AcouS STIFF® is software used for predicting the sound reduction index. Our program complies with ISO 717-1, NFS 31-051 and ASTM-E413 standards. In addition to our tutorials, our team teaches you how to use AcouS STIFF®.

Our inter-company training courses take place in Toulouse and Paris but can also be carried out in your offices on request anywhere in France and abroad. They teach the participants the basics that will serve to highlight the influence of the parameters that can be used to optimize a structure.

R as a function of embedding dimensions of the glazing

Presentation of AcouS STIFF® acoustic software (Acoustic Software Sound Transmission Index Full Forecast)

The sound reduction index of a wall can be measured in a laboratory specially designed for this purpose (decoupling of sending and receiving cells, shapes and sizes of cells, ....).

However the sound reduction index of a wall depends on a very large number of parameters. One naturally thinks of the thickness, or density of constituent materials, but particularly variable settings from one application to another, such as length and width of the panels are also of great importance, as evidenced by the following figure :

Under these conditions, the number of walls to be tested is infinite and a uniquely experimental approach, by the time and cost it represents, can not suffice.

Predicting then appears as an essential complementary approach.

  • Both approaches, laboratory measurement and calculation of estimates, far from being exclusive are complementary and necessary to one and the other
  • The experimental approach can be considered only as the number of cases to be tested, but the models simulation to be validated should be on individual cases properly chosen, of a comparison with experimental values.


AcouS STIFF® acoustic software is a simulation tool for calculations of sound reduction index.

Complex wall structure simulation

Software for predicting the sound reduction index

Acous STIFF® acoustic software is a simple and adapted tool that allows you to :

  • Determiner the sound reduction index of a simple or complex wall,
  • Assist in new product development,
  • Optimize measurement campaigns in a laboratory,
  • Appreciate the performance of a doubling in function of its support,
  • Extrapolate the performance conventional structures,
  • Forecast unconventional structures and their optimization,
  • Understand the acoustic behaviour of a wall.


The results are presented as graphs and /or tables showing the overall values in accordance with ISO717-1, NF S 31-051 and ASTM E 413.

Defining the types of walls calculable using AcouS STIFF®

AcouS STIFF® acoustic software can perform calculations of forecast reduction index of the following types of walls :

  • single wall (consisting of a single plate)
  • laminated or multilayer wall,
  • orthotropic wall,
  • wall composed of a porous material,
  • wall lined with a porous material,
  • detached double wall,
  • rigid double wall,
  • triple wall.


In addition, one can perform the following operations on the sound reduction indexes :

  • arithmetic sum of up to ten sound reduction indices,
  • difference (Delta) between two indices of acoustic attenuation,
  • heterogeneous walls composed of more than ten different wall elements.

The different types of bonds

The following mechanical connections are distinguished:

  • punctual: a regular distribution of connection points, expressed as a number of points per square meter,
  • linear: for parallel beam-type connecting lines, this distribution is expressed by the line-to-line distance in meters,
  • surface: the entire surface of the intermediate material forms the mechanical link between the outer facings. Only the uncoupling factor FD needs to be entered,
  • peripheral: only the base of the wall forms the mechanical link between the outer facings. The user can select from 1 to 4 sides of the wall, with a different FD uncoupling factor for each side if desired. For each side, the peripheral connection is expressed in meters. Only those sides whose length and uncoupling factor FD are entered will be taken into account in the calculation.


For the same wall, there can be several types of connection between the outer facings.

Calculation model

There are two types of basic components in AcouS STIFF®:

First basic component : the plate

This element is solid, homogeneous, isotropic, rectangular is shape, its thickness is small compared to its lengths and widths and also before the wavelengths of play, especially in solids.

Subsequently, this only works in Plate bending : no shear wave, surface taken into account.

It also represents a barrier which is supposed to be completely airtight; the speed of a particle of air on the Plate is equal to the speed of the plate at the point. Which distinguishes it fundamentally from the other basic component, the Porous.

