or other parts of structure the various types of floating floor construction for concrete floor are explained below.

Concrete floor with floating concrete screed This consist of a layer of concrete screed (1:11/2:3) not less than 5 cm in thickness and resting on a resilient layer of mineral wood quilt laid over the structural floor slab and turned up against the surrounding walls or all the edges. The quilt is covered with a waterproof paper to prevent wet concrete running through it.   Concrete floor with floating wood raft This consist of floor boarding nailed to wooden battens (5cm x 5cm size) to form a raft which is laid over 2 cm thick resilient quilt and in turn is made to rest over the structural concrete floor slab.

Suspended ceiling In this type the uses of suspended ceiling provides insulation against air borne sound and soft floor finish of resilient covering such as carpets, corks or linoleum etc.If sufficiently thick ,provide insulation against structure borne or impact sound . Soft floor In this type 5 cm thick light weight concrete screed gives a certain amount of insulation against air borne sound but in addition the uses of resilient floor gives a high insulation against both air borne and impact sound . The uses of dense topping has two fold functions. It provides a suitable base for the floor finish.It provides an impervious air tight layers ,sealing the top of the light weight screed.

Wooden floors •  In case of floors constructed of wooden joists, the problem of sound

insulation becomes more difficult particularly in the presence of heavy mechanical impact sound .

•  This problem in case of timber floors is taken care of either by making the wall thicker below the floor or making the floor itself heavy and stiff enough to reduce the vibration of the walls .

Use of suspended ceiling with air space •  In this construction ,a false independent ceiling is connected below the

solid or wooden floor by means of metal hanger , acoustic clips etc with an air space in between .

•  The construction offer good insulation against both the air borne as well as the structure borne sound and especially suitable in case of wood joist floor .

Window & door •  In case of window ,sound insulation of single window is improved by

making them as air tight as possible by filling the air space at the edges of such panels with sound absorbing material.

•  Double glazing of glass window improves insulation to a considerable degree. Sealed double windows or triple window of plate glass with an air space in between can be successfully used where sound proofing is desired.

•  In case of door ,the transmission loss or sound reduction increase with the increase in weight ,the sound insulation can further be improved by packing the sound absorbing material in the space between the jamb and frame .

Conclusion Ø  The increase in transmission loss or sound reduction of a solid massive

construction is slow in proportion to the increase in its thickness. Ø  If the material used is of porous and flexible nature, like hair felt, its

sound insulation is proportional to its thickness. Ø  In double wall or cavity wall construction an air space is generally better

than a filling material, since it may be detrimental to sound insulation, if it bridge the separated surfaces.

Ø  A cavity wall with two leaves having thickness of 10 cm each has 80% increase in insulation value as compared to a single brick solid wall of 20 cm thickness, without any increase in weight but with little increase in cost.

Ø  And solid glass panel have better insulation property as compared to larger and thicker flexible glass panel.