Karlson tuning

[dlhughes]

Does anyone really understand the tuning of a Karlson enclosure?

Let's say I wanted to tweak the external dimensions of a K15 to better match and integrate with some other gear. Are there some 'thumbnail' design guidelines for the shelf, port, etc. that are based on the volumes, F3 of the driver, and so forth? The only thing I've come up with is the 2:1 ratio of backchamber volume to front chamber volume, so far.

Here's what I have in mind... I have a 60W combo bass guitar amp, in which the low bass is really weak because of (1) a crappy driver, and (2) tiny 'ported' speaker chamber...too small for it's 12" driver. I'd love to build that out into another combo cabinet with a Karlson enclosure as its speaker chamber. But I'd like to reshape it just a bit to fit the amp chassis correctly. The unit is now in a cabinet that's 18" wide, which is a tad wider than the plans I've seen for a 12" Karlson. Plus, I want to make sure the Karlson enclosure will give me full loading and response down to 40 Hz. Otherwise, i might as well build the amp chassis into a 'head cab' and build a separate K15 cabinet to plug it into.
Can anyone here help me sort that out? Freddi?

[italynstylion]

I would really like to see a Karlson How To thread. I've been dying to try out that style of enclosure but haven't had a clue where to begin.

[dlhughes]

Originally Posted by italynstylion

I would really like to see a Karlson How To thread. I've been dying to try out that style of enclosure but haven't had a clue where to begin.

Would your interest in the Karlson be for hifi/home theater use, PA/sound reinforcement, or as a bass guitar cabinet? My interest is as a bass guitar rig. I've seen them here & there, but never really heard one. Actually I used to have one years ago, but never used it, eventually selling it. I didn't really ever give it a fair chance because back then I didn't know anything at all about them. I just sort of 'inherited' it from a friend. Wish I had it back, now that I've learned something about them!

[Cal Weldon]

Freddi, where are you?

[italynstylion]

Originally Posted by dlhughes

Would your interest in the Karlson be for hifi/home theater use, PA/sound reinforcement, or as a bass guitar cabinet? My interest is as a bass guitar rig. I've seen them here & there, but never really heard one. Actually I used to have one years ago, but never used it, eventually selling it. I didn't really ever give it a fair chance because back then I didn't know anything at all about them. I just sort of 'inherited' it from a friend. Wish I had it back, now that I've learned something about them!

My interest would be for PA use probably. I'm really interested in trying something for outdoor use for tailgating and get togethers.

[hitsware]

Originally Posted by Cal Weldon

Freddi, where are you?

Karlson Loudspeaker Discussion

[freddi]

I'm kinda ill - anyhow, the originals by their Z minimum were scaled in half octave steps - K8 tuned ~90Hz, K12 ~63Hz, K15 ~45Hz. I don't think K15 will play "flat" to 40Hz as its nearly 10dB down at 50Hz sitting in my small hillside yard. You could tune lower and gain a few dB down low and Exemplar must tune their coupler below 30Hz for sub duty.

the front shelf deflects a null, and keeps some mid and highs away from the top of the coupler. You could build without a front shelf, perhaps with a 25 degree angle baffle. The rear lowpass shelf can clean up the wave before it dumps into the coupler.

Acoustic and others built the tiny (~27-28" tall, 20" wide and 13.5" deep sans wing inset) coupler with a diagonal baffle which set tuning around 53hz but maintaining a large vent area. Due to size its cutoff is high for modern bass - I could stand it but I'm old.

like anything else, you could have peaking, or a sharp knee or a gentle bend at the LF corner point depending upon parameters and tuning you pick.

the coupler is probably kicking in about 1 octave above LF cutoff but I've see sine wave at 36Hz show much less movement than a 45-50hz tuned reflex the size of K15's rear chamber.

for lack of good modeling tools a bandpass sim is maybe better than nothing but a well done K-coupler will be extended and simulations so far don't match up. Maybe someone will do either a hornresp or akabak model.

for bass guitar use there's probably some flexibility - I could not fit K15 into one car due to its 18" depth.

for what its worth here's some impedance plots

[dlhughes]

OK....so how do you tune one? I did a little 'reverse-engineering' on the port slot as related to the backchamber volume, and came up with something nowhere near low bass frequencies...and then there's that gap between the shelf and the back of the cabinet.

