D-MAN Posted June 7, 2006 Share Posted June 7, 2006 Been researching horn channel folds as of late, and I have a question for Roy who helped design the Jubilee. The Jubilee AES paper discloses the use of a full-channel-width hard-surface 45 degree splitting wedge at the throat which accomplishes the 90 degree turn into the horizontal throat channels, which we all know is a good thing. And the 180 degree fold at the tailboard is picture-perfect. The attention these particular folds received (and change from previous PWK designs) brings up this question: Why was a partial-channel-width RADIUS technique (not so good) used at the front corner 90 degree folds? It seems like quite incongruent to me. It is clear that it was a purposeful choice, I was wondering what the reason for it was... Thanks, Dana Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 7, 2006 Author Share Posted June 7, 2006 Did a poor-mans experiment to check my calculations on turning a fold using a full-channel hard-surface (after Huygen) reflector. Sorry it may not be the best picture, but it satisfied me. I used the disk set from a defunct hard drive for a mirror. Dana Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted June 7, 2006 Share Posted June 7, 2006 D-Man, I hope Roy Delgado sees your thread and posts. Having met him at Hope last year think he is one super guy. He was able to communicate across the range of Klipsch fans from engineers to technical idiots like myself. One thing I was wondering about your post and measurements... I ask this to see if I am understanding your observation. Is your observation with the mirror indicating that this particular fold would properly be different than what is indicated in the drawing? If this is the case, I wonder if the published drawing would have been printed intentionally "altered" so as not to give away the design to competitors? Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 7, 2006 Author Share Posted June 7, 2006 What this really comes down to, is how wide of bandpass can we get out of these things? Channel width is going to be a physical limit, of course, based on wavelength at the top end. The general rule of thumb channel proportion (per Wilson) is 1/6th of the highest wavelength to be passed. Below that limit, the folds have a drastic effect down to 300 Hz, below which there is little effect as the wavelengths are getting much longer than the folds can harm. Where the line actually resides is still debated. Some say 500 Hz, some say as low as 200 Hz . No fixed value and not much literature available on this. The general rule of thumb is 3 octaves from the lowest frequency being passed. Some prefer 4 octaves, but not many venture above that. Certain rules of thumb exist to help, but it is rather unknown territory once one ventures away from the successful designs of the past... 90 degrees to 180 - radius or full channel. The radius-style is widely used in older designs where driver upper frequency corner falloff limitations tended to enforce the 3 octave "rule". The driver mass rolloff is still a natural limitation, but certain things can be done to enhance the upper frequency corner, and maintianing the phase relationships bassing through the folded horn. Here is a anotated pic of a Khorn under construction. Do NOT read this wrong: My intention is to point out certain aspects of horn folds, NOT THE DRAWBACKS of the KHORN DESIGN! However, if one is talking folded horns, what other design would YOU study? DM Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted June 7, 2006 Share Posted June 7, 2006 Thanks D-Man. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 7, 2006 Author Share Posted June 7, 2006 Daddy-D, sorry I was busy typing away and didn't catch you post until now. My test was not the Jubilee. It was just to see that what I figured for an angle reflection was correct, and as far as light is concerned, it is! I am right with you on your question about a possible "plant" in the plans, I considered that as a possibility also! But I don't think that it's very likely, considering what I know about PWK and Roy. Besides, it would not be likely that it has a great deal of effect, anyway! It's more like the PRINCIPLE of the thing...it just got me wondering. Sort of bad of us that we even thought of it! Shame on us! Dana Quote Link to comment Share on other sites More sharing options...
