High Efficiency Speaker Asylum

RE: Whittling K-Tubes

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This Post Has Been Edited by the Author

In Reply to: RE: Whittling K-Tubes posted by kenpeter on September 25, 2007 at 12:55:57

how did you draw such smooth curves?

here's an old K-post from Job Ulfman's Karlson Speaker Project forum by Dave Young - Carl N. thinks Dave's assessment regarding rear chamber is wrong ....

"I have built and used various Karlson couplers for PA since 1983. There have been 15" and 18" woofers in 2'x2'x3' Karlsons of my own design. For a while, I used X-15's for midrange with very
drastic equalization. I have used the Tube on top of a 12" Altec for small jobs. I have also made a 2" Tube coupled to a Renkus-Heinz 3300-8 for outdoor use. There are also some 12" coaxials in
use with a K-coupler for the highs.

As a low frequency cabinet, the Karlson is usable to 35hz with low harmonic distortion. Like any enclosure that depends on porting to augment the bass output, Theile-Small parameters have
to be taken into consideration. I have yet to measure anything of comparitive size that came close. They get ugly above 175 hz. and require a crossover set from 100-150 hz. The key to its low freq.
performance is the coupled front chamber. The increased air pressure loads the cone and dampens it. A front loaded woofer and a horn loaded woofer operating below cutoff doesn't have that advantage. Twice I've measured the 3rd harmonic of 40hz(120 hz) louder than the fundamental with 100 watts feeding the speaker. The Peavey FH-1 and a Yorkville 2-18 with RCF's. When the 1504-4 Black Widow was tested in a 12 cu. ft. Karlson, the 3rd harmonic
distortion went from 103% to 8%. I didn't have the Yorkville long enough to switch speakers.

The Karlson does add coloration to the midrange due to the reflections inside the front chamber. John was aware of the problem and figured if the interior panels were curved, there would be fewer sound waves reflected back into the cone. The X-15 is curved above the baffle but not on the sides. It uses three seperate panels above the baffle that are very difficult to cut
and fit properly.

I have an AP-100 that has been used for testing outside the office.
There is some coloration due to the parallel side walls. Amazing horizontal dispersion. The concept works but needs to redesigned to utilize the curved reflectors. The K-coupler has potential as a mid-high unit, but needs alot of R&D to get there.

As to the K-couplers use for high frequency propagation, if offers advantages and disadvantages. When a horn is coupled to a compression driver, there is a noticable increase in midrange
volume. When a K-coupler is attached to the same driver, the change is not as dramatic. The horn is easier to install in a cabinet with its flat flanges. The Transylvania Power Company's
Tube requires an added bracket(see Ernst Beck's article) In order to work properly it needs to be tilted back as the main axis of radiation is 35 degrees below 0. The horizontal dispersion is
very broad. And if you do mount a Tube with the flange flat to the baffle, it will be constantly getting hit and compromising packing in a car or truck. The 2" K-coupler was used on top of a front loaded 2-12" mid box. When the boxes were used outdoors, there were high frequencies present in the area in front of the stage with the cabinets on eighter side of the stage. This didn't happen when I used horns. The highs projected well into the field.

The sound quality of the coaxials improved when the horn was replaced with the K-coupler. However, not every coaxial speaker is designed with a coupler in mind. Again the horizontal dispersion improved. One was installed into a small monitor and you could stand 10'away at 80 degrees of axis and still hear highs.

In 1985 I redesigned the K18 as a 3'x2'x2' box with 2 casters on the lower back and 2 handles on the upper back. A smaller enclosure had outperformed a Cerwin Vega B36 in terms of LF extention and harmonic distortion. It was a good compromise for cutting 4'x8' sheets of plywood, transporting in vans and station wagons, and stacking in a multiple cabinet PA system. Best results were obtained using 15" pro woofers. Think about it. The low frequency cutoff is determined by the TS parameters and the port tuning. An 18"EVM has a VAS of approx. 17 cu. ft. and a Fs of 34 Hz. A 15" EVM with a B cone has a VAS of 8 cu. ft. and a Fs of 41 Hz. Put each in a 7 cu. ft. enclosure and see what happens. The 15 will produce more output at 42 hz than the 18 because its fb is lower. according to some tests done on April 4, 1987 at 100 watts input, the EVM 18 produced 117.5 db at 65 hz and 109 db at 40 hz. The EVM 15B :: 119.5 :: 65 hz & 115 :: 40 hz. So the design approach is to do the rear chamber first, the overall size second, the taper third, and the front chamber fourth. Use a driver with a Qts of .3-.35. JBL 140's and their like do produce a lower f3 but at the expense of reduced output below 80 hz. That box had a 20 db hole at 250 hz,. sounded ugly if the crossover was higher than 150 hz, and had your typical for a Karlson rough frequency response above 300 hz.
I had better sucess for bass players using 2, X-15 cabinets stacked with the bottom enclosure inverted.
Good Luck
David A. Young"

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