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Absorption Spectra

Spectra of the sound absorption coefficient are managed via the libraries Absorptions (menu Tables|Libraries (local) and (global)). The library can be extended by the user.

The data included in the default library:

  • Example spectra for low, medium and high absorption.
  • Absorption spectra from LAI-22, Table 9.

When referencing to a an absorption spectrum from the global library in a project, CadnaA will generate a copy of this spectrum in the local library Absorptions. The reference to a spectrum is established by its ID which is, therefore, mandatory to enter.

Furthermore, spectra from the global library can be copied to the local library by clicking the button „--> Local Lib.“.

Accessing Absorption Spectra

On the object dialog of obstacles (e.g. Building, Barrier) which may have different absorption characteristics the absorption spectra can be accessed after activation of the option „Absorption Coefficient Alpha“ and click on the file icon selector symbol (see, for example, chapters Building and Barrier).

dialog Building: The file selector symbol is outlined in red, for selection of sound absorption spectra (local or global), selectable after activation of option „Absorption Coefficient Alpha“

The following modifications are available:

  • clicking the file selector symbol in line „Absorption Coefficient Alpha“ gives access to the local library Absorptions or
  • holding the SHIFT key pressed while clicking the file selector symbol in line „Absorption Coefficient Alpha“ gives access to the global library Absorptions.

Export/Print of Noise Level Spectra

The sound absorption spectra from the libraries can - like any other table - by copied to the clipboard by clicking the button "Copy" or be printed or exported (see Text Files (.txt, .rtf)) by using keywords (see Table in the manual "Attributes, Variables, and Keywords"). Printing and exporting using this keyword occurs just for the local library:

#(Table, LibA)

Entering new sound reduction spectra

New sound reduction spectra can be entered in two ways:

  • starting from the object dialog of point, line and area sources by clicking the file selector symbol in the line „TransLoss“ (with or without holding down the SHIFT key) and entering the new spectrum in the particular library, or

  • via the menu Tables|Libraries (local) or (global)|Sound Reduction Indeces.

Note

In order to enter several sound reduction spectra it is recommended to enter the spectra via the Tables menu and to assign the spectra to each of the respective sources afterwards.

Regarding the general handling of object tables and the input of new data records via the context menu, see Object Tables.

Spectra - as with other kinds of library objects - can be edited directly in the respective table or - after a double click in a table row - be entered on the dialog Spectrum.

Dialog Spectrum

ID

It is mandatory to enter an ID for each spectrum. Please consider the respective rules for the ID (see Dialog Options Name, ID, INFO, ObjectTree, Master in the manual „Introduction to CadnaA“). In particular with library objects, a character is mandatory as the ID‘s first character.

Name

description of the spectrum

Source

description of the data's origin

Pocket Calculator Symbol

Via this symbol the present spectrum can be modified (see Modify Spectrum).

DeltaLA,a,str / Alfaw

displays the value DeltaLA,alpha,Str according to the German ZTV-Lsw 88 ZTV-Lsw88 and the weighted sound absorption coefficient according to ISO 11654 11654-1997 of the spectrum entered.

Option „1/3 Octave Band Spectrum“

after activation a third-octave spectrum can be entered

Button „Convert“

see Spectra, Conversion of Spectra

Octave or Third-Octave Bands

Enter the sound absorption coefficient for the each octave band here.

Arrow Buttons <-|->

to move to the next/previous dataset

Button "New"

generates a new table row below the row currently selected