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It is common for timber ceiling constructions to include a suspended ceilings made of plasterboard. In order to minimize the radiation from impact excitation, especially in the low frequency range below 100 Hz, a detailed analysis of the vibration behaviour was necessary.
An experimental modal analysis was carried out and the radiated sound power from the suspended ceiling was measured using a sweep sine excitation by a shaker connected to the top layer of the timber floor construction.
Since the experimental modal analysis was conducted using a high frequency resolution and with a non-stationary sound field, it was necessary to check the validity of the intensity measurements by comparing it with 1/3-octave band measurements. The results show very good agreement.
By this means the radiation efficiency can be measured simultaneously with an experimental modal analysis of a structure.
Measured transmission functions from structure-borne sound sources in a timber-frame construction
(2015)
The aim of prEN 15657-2 is to provide engineering methods to estimate the structure-borne sound power input from machinery in situations where the source mobility matches or is lower than the receiver mobility. This situation often affects lightweight constructions such as timber-frame buildings. To estimate the sound pressure level in a room that is adjacent or distant from the room containing the source, the installed structure-borne sound power has to be propagated across at least one junction in the timber-frame construction. However, at present there are no generic, validated calculation models due to the complexity and the large variety of timber-frame constructions. A simplified approach to investigate and compare the structure-borne sound transmission is to treat the framed construction as a black box and only consider one parameter, a transmission function which is the ratio of the sound pressure level in the receiving room to the injected structure-borne sound power level. To get information about the variation of this transmission function in different timber-frame constructions, measurements were made in both the laboratory and the field. Experimental results are presented showing the variation due to different building configurations and the effect of the excitation position on the transmission function.
The method is based on a simplified Statistical Energy Analysis(SEA) approach. The energy ratios of various subsystems are the main quantities to predict sound transmission. The method has proven to work sufficiently accurate for masonry and concrete buildings, where the building components like walls, floors etc. can be regarded as rather homogeneous structures. To adapt this method for solid timber constructions it is necessary to prove that basic SEA requirements are fullfilled by orthotropic materials and heterogeneous structures that occur in these building types. In a case study, an isolated T-junction formed by Cross Laminated Timber(CLT) elements is experimentally investigated. The buildings elements are subdivided in segments with typical screwed connections.
In the experiments the diffusivity of the vibration field is investigated, using point excitation with a shaker at several positions and many, randomly chosen response positions. MONTE-CARLO simulations are conducted for random but fix-sized subsets of the measured response positions to find the necessary number of response positions for an accurate determination of the vibrational energy.
As a result the distribution of the mean velocity levels can be approximated.
In a second approach a multiple linear regression model based on the least absolute shrinkage and selection operator(LASSO)is applied, because for lower frequency bands multicollinearity is expected.
In the context of linear regression modelling, data-driven methods are used to select optimal subsets of response positions, to get an estimating equation.
Competitive wooden floor systems - multi-objective optimization based on acoustics improvement
(2013)
The objective of this research project is the design of lightweight timber floor systems which have similar thicknesses to those of concrete floors but which perform better than concrete in terms of their environmental life cycle impact and in terms of airborne and impact sound insulation.
The availability of superior lightweight acoustic designs will increase the share of timber based floors within the Swiss construction market and will contribute to higher wood utilization in general.
A program for systematically developing validated finite element models for the development of lightweight timber floor systems has been proposed.
The use of Swiss hardwoods in floor systems will be studied and implemented where possible. Keywords: lightweight timber, sound transmission, impact noise