INNOVATION PATENT APPLICATION An Improved Demountable Sound Attenuating and/or a Retaining Barrier Assembly 5 FIELD OF THE INVENTION This invention relates to an improved demountable assembly suitable for use as a sound barrier and/or a retaining barrier. BACKGROUND OF THE INVENTION Within the next few decades it is expected by a number of demographical studies that the world's 0 population will undergo unprecedented growth. For instance, in Australia alone, it is predicted that the population will grow from around 22 million people presently, to around 35.9 million people by 2050 (Source: Australian Government, 2010 Intergenerational Report). With this dramatic increase in population, the reliance on dense housing projects is becoming an 15 increased priority, which tends to result in the housing projects moving into close proximity with large infrastructure, such as freeways, railways, industrial and commercial precincts, etc. A problem that is associated with this trend is that housing projects and suburbs are subjected to increasing noise pollution, which can decrease the quality of life of residents. -1 - A common solution for attenuating noise is to place a physical sound barrier between the sources of the noise and the structure affected by it. For instance, in the prior art, sound barriers erected from cast slab concrete panels or wooden panels are routinely used as sound barriers. In this regard, however, while concrete slabs or the like can be effective to attenuate sound, the use of such can significantly 5 increase the cost, labour and time taken to erect a barrier. In particular, in order to erect a barrier from concrete, heavy machinery is required, and having to source a significant amount of concrete for a particular barrier can be difficult and take up to several months due to high demand. As with concrete barriers, sound attenuating barriers that are erected of timber are also becoming less 0 desirable. Specifically, timber to be used in large construction projects is becoming difficult to procure due to government conservation policies and high demand, and thus due to supply and demand issues the cost of erecting a timber sound attenuating barrier is becoming significantly prohibitive. Moreover, erecting timber barriers is time consuming as each panel is generally required to be secured by fasteners to each other or an underlying support structure, and are thus generally also difficult to remove or 15 demount if required. In addition to the foregoing disadvantages of current sound barrier assemblies, barriers erected from concrete and more so wood requires significant amount of maintenance due to the exposure of such to the surrounding climate conditions. Specifically, common problems, such as the concrete cracking due 20 to significant drying and expansion over time, and the warping of timber are encountered. This -2signfincant increases the cost of maintenance as panels generally need to be routinely replaced, painted or re-treated. As such, there is a need in the art for a less costly sound barrier and/or retaining barrier assembly that is 5 less time consuming to erect and manufacture. Moreover, there is a need to move away from traditional materials, such as wood or concrete, when providing materials for use in a barrier having sound attenuating properties. OBJECT OF THE INVENTION 0 It is the object of the invention to eliminate or ameliorate some or all of the above disadvantages of the prior art by providing a novel and innovative demountable assembly suitable for use as a sound barrier and/or a retaining wall. STATEMENT OF INVENTION 15 In one embodiment, the invention resides in a demountable barrier assembly suitable for use as a sound barrier and/or a retaining barrier comprising: a plurality of panel members having a wall defining at least one internal space; -3each of the plurality of panel members having a leading and trailing edge each including complementary engagement means configured to receive and securely locate adjoining panel members in a vertically stackable manner; and a plurality of post members configured to support and cap the plurality of stacked panel 5 members to form the barrier. Preferably, the plurality of panel members are an extruded metal, metal alloy or hardened plastic. In the most preferred embodiment, the panel members are fabricated from extruded or roll formed aluminium. 0 In a preferred embodiment, the post members include opposed flange that define a channel, the channel being sized and dimensioned to receive and secure the panel members. Preferably, the post members are supported by a concrete footing or foundation member. 15 In a preferred embodiment, the engagement means of the leading edge is a protrusion that is configured to be received and securely located within a corresponding recess provided on the trailing edge of an adjoining panel member. 