XKi - X's ab initio Karlson 6th Order Bandpass

X - regarding the hole in response seen in some K, how might that be affected by the distance between the inner port and the center of the cone? Does it in any way behave like a BLH?

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200Hz is a 1/4 wave length of about 17in. Is the distance from the port to main driver about 17in? If it is, then yes, the distance makes a difference. I find that the K aperture contains and mixes the contributions from both waves. Without the aperture, the dips go away. But then we lose the magic dispersion and cone control of the aperture. Lining the back of the K aperture helps as well as the two side walls of the front chamber. I use melamine sponges.
 
might be in some of the little K - - - Look at this side view of a late 1960's K12. Those were sold with a blank vent panel so one could adapt per instructions (from what I've heard)

where would you place the vent on that upper board for the least dip effect ? It would probably be around 12 square inches area for normal K12 tuning.

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Perhaps it is interesting to see the result of a ABEC (BEM) simulation of the Karlson enclosure?
In this case equipped with a Philips 9710M driver.
The front curtains had to be modelled by a number of triangles, as ABEC can not handle elements other than rectangles or triangles.
The walls in the front compartment have an 50% absorption factor, as this seemed appropriate.

Tom
 

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@ TOM MACK = That's really COOL ! Karlson's originals did not use any absorption in their front chambers and was not needed in the 12 and 15 inch versions. If you reduce the absorption to ~ that of bare plywood, how does that change the outcome?

Is the top graph the cabinet without the V aperture ?

Can your model be "scaled" ? - it would be wonderful to have such a thing. I can barely work hornresp muchless fathom ABEC let alone work with it.
 
There are some limitations to what can be done in ABEC. The BEM-method creates a mesh of small triangles that serve as the boundary elements used to compute the sound field at the surface of the object ( i.e. the box) under investigation. If you need to extend the frequency range to higher frequencies, the sides of the triangles need to be smaller. They should be about equal to the wavelength. As a consequence of this, the number of boundary elements increases as the frequency range is extended. This number is also higher if the size of the box is increased. All this leads to increased demands posed on the computer memory. In practice, using an ordinary PC, and simulating the behaviour of a box the size of the Karlson, 3-5 kHz is the highest frequency that can be used. More memory would be the first step to take, but the demands on memory by the boundary element method are really very high
 
The response curves give the impression that there is a standing wave somewhere in the front part of the enclosure. The same peaks and troughs can be seen in the radiation resistance as determined by ABEC. This suggests a strong resonance in front of the driver.
However, when I changed the absorption factor in the front chamber from 50% to 80%, the change in the response was minimal.
Regarding the graphs, the top one is the box as is, the bottom graph shows the effect of a 6dB/oct correction below 200 Hz. It should be remembered that the ABEC simulation is a free-field simulation. The curves also show the diffraction effect of the box, sometimes referred to as " baffle step". This accounts in part for the rising response curve
regards, Tom
 
thanks Tom - that's quite interesting and sim for the original size "K15" uesful with 5KHz. It had a front "shelf" that deflects some HF down and out. If that shelf is deleted for the same cavity, it probably will have a greater dip right past 200Hz. I think cavity shape and depth have some influence upon the dips' depth and width but can't predict - only guess.

here's some graphs of what I've seen. The little Acoustic Control 115BK version of Karlson's "X15" is interesting as it tends to graph smoother than usual. Would that be partly due to the paths involved?

I think they can be made reasonably smooth without damping material in the front - but to what rules ? A smoothing stub
connected to the front chamber could be added in some cases.

old graph of K15 outdoors vs a bass reflex - both on cabinet center axis
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mic on ground graph of Acoustic Control 115BK - this cabinet is about 57% the size of K15 - there's no damping material whatsoever in the cabinet
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my 41" tall K18 indoors with EVM18B- Perhaps the taller aspect, shallower cavity traded
off some "hit" for flatter response. To my ears it sounds good with no front damping - but I like K12 and K15 tha way too
provide there's a good balance .

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layout of Acoustic's 115BK
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OT - X - one of us needs to try a modern R-J - The very first article was a slot loaded design with in-direct radiation - then at the second article, it was re-designed into a cabinet which mixed the rear wave with the front wave and a rectangular slot. From what I can conclude, the slot became a lopsided "diamond" in the first production models then the "lemon". Here's a good picture of the R-J with guess a 12" and its "lemon" from a 2017 Audio Karma thread.

Tom and X - since the R-J has a much smaller "cavity" than a Karlson (just the space of the sub-baffle sitting on cleats) -how does that affect the apparent "cone control" vs the Karlson. In fudged sims I don't see a Karlson reducing excursion much compared to a reflex but in observation, the original 15 inch Karlson model can jaw droppingly clobber with very little cone excursion.

I'm not sure if the same size lemon aperture was used on the 15 inch version - I'll have to look through the grill cloth of mine to see, Both the regular 12 and 15 R-J boxes were the same. I have a slim-line version of the 12.


(is there an online keystone correction app ?)
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Nice to hear that Workingman! Be sure you line the rear and front chamber with melamine reticulated sound absorber foam. Line the inside of the K aperture with foam core or 1/4in layer of melamine foam. I have found that switching from foam to wood boxes can lead to a boxy sound without the damping material. I do like the sound of the PA-130’s though.
 
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I'm not sure if the same size lemon aperture was used on the 15 inch version - I'll have to look through the grill cloth of mine to see, Both the regular 12 and 15 R-J boxes were the same. I have a slim-line version of the 12.

(is there an online keystone correction app ?)
Ww8OFFX.png

The lemon aperture is very close to a diamond Karlson aperture I died with good success. The front chamber can be made very small and it works well — although direct reflection from aperture edge may cause dips in mid to high mids.
 
the front chamber on the RJ is no more than 1 inch deep, and IIRC, frequency response measured very smooth. With an old EV SP15 fullrange , my RJ15 sounded far better than a Nirvana Super 10 in reflex on a Stanley Clarke acoustic bass solo. To be fair, I think the Nirvana was tuned too low (41Hz) Super10 did better in my Karlsonator12 which tunes 37Hz and K15 than the reflex box where it unloaded very fast.

The little RJ15 may be better than the Karlson x15 (does the Karlson's larger chamber reduce cone excursion in comparison ?) - An RJ cabinet would benefit being made of thicker materials and bracing.

(I need to get the keystone removed from that image for a pattern)

X - If I get another K12 done - where might a single vent be placed for smoothest measured response? It would be good to have a test mule to sort out such stuff.
 
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