BeFuddledinMn

LarryC, This is an amazing amount of information, knowledge and experience you've shared here! Thanks much to you and several other long-time members who have put in so much effort in unraveling these mysteries and then sharing it with everyone. I see now after reading - that your 1962 Klipschorns came with the 3x13 throat slot, right about the time that was first introduced. I can imagine the EV 15wk you auditioned on that would have had too much upper bass strength? I'm lucky to have a chance to test it thoroughly with the earlier 6x13 throat slot design - and also try a 3x13 mounting board with the EV 15wk as well - and measure the difference. What I won't be able to do is mount the woofers directly to the motorboard with screws - as I'm reluctant to alter or potentially damage the motorboard on what is a nearly pristine example of a 1956 Klipschorn. Your experience and report on direct mounting the woofer without a mounting board has motivated me to make another 3x13 slot mounting board for the k-33e and Crites cast woofer with ~ 3/8" actual Baltic birch - thinnest material that could get closest to no board - with some strength and density to avoid resonances. Of course, as I think you've alluded, I also wonder how much is dependent on the crossover - and whether the no mounting board and AK-4 and 5 networks are a "package deal." When Klipsch started offering the full AK-4 upgrade package (crossovers, bass bin doors, mid and tweeter drivers) did they include a recommendation to remount woofers directly on older 3x13 slot mounting board Klipschorns? Great stuff, thank's again for the education and help. I'm still targeting the third weekend in September to do the testing.

LarryC, Thanks for the added perspective. I'm certainly looking forward to doing the controlled testing with frequency graphs - on the various motorboards, and the woofers themselves. I'm anxious to learn whether or not the 1950's klipschorn bass configuration really measures better, sounds better with a correct crossover, or not - compared to the more contemporary configurations. I'm certainly encouraged by my recent, but brief listening test. One thing's for sure, when they eliminated the big, heavy EV 15wk woofer, they surely reduced the klipschorn's shipping costs!

Roger, Thanks for the good input. It would be nice to have a Stephens woofer as well. To answer your question, yes, the EV 15wk I have is the early heavy alnico monster - weighs about 45lbs. I have actually auditioned it by ear recently on a 6x13 3/4" motorboard in my 56 Khorn. The difference between it and the k33e with the 3x13 motorboard I've been running it with is night and day, no question, similar to your listening experience. However, I'm not sure at this point if it's an spl sensitivity head fake, or a real frequency response difference in the Khorn application. I'm also using the same "a" crossover with the 2.5mh choke inductor. Of course, the original crossover for the '56 Khorn, which I have saved, has a 5.0mh choke inductor as it came from the factory with the EV 15wk woofer and 6x13 throat and motorboard slot. The EV 15wk is nominally a 16ohm rated woofer (vs. 4ohm on the K-33e), and it has a huge impedence peak from ~10-30hz, but the rated and measured dcr is very close the the K-33e woofer in the mid 3's. Possibly another issue on the pile, particularly in the Khorn bass bin, but I'm already over my skis on that one, lol. I'm looking forward to getting good objective measurements with numerous variables. Hopefully that will reveal a few things. If nothing else, we're having fun trying to unravel some of the mysteries that Paul W. Klipsch left for us. Thanks again.

Thank you to everyone who contributed to this discussion. Helpful comments and information. I think the next step is to do some actual measurement and testing with various motorboard thicknesses and woofer combinations, as well as the slot combinations (6x13, 3x13). To do that, I'm preparing to use my single 1956 klipschorn properly placed in a good corner, as a testing platform. I've just completed making several motorboards of both 3/4" and 5/8" thickness from very high quality Baltic birch. ( the 5/8" birch most closely matches the old, true 1/2" plywood of the 50's and 60's, it's a near match to about 1/32") I've created both thicknesses for both the 3x13 and 6x13 slot designs. I've painstakingly router cut these with custom jigs to ensure accuracy in both the slot size and curvatures. Second, I've assembled three woofers for testing - a good, original EV 15wk from the mid 1950's, a good, original k-33e square magnet, and a new Crites cast frame woofer. I am planning on doing the actual testing toward the end of September, after assembling the right testing equipment, and scheduling a free weekend! My plan is to carefully measure the various combinations and post the results here on the forum for review. In addition to motorboard effects, I for one am very curious to see how the EV and Crites cast woofers perform on the 6x13 slot boards as opposed to the 3x13 slot with the K-33e commonly used. Stay tuned. Thanks everyone, BefuddledInMn

Greg, Great craftsmanship! Simply stunning work! Since you've restored a number of klipschorns over the years, I thought I'd ask you this question: what thickness were the original slide out woofer boards on the ones you've worked on? 3/4", 1/2"? I've seen reference to both. And, in your opinion, does that board thickness make any difference? Thanks in advance, love your good work and upgrade products!