20 -4 - BRIEF DESCRIPTION OF THE DRAWINGS In order for the invention to be better understood, reference will now be made to the accompanying drawings, wherein; Figure 1 is a head on view of an exemplary demountable wall assembly of the present 5 invention. Figure 2 is a cross section view of a portion of the preferred barrier assembly of the present invention, showing the relationship between the footing or foundation members and the ground surface. Figure 3A is a traverse cross section view of a preferred post member of the present 0 invention, also showing a portion of a longitudinal cross section of panel members. Figure 38 is a traverse cross section view of a preferred post member of the present invention, also showing a portion of a longitudinal cross section of panel members. Figure 4A shows a vertical cross section showing two preferred panel members of the present invention in a stacked configuration. 15 Figure 4B shows an enlarged cross section view of the engagement means of respective panel members of the present invention when in a stacked configuration. 20 -5- DETAILED DESCRIPTION OF THE DRAWINGS In a first preferred embodiment of the present invention, a demountable barrier assembly suitable for use as a sound barrier and/or a retaining barrier (10) is provided. As is best shown in Figure 1, which shows the barrier assembly in its assembled form, the barrier assembly (10) of the present invention is 5 shown to include a plurality of panel members (20) stacked in a vertical configuration and held in place longitudinally by a plurality of vertical post members (30). These features and other features of the present invention will be described and exemplified below with reference to the drawings. As is shown in Figure 1, the vertical post members (30) are held securely in position by respective 0 footing or foundation members (40). While the footing members or foundation members (40) act to secure the vertical post members (30), they also facilitate the post members of the wall assembly being erected in a substantially vertical manner, regardless of the corresponding slope of the ground over which the barrier assembly is to be erected. This latter function of the footing or foundation members is best shown in Figure 2, where the barrier assembly of the present invention is erected in a substantially 15 vertical manner due to the footing or foundation members (40) that are placed or formed within the ground (100) that is not horizontal. The respective footing members or foundation (40) can be manufactured from any known material available to those skilled in the art. However, in the most preferred embodiments of the present -6invention, such are fabricated from, but not limited to, a concrete composition commonly used in the building industry. Those skilled in the art would appreciate that the barrier assembly (10) of the present invention could 5 be erected over a number of different ground surfaces, such as but not limited to, terrestrial surfaces and/or man-made surfaces (e.g. concrete or the like). However, those skilled in the art would also appreciate that in some aspects of the present invention, distinct footing or foundation members, such as those described above, are not required to secure the vertical post members (30). In particular, in some preferred embodiments, the vertical post members (30) may be directly secured within the 10 ground surface on which the barrier assembly is to be erected (not shown). For instance, in embodiments where the barrier assembly of the present invention is to be erected over a concrete surface, the concrete surface can actually act as a foundation for the vertical post members (30) rather than using discrete footing or foundation members that are placed within the ground surface. 15 Moving now to Figure 3A, which shows a transverse cross section of a vertical post member (30) of the present invention, a preferred configuration thereof is shown. As shown in this embodiment, the vertical post member (30) includes transverse flange members (32) that form channels on both sides and extend along the longitudinal length of the vertical post member (30). These channel members are sized and configured to receive the thickness of each of the plurality of panel members (20) of the 20 present invention, which will be described in further detail below. Moreover, as the channel receives -7the panel members, such also have the role of terminal ends of the panel members when assembled which also aids to increase the sound attenuating properties of the barrier assembly of the present invention. 5 Before proceeding to describe the panel members of the present invention, however, it should be understood that the vertical post members (30) of the present invention can be provided in a number of different configurations to that shown in Figure 3A. Specifically, those skilled in the art would appreciate that the embodiment described above with reference to Figure 3A would be useful for erecting a substantially straight barrier, as when the panel members are received into the respective 0 channels such are aligned along a substantially similar plane. On the other hand, it is envisaged that the post members (30) could be provided in a configuration where when the panel members are received into the respective channels, such are aligned along different planes as is shown in Figure 3B. This is primarily achieved by increasing or decreasing the angle denoted by (6) in Figure 3B from 1800 to any desired acute or obtuse angle. As such, it is contemplated that each of the plurality of post members 15 (30) of the barrier assembly of the present invention could be of differing configurations so that the wall can traverse corners or change directions when desired. As such, those skilled in the art would appreciate that the orientation or configuration of the barrier assembly of the present invention when erected is not overly limited. -8- In addition to the foregoing, although not shown, it will be appreciated that where a post inember of the present invention is to be used as a terminal post member at each end of the barrier assembly, only one side of the vertical post member may include flange members (32) creating a channel sized and configured to receive the plurality of panel members. 