The departure angle from the diffraction slot is always the desired angle for the horizontal beamwidth. (Actually it is a hair less) The 2344 with a 100 degree horizontal beamwidth is 90 degrees between those surfaces. 2360 would be 80 degrees or so to hit the target 90 degrees.
I can't comment on the cause of 4430 glare/hardness. It isn't a perfect system but I wouldn't conclude it had to be the diffraction slot. Could be incompetant network design.😛
Their current trend is to forego the diffraction slot and simply do a blend of fairly straight side walls and end flaring. As mentioned a few posts back, this will give less perfect polars but better frequency response. They are quite far from classic exponential so I would like to see some raw horn curves to see what the low end looks like.
David S.
Let's move closer to the present. Anybody know how and when the small waveguides JBL refers to as "elliptical oblate spheroidal" fit into this history lesson?
Hi Dave:
Is it? I wasn't clear on this- the "cheeks" being curved the way they are I assumed the nominal coverage angle was somewhere a little past the slot. I guess the throats are long enough for the first little bit of the post-slot flare defines coverage down to XO freq, with the rest of the flare just keeping the stopband smooth.
As I recall, you were one of the designers of the 4430- was the network your contribution? Certainly they're not "bad" by any stretch, but relative to my own waveguides, that are an OS approximation and used, at that time, 2426h, there was definitely some additional harshness. Now, I couldn't have gotten the top octave at 97dB in a constant directivity horn anyway, with the 2426h, it had to be rolled off in the context of my system design which, at the time, was using JBL 2226h and the 2426h with a passive filter (and no B.S.C). With the lower sensitivity required to match the 2235h, the 4430 could try to get that top octave out and that may be what I was picking up on.
I would love to try loading some of the "buttcheek" horns with foam a la geddes, just from the phase plug to slightly past the diffraction slot. I suspect that the parallel surfaces in the throat have HOMs that would be significantly attenuated by this (as well as any axial/semi-axial standing waves)
The horizontal and vertical cross sections are identical, especially on the 100 x 100 horns. They start as straight sides and then flare away following a simple equation found to give good polars near cut off. Remember the vertical cross section expands from the throat entrance while the horizontal cross section begins at the diffraction slot.
Yes, I designed the network on the 4430 and 35, so I thought it was fair to take a potshot at it!
David
Yes, I designed the network on the 4430 and 35, so I thought it was fair to take a potshot at it!
David
Commenting on the question in the title, not the entire post. I have been working on a multiway hornsystem, and my experience is that you can't mix direct radiators and horns, not only because of differences in directivity, but also because of the effect of hornloading. I have tried to hornload everything above 500Hz, but it sounded bad. One way to circumvent the problem would be to use a fast opening horn from 300Hz, like in the Avantgarde Duo. People have been complaining about it its bad bass/midbass, but it is still a good compromise.
Combining AMT/true ribbon and direct radiator cone drivers sound better, but I prefer hornloading all the way.
Combining AMT/true ribbon and direct radiator cone drivers sound better, but I prefer hornloading all the way.
I tend to agree with you, and that's one of the reasons I really like constant directivity cornerhorns. But I will admit that it is often inconvenient - sometimes prohibitively inconvenient - so I think a DI-matched two-way speaker with flanking subs is a useful compromise.
Mine will be a 5- or 6-way. I have nothing to add about cornerhorns, except that I am sceptical, as I prefer longer horns, but I would love to listen to one some day.
Constant directivity cornerhorns aren't necessarily "short" and in fact, I would agree with you that many modern horns are too short for their profile and area. Where I see cases like that, acoustic loading isn't good so they suffer from excessive ripple.
The key feature of a constant directivity cornerhorn is that its source is acoustically close to the apex of the corner and its radiation pattern is therefore limited to 90°. There is no self-interference from the nearest boundaries because the sound source is acoustically close. That's the main feature, and beyond that, implementation is not specific to any particular horn. But I do think that well-designed waveguide/horns are perfect for this application.
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It wouldn't be too hard to convert a tractrix (?) to be somewhat closer to a wider waveguide with a radiused mouth by just removing some of the throat length and filling in around the new throat.
