For the effective isolation of low frequencies there is often no alternative to the use of structures which are heavy, rigid and highly damped. The photographs on this page show some of the techniques involved in such constructions. The top left photograph shows a sand-filled concrete block wall, mounted (floated) on mineral wool of a relatively high density (140 kg/m2). In the photograph below it, the wall is floated on a raised base of reinforced concrete (in this case to ensure that no water from roof leaks or pipe bursts could seep below the walls), on which was then placed a suitable elastomer before laying the first row of blocks. It can be seen that a constant wall height is being maintained as the room is being built. It is absolutely essential to continue to build one row at a time, around the entire room. If this is not done, the loading on the floating material will not be constant as it compresses. This can lead to the excessive loading of certain regions where more weight is carried when other sections of wall are joined to parts of the wall that are already fully loading the suspension materials. The result may also give rise to the cracking of the wall because new sections being built on uncompressed floating material will gradually go down as extra weight is applied, overstressing the joints where the first layers of the walls have been interleaved.
The floor bases are usually made up of two layers mineral wool, each of half the required thickness. This allows the displacement of the joints so that in the case of any concrete leaking though the plastic sheeting there is little possibility of it finding a path down to the structural floor. In rooms where cable tubes need to be embedded, they can be partially recessed into the mineral wool. The bottom left photograph shows a room with the nearest floor awaiting the concrete to be poured on to it. At the top left, another studio can be seen with people already pumping the concrete over the prepared floor. In the foreground it can be seen that the plastic sheeting and the reinforcing grid has already been placed over the tubes on the control room floor. A completed floor of a control room can be seen below, with the ends of the tubes still plugged with mineral wool, which was there to prevent any concrete from entering as the slab was being cast.
The centre left photograph shows a completed bunker, awaiting only the boarding of the ceiling. With a wall height of around 5 metres, the weight of the walls (20 cm thick) is in the order of two tonnes per linear metre.
The heavy work does not only include the isolation shells. The photograph of the stone room at Crash shows the ten tonnes of white marble, especially imported from the quarries in Italy where Michelangelo obtained the stone for his statue of David. At Producciones Peligrosas the room is made from black slate. The stone faces on the wooden walls that support them weigh approximately one tonne for every 3 square metres of wall surface. Without the weight and rigidity, the rooms would be less reverberant. In these two rooms, the stone walls are mounted (floated) independently of either the isolation walls or the structural walls. They are in triple shells because the sound levels within them, amplified by the reverberation, can approach 130 dBC with a drum kit and a powerful drummer.