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Comparing Vintage Klipschorn Woofer, Motorboard Slot and Midrange Performance


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For those like myself, who've had the privilege of owning some of the 1950's examples of the Klipschorn - with massive Stephens and EV Alnico woofers, 6x13 slot motorboards and wood/fiberglass K5J midrange horns with University SAHF drivers, there's always been an interest in knowing whether any performance differences exist between these early models and Klipschorns produced later in their evolution.  

 

Among the many questions, some, including myself, have always wondered:

 

- Do the early Klipschorn bass bins with the original 6x13 throat slot and massive Alnico magnet woofers perform "better"?

- Is the K400/401 a "better" midrange horn than the original final K5J?

 

A couple of years ago I mentioned on the forum my intention to take a shot at investigating the different Klipschorn woofers and motorboards, but life got in the way and it wasn't until recently that I was able to devote the time and energy to getting that done. I've gotten a lot out of the Klipsch community over the years with a lot of help from guys with names like Al, Bob, Dave, Dean, Gil, John, Larry, Roger and many more, so here's my attempt at contributing something back. I'm not selling anything nor am I affiliated with anyone who is in the Klipsch world. Nor am I an expert at speaker measurement, and I can't claim to have golden ears. With that said, here is my report:

 

Project Goal

 

To measure the performance difference, if any, between various Klipschorn woofers (EV 15wk, k-33e square magnet, Crites cast replacement), Klipschorn motorboards (3x13 vs. 6x13), and the Klipschorn midrange horns (K5J vs. K400/401) and midrange drivers (University SAHF vs. K55v, m, v dual plug). 

 

Methodology

 

To conduct the tests I:

 

- Assembled the woofers, midrange drivers and midrange horns along with several crossover networks and woofer inductors

- Made several Baltic birch motorboards with both 3x13 and 6x13 slots in 3/4", 5/8" and 3/8" thickness - master template cut for exact match and dry fit marked for exact throat aligment

- Setup a 1950's Klipschorn base with a 6x13 slot bin - to accommodate 3x13 and 6x13 motorboards - in a properly sealed corner

- Marked exact Klipschorn position to the corner with blue painters tape enabling exact repeat position as woofers and motorboards are changed

- Setup a mic stand on center axis approximately 8ft from the Klipschorn - Umik-1 USB mic aimed at speaker with height aligned to the midrange center

- Calibrated Umik-1 USB mic attached to laptop running REW measurement software with calibration file, connected to preamp system with testing volume uniformly locked at ~78db, preamp set on mono

- Testing then conducted with double sound sweeps in identical conditions

- All output set to 1/12 smoothing

 

Importantly, the methodology used here is aimed at measuring the relative performance between components and not absolute performance.

My experience has taught me that room conditions are the biggest factor involved, making absolute "reference" measurements far more complex than what has been done here, but these side by side comparisons have all been conducted in identical conditions and should have some validity. I will attempt to keep my comments on the results to a minimum. I'll start with the woofer/slot results first, and add the rest in the next day or two.

 

Woofer Results

 

IMHO, the performance turned in by the 62yr old EV 15wk woofer is impressive. One has to wonder what the measurements would look like with a brand new one in 1955. It's probably fair to say that with age, it's free air resonance is now closer to 40hz + , as opposed to the EV reference of 29hz when new. In my mind, the absolute performance of a Klipschorn bass bin in the 1950's has always been somewhat murky, with the occasional marketing pamphlet reference to full efficiency down to 36hz, and "excellent efficiency down to 30hz." But if the more modern Klipschorn bass bin has a sensitivity of 104db/1 watt/ 4ft,( or 105db/1 meter), do the Ev 15wk measurements here suggest that the old Klipschorn 6x13 bass bin with the large Alnico magnet woofers was a db or two more sensitive? In any event, it would appear that there are significant differences in the mid bass region performance. Is any of it noticeable to the ear and body? In my opinion, yes.

 

Note: All measurements show a consistent 10-12db gap down at about 80hz due to room/furniture interference. It's ugly, but artificial. The rest is more or less in line with the general frequency response exhibited by the Klipschorn.

 

In all cases, the k-33e and Crites cast woofer appear to measure slightly (1-2db) better in the 35hz region. Could the Ev 15wk's apparent disadvantage in the ultra low end be due to some deterioration in cone resonance due to age? 

 

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The Crites cast woofer appears to improve performance over the k-33e in the 250-400hz region. Somebody knows what their doing.

 

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As expected and documented by Dr. Bruce Edgar years ago, the 6x13 slot threat presents difficulties for the newer woofers above 300hz.

