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xrk971 20th June 2013 03:42 PM

A Speaker that Kicks Butt in Large Spaces
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I originally posted this in the KARLSON thread, but figured there might be some general interest from folks who normally don't read about the Karlson.

The cool thing about having models of various speakers is that it lets you do desktop comparos of the same driver in different cabinets, in different settings from the comfort of your latop (while riding a bus in my case). Details of my AkAbak model of the Karlson K15 speaker can be found here:

I noticed that many of the pictures of the Karlson show it in a large venue (stage, night club, dance floor, etc.) and I figured there must be something that might make the Karlson special for such occasions.

So I am taking one of my favorite deep bass extension MLTL designs that is flat as board and running it head to head with a Karlson. What I found surprised me.

Basically, if you are in smaller space like a room in a house, the MLTL is a great design as it lets you put the speaker right up against the wall. The first plot is the Betsy K in a 45 in tall MLTL (11 in wide x 16 in deep x 1.625 in tall x 11 wide x 4 in deep port at bottom, driver 9 in from top), speaker cabinet is flush against a wall and listening position is 1 m away. This is perhaps one the nicest frequency response curves I have of ANY design I have simulated and is consistent with Bjohanessen's WIBAQ.

Next plot, place a K15 with Betsy K flush against a wall and listen 1 m away and it really sucks. Very uneven frequency response.

Third plot, let's put the speakers away from the wall at 60 in and stand 5 m away from the speaker - something similar to how speakers might be used in a PA setting like a wedding. The Betsy K MLTL doesn't look so good anymore, bass has dropped and response overall very uneven. Most importantly, the ever important 50 to 60 Hz bass region that provides a lot dynamic punch is almost all but gone (75 dB) and peak bass has shifted to 90 Hz and is only 85 dB.

Fourth plot, put the K15 with Betsy K at 60 in from wall and listen 5 meters away. Notice the sound level is about 90 dB at 5 meters away. The response also has a pretty flat bass shelf to give a nice clean tight punch to the bass notes from 60 Hz to 100 Hz. Now that is something special! I don't know of another speaker with a $55 driver that can throw that kind of bass that far with 1 watt input!

Fifth plot, if I tweak the K15 cabinet by elongating it in the vertical direction by 1.33x and widen it by 1.07x, and enlarge the 21.5 sq in vent by 1.5x, we get a 5 Hz deeper bass extension to 55 Hz a flat bass shelf, and a nice response.

6th plot shows the polar SPL response at 5 m away for the MLTL at 60 in from wall, for 60 Hz, 200 Hz, and 500 Hz. The response is not very goo at all.

7th plot shows the polar SPL response at 5 m away for the original K15 at 5 m away for the same frequencies. Notice how close together the responses are over a pretty wide sweet spot.

So, in conclusion, every speaker has its ideal use and 'home'. The Karlson is at home on stage and should be seriously considered for a large room where volume and bass punch is important. You won't get ultimate deep 30 Hz bass like a MLTL, but you will get a nice reach with 50 to 60 Hz at butt kicking levels, with great spatial coverage and uniformity.

IG81 20th June 2013 04:15 PM

I always felt my K12 did not have enough room to breathe in my small-ish room. My living room is barely larger and has poorer acoustic, very K-hostile. My smaller SK8 does better. Using a vintage 10" fullrange driver, Richard Allan CG10T, the K12 could deliver impressive amounts of power and punch and retain good cone controle. The simulated polars are in accordance to what I've experienced as well. The K-slot will provide good dispersion as a function of it's width where the driver's beam intercepts it.

The Karlson is no free lunch and can have disadvantages too, but this goes for any enlcosure style and what you expect of it. Are BIBs also not disastrous in simulation and measurement? They'll do better when loaded byroom corners, but were are show here that the Karlson can not simply be looked at by using simple simulation that ignores room placement. I feel it has a plus where its own set of advantages differs from most other typical speakers and offers a unique experience. It'll take a horn much larger than the Karlson for the same driver to deliver that kind of power IMO.


