yet another version of the early Khorn woofer throat, several large pics

[LarryC]

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On 4/12/2004 9:31:38 AM Tom Mobley wrote:

...Larry, thanks for hopping in here. I was under the impression that Klipsch used the 6 x 13 slot on the early units with the Stephens Tru-Sonic driver. Having now seen the 3" motorboard mounted against the 6" cabinet, I'm wondering if this was the setup on the Stephens also. Maybe khorn58 will drop in and lend a hand. He has had more of the really old units than anybody I know of.

I might round up a a piece of real thin plywood like 1/4" or so, cut the 3 x 13 slot in it and just sandwich it in between the driver and the cabinet. it would come pretty close to what you did. I don't think I'm up for trying to patch down the size of the slot. Or I might just try running it with the 6 x 13" slot and mounting the driver directly to the cabinet like you did.

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Tom,

How you attack this will be interesting. All your ideas sound like they have potential, including the thin mounting board with the 13" X 3" slot. You might seek advice from Klipsch about whether my added compression with the mounting board was only because of the longer (1-inch-thick) passage with the motorboard plus mounting board. Since your motorboard passage is 6" high, you would only have a half-inch-thick passageway, tho' with added steps outward soon after that.

If those things don't do much, I have a feeling you should try a K33-E, since that's the woof K-horns ended up with, and it and the 13" X 3" slot are designed for each other. I have a spare K33-E, but just injured my foot and can't get it to you very quickly unless someone helps. I also have a good 15WK, whose discontinuation seems to have started all this messing around with the bass throat, but it might not sound good in a K-horn with a network not designed for it.

Good luck! I am NOT either an expert!

Larry

[John Warren]

knkn

[Marvel]

Tom,

Instead of modifying the original motorboard, how hard would it be to make a new one with the 3x13 slot in it? Seems like that would be easier to do and not compound any funny issues with the two layers.

Use the original for the basic pattern, a few tee nuts, etc. ...

Marvel

[jorjen]

Tom,

Looks like the motorboard has the 3x13 slot in it, right? If you knock off the wedges, you are left with a motorboard with a 3x13 opening, right? Just want to make sure I am seeing things clearly. Also, why could you not just leave both slot sizes alone(if the 3x13 slot is the desired slot, which I believe it to be). If you couple the 3x13 sized motorboard slot to the larger 6x13 slot on the horn side, are you not still just playing to the smaller of the two slots anyway? The 1/2" upper and lower lip of the larger slot on the horn side will be 1.5" away from the opening(top and bottom)of the 3x13 slot, should not interfere with anything. I do not see a practical need to decrease the size of the slot on the horn side, am I missing something?

[Tom Mobley]

Nah, I think you've got it right. That's what I'm going to do first. If it doesn't help the rolloff, I'll yank one of my fresh K-33 out of a LaScala and try it in there.

Anybody know what the free air resonance is for the Jensen P15LL driver? The standard model appears to be 38, but that would be somewhat high for a Khorn. Was there a special model for Klipsch? Somebody who models this stuff with a computer came up with a graph showing the response to die at 40-45, which is exactly what it is doing.

Thanks for your input everybody.

[khorn58]

Tom,

All my early Khorns from the the 51's to the 59,s khorns all have the large motor board hole.

My 58 khorn style d came with the jensen 33j which has plenty of low bass Not lacking at all. I like the jensen khorn sound. I have no plans to modifi any of the early khorns I have. I might add try some later khorns If I ever come across some late 60,s to early 70,s just for fun.

I have never felt notr any of my freinds that the old khorns Im have lacked punch low bass at lest with music.

for modern rap with below music bass and movie sound track maybe the lack. But i have no need for bass that low.

[garymd]

I'm no expert on the subject but I was an observer of the mod Larry made to his. Say what you will, but taking out those wedges had an incredibly positive impact on Larry's Khorns. He gave up nothing and gained everything. Bass response improved enormously.

Tom,

Go for it. If you have bass issues, taking those out will certainly improve the situation. JMHO of course. Every time I hear his khorns now I turn to him, grin and say, "listen to that bass!"

[ZAKO]

Tom.....The Jensen P15-LL were 38 hz & higher. They were then treated with a special chemical on outer surround to lower free air resonence. This may dry out & shift resonence. It wasnt an exact cure. I suspect Our K 33-E will shift resonce too But Ill be dead by then.

[LarryC]

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On 4/12/2004 10:10:02 PM khorn58 wrote:

Tom,

All my early Khorns from the the 51's to the 59,s khorns all have the large motor board hole.

My 58 khorn style d came with the jensen 33j which has plenty of low bass Not lacking at all. I like the jensen khorn sound.

