[Vintage-Audio] Karlson Speaker

[Robert Nickels]

Duane B. Fischer, W8DBF wrote:

>Now there would be some sweet sound! Infinite baffle, bass reflex or folded
>horn? 
>  
>
Duane, the Karlson webpage contains a description  of  the theory that 
is taken from an article in Sept. 1952 Audio Engineering magazine that 
I've edited a bit to improve clarity.  I know you're pretty good at 
visualizing things without the drawings that accompany this text so I 
hope this helps answer your question.   To get a mental picture of a 
Karlson, imagine a 12 or 15" wide-range speaker mounted to a baffle 
board in the bottom of a 34" tall by 20" wide 3/4" thick plywood 
enclosure, tilted back at about a 30 degree angle.   But instead of a 
solid front covered with grille cloth, the Karlson has a 3/4" plywood 
baffle on the front  that has been cut in what looks like an inverted 
vee.   In fact the angle of the vee follows an exponential cuve, and 
this is what makes it unique   With this image in mind, hopefully the 
rest of the description makes sense:

The Karlson may be called a broadband-resonator; the resonator in the 
design is an air column (a pipe that is closed on one end like a pipe 
organ or pop bottle).  Closed pipes however have a nasty habit - they 
not only resonate on a fundamental frequency, but also on the odd 
harmonics of this frequency. (A speaker attached to a closed-pipe 
resonator would show objectionable peaks in the response curve.)

At frequencies of which the column length equals half the wavelength or 
a multitude of that, the reflection at the open end of the pipe is out 
of phase, causing an acoustic short circuit and sound cancellation.   
But if we cut a slot down the open end of the pipe, then the effect is 
that the pipe doesn't have a distinct length anymore, causing the peaks 
at odd harmonics to widen.   If we make the cut stretch up to 2/3 of the 
pipe, and make the cut exponential in width, the peaks broaden and 
overlap so much that a broadband relatively flat response results.   .
 
The "pipe" in the Karlson design is created by tilting the driver at an 
angle so part of the sound energy is directed upwards into a dead space 
in the cabinet.  The front surface of the enclosure forms one wall of 
the pipe, and is cut with an exponential curve.   It is claimed that the 
tapered opening "broadly fans the listening area uniformly and 
eliminates the stridency and racuous qualities associated with high 
freqency "beaming".    Karlson also claims "in the bass region such 
loading also provides an exceptional range and dynamic output".
 
In looking over the gallery I see guys have implemented the concept more 
literally, putting the driver at  one end of a 12" diameter  Sonotube 
concrete form tube, and cutting the exponential opening down one side of 
the tube wall.   It would be really interesting to see how this simple 
looking concept actually works!  John Karlson obtained US Patent No. 
2,816,619 for his speaker design and made a point of warning would-be 
copycats in his articles.   You have to wonder if like Edwin Armstrong 
and other inventors he may have spent more energy protecting his design 
than in making money from it, since the Karlson Company doesn't seem to 
have survived into the 1960's.

73, Bob W9RAN