Factores externos que inciden en la ansiedad

above the separating partition, is shown in Graph 5.102_.

Graph 5.10: Transmission loss of thermal insulation batts of different densities installed above the separating wall within the plenum2

Halliwell and Quirt also measured the effect that the suspended ceiling played on the sound transmission between spaces. A continuous ceiling, split panels and two separate grids were installed to find the difference in sound transmission with compressed glass fibre batts installed above. Graph 5.12 shows the effect that splitting the panel (large dashed line), having a continuous grid (small dashed line), and having two separate grids installed which butt to the side of the wall (rather than laid on top of the wall). While the TL is similar at low frequencies at mid and high frequencies, the TL of the split grid increased dramatically when compared to the continuous grid. This was attributed to vibration transfer through the continuous grid. These vibrations would not be transferred in a split grid, and are even further reduced, if two separate grids were installed. With two unconnected grids, no vibration transfer can occur and therefore at the higher wavelengths where this is of concern no flanking can take place2_.

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Graph 5.11: Transmission loss of different grid and ceiling tile set-ups within a CFN facility2

Extending the idea of adding absorption to the plenum perimeter walls, Royar and Schmelzer73

analysed the difference in having an open sided plenum to that with fibrous insulation on all four sides, with and without porous ceiling tiles installed. This was to compare the effect of an open plenum with one that simulated an open plenum (using absorption on the perimeter walls). Graph 5.13 shows the TL difference between absorption on the perimeter walls (solid line) compared to no plenum absorption (dashed line). The left graph is for ceiling tiles that are not absorptive, and the right graph is for ceiling tiles that are absorptive73_{. The graph shows that with reflective ceiling}

tiles the difference between having an open plenum side and absorptive plenum sides is high (up to 8 dB at any single octave band). This is less prominent with a porous ceiling tile installed73_{. Due}

to the open nature of the plenum, and the difference in size between the plenum perimeter openings and the room in which the model is built, impedance differences in the air may reflect some sound back into the space, decreasing the overall sound transmission. This would not happen with absorption, as the sound would be absorbed rather than reflected by the impedance mismatch between the two air volumes. This impedance mismatch would not be present in a typical plenum as the plenum is continuous, rather than open to a much larger room.

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Graph 5.12: Transmission loss of a suspended ceiling when the plenum perimeter walls are removed, and when the plenum perimeter walls are lined with absorptive material73

In addition, Royar and Schmelzer compared the effects on TL of the difference in suspended ceiling height (45 mm to 80 mm, at a 1:10 scale) with and without absorption to three perimeter walls to find if the cavity depth changes the sound transmission between the spaces. Graph 5.13 shows the difference between a 45 mm and 90 mm plenum depth with absorption (shown as solid and mid- dashed line, denoted at 45 mm SLR and 80 mm SLR in graphs), and without absorption (large and small dashed line, denoted as 45 mm none and 80 mm none)73_{. It was concluded that when}

absorption was present on the walls there was little difference in sound transmission between the rooms for a different depth cavity73_.

It is important to note that the facility that Royar and Schmelzer used for their research was a 1:10 scale model. In addition, it allowed the removal of plenum side walls, and different plenum depths, so therefore did not comply with the relevant standards but probably provides an indication of performance in a full scale CFN facility.

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Graph 5.13: Difference in transmission loss between a lined and unlined absorption plenum at 45 mm and 90 mm plenum depths73

5.8 Summary

The TL of homogenous panels has been extensively researched. The effects of leaks in panels have been considered previously, no specific work concerning leaks within a suspended ceiling has been identified. The ceiling tiles sit on the suspended grid system and are mounted with clips being used to hold the ceiling tiles such that they do not fall down in the event of an earthquake. However, significant leaks are likely to occur between the ceiling tiles and suspended grid system.

There are two international standards (ISO 10848-2:2006, and ASTM E1414-11a) that prescribe the construction and measurement methodology for the determination of the TL of sound through the plenum sound path between adjacent rooms, called a ceiling flanking noise facility. Single number ratings can be used to quickly compare two products. The Rw parameter was developed for

the ISO 10848-2:2006 measurement methodology, with the CAC rating developed for the ASTM E1414-11a measurement methodology.

Extensive research and testing has been completed on single panel homogeneous systems. However, the TL of a suspended ceiling, taking into account the TL of the grid, ceiling tile, and leakage around the grid has not been published. Hamme’s research on reducing sound through the

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