Akabak: modelling horn bends and cross-section discontinuities

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Hi

been trying to model some tapped horns in HornResp and Akabak. In Hornresp I have been fudging the S3 value to keep the overall cabinet volume correct according to CAD drawing of the physical horn. As my design has several bends and a large cross section discontinuity near the mouth I am trying to write a more detailed model in Akabak.

http://www.randteam.de/papers_jp/aes_Euphonia_e.pdf

page 3 of the above article (taken from the Akabak manual) suggests that bends can be modelled by inserting an acoustic mass between the ducts either side of the bend and that cross-section discontinuities can be modelled either by inserting an acoustic mass or making the duct length slightly longer. To model a 90 degree bend it is suggest that the mass should be 1.85/WD kg/m^4 where WD is the width of the duct perpendicular to the plane of the bend. This does not seem right to me - can anyone confirm/clarify the thinking behind this?
The article does not go into any depth about modelling duct discontinuities - can anyone shed any light on the procedure for finding suitable values?

Phil Pope
 
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