Sound reduction index prediction of double-layer gypsum panels through the transfer matrix method

Gypsum board walls are widely used in today’s buildings. A possible way to considerably increase the sound insulation performances of such lightweight walls is to apply double-layer gypsum panels screwed together. Being the boards separated by a thin air gap, there is no shift of the critical frequency from the single-layer case. Moreover, it is possible to obtain an improvement of the sound insulation performances provided by the additional mass given by the double layer. The thin air layer is, however, responsible for a loss of acoustic performance due to the cavity resonance effect in the frequency range between 800 and 1600 Hz. In this article, the increase in the acoustic insulation achieved through the use of coupled gypsum boards is studied and a modelling technique based on the transfer matrix method is used to simulate the acoustic behaviour of the resulting structure; in particular, the thin air layer between the coupled boards is modelled. The simulations are compared with laboratory measurements carried out according to the international standard series ISO 10140. The transfer matrix approach is found to be suitable to describe the problem, provided that a modified model for the air gap between the boards is applied

Satellite flies (Leucophora personata, Diptera : Anthomyiidae) and other dipteran parasites of the communal bee Andrena agilissima (Hymenoptera : Andrenidae) on the island of Elba, Italy

Solitary and presocial aculueate Hymenoptera are parasitized by a range of dipteran species in the families Anthomyiidae, Bombyliidae, Conopidae, Phoridae, and Sarcophagidae that are likely to impact on their hosts. We undertook a study over several years of a univoltine and communal bee, Andrena agilissima, and its main dipteran parasites, in particular the satellite fly Leucophora personata (Diptera: Anthomyiidae). Behavioural and ecological data were collected from one nesting aggregation of the host bee on the island of Elba, Italy, from 1993 to 2003, and from a foraging site of the bee, ca 5 km from the nesting aggregation. Other Diptera associated with A. agilissima at the field site were the bee fly Bombylius fimbriatus (Bombyliidae), the conopid fly Zodion cinereum (Conopidae), and the scuttle fly Megaselia andrenae (Phoridae). The phenology of the Diptera broadly overlapped with that of their host across the season of activity (end of April and all of May). Diurnal activity patterns differed slightly; L. personata in particular was active at the host's nesting site before A. agilissima. Female satellite flies also showed a range of behaviours in gaining entry to a host nest. We summarize published data on this and other Leucophora species that parasitize Andrena host bees. Host bees returning to their nests occasionally undertook zig-zag flight manoeuvres if followed by a satellite fly that were generally successful in evading the fly. Satellite flies that entered a nest, presumably to oviposit, were less likely to remain therein if another host bee entered the same nest, suggesting that one advantage to communal nesting for this host is a reduction in brood cell parasitism by L. personata. We provide the first clear evidence for parasitism by a Zodion of any Andrena host. Both L. personata and M. andrenae concentrated their parasitic activities in the zone of the host nesting aggregation with highest nest densities. Three of the Diptera, L. personata, B. fimbriatus, and Z. cinereum, seemed to have extremely low rates of parasitism whilst that of M. andrenae appeared low. Though they have refined parasitic behaviour that allows them to gain entry into host nests (L. personata, B. fimbriatus, and M. andrenae) or to parasitize adults (Z. cinereum), these parasites seem not to impact upon the dynamics of the host A. agilissima at the nesting aggregation, and the host possesses traits to reduce parasitism

Uncertainty of façade sound insulation measurements obtained by a round robin test: the influence of the low frequencies extension

he international standard ISO 140-5 for the measurement of the sound insulation of build- ing façades will soon be replaced by the new standard ISO 16283-3. This revision includes the procedures for measurements at low frequencies down to 50 Hz. The uncertainty of fa- çade sound insulation, in particular at low frequencies, was evaluated by a Round Robin Test, conducted in a full-scale experimental building at ITC-CNR. Each of the 10 teams in- volved in the RRT replicated the tests 5 times, for a total of 50 measurements. The different measurement positions inside the receiving room are compared. In particular, all the teams involved in the RRT assessed corner and center room positions; their energy average values according to ISO 16283-1 are considered and the relative uncertainty in terms of repeatabil- ity and in situ reproducibility standard deviations are compared with the ones measured and calculated following ISO 140-5