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Tom, I wonder if that means you could mount your Jensens directly to your 6" X 13"-hole woofer panels and bypass the mounting boards altogether? It sounds like Jensens found their way into these K-horns while the factory was trying to make new woofers work with inserts and 3" high slots. You can fill in drilled holes if you try that out and want to reverse course.

Larry

[Tom Mobley]

>> But Ill be dead by then

Ah, an elegant solution to a nasty problem.

OK, pulled the little blocks out last night. They are just screwed to the front of the motorboard, not glued. Fell right off. Put the speaker back together. This morning ran a quickie test with a test CD I used before. My Eico allows me to run either channel or both, so turned it to the "fixed" speaker and started at 100Hz, worked down to 80-61.5-50-40-31.5-25-20. Previously the speakers were good to 50 and but 8-10dB down at 40 and not much of anything below there. Now, the fixed speaker is good to 50, down ~3-4dB at 40, back to more-or-less flat at 31.5, down 12 or so at 25 and 20 at 20. Went back to the stock, unmodified speaker and re-ran the sequence and got just what I got before, good down to 50 and falling off a cliff below there.

So, my take on this is that that the Klipsch experiment or whatever it was is a failure and I'm surprised it made it into production. The difference is easily audible and not subtle. With both channels driven the stereo image is centered at 50, but the un-fixed speaker just disappears at anything below that, it's like only the right channel (in this case)is working. Just for giggles I switched the speaker wires on the back of the amp, and the results switched sides as would be expected.

More subjectively, listening to music with substantial LF content like Pomp & Pipes, the unfixed speaker just disappears when the organ starts hitting the low notes, the image moves way over to the good side. This is easy to discern.

My thanks go out to Larry Clare for taking the initiative to run this down on his own speakers, he was walking on uncharted ground there and came up smelling like roses.

Now, do I have the desire to tear down an LS to get a K-33 to try it out? I seem to be lacking motivation for some reason. Probably just lazy.

As always, YMMV, IMHO, all that jazz. But after seeing both of these deals I would have little trouble recommending that somebody with late 50's---early 60's Khorns have a little look-see. The mod is easily reversible if somebody detects that it hurts the sound in some other way while extending the LF response. It's always possible that PWK thought some improvement in some other characteristic of the sound outweighed the loss of LF extension. I don't hear that but somebody else might.

[Tom Mobley]

Larry, I thought about that, marked the cab for the holes and bought the right-angle extension for my drill. But, several have said that the Jensen and K-33 won't work with the large opening. Apparently they just don't have enough oompf to handle the lower impedance that would result.

We posted at the same time, I didn't see yours before I started writing mine. I think I'm going to quit on it for now. I need time to work on the house and yard and I want to invest some late-night listening time on familiar material to be sure there is not some unanticipated negative change in the overall sound presentation from this deal.

[D-MAN]

The Khorn with a motor board and the baffle cavity opening of the same size can both be modified to feature a radii applied to the short ends of the 3" x 13" slot with no resulting issues. I am not talking a circular cavity opening, just a radii applied to the short end. I however would not expect to actually be able to hear a difference as the change in area would be very slight (just a couple of square inches) and if you think that adding 2 inches or so total square inches at the cavity opening are going to give you a major change then I've got a bridge that I'd like to sell you... That is why I think that doing this particular mod is much more trouble than it is actually worth.

If you are talking a completely circular opening then it should be substancially smaller to account for the same frequency limiting abilities with this caveat: The issue with a circular opening and a Khorn is that the cavity opening is feeding a rectangular horn, and that theoretically can cause unequal wave expansion resulting in increased throat distortion (probably impossible anyway due to the pre-existing baffle opening of 13 inches in width). The caution here is that the mating throat opening has to also be modified to accept the changed area without constriction. In such a case, I would recommend that the baffle opening be modified to the "old" 6 x 13" rectangular size as original in the PWK design and that the motor board then be used to experiment with different openings and the effects thereof, including the "modern" nominal 3 x 13" opening.

The Khorn exponential horn throat dimensions are in fact capable of receiving a 6" x 13" rectangular throat cavity opening although since the 1960's the nominal opening has been 3" x 13" (the horn internal dimensions remain the same regardless of the opening employed). This can be reduced to the equivalent 8.75" x 8.75" square or even a circular opening of the same area. The cavity opening being about 1/2 the maximum size for the horn is a frequency-limiting slot filter used to match the output of the midrange horn/crossover combination employed. The difference in frequency limiting resulting from a slot vs. a circular opening are not going to be substancial providing that the opening area involved is equal.

Also there is not enough room available in rounding the slot ends and remaining within the confines of the driver cone (not the surround) to substancially alter the response of the filter to a degree that you could probably hear, anyway...

If you have problems with this, or think that I am making this up, PLEASE READ UP ON IT!

DM