Dome with horn
File: Dome - Horn.axi
This example carries on with the simple dome example. Here we attach a short horn, so that the diaphragm is displaced into the infinite baffle as can be seen in the field plot at 10kHz.
For the BEM such problems are involved because the infinite baffle Green-function does not allow for "something" behind the baffle. AxiDriver solves such problems by "stitching" together two BE-domains. If you check "Show Patches" above the field-plot the finite-elements are shown. Note, that the infinite baffle is not meshed, but there is an interface cylinder in front of the speaker at which sound pressure and velocities of two sub-domains are matched. For more on this topic see this paper... The elements going horizontally just above the diaphragm are so called CHIEF-points.
The model of the horn is specified on page Baffle.
Baffle front 29mm 1mm 35mm 3mm 50mm 2mm
Each line of this text-editor corresponds to a ring. The first value is the diameter and the second the height of the ring. The very first ring is implicit and does not need to be specified. It is at the base of the dome plus the suspension and magnet (if defined). "29mm 1mm" thus defines a little tube. The base diameter is 25mm + 2·2mm = 29mm, which is the same at height of 1mm. "35mm 3mm" defines a funnel of height 3mm, with base diameter of 29mm and top diameter 35mm, and so on.
If we do the same spectral analysis as in the previous example then we observe an increase of sound pressure at higher frequencies of approx 3dB. The spike at approx 15kHz is produced by the first mode along the axis. c/(4·L) = 14.3kHz gives a rough estimate of this mode, with c = 343m/s and L = 6mm.