See the example below - in an impedance tube there is no air behind the sampe normally so take that away, and no need to assign fixed displacement since it is an acoustic element and no need for coupling since it is pure acoustics (the Bazley is pure acoustics). Have in mind we are using the latest release 20201 R2 with harmonic acoustics (I do not use and can not help with the act extension since this is not native)
All the best
Erik
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