That's an interesting bit of information. I would have only guessed that a complete circle was used to create a small compression chamber. More continues to come to light. Still, were the circle board ever implemented? And, what thickness was used with the later slot boards and does it make any difference?

This is all helpful, with great links to excellent previous discussions on related puzzles, but different sources put the board thickness at 1 1/2"' , 3/4", and 1/2". Some illustrations show a complete 13" circle, others show a square slot cutout. And, aside from slot size, what effect, if any, would different board thicknesses and full circle vs slot cutouts produce? Certainly, I would have to believe that full circle cutouts would imply a compression chamber between the woofer and throat, albeit small, with any board thickness. Perhaps Klipschorn owners from the 50's, 60's, 70's and 80's can report on the configuration and thickness of their original woofer boards to establish exactly what was used and when as a start? After all these years, PWK's brilliant design still seems to hold some mystery...... BeFuddledinMn

It seems that the use of a woofer mounted slide-out Motorboard was used in the Klipschorn up until the late 70's, both with the earlier 1950's 6x13 throat, and the subsequent 3x13 throat used from approximately 1963 to present. However, from what I've been able to see and read from old klipsch plans and knowledgeable forum comments, it's less clear as to the thickness and configuration of these removable woofer mounting boards. Were they originally 3/4" thick or 1/2" thick? Were they as the original klipschorn patent documents illustrate, a complete 13" circle cut-out, or, were the cutouts the shape of the throat (3"x13" or 6"x13")? Did this change over time? And, in terms of board thickness, does 3/4" vs. 1/2" thickness make any difference in the bass horn performance of the Klipschorn - with either the earlier larger throat 1950's models or the later smaller throat model of today? Lastly, why was the removable mounting board eventually eliminated? Was it eliminated to increase back chamber volume ever so slightly to improve k33 driver performance, or accommodate a driver specification change? Any thoughts or insight on these questions would be welcomed. Thanks to all in advance. - BeFuddledinMn

FYI - the order of those pics in my prior post is all screwed up. Lower right is my 1956 k500-5000, lower left pic is 1957+, upper left is a very early model ~ 1952 or 1953??? and the top right is I believe a 1954-1955.

This is a fascinating discussion and thanks to all of you for sharing your knowledge and experience. Below are several pics of k500-5000 crossovers , the first one is mine from Sept, 1956. The others are from 1952-1954, then one from 1957 or later I believe. I have now installed a modified "a" network with 1db attenuation for the k55/k-5-j mid section rather than 3db. I'll share my unqualified listening experiences and thoughts when I get a chance later this week to test against the standard A and a/4500 networks. I guess I could also throw the k500-5000 back in - might be interesting to listen for the higher woofer crossover at 500hz with the k-5-j. If anyone can recommend a good software package and equipment to measure frequency response it might be fun to test each option and then post the results. Thanks again gentlemen! Best, Michael

The Klipschorn timeline suggests that the K500-5000 crossover used with the K-5-J mid horn was phased out in the late 50's in favor of the "a" network. Interestingly, this article and horn analysis shows that the k55 produces higher sensitivity with the k400 horn - across nearly the entire frequency range, and significantly on both low and high ends. The "a" network uses 3db attenuation for the k55/k400 combination. It would seem that perhaps no attenuation would have been necessary with the k55/ K-5-J horn combination. I wonder what attenuation settings were used with the k500 - 5000 crossover as well as the early "a" networks used in combination with the k55 driver / K-5-J horn combination. This also raises the question of possible bass bin sensitivity changes in the early years - and if so, corresponding changes in sensitivity matching between the bass and mid sections. Any information on this would be fascinating. For what it's worth, I currently have a 1956 Klipschorn that came with the k-5-j and k500-5000 crossover. I now run it with two top hats - one with the k55/k-5-j horn combination with a crites a/4500 network, and the other with a k55/k401 horn combination with a crites "a" network. Perhaps I should be running the k55/k-5-j horn with the "a" network and 0 db attenuation on the mid section? In terms of my contemporary listening experience, I don't have golden ears - yet to me the sound contrast is clearly recognizeable - the k55/k-5-j combination sounds much more transparent, open and realistic to my ears - yet a bit softer with less punch, than the k55/k400 combination. I could easily see many opting for either flavor based upon preference. Thanks in advance.

I believe the sensitivity of the hf200 16ohm is ~ 109db. Not sure what the fc260 tractrix does to that up or down.

I recently picked up a used pair of the Volti fc260 tractrix horns and I'm wondering if the Faital pro HF200 driver would be a good economical choice as opposed to the more expensive b&c dcm50 or bms 4592 drivers. I'm planning on running these in a three way setup and crossing from the klipschorn base in at 400hz. Thank you in advance for any input.

This is the kind of wonderful and rare information that makes this site stand out. Great analysis of the early K-5-J wood horn by PWK himself! Much thanks to Gil McDermott for sharing this.

Ditto, outstanding service and advice!