Bass Cab Karlson / TH Horn Challenge:

[nazaroo]

Here's the challenge:

The size of the outer box is fixed:





I want to turn it into a good high-power (SPL) Bass Cabinet.

I would use either a 12" like the MCM (price and specs are good!),
or a 15" woofer.

The shape seems to cry out "folded horn", "tapped horn", "Karlson-mod" or something!

It should be loud enough for medium/small gigs,
but not require scads of amp watts to drive it, hence my 'horn-tech' appeal.

Here's the idea:

I turn the top half of the cab into a bass-guitar-cab,
with the speakers facing down.
To protect the speakers during transport,
you could have a shorting-jack to freeze the cones.

Now the bottom is like a speaker-cover with wheels.

You wheel it around face-down,
but for playing you unclip it from the wheels/bottom,
and tip it on its side.

The inside dimensions are about 20" x 26" x 14" = 4.2 cu. ft.

Minus some reinforcement/folding hornwork, say about 4 cu.ft. or less.

Is that enough for a couple of 12" or a 15"?

It needs a good cleaning out.
It had some drum parts, and alot of deteriorating foam in it.

Please, those of you who love THs, or Karlsons, or FHs,
give me a clue in the way of a usable blueprint.

I'm an ok carpenter, but I'm not a pro speaker-builder!

It could be in the form of a slip-in inner cabinet,
or just a framework using the outer-cab itself, with reinforcements.

All ideas welcome!

[weltersys]

Originally Posted by nazaroo

Here's the challenge:

I would use either a 12" like the MCM (price and specs are good!),
or a 15" woofer.

The shape seems to cry out "folded horn", "tapped horn", "Karlson-mod" or something!

It should be loud enough for medium/small gigs,
but not require scads of amp watts to drive it, hence my 'horn-tech' appeal.

Here's the idea:

I turn the top half of the cab into a bass-guitar-cab,
with the speakers facing down.
To protect the speakers during transport,
you could have a shorting-jack to freeze the cones.

The inside dimensions are about 20" x 26" x 14" = 4.2 cu. ft.

Minus some reinforcement/folding hornwork, say about 4 cu.ft. or less.

Is that enough for a couple of 12" or a 15"?
Please, those of you who love THs, or Karlsons, or FHs,
give me a clue in the way of a usable blueprint.

Shorting jack is not needed, the cones will move little in transport, far less than with moderate power on the gig.

The first cabinet I built was a Karlson, I did not like the midrange coloration the "Christmas Tree" creates.
I sold the cabinet to a bass player who did like that sound.
A Karlson is a BR, the added air mass in front does tighten up the bass a bit, but not enough to negate the coloration IMHO.

You need to define how low you want to go, the low E on a four string is 40 Hz, the low B 32 Hz.
Hitting either fundamental with a TH that size will require a lot of folds, adding a lot of weight, and won't be much, if any louder than a BR. A TH will only be flat for the bottom two octaves or so, then has huge peaks and dips.
I would not consider a TH to be usable for bass guitar unless using a top cabinet above it, requiring DSP for proper integration.

The size mentioned is far to small for a FLH (FH) unless you don't care much about the bottom octave of bass guitar, and upper articulation.

A low tuned BR using a 15" would be the best bang for the buck, a 2x12" with the right cones could go a bit louder, lower and higher.

That said, the most popular bass cabinet is the Ampeg SVT, using 4 pairs of sealed 10" speakers. It rolls off at 12 dB per octave from around 60 Hz.

You could fit four 10" in your cabinet using a "V" shape baffle, which could extend in to the lid. That would be my choice, ported or not, if ported I'd choose an Fb below the low string's fundamental frequency to keep the cones from flapping on low notes.

Art

[nazaroo]

Originally Posted by weltersys

Shorting jack is not needed, the cones will move little in transport, far less than with moderate power on the gig.

The first cabinet I built was a Karlson, I did not like the midrange coloration the "Christmas Tree" creates.
I sold the cabinet to a bass player who did like that sound.
A Karlson is a BR, the added air mass in front does tighten up the bass a bit, but not enough to negate the coloration IMHO.

Thats what I was thinking also about the Karlson.
This might be the perfect place to give it a try,
using the 12" MCM driver.

