Got my first Karlson! Europe made K15 clone

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I always wanted to try a Karlson, what it sounds like. But it was down low on my project list. Therefore I got excited when I saw one for sale, as they seem to be rare in Europe and almost unobtainium in CZ. For ca 70 Eur I got this German made K15 clone. The speaker inside is DAS BI-30 15" speaker, it must be really old. The box itself looks very well made from plywood. There is some kind of crossover inside, throught the hole I could see two caps and one coil.

It is supposed to be fully functional, I need to replace the XLR connectors by Speakons and do some listening and measurements.


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CooL ! - is that an asymmetric mouth tweeter horn mounted above the 15" driver? IF the woofer has a reasonably bright midrange then it may sound pujnchy. A "good" K15 can outpunch FLH of its same size. They don't go low but the power where they have it is phenomenal compared to reflex for a given excursion.

Where is the port and about how large of area? K15 back in 1952 had a (~260 area. In 1956 the port was reduced
in width giving ~32 sq.inches area. That did not make it go lower but probably lessened output around the response "W" area.

Wonder what it ran? - Techno?? The "wings" look well braced to the front shelf. The first commercial K-couplers like that were probably those by Transylvania Power Company and about 5 more folks who built pretty much the same design. That K-coupler was little and aboujt 27 inches high by 20" wide by 15" deep and likely based on Karlson's "x15" speaker

That woofer looks in great shape.
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There is no tweeter, it is just the port, area is around 170 cm2. I removed the crossover, there were actually two ferrite core coils, one fell apart. So there was a 2nd order crossover of unknown frequency. now there is a speakon with direct connection instead. The woofer fs measures slightly below 50 Hz. I tried it briefly with 50 W and it really kicks:) My bass horns go deeper, but the K15 sounds louder.

It was used in a dance band PA playing live pop songs. I will need to do some measurements to see, whatit does. I definitely like the sound and also need to try to measure without the wings.
- a regular K15 is runed around 48Hz with the big slot port (4.5" x9") whose base sits against the shelf - divider.. That D.A.S. sounds like a real good match.

Does your K15 have a rear shelf? - If so, how big is the gap to the rear panel? Also, assuming a front shelf (?) - how large is
the gap to the wings?

Karlson cabinets can be very articulate with the front chamber doing something in the H2 and H3 area of bass notes. (I literally have over a ton of horn cabinets yet good respect for K15 - its quite cool for 1951 or 2021 :D)

If you jhave an extra tweeter horn - or compression driver to use a K-tube - that would be good. A K-tube the size of that sold by Transylavania Power Coimpany, is smooth, a nice dispersion pattern and very good sound where it works. Various cymbals sound good. Being only a little tube, there's little loading and they're relegated to ~1K5 up - depending upon driver. You could roll up a POC K-tube out of paper to try.

Transylvania's K-tbe was ~5.3" long and had a 2 degree sidewall taper - probably to follow Karlson's idea like the inclined plane for the front chamber of his speakers. A straight 5.3" long 1" Id pipe with slot based on a half ellipse pattern works about the same.

Some of Transylvania's K-tubes had a crazy (to me so far) roller pin placed a bit from their throat - you can see in the picture
below I jammed a little wood dowel to do the same. I've used one of these K-tubes on top of a dual 15" JBL reflex cabinet and it did OK so sensitivity cam be pretty good.


From what I can gather, Karlson's "X15" speaker introduced in 1965 had a mini "klam" tweeter at first then moved onto a slotted pipe and compresision driver.. The K-tube below is a clone of one found in a vintage X15. It works very well to have the piipe internally mounted since the exit is pretty close to the main aperture.

I wish Wolf von Langa had continued working with K-stuff but probably worried they'd be difficult to sell.

The cabinet over to the right is an Acoujstic Control 115BK - much like the Transylvania cabinet and "X15" in size.
Being ~57% the size of K15, it gives up a half octave in bass extension and is more like a midbass horn in range. It sounds
very good with various K-tube on top and if scaled to K15 size, would accommodate an 18" speaker.

I have a "K18" with curved reflector whicfh sounds very good. I just don't know how to design them other than a guess.


This is my K18 with curved reflector - its good on opera - whatever and just a bit more volume overall than K15.
Its K-tube normally mounts inside as you can see a hole above the woofer.

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I will make some measurements later today. There is a front and rear shelf.

I have BC DE500 and Beyma CP385/Nd at hand to try the K-tube. I would actually have one 3D printed - if I can draw it up in Fusion 360. Is there any information on how exactly should the slot look like?
the way I made my scheudle 40 1"ID pipe K-tubes was to print a half ellipse based on an 10.6" major axis with minor axis being pik XZ the outside diameter of the pipe sans 1/8" at the start of the slot to provide a gap. It may be reasonablyh non-ctitical. Because of the thickness of the pipe wall, the slot ended up somewhat smaller.

A K-tube like that can be extended in length but I think adding an unslotted stub may introduce a dip (?)