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When using the EV 15wk in their own versions of the folded cornerhorn, EV specified a woofer inductor in the 2.8-3.0mh range. Depending upon the crossover point to the midrange, IMHO, the EV 15wk measures AND sounds good in the Klipschorn with inductors from 2.5mh to 3.0mh. In my opinion, room acoustics and personal tastes are the real determinants here. 

 

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The internal 6x13 Klipschorn chamber without woofer and motorboard.

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Raw Klipschorn bass cabinet sealed into corner with gaskets and a custom made plywood corner backer board. 

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The k-33e woofer installed:

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The Crites cast woofer installed:

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The EV 15wk Alnico woofer installed. I'm getting too old to be down on my hands and knees wrestling a 45lb woofer into position! 

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Midrange Tests

 

Here's a couple of pics I took of the assembled midrange horns, drivers and crossovers used, along with the midrange platform boards I built to easily change out the entire top section from one horn to the next. Because of the general interest in the more recent wood midrange tractrix designs for use with the Klipschorn, I've included some testing and comparison with the Volti FC260 2" throat tractrix horn using the B&C DCM50 8ohm driver. 

 

 

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Midrange Test Results

 

Comparisons of the K5J and K401 horns - using any of the k55 drivers, with and without networks, show a great similarity to the tests done by Paul Klipsch when introducing the "new" k400 in the early 1960's. Originally, the K5J was crossed to the tweeter at approximately 5000hz. The rough response of the K5J above 3000hz seems to illustrate why.

 

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After discussing PWK's results with several forum members in the past, it was generally agreed that while using the k55, the K5J was about 2db softer over most of its range vs. the k400. Thus, I asked Bob Crites to make a modified "a" network with -1db attenuation for use with the K5J, vs. the -3db mid attenuation used with the standard "a" network used with the K400. This brings the sensitivity back in line with the woofer and provides a better apples to apples comparison between the horns. Now it's easier to see that while the K5J is weaker on the higher end, it has some real punch in its lower range.

 

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More, tests reveal the subtle trade-offs between the k55v and k55m on the K5J horn. The k55m is usually a db or so "hotter" than the k55v in my experience, but not across the entire range and the plus/minus tradeoff is different with this horn, than with the k400/401. 

 

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For those who've always wanted to see how the University SAHF driver (originally paired with the K5J) compares to the standard k55v on the K5J here is the result:

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SAHF compared to k55v on the K5J with the -1db mid attenuation network. Interestingly, the SAHF has more strength under 300hz than the k-55 - which has always been lauded for what few midrange drivers can do - its ability to reach down low. The SAHF also has a smoother exit response from 4000hz on, but the prominent dip between 1000-2000hz bothers me a bit. As far as the sound, my apologies, but I have spent zero time listening to the SAHF.

 

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The highly regarded K55v DUAL PLUG driver shows an interesting contrast to the k55m on the K5J. Some would say, and my personal experience agrees, that the K55v dual plug driver gives up a tad bit of sensitivity in favor of a smoother and more general extended response all the way to the promised 6000hz on the k400/401. It appears to help quite a bit here with the K5J as well. Moreover, it would probably be correct to adjust the midrange attenuation to 0 with this driver when paired with the K5J and thus delivering the best K5J/k55 performance possible, and a decent shot at using a 6000hz high frequency crossover point. Of course there may be even more K5J performance with John Allen's new A-55G mid driver, which I have yet to try. As far as the sound, they are definitely different and I greatly prefer the K5J to the k400, even with a 6000hz crossover, but I believe that personal preference and room acoustics would have a big impact on the voting. 

 

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For those interested in the midrange "upgrade" path, here are the results comparing the Volti FC260 with B&C DCM driver, to the stock K400/401 and k55 setup.

 

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With a -7db attenuation setting used below, the Volti/dcm50 combination is close in sensitivity to the k401/k55m. It looks to me like a -6db attenuation setting would be an even better match, maybe -5db when paired with a Stephens or EV Alnico woofer with the 6x13 throat. The B&C DCM50 driver rolls off naturally on the FC260 around 9500hz. In this case, the custom network used here utilized a .15mh inductor in a 1st order midrange bandpass that begins the roll off at about 7500hz. IMHO, the FC260 sound is fantastic to my ears, and at a minimum, offers an alternative sound to the K400/401. Measurement and sound are two very different things, and I've never seen and heard a better example than this particular comparison - where the measurements look so close, but the sound is miles apart.