You need to define how low you want to go, the low E on a four string is 40 Hz, the low B 32 Hz.
Hitting either fundamental with a TH that size will require a lot of folds, adding a lot of weight, and won't be much, if any louder than a BR. A TH will only be flat for the bottom two octaves or so, then has huge peaks and dips.
I would not consider a TH to be usable for bass guitar unless using a top cabinet above it, requiring DSP for proper integration.

The size mentioned is far to small for a FLH (FH) unless you don't care much about the bottom octave of bass guitar, and upper articulation.

A low tuned BR using a 15" would be the best bang for the buck, a 2x12" with the right cones could go a bit louder, lower and higher.

I'm glad to hear that 2 12" will fit in this with good results.
That would double the wattage, and presumably make it significantly louder.

That said, the most popular bass cabinet is the Ampeg SVT, using 4 pairs of sealed 10" speakers. It rolls off at 12 dB per octave from around 60 Hz.

You could fit four 10" in your cabinet using a "V" shape baffle, which could extend in to the lid.

Wow that also would be great, to cram 4 x 10" in there!
I will get the measurements for the rest of the cabinet!
I hadn't thought of extending the usable box space!
Do you mean a convex 'V'? so that the speakers faced away from each other say left and right?

That would be my choice, ported or not, if ported I'd choose an Fb below the low string's fundamental frequency to keep the cones from flapping on low notes.

Art

I also would like to make sure this cone-flapping can't happen.
But I don't know how to actually do it.
Any instructions, pointers, advice on this?

[nazaroo]

Okay, I just measured the inside of lid, and it will allow
an additional (outer dimensions)

20" w x 26" t x 6" deep extension, of lets say 3/4" plywood front
18.5" x 24.5" x 6" (internal) = 2379.5 cu in = 1.38 cu ft.

That brings the cab to well over 5 cu ft of space available internally.

Thats the same or larger than a Marshall cab.
i.e., it should support 4 x 10" and give good bass,
or 2 x 12" as a simple closed cab (or small ported).

but I'm still thinking there's now room in here for a Karlson...

[nazaroo]

Here's what I was picturing:


This frame would snug-fit inside the box, extending it 6 inches.
2 inches would overlap, for something to screw to (total of 8 inches).

This makes the box effectively about 20"x20" x 26" (external).

[weltersys]

Originally Posted by nazaroo

Wow that also would be great, to cram 4 x 10" in there!
I will get the measurements for the rest of the cabinet!
I hadn't thought of extending the usable box space!
Do you mean a convex 'V'? so that the speakers faced away from each other say left and right?

I also would like to make sure this cone-flapping can't happen.
But I don't know how to actually do it.
Any instructions, pointers, advice on this?

To keep the cones from flapping, AKA unloading, port the cabinet around the low E or B (40 or 32 Hz) there are many online port calculators to determine what size and length port(s) to use. Dividing the cabinet internally in to two sections is a good idea sonically, and would allow more amp /impedance flexibility.
Slapping or popping strings can put out full tilt boogie power down to only a few Hz, so you need to watch that.
Sealed cabinets (like the 8x10" SVT which has four chambers) provide more cone control down low, but have less output down low than a BR.

I prefer a concave "V" for the extra air load it provides, but a convex "V" would work O.K. too, ether would allow 4x10" in the cabinet.

Art

[freddi]

the Karlson is a coupled cavity design - here's an outdoor comparison of a reflex about the size of the 15" Karlson's rear chamber tuned to around 50Hz (quite close to Z_minimum for the Karlson with both cabinets using the same driver and same two-tone size drive

note - the sideband modulation for the Karlson is 10dB lower than that for the reflex.


another thing, while the reflex will have a near-cone null at its fb ~50Hz, the Karlson with fb ~50Hz will exhibit a near-cone null about one-half octave lower than the reflex. (~36Hz depending a bit at what height the mic is placed near the cone) -- power handling on the Karlson will be better below 50Hz than the reflex and better in the region where the front chamber is resonating.

note the amplitude of the lower sine frequency on both speakers - the Karlson is only about 1.5dB louder - but cleaner. The rear chamber volume and tuning will pretty much set the bottom end shape and cutoff.

you don't have a huge amount of airspace to play with in this cabinet so may be better off building a Karlson from scratch. Typically for 15" the front chamber runs around 1-2.2 cubic feet and rear chamber 2.2 around 4 cubic feet (empty). Metro in Greece built an interesting Karlson type called "T15" and Gregg Baker pretty much got the dimensions down.

multiple sealed woofers are always a classic way to do bass guitar - I come from the time when few worried about cabinets flat to 40 or below nor tweeters.