5 In preferred embodiments, the vertical post members of the present invention are fabricated from any rigid material known and available to those skilled in the art. For example, the vertical post members could be fabricated from hardened plastics, metal or metal alloys or the like, but not limited thereto. 0 Moving now to Figure 4A, a perspective view of a cross section of a preferred panel member (20) of the present invention is shown in further detail. In order to show the relationship between each panel member in a stacked configuration when the barrier assembly of the present- invention is erected, two separate panel members (20) in a stacked configuration are shown in Figure 4A. As shown, each of the panel members (20) includes an outer wall (21) that defines an internal space (23). While not 15 mandatory, in a preferred embodiment, each panel member (20) can include at least a single substantially transverse member (23) spanning the width of the panel member (20) that helps to provide strength to the panel member. As shown in Figure 4A, the substantiality transverse member (23) creates more than a single internal space or longitudinal channel (26) and (27) in each panel member (20). 20 -9- As denoted by reference numerals (22) and (24) in Figure 4A, each panel member (20) includes a trailing and leading edge, respectively. The leading edge (24) and trailing edge (22) of each panel member (20) has engagement means (25), as is best shown in Figure 4B. In this regard, when the barrier assembly of the present invention is erected, the engagement means (25) of each adjoining panel member abut with 5 one another to securely locate each panel member (20). As shown in Figures 4A and 4B, in a preferred embodiment, the engagement means of the leading edge (24) of the panel member (20) is a protrusion that is received and securely located within a corresponding recess provided on the trailing edge (22) of an adjoining panel member (20). 0 It will be appreciated by those skilled in the art that the engagement means (25) provided on the leading and trailing edges of each of the panel members (20) are not overly limited to any particular configuration. In particular, any known configuration, such as but not limited to, a tongue and groove configuration or click and lock type system, falls within the scope and spirit of the present invention. 15 Those skilled in the art would appreciate that the panel members (20) of the present invention could be fabricated by any known material, such as but not limited to, hardened plastics, extruded metal or metal alloys or a combination thereof. In the most preferred embodiments, it is contemplated that the panel members are fabricated from extruded aluminium. - 10 - When in use, the barrier assembly (20) of the present invention is useful as a simple retaining wall and/or preferably as a sound attenuating barrier. Specifically, it has been found that the barrier assembly of the present invention is significantly quicker to erect than prior art barriers due to the fact that the panel members of the present invention can be quickly vertically stacked and secured to 5 adjoining panel member without the need for fasteners. Moreover, the barrier of the present invention can be erected without the use of heavy machinery, and thus can also significantly decrease the costs associated with erecting a barrier, having significant commercial advantages as the requirement for sound attenuating barriers in dense housing precincts increases. Lastly, the inventors of the present invention have also found that the barrier assembly of the present invention is very efficient at 0 providing sound attenuating properties. While not wishing to be bound to theory, it is contemplated that sound waves are attenuated due to the at least one internal space provided by the walls of the panel members (20). It should be noted that other advantageous of the present invention would be apparent to those skilled 15 in the art after reading the forgone description. VARIATIONS It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons -I11skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth. In the specification the terms "comprising" and "containing" shall be understood to have a broad 5 meaning similar to the term "including" and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the terms "comprising" and "containing" such as "comprise", "comprises", "contain" and "contains". - 12 -