I realize that even the mighty 8X10 Ampeg bass cabs don't really play flat down to 40 Hz. I'm told that one doesn't really want that in a bass guitar rig, anyway, though I can't imagine why not. And most of the drivers (the 10's, at least) sold for that application roll off -3db at about 50-55 Hz, to boot.

Here's what I'd really like to do...
As I mentioned, I have a 60W bass combo amp with a sucky 12" speaker in a sucky enclosure. Now, 12's always sound too 'middy' for my bass-player taste to begin with. I've really never heard a bass amp with a 12" that I liked. But my thinking is that if I built a new combo cab for this little amp with a 12" Karlson type enclosure (amp chassis mounted in its own compartment at the top of the cabinet), that 'middyness' that seems inherent in 12" speakers would be somewhat subdued. The 'old' Acoustic Control Corp. built a little Karlson combo amp, I believe with a 15" in it. Never actually heard one, but have been told they were pretty awesome. This is what I'd like to do with my 60W amp; combo it with a 12" Karlson enclosure to gain efficiency and enable that 60W to do a little more in terms of filling up a space. It would surely come out still lighter in weight than my 300W 2x10 combo (at a whopping 82 lbs.!), for use in smaller venues and rehearsal. The current cabinet is 18" wide, so I'd like to keep that so that the amp chassis will fit the cabinet the same way it does now.

So, I need some help in designing the Karlson part of it to be 18" wide instead of the 16 1/2" or so of the usual 12" Karlsonette and to go as low as possible. I have a driver picked out, with a couple of alternates. I just don't know how to tune the port and the shelf to get where I want to go with it. the 2:1 backchamber/frontchamber volume rule, I know about, and I could get a drawing together as far as that goes. The rest is a mystery to me; the shelf & port. I guess I could knock a few together out of cheap ol' particle board with different spacings in those areas and see what happens, but that's awfully labor-intensive.

If a 12" just won't go low enough for me, the alternative is simply to build a head-cab for the amp chassis, and a separate K15 enclosure (the one I found on the Web with the 'latest mods') to plug it into.

Any thoughts on that?

[freddi]

in an 18" wide cabinet you could use a 15" speaker but the volumes would have to be adequate - -Acoustic Control's 115BK had only around 3 cubic foot total airspace for the 15" and gives a high cutoff (~80Hz half space) with good sound. - if using a 12" you might be able to narrow 115bk to 18". You could make a scale coupler from K15 to 18" width for a 12" speaker giving a 0.8 scale box. A vent calculator should get you into the ballpark if making a new coupler - a front or rear shelf at or near the vent boundary will make it tune lower plus the front aperture is also acting as part of the system port - the front shelf does not need to be used and Karlson didn't employ it in the smaller couplers.

over at Gregg's Karlson forum there's calculators for wings so you can make them for your new size coupler. Starting gaps range from ~3/8" up to 3/4" as on my KK-Audio K-couplers which sound great with the Transylvania Tube on top.

K12 made after 1955 had a distributive slit vent which will distort on sine-wave - but it plays well on music.

for bass guitar I think you could build a number of ways and come up with a fun coupler.

if you want nearly flat to 40Hz and high output, there's a one-sheet tapped horn thread where jbell is showing a new tapped horn about the size of K15.

[dlhughes]

Well, then, I guess the questions that remain are:
-Do I tune the port as if the backchamber were a standalone bass-reflex cabinet, i.e., tune the port to the F3 of the driver? If so, what about actually putting a duct-port in there between the two chambers? My reverse calculations, though, tell me that the ports in Karlsons are tuned pretty high in relation to what it would need to be in a standalone reflex.
-And what about the shelf? I understand that the rear end of the shelf acts as a lowpass filter. How do I determine what the gap should be between that and the cabinet back panel?

I can't see the flared slot as being all that super-critical, as I see designs in which that curve is simply a radius, as opposed to a true exponential curve. I figure there's a fairly decent range of 'close enough' on that. Having laid some of these out on AutoCAD, I find that there's a radius that matches up with the exponential curve on the smaller sizes within about 1/8" at any given point on the curve. Surely that's 'close enough'.