Quote Originally Posted by Steve Schell View Post
Hi GM, your post sent me scurrying for Abraham Cohen's book "Hi Fi Loudspeakers and Enclosures", always a good thing. For those who haven't read this book, try to find one at abebooks.com or somewhere, as it is essential reading.

Were you referring to the picture of the Altec 3000 tweeter and illustration of the pattern? I may be all wet, but it seems to me that at least on a radial midrange horn like the 811, the dispersion pattern has pretty much been determined by the time the sound energy reaches the fins. Being a radial horn with two straight sides, the horizontal pattern would be largely that of a conical horn with its excellent directivity.
Greets!

Agreed, a bit dated in some ways, but its info has withstood the test of time and helps one to cut through marketing BS.

Right you are, but what do you get from a conic expansion? An on-axis hole in its HF response, but this isn't the case with the sectoral horns due to all the reflections at the mouth just as RonSSS noted. Hopefully, we can all agree that one must be on axis to them to hear the highest frequencies.

That said, it is subtle in a typical HIFI/HT app unless considerable CD horn EQ is used to flatten its response out to > 15 kHz and of course older and/or long term abused ears such as mine aren't going to notice it much, if at all. I could when I was younger, though I didn't realize how much they added until I cut out the vane welds and bridged the gap with a GE silicone gasketing product. Ditto adding damping to the sides of the horn. This widened the 'sweet spot' a bit at the expense of some top end 'air' and why historically I've nixed the tweak unless a super tweeter system is added.

Consider too that a horn's response changes somewhat at high SPLs same as a point source driver, so for the cinema app that the sectoral horns were designed for, the vanes are a must for firing through a screen due to an on axis flattening of its response and why I've periodically suggested making grills from screen scrap as I did for my previous system as an acoustic solution to an acoustic problem. Of course this requires more power for a given average SPL and especially transient peak SPL, so not for flea power systems.

GM