Jump to content

The Klipschorn Motorboard?


Recommended Posts

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

Edited by BeFuddledinMn
Link to comment
Share on other sites

I didn't know it was eliminated, but it may have been.  As far as I know its was always 3/4" plywood, and the reason for the different size 6x13 was for the EV 15 WK, when they moved to the Eminence version they didn't need the opening to be as big so they moved ti to the 3x13.  At least that is how I understand it.  There may be more along with a more detailed answer.

Link to comment
Share on other sites

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

post-60923-0-13280000-1439302849_thumb.j

post-60923-0-68200000-1439302886_thumb.j

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

  • 2 weeks later...

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

  • Like 1
Link to comment
Share on other sites

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

I am assuming that your EV15-WK is the earlier Alnico Magnet Version?

If so, I own a pair and have tested them, a Crites, a K-33E Round magnet, A K-33E Square Magnet, a K-43E, and a K-44E Woofer all in a LaScala. I used to own over 40 some 15 inch Klipsch Woofers.

My brother in Law and myself found the Electro Voice to stand out over the others. We listened to all woofers with both the top end playing, and just the woofers themselves.

I have heard that the Sevens Trusonic sounds even better, but have never done an A/B comparison.

I will wait with anticipation for you to post your findings of what you find in trying out your various motor boards.

Roger

Link to comment
Share on other sites

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.

  • Like 1
Link to comment
Share on other sites

Twistedcrankcammer:  "My brother in Law and myself found the Electro Voice to stand out over the others. We listened to all woofers with both the top end playing, and just the woofers themselves.  I have heard that the Sevens Trusonic sounds even better, but have never done an A/B comparison."

 

 

 

The difference between it [15WK] and the k33e with the 3x13 motorboard I've been running it with is night and day, no question, similar to your listening experience.

 Amen to that.  It was a big loss to Klipsch sound quality when E-V discontinued that great and powerful woofer.  The loss showed up in deep Klipschorn bass, and in Cornwall mid-range and treble.  I always regretted that E-V or another manufacturer never replicated that masterpiece.  I suspect the Cornwall III would sound a lot better with one, too.

 

Unfortunately, the old 15WK doesn't balance with current X-overs like the AK-4.   Networks would probably have to be re-engineered. 

Edited by LarryC
Link to comment
Share on other sites

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!

  • Like 1
Link to comment
Share on other sites

Hi BeFuddled,

 

When I looked into my '62 K-horn, I found a separate woofer mounting board, with rails to hold the woofer in place in addition to mounting bolts.  However, Klipsch had installed pyramidal things in the throat for some now-forgotten purpose.  Since the woofer this was made for was long gone, I removed the inserts.  It still didn't sound right, so with the advice of Mark Kaufman, then at Klipsch, and consultation with D-man of the forum, I permanently removed the mounting board and screwed the present-day K-33 directly onto the motor board.  This cleared up the uneveness in the highs and all has seemed well since.

 

I'll find post the link with the full story.  As I understood it, the double thickness of the motorboard and mounting board added a resistance (or reactance?) factor to the woofer output, which RAISED the frequency response around the 450 Hz crossover point.  This meant the bass horn was reproducing excessive output perhaps as high as 600Hz!  Eliminating the mounting board and double thickness smoothed out the hi-freq bump.

 

The point is that you may have to listen carefully for uneven response, and do what I did to adapt my '62 to the current K-33.

 

Lemme go look for the link.  Unfortunately, the great pics that I had in the thread didn't survive the last forum software change.  I might be able to dig them out if you really want them.

Edited by LarryC
Link to comment
Share on other sites

Here you go:

 

https://community.klipsch.com/index.php?/topic/38719-restoring-the-standard-bass-horn-throat-in-a-62-pair-of-klipschorns/

 

The 1959-era Klipschorns with EV 15-WK woofers had astounding bass power!  We marveled at the Saint-Saens Third Symphony played over these speakers.  Discontinuing the 15WKs was a terrible loss at the time. 

 

No doubt the bass horn and throat had to be reworked now and then to adapt to the whims of woofer manufacturers.

 

Larry

Edited by LarryC
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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?

- BeFuddledinMn

 

could be easier to mount the woofer on the board first, then mount the board into the cab.

 

 

Link to comment
Share on other sites

I can imagine the EV 15wk you auditioned on that would have had too much upper bass strength?
It had too much bass in part of its range, I don't recall if mid or where.

 

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.
One possible problem with that is the total thickness of the slot.  Recall that the total thickness of mine was doubled by the combination of the mounting and the motherboard.

 

I suggest you try raising Dana, "D-man," to get his thoughts and suggestions. 

 

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?
It's very likely that it's all engineered together in combination.  The AK-4 was installed on then-current (2002) K-horns.  A small, not very significant circuit change was made not long after that.  As you say, Klipsch then made an AK-4 upgrade kit, with the parts you mention.

 

I worked closely with Mark Kaufman in deciding on the kits for my K.  We discussed each move I made in the process:

  • The purpose of the mysterious pyramidal inserts in the horn throat, whether to remove them, and how to do it.
  • How to deal with the unexpected peakiness around 500-600 Hz; suspicion focused on the double thickness of the mounting and the motor board.
  • How to remount the woofer without the mounting board.  I traced the bolt locations by using it as a template.  I could drill only half the T-nut holes from inside the bass bin, so Mark recommended simply using large wood screws for the other bolt locations.  These held the woofer very tightly, and has worked perfectly well.

I'm sure the slot size issue was raised, but don't recall the discussion.  Mark was consulting with Roy and Jim in all of this, but no one seemed to think a 6"wide slot was desirable.  The bass horn is a very complicated labyrinth, and I'd be a little surprised if that kind of slot could be cut after the horn is built.  Who knows, though, maybe it would have been wonderful....

 

I couldn't have used the 15WK's anyway -- they picked up a lot of EMI that I have in my house, and the hum was intolerable.

Link to comment
Share on other sites

LarryC,

Thanks for the clarifications and suggestions. You raise an excellent point with the mounting board slot being doubled up in the 3x13 motorboard models, but wouldn't be AT THE SLOT, if using the 3x13 slot mounting board on the 6x13 motorboard models. I'll take your suggestions and reach out to D-Man. I also need to get some input on the approximate woofer inductor I should be using in testing the EV 15wk woofer. I know that the 1950's Klipschorns that came equipped with the EV 15wk woofer used a 5.0mh bobbin wound inductor with a designated crossover point of 500hz. I'd like to set the woofer crossover a bit lower at 400 or 450hz for the tests, but it would appear that the crossover impedance of the EV 15wk at 400 or 450hz, would be somewhat higher than the K33e which uses a 2.5mh inductor to crossover at 400hz on an "a" crossover network. Maybe someone has some perspective and experience with that.

Thanks again!!

Link to comment
Share on other sites

Update on Klipschorn motorboard and woofer testing efforts:

I'm still waiting for some additional input on the woofer inductor issues with the EV 15wk woofer to establish an appropriate crossover at 400-450hz. I'm also still waiting for some special crossover parts for the crossover build that would be used to test this woofer in the Klipschorn. Because of the delays on both fronts, testing of the various woofer and motorboard options will now occur sometime in mid October once the crossover design has been finalized and build has been completed and tested by itself with the EV 15wk woofer. Everything else is "ready to go" , lol.

Thanks again to everyone who has contributed their knowledge and shown interest in this effort.

BeFuddledInMn

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...