I found the documents I mentioned earlier about solving the wave equation for oblate spheroidal devices. I seemed to recall they were not audio, but in a semi-related field. I believe they are still germane to this discussion.
I do, however, think the description of the OS profile as catenoid is wrong. It may be something like a catenary, perhaps sort of a "catenary throat" waveguide to use Hughes parlance (e.g. quadratic throat). But after studying the curve more closely, I do not think I would call it a catenary curve. It is a hyperboloid - which resembles a weighted catenary - but I think that's the extent of it.
Earl Geddes has described the oblate spheroidal flare profile as a catenoid, and I guess I parroted that without checking. We talked about that shape in person, as well as online discussions. Earl even called it a catenoid in his letter to the editor of AudioExpress, about Bjorn Kolbrek's article on horns and waveguides.
In fact, the OS hyperboloid does look similar to a catenoid. But now that I have looked at it, I no longer think it is one. I'll be correcting that on any websites I have access to, so as to no longer refer to the flare profile of an oblate spheroidal horn as catenary.
- Landesman dissertation about wave propogation based on the Oblate Spheroidal coordinate system
- Landesman Paper about the OS coordinate system
I do, however, think the description of the OS profile as catenoid is wrong. It may be something like a catenary, perhaps sort of a "catenary throat" waveguide to use Hughes parlance (e.g. quadratic throat). But after studying the curve more closely, I do not think I would call it a catenary curve. It is a hyperboloid - which resembles a weighted catenary - but I think that's the extent of it.
Earl Geddes has described the oblate spheroidal flare profile as a catenoid, and I guess I parroted that without checking. We talked about that shape in person, as well as online discussions. Earl even called it a catenoid in his letter to the editor of AudioExpress, about Bjorn Kolbrek's article on horns and waveguides.
In fact, the OS hyperboloid does look similar to a catenoid. But now that I have looked at it, I no longer think it is one. I'll be correcting that on any websites I have access to, so as to no longer refer to the flare profile of an oblate spheroidal horn as catenary.
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I think what may have been in your thoughts is an oblate spheroid section can have the same shape as a catenary, as can a section of a prolate spheroid or elliptic cylinder. There is such a thing as an elliptic catenary, also sometimes called a roulette. But the tangent that passes through the elliptic is not, and this tangent line is what actually forms the flare profile of the (OS, PS or EC) waveguide.
A catenoid is a Salmon family horn. It is useful at low frequency. The tangent lines that form the OS or EC profile are not catenaries, but when parameters are chosen that create a narrow beamwidth device, it looks very much like a catenary and even acts like one, loading quite well at low frequency. I know this because I have made and tested narrow beamwidth OS/EC waveguide/horns. So even though it isn't a catenary - and isn't really part of a continuum of catenaries - it sort of acts like one.
It has been interesting to re-examine these curves and how they relate to wave propogation. I remembered a lot of it from earlier studies, but some comes with new eyes. For example, there are so many disciplines that use oblate spheroidal and elliptic cyllindrical devices. Examples are microwave, optics and sonar. It's a shape that has gained almost universal acceptance.
This again prompts me to tip my hat to Earl Geddes for bringing attention to these elliptical coordinate systems for horn loudspeaker systems. Other industries had found these shapes but audio had not. Without Earl's suggestion, we'd all still be fighting with straight-sided conical horns with sharp edges, or giving up on uniform directivity and going back to exponential or tractrix horns for hifi.
Excuse me, my math skills are non-existent, but Wayne compared wgs to optical systes. Can one think of wg/horn profiles like lenses with varying magnification? A narrow beamwidth horn is like a lens that has stronger magnification in the middle like a fish-eye lens etc.
You may have already mentioned it, but what is the issue with a tractrix horns? Please provide some measurements if you have.
I have the polars of Klipsch's K-402 and it looks better then any waveguides I've seen. It doesn't beam very much either.
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There is a problem with some of the "names".
The Klipsch K-402 is not a tractrix horn. They refer to it as a "modified tractrix". The actual rate of expansion is probably conical in the mid section and a tractrix expansion at the mouth.
Yes, it is a CD horn horn and it does not beam at the high frequencies
Mathematically they are not the same problems and I don't see the analogy as working either.
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