where are the fullrange Karlson-type couplers?

[freddi]

I've not seen any regular Karlson type built for fun - only a few Fulmer-slot lines -- here's a very crude 0.317 cubic foot bulk coupler with MCM 5" (which used to be around $10 before inflation) and external dimensions of 8"x10.75"x6.375" next to a factory Karlson Eight - when are the FR-ers going to make some kawdust?
http://img696.imageshack.us/img696/4892/8kk5.jpg

[Henkjan]

would be fun to put a modern day driver in an old school cab.... are there any design guidelines for this?

[freddi]

traditionally they're usually designed with baffle tilt of 20-30 degrees from vertical. Rear chamber volume and tuning pretty much sets the low frequency cutoff and front volume is about 1/2 that of the rear chamber. The front chamber is made reflective with several coats of shellac.

At some point in size I suspect the coupler is doing a good job of minimizing cone excursion - largest I've built are for 18" woofer.

Historically the regular Karlson couplers were built built in three sizes:15/12 and 8" and those were basically scaled so the eight inch coupler had its cutoff an octave higher than the 15" model. They were sold in the days of "mix and match". The 12" couplers can work better with 8" drivers and exhibit less cone motion with better bass than an 8" driver in the 8" coupler. I've not tried small drivers in the 8" cabinet (its Fb is normally around 85Hz but Karlson had a sheet saying there were conditions where it was beneficial to seal the vents)

Moray James has built t-line rear chamber couplers, Carl Neuser used higher aspect. Steyr made a coupler for FE126

Here's a post from Gregg Baker's Karlson speaker discussion forum with some small couplers and dimensions for the 8" and 12" coupler:

where are the mini K-couplers?

[freddi]

FR-ers could have a few variables to work with: aspect ratio, baffle angle, rear chamber volume, rear chamber tuning, vent placement, vent type, front chamber volume, rear lowpass choke gap area, front aperture area and flare (a two variable calculator for generating curves is over at Gregg's Karlson forum), reflector angle, initial gap of the aperture. (removable wings are suggested for prototyping)

[freddi]

Karlson are anti-Toole-Geddes in approach but someone eventually might have fun with little couplers. IMO, follow the originals at first for concept - aspect, keep the front chamber lively, empirically test a few different curve wings (Carl runs :radial, P=1, Q=1.7 which opens a bit faster than radial; P=1, Q=3 which is tighter than radial during the first half; trax, etc.) and their initial gap by ear. Play with an upper reflector, possibly do curved one.

Its going to be like making an acoustic guitar to some extent with regards to the aperture controlling the tonal results vs the sound hole on the guitar and as usual, RTA is useless vs ear-brain. At some point a rear lowpass choke may be of value. Moray likes little K and has worked with T-line rear. (I'm more primitive and less a woodworker) There's the nebulous deal of how large to make the front chamber. I once ran a v-vent reflex next to K15 with K15 running only its coax tweeter from 1K6 upwards and that combo emulated the K to a good degree. 2 cubic foot just for a tweeter is a bit much.......

Here's a dirty splintered s(crap)(?) coupler 10.75 x 7.875x6.375 inches with beat MCM 5"

YouTube - Scrap 5" Karlson - coupler with MCM fullrange

(btw - BetsyK was fun in the 1954 K12 - good cone loading - very little cone excursion - in ways that had better "bass" than my Klipschorn - shorting ring would help its highs - 1772 will go into K12 sometime)