[bentoronto]

nazaroo -

Judging from your signature insult of Klipsch, you really don't want to know what he says about Karlsons (I had a Karlson-15 which was wonderful back then, in 1957).

For sure, freddi's insights are trustworthy on Karlsons - and make more sense than Karlson's own theory!

People may differ about his speakers, but that remark about Klipsch is way crazy wrong and gratuitously nasty. Anyone who had contact with him, ahem, ahem, will say the same.... esp. if you feel intensity or commitment is the opposite of BS.

Do find something positive to include in your signature or nothing.

Ben

[weltersys]

Originally Posted by freddi

the Karlson is a coupled cavity design - here's an outdoor comparison of a reflex about the size of the 15" Karlson's rear chamber tuned to around 50Hz (quite close to Z_minimum for the Karlson with both cabinets using the same driver and same two-tone size drive

note - the sideband modulation for the Karlson is 10dB lower than that for the reflex.

multiple sealed woofers are always a classic way to do bass guitar - I come from the time when few worried about cabinets flat to 40 or below nor tweeters.

Freddie,

Glad to see you are still happy in Karlson land!

Normally, an AC spike would be a harmonicly related integer, I would expect it at 30 Hz , not 25 Hz.

If the 25Hz spike was due to AC, it should have been present in both tests.
The spike was probably was not due to wind, or it would have been much wider band.

The difference in distortion is signifigant, around 6% for the Karlson compared to 18% for the BR, but it may be that the Karlson is actually tuned much lower, possibly a dual tuning of around 25 Hz and 50 Hz.

You could verify (or disprove) my speculation watching a dot on the cone while sweeping downward with a sine wave tone of large enough amplitude to see the cone movement, which will be at minima at the tuning frequency (s). I find that technique more accurate for determining actual Fb than impedance minima.

At any rate, your test shows clearly the problem of BR cabinets driven below Fb, distortion is high with only one watt of input in a time when “small” bass amps are around 300+ watts.

Art

[freddi]

re:AC - it was the air conditioner resonating the side of my weak house - I shut it off in the later test.

re:Klipsch - I know of a Karlson fan who said K15 loaded with good coax and wall standing or corner mounted was often preferred in its day to Klipsch's K-horn -(I currently have 3K-horn so know them reasonably well) - I suspect Karlson gave Klipsch some heavy competition. According to Wayne Green, Karlson ruined the business early on - of course smaller speakers were becoming the vogue anyhow.

re: PWK's K15 graph - it was accurate other than spl - but let's compare K15 to a competent bass reflex with a sizable area vent, RCA-Fan's V-vent design. V-Vent is something like an Onken (Jensen Ultraflex)

the yellow trace is the Karlson tilted up so its baffle is perpendicular to the ground - these are ~ground-plane traces. The reflex has as much "hole" as the Karlson. Small-signal the lower tuned reflex goes lower but works much harder than the Karlson at high spl. Their tonal balance is of course different. The aperture's starting gap width can affect proportions of mids and highs which pass through the slot plus affect overall system tuning so there's a lot of stuff for the hobbyist to balance


in case anyone is wondering how the reflex would look if its woofer was close to the ground
here's that box in upright vs inverted position


in the 1964 HiFi workbench show with John Karlson, Karlson said the secret to his speaker
was a special type of cavity.

a bass reflex has a near-cone null at its tuning - Karlson couplers the size of K15 have a near-cone null
about 1/2 octave below tuning.

here's the V-vent reflex tuned to around 40Hz and an 8 cubic foot Karlson type tuned in the mid 40's(the hole would have been fixed if the K had the front shelf like K15. Smooth Ks can be made without the front shelf.