 

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Woofer & Midrange Combination Tests

 

For those interested in how the combination of woofer and midrange measured in the tests, I compared the EV 15wk 6x13 with Volti midrange against the Crites 3x13 setup with k401/K55v dual plug midrange below. Tweeter was connected on the k401 setup, helping over 5000hz. I'll leave it to others to judge if the measured difference between 100-600hz is significant/meaningful/worthwhile. 

 

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Here's the EV/Volti combination compared to the Crites 3x13 in combination with Volti/DCM50 midrange:

 

 

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If you have a newer Klipschorn after 1962 with the 3x13 slot, or you can't find or have blown your Stephens or EV15wk for your early 6x13 Klipschorn, here's a look at the Crites and Volti combination on either the 3x13 or 6x13 slot motorboards. 

 

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When I have more time in the next few days, I will finish this post with:

 

- Comparison between  6x13 EV 15wk/k5J setup and the 3x13 K-33e/k401 woofer & midrange setup

- Comparison of motorboard thickness - 3/4", 5/8", 3/8", impact on bass bin performance 

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BeFuddledinMn ,

 

An intriguing project.

 

Have you more photos, especially of how you changed motorboards in the 1950's Klipschorn base, or is it simply a matter of unscrewing one motorboard and replacing it with another ?

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Interesting project you have done. I also have Klipschorns, so can appreciate how much work you have done, and admire your efforts to be consistent. What can you tell us about that same 80Hz dip that every driver exhibits? Is it the speaker, or could it be the room acoustics?

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Thank you very much for the questions. I will upload more photos that illustrate the motorboard placement, but the site only allows 2mb at a time so I will have to convert some photo files to lower resolution first apparently. 

 

The dip at 80hz can be ignored as a room issue caused by a piece of furniture I didn't want to move. It's consistent in all readings. I believe that dip is about 10-12 db off the real mark. Unsightly to be sure, but not important for my purposes here.

 

However, it's a great example as to how much room issues can impact performance and measurement.

 

Here's another picture of the woofers and motorboards used:

IMG_1441.JPG

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Wirrunna,

 

I've added a number of photos to the original post, including several that illustrate the woofer/motorboards as they look installed. In the older Klipschorns, the woofers are screwed or bolted to the motorboard, which is then slid into position and held to the soundboard with two angle iron retention bars that are adjusted tight with wing nuts on each end. Thus, changing woofers is not that bad IF you have each woofer mounted on its own motorboard. If not, it is somewhat tedious to remove a woofer from the motorboard and then attach another. Particularly when you also have to open and close the woofer access panel each time, removing and replacing 8 door panel screws carfefully by hand.

 

Best,

 

-BeFuddledInMn

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GREAT idea for a thread, very enjoyable reading. Thanks for the effort.

 

By the way, did you buy the B&C DCM50's for this project? If so and you are going to sell them after your experiment is complete, please let me know.

 

Jordan

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Thanks to all of you for the kind words! 

 

Jorgen,

 

To answer your question, I've had and have been using the B&C DCM drivers for awhile on the Volti FC260 horns and have no plans to give those drivers up. While I used to use the k5j midrange horns exclusively, I now prefer using the Volti/dcm50 combination as my standard configuration for the Klipschorn. However, I now use the k5j's on top of cornwalls for my own version of the Cornscala.

 

Here are some additional pictures of the midrange setups during testing:

 

The Volti Fc260 in custom top hat:

 

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The K5J horn: IMHO it sounds really good, but is even harder to beat for the cool factor....

 

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The K400/401 mounted on a "decorator" baffle board:

 

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Bob Crites inspired - old school Cornscala: a mid 60's Cornwall II with a K5J midrange and Beyma CP25 tweeter on top. Crossed at 400hz, it sounds very good.

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Schu,

 

My two cents on the tweeter placement issue: Although I don't spend a lot of time worrying about it, I know through dozens of tweeter tests that tweeter placement can have a big impact on measurement. In my experience, the real world impact is dependent upon seating position and distance, the farther from the speaker, the more it seems to simply blend, but then again, at my age, I'm not hearing much above 12khz anyway, lol.  I do know that the Volti approach is used in their high-end speaker offering, and it gets rave reviews from the industry "experts" for what that's worth. In my own tests though, the same k77 tweeter measured at equal distance on center with a k5j internal horn mounting, measures a bit different than when mounted in the newer Klipschorn top hat baffle board above the k400/401.  To my ears, the Beyma CP25, set back to match the midrange driver distance, and elevated on top of the custom hat I use, sounds pretty good, crossed at 6000hz or 7500hz. Of course, there are a couple of real tweeter experts/vendors on here that could probably chime in with more depth than I can muster here. 

 

Best,

 

BeFuddledInMn

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