Important parameters :

  • length, width (m)
  • thickness (mm)
  • density (kg/m3)
  • Young's modulus (in N/m2) : is the stiffness in tension or compression of the material forming the plate. This is the dynamic Module of Young, which may differ slightly from the static module.
  • internal loss factor (dimensionless) : combining the magnitude of the intrinsic material losses and those due to mounting. The material database provides such value, which can only be approximate and has been developed through practice.
Second basic component : the porous

It consists of a solid element or an aggregate of solid elements with blank spaces that could be saturated by a fluid. It presents itself as the assembly of two phases :

  • a solid phase representing the skeleton or structure of the environment consists of :
    • fiber in the case of mineral wool (rock, glass) or of textile fabrics,
    • a matrix in the case of foam,
    • grains in the case of sand, stacking logs...
  • a fluid phase, for example a gas saturating the voids of the skeleton, in this case it will be air.

All porous materials characterized by such behavior in the acoustic software AcouS STIFF® are permeable to air, for example, foams are open pores.

Indeed, the acoustic behavior of closed-cell foam (e.g. polystyrene) is of the type Plate. This is the fundamental difference between the two basic components.

Important parameters :

  • thickness (mm)
  • resistivity to the flow of air (or in Pascal s/m2 or rayls/m): measurable physical parameters, intrinsic characteristic of a porous material. It is to some related to the density which it incorporates among other information. It calculates the coefficient of grain flow (currently informative parameters) from the density of porous material, in order to provide feedback to users accustomed to using this coefficient.
  • Young's modulus (in N/m2): comparable to the compressibility of air saturating the structure; isothermal compressibility at low frequencies because there is heat exchange between air and the structure during adiabatic acoustic vribrations, from a certain frequency located sufficiently high in the audible range not to be taken into account.

Exemples of AcouS STIFF®

Check out some examples of possible arrangements with AcouS STIFF® software.
This list is not exhaustive.


Double skin :

  • Double skin cladding with a double skin steel tray 75/100 + VN30 + VN70 + steel cladding of 75/100
  • Calculation : RW = 46
  • Measure : RW = 45

Steel deck 75/100 :

  • Steel 0.75 mm
  • Calculation : RW = 23
  • Measure : RW = 22


Steel deck 63/100 :

  • Steel 0.63 mm
  • Calculation : RW = 16
  • Measure : RW = 15




Reinforced concrete 8 cm :

  • Reinforced concrete 8 cm
  • Calculation : RW = 46
  • Measure : RW = 47

Reinforced concrete 10 cm :

  • Reinforced concrete 10 cm
  • Calculation : RW = 49
  • Measure : RW = 48 à 51

Cellular concrete

Cellular concrete 14 cm :

  • Cellular concrete 14 cm
  • Calculation : RW = 41
  • Measure : RW = 40

Cellular concrete 20 cm :

  • 20 cm aerated front coated concrete
  • Calculation : RW = 46
  • Mesure : RW = 46




Doubling on gypsum :

  • Gypsum 7 cm + glass wool rigid than 5 cm + 1 BA10
  • Calculation : RW = 56
  • Measure : RW = 55

Reinforced concrete 20 cm :

  • Doubling on concrete 20 cm : reinforced concrete 20 cm + 8 cm glass wool rigid + 1 BA10
  • Calculation : RW = 71
  • Measure : RW = 73

Doubling on Brick :

  • Brick hollow 5 cm with an air gap of 1 cm + 3 cm of glass wool rigid + 1 BA10
  • Calculation : RW = 54
  • Measure : RW = 54

Doubling on frame :

  • Reinforced concrete 16 cm + 3,5 cm air gap + 7,5 cm of glass wool a semi rigid +1 BA13
  • Calculation : RW = 74
  • Measure : RW = 74


Wood floor :

  • 1 wood panel (CTBH) de 22 mm + 165 mm air and 200 mm IBR + 1BA13
  • Calculation : RW = 61
  • Measure : RW = 62

Floating floor :

  • Reinforced concrete 14 cm with Rocksol 15 mm mortar and a cap of 4 cm
  • Calculation : RW = 58
  • Measure : RW = 58


Single glass :

  • Glass 6 mm
  • Calculation : RW = 29
  • Measure : RW = 30

Laminated glass :

  • Laminated glass consists of a 5 mm glass + viscoelastic + 5 mm glass
  • Calculation : RW = 38
  • Measure : RW = 39

Double glazing 44.2/20/55.2

  • 2 laminated glass 4 mm, air gap of 20 mm and 2, 5 mm laminated panes of glass
  • Calculation : RW = 48
  • Measure : RW = 47 à 49

Facade with interior insulation

  • 21mm pine/fir +32 mm air space +2 LV of (145mm+45mm) +BA13
  • Laboratory test: Rw = 55dB
  • Measure : Rw = 54dB

