Is there a "best" cavity shape and aspect tor a mid sized Karlson box ?
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| Posted on August 17, 2018 at 10:35:25 | ||
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Posts: 3852
Joined: December 6, 2001 |
Karlson's little K12 had about a 0.6 cubic foot front chamber which initially in 1954 had a chamber shape like that of K15 but sans the front shelf. Around 1956 a single upper panel canted 10 degrees forwards and vented with 6 distributed (and resistive) slots was used. That version remained til K's death in 1873. In 1965, a smaller two way 15 inch Karlson speaker was introduced called the "X15", and featured a 3 panel approximation of a 1/4 ellipse curve upper reflector. This speaker was concurrent with Karlson's second and final "Acoustic Transducers" patent 3540544. Thins like vent placement, vent area, can affect response in these cabinets. It was deemed by Karlson that the curved reflector (which in the patent included curved sides) would produce smoother frequency response and better polars. A K friend suggests using higher aspect than the original and large curved reflectors. Lets say i want to make a little midbass K-box the size of Karlson's "X15 and about 28" tall, 20" wide and 14" deep. What front cavity shape and venting do you think would work the best? I look at this size and Karlson's "K12" as practical alternative to small front loaded horns in systems requiring subwoofer, or for small PA work. an additional chamber could be added to the top of the front chamber - whether worth it = "don't know" anyhow - if forced to think about making such a speaker, what would you make for best subjective result? when good coaxial are not available, a K-tube tweeter either internal or on top will do a good job and often sound better than conventional waveguide or horn - If - not run too low. John Karlson introduced a new 15 inch K-coupler in 1965 which was loaded with a low qts 15" CTS woofer and called "X15". It was only about 1 cubic foot larger in external bulk than his K12 cabinet. It was sometimes advertised as "X15A" which may have designated the change from a 3" peaper cone tweeter in a mini - "klam" to a metal slotted pipe tweeter with 1 inch format compression driver. At ~57% bulk of the original Karlson 15 (aka "K15"), X15 lost about 1/2 octave in low frequency extension compared to K15. The X15 size variant which appeared perhaps around 1980 and built by a number of companies (Transylvania Power Company, KK-Audio, Westwood, Acoustic Control and at least one more) had a large vent, a tapered rear section, and meausred quite smoothly even without any damping material.  Karlson's X15 side view dimensions (external width was ~19.5"0  K12B - proposed X15 size for 15 inch speaker with distributed slot vent  Carl Neuser's first X15A size coupler later made with curved reflector. One can see the vent spacer blocks for adjustment plus it had an adjustable rear lowpass gap for tuning and testing.  X15A with Fostex Sigma 208 coupler on top. The K-tube in the 15 inch coupler is from a vintage X15 circa 1966-67  Tuning and room response data for Carl's X15A with Klipsch K33E woofer  TB46 plan for a little 15" Karlson aperture woofer - its tuned ~41Hz so a half octave lower than traditional Karlson of this size.  Acoustic Control 115BL (X15 sized coupler) Side view dimensions - external width = 20.5" 115BK works pretty well - I don't know if it scaled up or down well with regards to smoothness. If scaled 1.2:1 then has about the same bulk as the Karlson K15 but will mount an 18". (I've had good luck with 18" K overall)   115BK EVM12L - outdoors - mic on ground - there's no damping material at all in the cabinet   Walter Zintz's Transylvania Power Co. made the small couple and an excellet K-tube. I think they also had a doubled size version of "THE TUBE" for 2 inch format compression drivers.  
Karlson Evangelist
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| RE: Really? this enire Forum is the personal Phantasy arena for Freddyi?, posted on August 21, 2018 at 04:10:11 | |
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Posts: 367
Joined: July 27, 2001 |
Could Barely have said it better myself . . .
