Sound
Reduction Index TA Modal Version 7.0
Prediction
of the sound reduction index of walls, partitions etc...
RW(C;CTR) en ISO 717
©
Tisseyre & Associés 2002
IDDN
FR 001 420 006 00 RP 1999 000 30500
Presentation
- Principles of the calculation - The
software - References
This sound reduction index prediction software can simulate various construction elements (also designated as plates): single, complex, orthotropic, heterogeneous.
TISSEYRE & Associés proposes this prediction tool resulting from expertise acquired during a twenty year confrontation with concrete acoustics problems.
Based on experience acquired within engineering missions, research and development of products for the industry and internal research, Tisseyre and Associés isolated the essential characteristics of physical and geometric constitution of panels: relevant characteristics in modelling the sound reduction index.
The
sound reduction indices produced by this software make it possible to
calculate insulation between dwellings, with simple or complex envelopes
elements
A calculation example
Zinc roof with standing seams and insulation, on a perforated steel tray
Total thickness : 210.7 mm
Dimensions : 4 m x 4 m
Results
---------------- 
The formulation of Cremer and Sewell [1] at low frequency was the basis of the CAGT PIAA and STIFF programmes, the latter stemming from CAGT PIAA.
A thorough theoretical study lead to the programming of the SOUND REDUCTION INDEX TA modal software.
The modal calculation development is based on a large quantity of scientific work achieved in this field in the recent years.
The calculation model so developed is analytical. The modal theory is based on the hypothesis that a finite plate subjected to an excitation responds on the basis of its modes (deformation).
Example of a mode : mode 2,2
Low frequency
The modal theory makes it possible to take the dimensions of the plate into account, and therefore the reflections on the edges. The precision of the sound reduction index is then improved, especially in the low frequency range where accidents are frequently observed.
The prediction of the sound reduction index is carried out in two steps :
1/ Calculation of the vibratory movement of the plate
The expression of the transverse displacement of the plate is developed according to a basis :
An adequate choice of this basis makes it possible to take the various boundary conditions into account.
Boundary conditions :
Visualization of the boundary conditions' influence is possible, thanks to the modal theory.
Four types of boundary conditions are available :
- Plate posed on its edges
- Embedded
- Free
- Guided
SOUND REDUCTION INDEX TA modal also permits non-homogeneous boundary conditions along the edges of the plate.
2/ Calculation of the plate's radiation
The radiation characterizes the fluid-structure interaction. In the present case (construction), the plates are immersed in air.
As the fluid's mass is negligible with respect to that of the plate, the light fluid hypothesis is retained.
----------------
Inputs
- Dimensions of the plate, geometrical characteristics, thickness,
- characteristics of the materials: Young's modulus, volume mass, internal loss factor,
- linear, punctual, surface connection; no connection.
Owing to the compilation of 2500 sound reduction index test reports, the current software integrates all the physical parameters necessary for the modelization of all panels encountered in construction.
Types of plates
SOUND REDUCTION INDEX TA modal lets you carry out calculations for the following types of partitions:
Results
The results are presented as graphs and tables displaying the global values in dB(A), STC, Rw(C,Ctr), Belgium index, dB, as well as the third octave or octave values.
Examples
Dozens of comparisons between the Cremer-Sewell and modal approaches were carried out, using our experimental data bank. A representative selection of typical variations is presented here.
1. 6 mm single glass pane
At low frequencies, the modal formulation provides a good agreement with experimental values. The Cremer-Sewell formulation is inferior to experimental values.
Near the critical frequency, the Cremer-Sewell formulation is well above experimental values.
KEY
--- Modal theory
--- Cremer-Sewell theory
--- Measurement
2.Acoustic resin laminated pane
The low frequency behaviour is nearly similar to the experimental curve in both calculations.
Beyond the 1000 Hz octave band, the modal theory yields a satisfactory prediction of the sound reduction index.
The Cremer-Sewell formulation underestimates the sound reduction index by 7 to 8 dB.
3. Clestra-Hauserman "Synchrone"partition: double orthotropic plate
Similar hypotheses of connection between faces are used in both calculations.The modal calculation is very close to the measured values. A good agreement of the low frequency behaviour of this steel double partition as well as the useful presence of multiple critical frequencies due to stiffness brought about by the posts can be observed.
The Cremer-Sewell formulation smoothes out the low frequency sound reduction index variations. It underestimates the low frequency performance, and overestimates the mid and high frequency performance by 5 to 10 dB.
----------------
- 1. E. C. Sewell, Transmission of reverberant sound through a single-leaf partition surrounded by an infinite rigid baffle, J.Sound Vib. (1970).
- 2. A. Berry, A new formulation for the vibration and sound radiation of fluid-loaded plates with elastic boundary conditions, J. Acoust. Soc. Am. 96, 889-901 (1994).
- 3. C. Lesueur, Rayonnement acoustique des structures, Editions Eyrolles (1998).
- 4.
T.Buzzi, C.Courné, A.Moulinier, A.Tisseyre, Prévision
d'indice d'affaiblissement acoustique : approche modale - Application
aux parois orthotropes, Actes du 6ème Congrès Français
d'Acoustique (avril 2002)