GM 20th June 2013 05:14 PM

The K15 is an 8th order band-pass [BP] and tuned for enough mid-bass, lower mids gain BW to not need any BSC, so simmed results are consistent with reality and as such it ideally needs a 250-500 Hz upper BW limit depending on XO slope order and how much audible 'ringing' [euphonic distortion] is acceptable; though IIRC Freddy pointed out that it was designed specifically for large duplex drivers such as the Altec 604C or similar, which have a ~1600 Hz/2nd order XO point/slope and critically damped mids/lower HF, so while I’ve never auditioned this combination it technically could in theory make for a very ‘musical’, ‘toe tapping’ speaker if driven with period correct electronics.

This was a time of high output impedance systems though, which included variable DF tone controls, so a considerable amount of response shaping was typically available to tonally balance a speaker system to the limits of any available recordings, ergo should be taken into consideration when adapting the design to modern day drivers, electronics.

Some other Ks are either 6th or 4th order BPs, so have progressively decreasing gain BW, ergo can be XO'd higher up.

In short, for smaller rooms, either use a higher Qt driver and/or a lower order BP alignment since less BSC is required.

Yes, acoustically small/short pipe horns such as the BIB do indeed ‘ring like ten penny nails struck with a ball-peen hammer’ if not at least loaded in 1 pi space [wall/floor] and preferably 0.5 pi space [corner].


IG81 20th June 2013 05:53 PM

Speaking of adjustable DF, I'm about to build a very simple chip amp with an hopefully workable scheme to go from voltage drive to current drive. I'll be testing it on my small Karlson SK8 (K10 size actually) with FF225WK inside. I also have some small 5" Vifa midbass that have a very low Qms of ~1.1 and are fairly extended, ~5-6kHz on-axis, this should be fun.


xrk971 20th June 2013 07:25 PM

What is DF?

freddi 20th June 2013 07:35 PM

(DF = "damping factor") - was that a typo on the K15 vent in the post above? (stock K15 vent was 32 or 40.5)

GM 20th June 2013 07:46 PM

FYI, here's the sort of output impedance and DF adjustment the 604C or similar were designed for:


xrk971 20th June 2013 09:26 PM


Originally Posted by freddi (
(DF = "damping factor") - was that a typo on the K15 vent in the post above? (stock K15 vent was 32 or 40.5)

That is not a typo but is a result of me misinterpreting the drawing as posted from various sources of the K15 cabinet. The main one being this one:

I have to say that one the most critical dimensions is the port height and it is not explicitly shown anywhere. Even in the Karlson article, where does it say 9 inches or whatever?

Google Image Result for

But, as it turns out, 21.5 square inches based on the 84 mm wide dim and 165 mm high dimension that I got from somewhere appears to work quite well with the Betsy K. :) Luck.

freddi 20th June 2013 10:36 PM

had to look at one of my blonde K15's - their stock vent is 8.875" tall x 4.5" wide. I had a K12/Karlsonette copy, blocked its regular horizontal vent and introduced a rough rectangular vent with only around 7 or so area - that seemed to cause quite a suckout. Vent placement probably matters somewhat besides vent area. Acoustic Control made a little 15" K-coupler about the size of the Karlson X15 system with a 27 vent which measures reasonably well. I don't know how 115bk might perform scaled.

Karlson's distributed slit vent K12 like other distributive tight vents can distort on sinewave - but sound pretty good with acoustic instrument transients.

here's a crude side-view sketch of the Acoustic 115bk coupler - its internal width is about 19" and the wings radial arc

xrk971 20th June 2013 10:43 PM

The distributed slits was going to be one of my next cases if I don't run out of nodes in AkAbak. The limit is 52 I think. I think there may be a trick to simulating 7 thin slits vents as a single one: make the cross sectional area as one vent x 7 vents tall. Physically would not fit in a real cabinet (except as a zig-zag switchback style jigsawed vent). This would only use the 2 nodes already used for the single large port vent.

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