Simple HR question

When calculating L12 length, where do you measure L1 from, middle of dust cap?

Playing with Martinssons Tham15, so middle of cone gives one L12, but there is 7.5" of driver either side of this. Is this why "measured" varies from HR quite often for the better, as there are multiple horn lengths? For long horns, I presume this effect is lessened, but on short horns, you have significant multiple lengths? Effectively, for a TH, you have multiple 1/4 wave lengths of horn path, which means you even out the predicted humps in response, from just one horn length?

I.e if you consider slices of cone perpendicular to L12, at centre of dust cap L12 , there is a 15" wide strip of cone surface acting. As you move to each end of the cone L12 +7.5" or L12 -7.5", there is less cone strip/area acting, but at a possibly significant different L12?

TENSiON wrote: Roughly the equivalent of 1/6th to 1/8th 1/4th octave smoothing in the case of a Tham-15 (1.94m path length, 32cm effective cone diameter, 40-120Hz evaluation range). Might be a bit off though - it's late and brain refuses to fully cooperate Edit: After giving it a second thought, the path difference in case of tapped horns is actually 2 cone diameters as the wavefront originating from the extreme far end of the back side of the cone has to cross the cone 2 times to arrive at the extreme far end on the front side. So the boundary conditions for the calculation are: HR path length (S2) ± effective cone diameter. However... If the transducer was square, this would account for a 1/3rd octave smoothing effect, but as the cone is circular and the bulk of its Sd is concentrated around the centerline, it has to be accounted for when evaluating the effective path differences and how it affects the final results. Based on this I would estimate that the final real world result is somewhere in the ballpark of 1/4th to 1/6th octave smoothing (for the specific case of THAM-15).

I was wondering if it would have a significant effect. On Martinsson's blog, and from my fiddling on HR, you get quite a peaky output, but his measured response is pretty flat, and I am trying to work out what effect is causing this difference?

Also along the lengths of L2-L3, do these lengths of individual "pipe", i.e each length between corners/bends "resonate" or do they out of band, say 200Hz plus, or not significantly at all.

It has just been bugging me that the Tham15 HR is good, but a little peaky, whereas measured is much more favourable, with the troughs between peaks appearing filled, not peaks lowered. If I can work out what improves outside of HR, to flatten response, I may be able to apply this to other TH projects.