Cogito wrote:
Roscoe Primrose wrote:
I think you're missing the point. Exponential horns are a fine thing. The 511 departs from being an exponential horn in the throat area. That's not opinion or hearsay, that's plain measurable geometry. No amount of damping can change that.
Roscoe
That sudden transition in the throat area seems to be a design feature, not a flaw.
Here is the excerpt from Altec literature:
511B/811B:
Exponential expansion and
straight throat configuration ensure uniform control of the sound dispersion pattern -- 90 degrees horizontal by 40 degrees vertical -- and exacting reproduction of the middle and high frequencies.
http://alteclansingunofficial.nlenet.net/proloudspeakers/sectoralhorns/511B&811B-Data.pdfAfter some reading, there is some misunderstand -- at least on my part -- about 511s.
Altec 511Bs are not exponential horns. They are Radial/Sectorial horns, ie, exponential vertical axis and canonical horizontal axis. No part of the horn is strict circular except for the start of the throat.
The quote above from Altec, "Exponential expansion and straight throat", gave me the impression that throat is straight like a tube which suddenly flares into a canonical horn causing diffraction. If I look at the horn closely (see pics below), the throat quickly becomes a rectangle and slowly flares until the a point where exponential and canonical geometries kick in. The "straight throat" in Altec specs is referring to the vertical walls of the throat, which are supposed to be straight because of the canonical geometry on the horizontal axis.
The flare looks too steep from outside, but it is similar to that of Emilar EH500. Inside of the horn, the transition from throat to mouth is nicely curved.
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The horizontal walls of the throat follow the exponential curve and they condense at the beginning of the mouth to start a new exponential pattern. This also looks to be very similar to the pic of Emilar EH500 (J-ROB, can you post the horizontal axis pic when you get back?)
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Since the throat is the sectoral horns is expanding and there are no sharp edges, I now do not believe that our hypothesis of simple diffraction does not apply here, that is not to say there will be no diffraction in the horns. What ever little diffraction is present in the sectoral horns is inherent part of the geometry.