ajsons Posted June 7, 2006 Share Posted June 7, 2006 I think they tried to keep the "linear expansion" idea in the design. The designers chose three straightest parts of the horn to analyze the flare rate. Point A (throat) to B (the corner in question) expands at a fast rate, which turned out to be 97hz. A full Huygen reflector will result in a narrower distance between the corner of the doghouse and the reflector, and will appear to have a lower (incorrect) flare rate. The designers should have chosen a point B before the bend, and put in a Huygen reflector at the bend. Armando Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 7, 2006 Author Share Posted June 7, 2006 Interesting point. I don't know what the reason could be... A true full-channel Huygen reflector DOES indeed appear to be a smaller channel. That's completely normal (and expected!).Daddy-Dee, the difference in the Jubilee corner radius reflector from the Huygen-style mirror experiment above is that if the Jubilee corner channels were mirrors, only half of the light would make the turn, and the other half of the light would reflect directly back to the throat (where it came from). That is valid if soundwaves act the same as lightwaves, of course. It is just a different way to look at horn channels. But when you start to look at horns this way, it's quite appalling how much backward reflections occur in the wrong direction... take the La Scala as an example with NO corner reflectors at all - and now the question remains - how much does all this matter? The real answer is: how high up do you want (and can effectively get) the upper frequency corner and what are the variables involved? Dana Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 8, 2006 Author Share Posted June 8, 2006 The LS serves as an example of how to enforce a -6db rolloff using untreated folds and a somewhat ineffective throat splitter, etc. Heretofore, I always thought it was done for economic reasons, but now I think that it was to mate effectively with the chosen top-end drivers, with economical considerations taking a back seat. The Jubilee is basically 2 stacked scaled-down La Scalas (to 12" driver) with much more effective treatments at the folds; clearly intended to extend the bandwidth. At least that's my take... Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 8, 2006 Author Share Posted June 8, 2006 The University Dean using a cursory planar reflection analysis as rather badly drawn by me using MS Paint. My conclusion is that it would require some redesign work to raise its upper bandpass. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 8, 2006 Author Share Posted June 8, 2006 I do think that the Khorn itself could be modified to increase its upper bandpass I would estimate at around 500 or 550Hz or so. This would have to be done at the building stage, but for those of you building clones, that is the time to encorporate the changes. 1) use full-channel width Huygen-style throat splitters (ala Jubilee). 2) use full-channel horizontal reflectors at the top and bottom of the front vertical channels. 3) add additional bracing (ala Speakerlab K) to the back chamber top and bottom (inner horn channels). This won't effect the bandpass, but it will reduce loss due to vibration. 4) add full-width 45 degree splitter at the tailboard (ala 1946 plans posted by Armando). 5) switch to a driver with higher bandpass than K33E, however, this practically guarantees that it will be more expensive than the K33E. 6) Adjust crossover for new driver and higher crossover point. There are inherent limitations still, such as the horizontal to vertical change in the horn channels, which will have an effect on the waveform which cannot be minimized but who knows exactly what that effect is? This certainly will remain an unknown. I imagine that PWK experimented with this very issue and probably knew for sure. Now considering that PWK and Roy also thought about these very issues, they went to another design, the Jubilee. I would like to know if they tested the above list of mods simultaneously or decided to go with a completely new design right off the bat? It is clear from the 1946 plans that over the years, most of the above was tried at one point or another. Another consideration is that it was more acceptable for PWK to do a new design rather than upgrade an older one, which might have the effect of upsetting the Khorn owners with the implication that the Khorn wasn't quite up to snuff to begin with. Certainly not the case, but it is understandable that the implication would exist by proxy. I can easily understand the allure of a completely new design and the technical "freedom" that it embodies. Dana Quote Link to comment Share on other sites More sharing options...
filmboydoug Posted June 9, 2006 Share Posted June 9, 2006 Dman, (idiot question alert!!) If someone had the woodworking skills, how well would it work to round off the corners so the horn is more like a brass instument? see attached crappy art... Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 9, 2006 Author Share Posted June 9, 2006 I think that a true wide-radius circular turn where the radius channel is sufficiently wide is great as determined by the width of the channel compared to the wavelength being passed. The problem occurs when one side of the waveform has a longer distance to travel around the tune than the shorter path, like a racetrack, where the inside turn is always faster... It could be done, but not economically; in wood, that is. See some of Bill Fitzmaurice designs for examples of this approach. DM Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 9, 2006 Author Share Posted June 9, 2006 Here is another shot from this website: http://www.billfitzmaurice.com Bill Fitzmaurice is a leading proponent of this type of horn fold, which is characteristic of his DR horn designs. He takes special care with the bend geometry, one side compensates for the other, combined with drivers with a compensating response curve to accomplish the "fold". Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 9, 2006 Author Share Posted June 9, 2006 Another shot of the DR. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 9, 2006 Author Share Posted June 9, 2006 And finally, this one says it all... Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 9, 2006 Author Share Posted June 9, 2006 It isn't going to get much prettier than that! That is fine woodworking there. The consideration is wavelength. Of course the lows go through all of these almost as if they weren't folds there at all... but the mid-and-upper bass frequencies are the trouble makers. So which type you go for depends on the desired bandpass, and where you want to crossover and where you HAVE to crossover based on the approach selected. No fixed rule. Only hands-on experience. DM Quote Link to comment Share on other sites More sharing options...
seti Posted June 10, 2006 Share Posted June 10, 2006 Wow dam fine work indeed. I want to hear a pair. Quote Link to comment Share on other sites More sharing options...
capo72 Posted June 10, 2006 Share Posted June 10, 2006 Here is another shot from this website: http://www.billfitzmaurice.com Bill Fitzmaurice is a leading proponent of this type of horn fold, which is characteristic of his DR horn designs. He takes special care with the bend geometry, one side compensates for the other, combined with drivers with a compensating response curve to accomplish the "fold". That is a really interesting design. I'm intrigued to buy the plans for that. I just wish it was designed around a 15" woofer. I've got some K-33's laying around that are begging for a new cab. I wonder how that bass bin would sound with k-55-v on an Altec 511B and Bob's new tweeter? This has really got me thinking. Jeremy Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 12, 2006 Author Share Posted June 12, 2006 The driver's compensating response I spoke of was a rising reponse in the high end, to compensate for losses to those frequencies incurred in turning the folds, which is definitely not something the K33E is particularily noted for! Something to think about, anyway. DM Quote Link to comment Share on other sites More sharing options...
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