Separating walls

Single-frame walls:

  • 2 BA 13 of 12.5 mm+36mm air space +100mm LV+36mm air space+2BA13 of 12.5mm
  • Laboratory test: Rw = 61dB
  • Measure : Rw = 61dB

Dividing walls in solid laminated panels:

  • 94mm-thick panel
  • Laboratory test: Rw = 34dB
  • Measure : Rw = 34dB


Gypsum wall:

  • BA13+45mm LV+BA13
  • Laboratory test: Rw = 46dB
  • Measure : Rw = 46dB


  • 15mm plaster+326 mm straw+15mm plaster
  • Laboratory test: Rw = 45dB
  • Measure : Rw = 45dB

Hollow concrete block

Hollow block 100 coated on 1 side:

  • 3 faces, 115 mm thick
  • Laboratory test: Rw = 43dB
  • Measure : Rw = 42dB

Hollow block 200 coated on 1 side:

  • 3 faces, 215 mm thick
  • Laboratory test: Rw = 55dB
  • Measure : Rw = 55dB


Isophone-portaphone door

  • 40 mm portaphone+80mm air+40mm isophone
  • Laboratory test: Rw = 57dB
  • Measure : Rw = 58dB

Door without floor seal:

  • Laboratory test: Rw = 24dB
  • Measure : Rw = 24dB




Steel roof:

  • 5mm bitumen (waterproofing)+100mm LV+0.75mm steel+80mm air+100mm LV+80mm LR+0.75mm steel
  • Laboratory test: Rw = 55dB
  • Measure : Rw = 53dB

Tiled roof:

  • 10mm flat tile roof+57mm air+280mm LV+BA13
  • Laboratory test: Rw = 54dB
  • Measure : Rw = 53dB



The AcouS STIFF® software, developed by GAMBA Group, simulates the sound reduction index of complex walls.

This tutorial is an overview of this software.

1. Overview

2. AcouS STIFF® Software: Sound Reduction Index Simulation of partitions

How to simulate the sound reduction index of partitions with plasterboard and insulation with AcouS STIFF® software ? Tutorial by GAMBA Group

Training objectives : :

  • Provide participants with the basic knowledge to understand the acoustic behavior of a wall and to highlught the influence of parameters which can be used to optimize a piece of work.
  • Mastering the use of AcouS STIFF® software.


People concerned : :

The course is valuable for engineers who design or prescribe the walls, including :

  • the engineers of studies who propose solutions for constructive systems,
  • technical sales people responsible for prescribing a work derived from a system catalog,
  • the engineers of R&D department responsible for the development of a wall or a mounting system, or manufacturing technology.


For further information, please contact Marion Lorin

AcouS STING® - Software used to predict the level of impact noise

Diag LEXD® - Prevention of hearing risks connected to the exposure of noise

AcouS STING® - Software used to predict the level of impact noise

AcouS STIFF® - Acoustic Software Sound Transmission Index Full Forecast

AcouS PROPA® - Software for modeling acoustic propagation in premises and outside

Related services

For all our software, a complete range of products and services is at your disposal :

Maintenance contract

This maintenance contract provides among other things : the maintenance of the software and the dongle, the delivery of software updates for free for holders of the maintenance contract, phone support, special discounts on other software


Each year a new version containing additions or changes in the software is available.

Training and seminars

We regularly organize inter-company and intra-company training courses on the use of the software.

Day of information and exchange

Each year and each software program, at least one day of information and discussion is held with the users of such software.

Calculations on demand service

We can do calculations of acoustic simulations on request with the use of our software. You can avail of these services free or at very favorable terms for an annual fee.

For more information, please contact us

You will find below answers to some questions you ask and which we hope will give you the information you seek.

The software can model all types of wall partitions, walls floors, roofs.

Yes, the overall values in Rw (C, Ctr), dB(A)/pink, dB(A)/road, and STC are calculated according to national and international standards (ISO 717-1, NFS 31-051, ASTM E413,...)

Yes, the software calculates the global indices such as the U.S. STC (Sound Transmission Class).

Yes, the software comes with a database covering the most common materials and widely used in France and Europe.

Yes, just create simple or porous siding in a file from the database, give the name of the component that you want and enter its physical characteristics (density, Young's modulus and factor loss for material type "plate" and resistivity to air flow for porous materials with open pores).

