Statistical characterisation and responses of acoustic screens and two-layers systems

The present dataset contains measurements of the acoustic response of screens in an impedance tube with different backings. It includes as well the characterised parameters for the screens and backings.

License

This dataset is released under Creative Commons with Attribution (CC BY). Any reutilisation of the present dataset in scholarly works must properly cite this work and its authors:

Statistical characterisation and responses of acoustics screens and two-layers systems
M. Gaborit, L. Jaouen, O. Dazel, P. Göransson
DOI: 10.5281/zenodo.3358921

Protocol

Two different films (one woven and one non-woven) were sampled 40 times in order to characterise their parameters in an impedance tube. Sampling is manual, the tube inner diameter is 44.44mm and the samples are cut to a slightly large size in order to be clamped inside the tube for measurements.

The films are tested in different configurations including some with backings. Two types of backings are considered (melamine and glass wool). These backings are also characterised using 3 and 2 samples respectively. When measuring the response of the film on a backing only 20 samples of each film were used.

All measurements span the [4, 4520] Hz band. The setup is calibrated anew before each measurement session.

Films' characterisation

The films are clamped in the seam between the two parts of the tube, a 200mm air plenum is formed downstream and ends with a rigid backing. The samples for each type of film are measured within 4h.

The characterisation procedure implements the method described in the following reference:

• Jaouen L. Bécot F.-X. JASA 129(3) pp. 1400 - 1406, 2011

Backings' characterisation

The sample and backing piston are placed to give a rigid backing and have the sample's surface flush with the seam between the two parts of the tube. In the case of the glass wool, the material has a slight (below millimetre) embossing and the supporting surface is placed flush with respect to the seam (the top of the embossing is not considered as the sample surface).

The characterisation procedure implements the method described in the following references:

• Olny, X. & Panneton, R. JASA 123(2) pp. 814 – 824, 2008
• Panneton R. & Olny, X. JASA 119(4), p. 2027, 2006

Response measurements

To measure responses of the film/backing systems, the backing are placed as described in the previous paragraph. The film is clamped in the seam as described in the "Films' characterisation" section. A plastic grid with thin struts is placed upstream to prevent the film from bending. This setup allows for easily changing the film without replacing the backing sample. Films' samples 1 to 20 are used for response measurements. Measurement of the grid response on a rigid backing and an air plenum of 200mm are provided for reference.

Hardware

• Mecanum 3-microphones tube, diameter: 44.44mm

Software

• Matelys TubeCell (rig control)
• Matelys RoKCell (characterisation)

The piece of software controlling the rig implements a 3-microphones technique described in the following references:

• Iwase T. Izumi Y. J. Acoust. Soc. Jpn J 52(6) pp. 411–419, 1996 (in Japanese)
• Iwase T. Izumi Y. Kawabata R. in proc. Internoise, 1998 (Christchurch, New Zealand)

Structure of the datasets and files

The present dataset comprises two parts. The actual traces and associated measurement parameters as exported from TubeCell are found in the directory measurements. The results from the characterisation process as exported with RoKCell are in the characterisations folder. These results were augmented with direct measurements of the weights and thickness of the samples (both for the films and the backings).

Measurements

The measurements are stored in the measurements directory. There are several sub-directory for each of the measurement sessions:

• backings: measurements for the caracterisation of the two backings (all samples, with and without grid)
• grid: measurements of the grid alone on a rigid backing and with a 200mm air plenum
• nonwoven_alone: measurements for the caracterisation of the non-woven film on a 200mm air plenum, no grid (all 40 samples)
• woven_alone: measurements for the caracterisation of the woven film on a 200mm air plenum, no grid (all 40 samples)
• nonwoven_on_glasswool: measurements of the response of 20 non-woven film samples clamped with a grid upstream and the same glass wool sample downstream on a rigid backing
• nonwoven_on_melamine: measurements of the response of 20 non-woven film samples clamped with a grid upstream and the same melamine sample downstream on a rigid backing
• woven_on_glasswool: measurements of the response of 20 woven film samples clamped with a grid upstream and the same glass wool sample downstream on a rigid backing
• woven_on_melamine: measurements of the response of 20 woven film samples clamped with a grid upstream and the same melamine sample downstream on a rigid backing

Each measurement is stored into a .irk and a .rok file. The first one contains some meta-data on the measurement process, the second contains the actual traces.

Structure of irk files

The .irk files contain the following meta-data:

• Date
• Medium ID
• Thickness
• Size of the air plenum
• Measure parameter l
• Measure parameter s
• Sampling frequency
• Tube radius [m]
• Average 1
• Average 2
• Temperature [°C]
• Atmospheric pressure [Pa]
• Humidity [%]
• High cut-off frequency (generator) [Hz]
• Low cut-off frequency (generator) [Hz]
• Position of the cavity microphone
• Comments

Structure of rok files

The .rok files contain the following vector (column-major). The first line is to be omitted when reading the files, it contains the columns title. The columns are these:

• Frequency (Hz)
• Absorption coefficient
• Real part of the reflection coefficient
• Imaginary part of the reflection coefficient
• Real part of the normalised surface impedance
• Imaginary part of the normalised surface impedance
• Real part of the transfer function
• Imaginary part of the transfer function
• Real part of the normalised density
• Imaginary part of the normalised density
• Real part of the normalised compressibility
• Imaginary part of the normalised compressibility
• ... frequency response functions used to compute the previous quantities

Characterisations

The directory characterisations contains YAML 1.2 files created from the output files of the characterisation software, exploiting the measurement data. There are three subdirectories:

• backings contains the characterisation of the backings (each sample and an average file)
• nonwoven contains the characterisation of the non-woven film (each sample and an average file)
• woven contains the characterisation of the woven film (each sample and an average file)

More information

For further inquiry write to gaborit at kth dot se