Although it is not a “tapered” transmission line, it is certainly true that the coupling chamber of about 50 litres, located behind the woofer, would have had equally marked effects on the frequency position of the resonances measured at the opening and, in those circumstances, the application of the classic equation f=c/(4xL), where c is the speed of sound and L the length of the duct, to calculate the speed of sound at those frequencies, would have given misleading results.
I have never tested the properties of natural wool inside the TL, but I have reconstructed Bailey’s speaker with the simulator. A comparison of the frequency response graph of the simulated system with the one in the article confirms a reduction in the speed of sound by a factor of 0.8 as indicated by Bailey himself.
Augspurger in [3] also argues that wool is not able to halve the speed of sound and that, even if it were, the results would not be those hypothesised by Bradbury. With his software he therefore simulates a TL tuned at 100Hz and, keeping the amount of absorbent material constant, varies the speed of sound in a range from 0.4 to 0.8 times that in air. The result is visible in Figure 2.