Yes, they can be displayed in tables and on graphs. This data is customizable via context menu "Properties" window "Reports" tab "View" and "Results".

Yes, they can be displayed on graphs via context menu "Properties" window "Reports", "View" tab.

Yes, you can import your RE packet or one by one from a spreadsheet (like Excel, Open Office,...); workbook for that use context menu "Paste RE (Import spreadsheet)" the window "Walls Explorer".

For the properties of PU, they can be found in an SNPA test report concerning floating screeds on thermal insulation with or without SCAM. Rapport : 1 Rapport : 2
In fact, polyurethane is not entered in the database. Sometimes it acts as a spring and sometimes as a mass.. in this case I would go for a spring if there is a bitumen seal underneath and a mass (therefore multilayer) if you have a PVC seal on top.
Yes, it is possible to integrate acoustic test reports into AcouS STIFF. On the other hand, if the RE of a roof is added to an R of a suspended ceiling, the interaction between the two (mass/spring/mass, cavity reverb, connection, etc.) will not be taken into account, the result will therefore be false from a physical point of view. I therefore advise to do the simulation of the roof (calibration calculation measurement from the test report) and then to integrate a suspended ceiling below in simulation. Example: If the steel roof is a bitumen waterproof roof + insulation + steel: simulated with double wall Then simulated with triple wall by taking the elements of the double wall and integrating the suspended ceiling. Additions of experimental and simulation values are dangerous and can only be done when no interaction between the two elements exists.
We can take gravel into account, but the method depends on whether we make impact noise or airborne. In the air, you can do multilayer, so you put the CLT on one layer and the gravel on another. For gravel, you can put the right density and thickness. Must indicate a low Young's modulus so as not to have a critical frequency in the observation spectrum and put a fairly large loss factor, but in any case will have no impact given the position of the critical frequency that you will choose. For the shock, we cannot make a multilayer, we must therefore create an equivalent floor, which has the total thickness CLT + gravel, the surface mass which is also the sum of the two. You have to keep the Young's modulus and the loss factor of the starting CLT, or readjust the surface Young's modulus so that the EQ floor is the same critical frequency as the starting CLT if it has really moved a lot.

Yes, you can define leakage percentages for the panels.

AcouS STIFF® allows to take into account that direct transmissions on the other hand we have another calculation module called AcouS STICS 21® who is in the test phase which allows lateral transmission calculations to be made.

Yes directly in the Windows file manager like any other file or create another with "File" then "new file"? Yes.

From the glazing module, it is possible to model the two glazings making up the double joinery. These two simulations will give you the characteristics to enter in the triple wall (if double glazing and monolithic glazing) or your quadruple wall (if two double glazing) modeling your double joinery.

To make the simple walls, you just have to go through the materials tab, select the different materials, you "drag and drop" from the materials tab to the wall construction window and so it will create the simple walls for you.

The insulation calculation model (DnT and L'nT) is based on the ISO 12354 series of standards which itself is based on the assumptions of the SEA for the analytical approximations. For the wall prediction models (R and Ln), the models depend on the subjects, they are taken from the literature and are analytical models of behavior.

Yes, you have at your disposal after downloading manuals and tutorials on each software. (see picture below) 

After the installation for the first time the file (DEMO.sia) is found in this directory: C:\Users\......\AppData\Roaming\GAMBA Acoustics and Associates\STIFF_FR\Data To access it, go to the Windows bar, press the Windows key and type “%appdata%” When opening the following file explorer window C:\Users\......\AppData\Roaming Choose the GAMBA Acoustique et Associés\STIFF_FR\Data folder and your default “demo.sia” file is in this directory (image below) And then you can open or create other files with “.sia” suffix with file menu as a standard file.
Regarding this question, several points:
  • AcouS STIFF®: sound reduction index
    • If you have an R test report for a false floor on concrete, you can readjust it (preferably using the deltaR to more easily understand the separation factor)
    • Then you can recreate a double wall by integrating an OSB wooden floor instead of the concrete floor while keeping all the other parameters.
  • AcouS STING®: impact sound level
    • You can readjust a false floor deltaL on concrete floor from the floating covering module that you can reinject on any so-called inert floor (concrete, slabs, hollow core slab, pre-slab, etc.). On the other hand, you will not be able to put it on an OSB wooden floor (even taking the latter from an experimental value because it cannot be simulated in Ln for the moment)






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