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|20th November 2006, 02:46 PM||#1|
How might one design Karlson-type cabinets?
any Karlson builders here or folks who might have a fresh look at how to balance various factors into a workable/fun box?
ideally the coupler should not "honk" too much, The upper deflector angle and area may be important to smoothness and image height. Coupled cavity effects should be taken into effect.
Port placement should be taken into effect. (some K's sued de-Q-ed vents) The enclosure should not be beyond a certain bulk nor too small although smaller k-coupler are possible and Karlson took tradeoffs of ~1/3-1/2 octave LF extension in a "X15" dating from ~1965 using a 15" CTS.
The 1952 K15 had ~7.73 cubic foot bulk, about 42 cubic inches rear chamber volume per sq. inch of cone area and a superficial volume for front chamber about 1/2 that of rear chamber.
Baffle angles normally range from 30 fro K15 down to 20 degrees balck for Acoustic Control's 115BK.
Moray James has built a number of smaller couplers using fullrange and t-line rear loading. I've only played with the old-style.
Ken Lehman looked at a stub approach on the front chamber to smooth response.
X15 system ad circa 1965-66
A builder's interpretation of that system and long slotted HF waveguide
My guess for simple 18" coupler with 23 degree baffle, 10 degree port panel and 2-4.5" by 4.5" hole in board vents. Box was 32H x 22.125W x 16 deep. A lowpass shelf can be tried and will at least stiffen up the baffle. The wing's gap is larger than normal so fb moved up a couple of Hz but tone was better imo trying to make an 18" rattle high.
A 1955 Karlson Twelve
Z-input of 115 BK by Acoustic Control with EV 15L
Z-input of a tall coupler with 18" Eminence
|20th November 2006, 06:57 PM||#2|
Join Date: Feb 2002
Location: Western Sydney
I think the approach would depend on the application,
for modern Hi Fi, I think a lower response than traditional K Box is required, which means the resonant pipe section needs to be longer.
For PA, traditional K is good, but in both cases high cutoff probably needs to be below the dip caused by the wings? 200Hz?
Possibly the dip could be avoided by rearranging so that the driver isn't firing directly at the wings?
|20th November 2006, 07:42 PM||#3|
Hi Pete - some angle combos don't cause much "bounce" dips.
smaller Karlson could certainly use subwoofer coming in ~80hz although one builder uses Leach type transform to flatten X15 size to ~16Hz. K15 retuned "is" Exemplar's choice for subwoofer.
regarding a longer front - not sure if they work that way but don't have a long coupler to compare -- do you mean something like a tall coupler with t-line vent terminus at top of coupler?
K15 with weak but reasonably linear motor shows 10dB reduction in two tone sidebands vs same driver in reflex the size of K15's rear chamber and tuned to ~50Hz . A low Q 18" on single tone was 10dB or so cleaner than a commercial pipehorn.
here's sideband reduction with Beta 15CX
why might a Karlson reduce cone excursion on "transients"? - what does this tell us aobut music power spectrum and if this is really happening, where will it be effective?
FWIW I look at the 3rd impedance peak so see if response is follower coupled-cavity behavior with something simple like WinISD.
a slot in a pipe doesn't make a traditional Karlson like K15. "reverb" can be attractive "X" amount of time and can be good on vocals depending upon recording. They can go bad - haha
here's two shelfless couplers (one 30 degree tilt- other 23) vs K15 all loaded with 18" (chopping off some Sd in K15) IIRC this is with mic laying on ground and back ~2M - one has to remember the mic is off axis in a sense at this perspective. A 5" board poked into the 30 degree shelfless coupler will make its plots look more like K15 and it will sound more like it too. The shelf can deflect some HF so might not be best if horn if put on top and run at high xover.
to drop a name - Steve Schell of Cogent likes K15 and says will outplay horn of its size.
3- couplers with 18" - one 8CF tuned kinda low, K15, then a 23 degree coupler with 6.2CF bulk The 18" with Qts ~0.25 is easier to deal with for avoiding peaking nera the LF corner
a 42" tall coupler with same higher Q 18 as in 6.2CF coupler above - fb is lower but it still wants to bump a bit and could use lower Qes
the 3rd Z peak is lowered in the taller coupler indicating I think, lower front chamber lumped tuning. There might be certain combintaions of tilt and height where its optimized and where the tuning being know or estimated can be juggled to get a flatter passband with a bit more LF in a given bulk. The 6.2CF coupler ran a low Q 18 pretty well with only 80l rear chamber and cone deflection was low at 300 watt peaks. I added 20L as a fold-over stub to its front chamber to see effect on 3rd Z peak and response.
I think for the adventuresome diy-er - Karlson-type might be a small way to do midbass horn dynamics and worth a try vs other stuff - if nothing else for fun. 5% or higher rated drivers wiht reasonably low mass might be best overall for mid-upper bass punch (?)
regarding "not firing directly at the wings" - might you post a sketch?
|21st November 2006, 04:37 AM||#5|
Hi Pete - it would be interesting to see if that would behave (relative to coupler Z peak) like a bandpass or something "new" - what do you think would be likely scenarios? - would you have the rear chamber sealed, vented into front chamber or externally vented? Freddy
here was in-room result of adding a 14" high cap to the front chamber only of a small coupler with 18" driver - wish the data had been taken outdoors...
look how far the 3rd Z peak dropped as result of the 14" tall cavity added to front chamber
in contrast heres the same coupler with a 6" high cavity added to front chamber only - I think things from this perspective look kinda BP
|24th November 2006, 12:56 PM||#7|
-- seen one example of passive radiator on a karlson subwoofer using isobarik 10". Can those who are hip to MJK's mathcad sheets work out what will happen for the rear section with longer folded pipe? Would Bob Bullock's TLBOXMODEL figure it out faster? - (I've never been able to get a screenshot of these programs under Win XP - can it be done?)
seems like composite response of a K-t-line would be somethng like the rear section blended with bandpass type so ifs tehrs opportunity for peaking the BP will at least predict the whereabouts of the first peak.
her's CN's high-mass cone pick of woofer in a coupler tuned to ~32 with 3" right angle vent - Le is high @~4.1mH - I think it peaks like a BP - he says his coupler plays fine so if so a X15 with 25 degree/10/degree then 35 degree downwards deflector is better for 1844 than Karlson's coupler which was built around a low-mass CTS15 - I can't get 1844 to play smooth 2-way to a k-tube. I know other coupler angle combos will not give those deep ground-palne nulls - at least with old-style lower mass woofer. The coupled cavity peak can be predicted roughly with WinIsD looking at the coupler's 3 Z peak (assuming its vented)
1844 in the right coupler might be cool as a 3-4 way. CN uses a Leach transform to flatten it to 16Hz and 1844's 9mm xmax would have no problem with that EQ - given sufficient power, I'd think 1844 burn up before moving much. 1844 is less sensitive in the mids than things like EV15L.
Martin 184415269/151269 Eminence
CN's X15 size coupler which works OK with 1844 (vent gaps probably set to ~1/2")
btw - how does one start a new thread at DIY? - can't find icon today?
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