Here's K- enthusist Carl's extended X15 type K-tube vs a simple one I made. I think the diameter transitions are the cause of the rough looking graph with his pipe. The rolloiff after 12KHz was just the nature of the old alumiinum diaphragm Eminence driver. Without that "stub" I suspect the 1K2 dip on the red trace might disappear (?)

There's a slim chance I still have the math equation from Carl on the Transylvania K-tube slot. If you can find them cheap - grab them.

Carl's X15 tube used a strange looking able sliced tube within the larger tube. Another X15 seen appeared to use more like a 1.25" ID metal tube with a parabolic slot - Karlson must have been experimenting to see what worked.


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Some measurements of the K15 clone: 841 x 564 x 447 mm (external HxWxD), front shelf 433 mm from the bottom, 113 mm wide, 97 mm to the wing backs. Rear shelf is 100 mm wide, 85 mm to the back wall. All made from 16 mm plywood. Measurements taken with tape measure, so it is +- a mm or two at the hard to reach places.

Edit: As a bonus, a rendering of the K-Tube STL file:)


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those look splendid ! - - how thick are the walls ? how long did it talke to print one tube ?

typically they're tilted upwards somewhat - like 30 dregrees if sitting on a k-coupler with that baffle angle


the one below is probalby tilted a bit too much - that's just the way it rested on the magnet for the picture - thinwall 1 inch pvc was a bit too thin but played well a lower volumes


they apparently can be made pretty long probably mainly to put the exit where its needed - I'd like to see the response on the one below. Its tiltle downwars with slot "up" as was Karlson's "X15". A K15 size could be built with an internal K-tube. I think with the front shelf deleted, front coupler depth would have to be lessened as to not have a deep response hole around 250Hz. A change of baffle angle to around 22 degrees might achieve that goal.

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you might experiment using a larger cardboard baffle at the driver exit plane to see if that helps the low end blend. Also carpet felt or some something absorbant laid on the top of your K15/whatever cabinet will reduce reflections off the cabinet's top. A K-tube like that is pretty much self equalizing so no contour of the highpass network is needed,. In some situations you might (?) prefer the K-tube to a waveguide or tweeter horn.

here's a diiffernt picture of one of those long L-tubes. That could be useful to extend a coax or compression driver's contribution
to Karlson's "Klam" type which buries things deeper than his "Ultra Fidelity" series.

Here's my old klam 15 with a tube temorarily extended and crammed down the coax's horn throat. That klam turned
out pretty well and sounds good without the k-tuibe extension - just somewhat more "reverberant". Its
length could be shortened a bit as the back chamver is somewhat too large for that Eminence 15CX.


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Here are some random measurements around the room, vertically +- around the top of the cabinet and some 1.5 - 2 meters away.

The orange trace is around 45 degrees of axis. So I would say a 90 x 60 horn on top of the cabinet crossed over at ca 1 kHz should be a good match. I think I will try one of my JBL2380 clones with a JBL2445. I will also do a quick test with the K-Tube crossed over at 3 kHz, but do not really expect ideal results.


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That's a nice response - sometime if not toop much labor, would you draw the port ? (doies it have an odd shape?)

Most of my compression drivers worked well with 1K8 highpass (3rd order)

2380 wih CD EQ should be pretty nice on vocals, etc.

Just thinking of K18s - mellow and powerful sounding at low level for music listening. The one I have which says "very good sounding", sounded congested when the same wings were swiveled in at the top to form a 5/8" starting gap. When opened as seen here, it did sound very good - and of course did not go very low as maybe only 70 liter back chamber for the 18" speaker.

As I'm getting old , I want you to think about the front chamber shape and aspect. Is there an ideal shape for the chamber. Can Karlson's Fig.6 and Fig.8 reflector system per patent 3540544 do good?

What can one do to avoid a response hole?

I assume making K's past a size is counterproductive and they should be kept in the punch regiion although David A. Young built a B36 sized K with about an 8 cubic foot rear chamber which had low distortion.

I'd like a really good little "K10" size K-coupler.

18 inch driver K-coupler
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Thanks for the port details. Does its 8cm base sit directly on the "shelf"?
- - wonder what that shape does vs round or square - ?

Here's an old (~2003) "Jam Cam" picture of one of my K15 topped with a 1' format radial horn. As a midhorn with ~700Hz crossover topped with with an Audax ring radiator tweeter, that horn sounded very good with Nick Cave. IIRC that horn was around 26" deep to its
moutning plate. It akso was energetic as a tweeter with 1K8 crossover.

I've played with a fair amount of "fullrange" speakers, and can't rememver any having the presence
and realsism on Cave's voice as that setup. I've done a lot of counterproiductive mucking.

In contrast, I could not get Bruce Edgar's 250Hz tractrix horn with alnico JBL LE5 to sound as good as that radial horn.
Maybe its best to not go much below 1K for a midhorn crossover with K15 -?

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