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Sound Radiation from Elements & Openings

The Austrian guideline OEAL 28, edition Dec. 1987 ÖAL28-1987 specifies frequency independent directivities for the radiation by building elements and by openings within the building‘s facade The directivity for the radiation by building elements has been modified with the amendment of 2001 ÖAL28-2001.

Directivities according to ÖAL 28 on the Directivity dialog

After withdrawal of ÖAL 28 guideline (replaced by ÖNORM ISO 9613-2) a so-called „instruction note for modeling the sound propagation according to ÖNORM ISO 9613-2: 2008 and ÖNORM EN 12354-4: 2001-02-01“ forum-2001 emphasizes that the guideline regarding the specifications for sound radiation „is still valid“. Furthermore, it has been clarified that the directivity correction for elements just „applies to elements with low bending stiffness while „... for heavy building elements no specific directivity correction has to used“ (translated from German). There are three ÖÄL specific directivities available:

  • Element (ÖAL28): according to edition December 1987
  • Opening (ÖAL28): according to edition December 1987
  • Element (ÖAL28/01): according to amendment ÖAL28, February 2001

The directivity of components elements and openings according to ÖAL28 are independent of frequency.

Directivity Correction ΔLΦ

Directivity with angle Φ(hatched: radiating surface)

Depending on the angle Φ referring to the surface normal the following expressions for the directivity correction ΔLΦ apply:

Directivity of elements, edition 1987

\(0°\leq \Phi \leq 85°: \Delta L_\Phi = -3+(3*\frac{\Phi}{42.5°}) dB\)

\(85°< \Phi \leq 135°: \Delta L_\Phi = 3-10\lg(0.4(\Phi-90°)+3) dB\)

\(135°< \Phi \leq 180°: \Delta L_\Phi = -10 dB\)

Directivity diagram (surface normal pointing in direction 0°):

Directivity of elements with low bending stiffness, edition 2001

\(0°\leq \Phi \leq 85°: \Delta L_\Phi = 0 dB\)

\(85°< \Phi \leq 107.5°: \Delta L_\Phi = -10\lg(0.4(\Phi-90°)+3) dB\)

\(107.5°< \Phi \leq 180°: \Delta L_\Phi = -10 dB\)

Directivity diagram (surface normal pointing in direction 0°):

Directivity of openings, edition 1987

\(0°\leq \Phi \leq 45°: \Delta L_\Phi = 4 dB\)

\(45°< \Phi \leq 85°: \Delta L_\Phi = 6\lg(\frac{90°-\Phi}{10}) dB\)

\(85°< \Phi \leq 135°: \Delta L_\Phi = -2-6\lg(0.4(\Phi-90°)+3) dB\)

\(135°< \Phi \leq 180°: \Delta L_\Phi = -10 dB\)

Directivity diagram (surface normal pointing in direction 0°):

Application

In practice, radiating elements and openings are parts of the outer envelope of buildings. In this case, the directivity vector is by default directed automatically (see Directivity at Industrial Sources, Automatic orientation depending on source type).