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| RE: Really? this enire Forum is the personal Phantasy arena for Freddyi?, posted on August 22, 2018 at 12:35:26 | |
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Posts: 14371
Location: East Coast Joined: October 4, 2001 |
Looks good! Dave
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| RE: Really? this enire Forum is the personal Phantasy arena for Freddyi?, posted on August 22, 2018 at 14:45:59 | |
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Posts: 3852
Joined: December 6, 2001 |
trapezoidal structure may help - there's very little problem to begin with in the little Acoustic Control 115BK but I don't know if it will directly scale without issues. Look at the 1/24 octave graph of my high aspect K18 which has a curved reflector - its not shabby at all - and it sounds and behaves well - but I don't feel confident on "how" to design a good K other than some guesses and luck. It should be nice with a good 15" and I;ve plenty but rather do a shorter but still high aspect Fig 6 - perhaps 36" tall and 20" wide for a 15" speaker. Besides, its fun having a low mass 18" which goes out to 4KHz on axis. There's no front shelf but there is a rear lowpass choke shelf. This is a potent little cabinet and I suspect it will beat some of my horns on transients.
Look at these approximate ground plane traces of a 1954 Karlsonette, an X15 copy with one of Carl's favorite woofers versus that of the Acoustic Control 115BK. Perhaps there's some bounce effects but the 115BK is quite a bit smoother and had no damping material whatsoever. "DIPPITY DO VS DIPPITY DON'T"
I think using Bondo at the sidewall to baffle junction could be interesting - again effect not known til tried and measured on and off axis. (It may sound "faster") One method of smoothing reflections was shown some time ago by Ken Lehman - I've used a simpler rectangular section cavity tied to the top of the front chamber and lightly fill it with damping material. That contributes to the front cavity volume and does some smoothing. Here's a sketch by Matthew Morgan J of a Karlflex showing where it would be:
and alternate tower configurations. BTW- when MMJ built the test Karlflex 12, the front chamber in that design runs quite small compared to a Karlson K12 so at one point he basically eliminated the K aperture.
"THE" current popular favorite build for a K-type is GregB's "KARLSONATOR" and has been scaled all over the place by xrk971. GregB's official Karlsonator was first drawn in 12" 8, and 6" versions. Tuning on those runs ~37Hz for Karlsonator 12, 41Hz for Karlsonator 8 and 60Hz for Karlsonator 6. In contrast to original Karlson tuning, that's a half octave to over a full octave lower tuning. Its offset driver and damped stub provide reasonably smooth response.
The aperture does not have to visually subtend a cone's diameter to get good result and without excessive "reverb". Here's a small K18 made like the 2nd K12 that's ~25 degree baffle with 10 degree forwards port panel. That relatively narrow aperture sounded very good and better than the same 18" as a direct radiator (picture shows an Altec 15" 421-8). With this particular aperture setting, a wider starting gap was needed for good sound quality. When the top of the wings were swiveled inwards to provide a 5/8" gap, tonal quality lost "air" - bass transients sounded "stuck" and somewhat "thuddy". There was no real significant differences between the 5/8" gap and the 1.2" gap yet the 1.2" gap sounded vastly superior with music. To build a new 15" coupler one might got that route. This one had a smaller back chamber than K15 so LF cutoff was raised. I imagine a somewhat different aperture would allow a tight starting gap with good subjective result.
here's an old blurry thumbnail enlarged of that cabinet with 18" and Smith Distributed Source Horn on top. I later tried raising the wings (not needed plus wider slot) and added a 20 liter chamber to the top of the front chamber - that 20 liters lowered the LF cutoff a bit and its damping effect smoothed the graph. My main failure with K is lack of carpentry talent plus hands have gone numb in recent months.
Lets get back to the little X15 size. X15 was released (at least in the press and AUDIO Annual directory) in late 1965. As it and Carl's X15 are 28 inches tall, that only leaves some possibility for a curved upper reflector. Here's a crude way of showing how that might fit the Acoustic Control 115BK (~X15 sie at 27" tall, 20.5" and would be just 13.5" deep without the 1.5" inset of its wings. What would this chamber do?
Lets compare these two six inch driver K-type one has a curved reflector with more volume towards its top - the other a K8/12 type extended in height. What does one do vs the other? That would be something to discuss with Carl. Diyaudio user "AmadeusMozart" posted some measurements on his build of the SK6.5
JanS Fig.6 K15 (he also speaks of a Fig.6 K12 in the thread above) i remember Jan's discussion and by the machine translation of the word "gate" he meant adjusting the port. Look how he incrementally blocked the port. There's not much port left. (I think it might not graph well in the 250Hz region but that's just a guess)
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