Progress today
Routed the two slanted back pieces. First time using this kind of router.
There are several fillets to make and I used square and triangular standard parts to make what I needed.

Added the two braces as per building instructions, this is looking down in the pipe with the front facing down

Then I screwed and glued the corner fillets in place, while this is setting I am taking a break to be sharp before the critical assembly of those tricky back pieces.

The pieces  will be predrilled and dry assembled once to make sure that all meet up resonably well.

This graph is what started me with folds and harmonics. As you can see a single fold gives the best suppression of harmonics.  Tyrland had both driver and pipe opening on the top surface. In my case I have the driver on the forward face and the opening at the top rear. Measurements are at the center of the pipe opening and 1-2 cm in front of the dustcap of the driver (NF, near field)

I start with the IMF folded one.  Drivers are two PP cone 5” woofers with Fr of about 60 Hz. The Peerless one has a Q of 0.5 and the Taiwan one a Q of 1.0. Pipe:22 cm wide and taper from 20 to 5 cm.

Pretty much as I expected. 3-7^th harmonic is clearly seen. Note that the peak output is at 40 Hz while the dip in driver response is above 45 Hz.

Here there are peaks all over 500-1500 Hz! Note that the peak output is below 40 Hz while the dip in driver response is above 45 Hz.

Now it is time to investigate that pipe folded once that is supposed to intrinsically tame that third harmonic. . Pipe:22 cm wide and taper from 20 to 5 cm.

Lets start with the Peerless again

  Note that the fundamental has more of a peak and it also matches the dip in driver response. The  3^rd and 5^th harmonic is the same and the 7^th is worse. Not what I had hoped for.

Very broad fundamental and harmonics that is no improvement.

Then I have the Daline fold. That is a top chamber and then 3 equally wide pipe section of 5.5cm  with the opening at the very bottom of the rear panel.

Here the Q of the fundamental is lower, harmonics similar to the IMF fold.

Very low Q fundamental and some peak suppression in the 500-800 Hz range.

I do have impedance measurements as well but then I will overload the post.

It does seem that the harmonics is not only due to pipe geometry but that features of the driver comes into play.

There is obviously a lot to learn. More to come…

The aim of this study is to evaluate different damping material of a box of 15 L with a KEF B200 driver.

Materials tested

1.  Fine BAF salvaged from loudspeakers over the years. Tested at 0, 100, 200, 300 & 400 g giving a packing density from 6.7 to 27g/l =(kg/m3). Firmly packed at highest density. Evenly distributed at all tests.

2. Pharmacy type cotton.Tested at 0, 100, 200, 300 & 400 g giving a packing density from 6.7 to 27g/l =(kg/m3), some space left at highest density. Evenly distributed at all tests.

3.  Coarser BAF sheets for bass reflex boxes 83 gram each (Biltema) tested at  0, 83, 166, 249  and 332g (the 5th mat in the pack did not fit) Uneven distribution with the sheets against the back wall and then piling forward

4. Open foam one sheet 50 mm thick covering the back of the box was 100 g and only one of them fitted.

To to conclude different types of BAF and Cotton and at least the foam I tested does seem to give similar results in lowering the Fr and reducing the Qms that is increase resistive losses.

Next time around, if there will be one!

Having  the driver the other way around so that the magnet structure does not interfere with packing the box. Perhaps also test the african sheep wool that I have.

Final notes about the Kuben horn

I tried different drivers for the Kuben, typical horn drivers offers far higher sensistivity than a classical closed box type HiFi driver like the Gamma LA-1231. The Gamma on the other hand offers better balance between the 50-100 Hz octave output rellative the the output above 200 Hz than the PA driver. So for home use something along a "normal" HiFi driver might work better than a classical horn driver.

With the DorSpen I could extend the bass response by adding a serial capacitor, so why not try it with the Kuben and the Emminence driver?

The impedance is lowered below the resonance frequency and increased above it, this should work!

No it doesn't!
I have no idea why at present. Now the Kuben horn resides in an other garage than mine, so I have no way to work further with trying to straigthening out that question mark. Time to do some research about resonance patterns in pipes of different folding geometries and other basic stuff.

I have gone back and fourth with the dome tweeter. Now I will make a try in modifying a Swedish vintage dome Luxor that hopefully will be intrinsically flatter than the KEF T27 and the Seas H086 both of which I have been less than happy. With a good response it is less of a problem getting the crossover to work well. If I can tame the peak at 10 kHz I should get a good driver all the way from 2 kHz to 20 kHz.

I used omnimic to measure how the KEF 104aB filter worked with my drivers, unless stated otherwise distance was 50cm and on axis of tweeter.

The high pass filter section of the filter works well but the boost above 10 kHz is notto be found.

With regard to the woofer section it looks as expected, as measured on axis of woofer.

Adding the two resulted in a severe dip in response- 10-15 dB, black curve
Reversing phase on tweeter reduced the dip by more than 5 dB brown curve
Removing the L2 (0.6 mH) reduces the dip further, green curve.
I also tried removing the parallell cap to get a 6dB filter, and while it eliminatess the 2.5-3 kHz dip it also lowers the 500 Hz to 2 kHz range to much

 Measuring at 1 m gives similar results, with the dip and a too hot T27
The T27 is not flush mounted, edges are not rounded and there are some large bolt heads sticking up that holds the woofer so some of the peaks and dips really is not the drivers

I will have to take a look on how the competition in my collection of drivers measure up compared to the T27.

The T27 has a peak at 10 kHz as well as dropof above that when crossed over by a 18 dB filter, KEF then made a more advanced one.

So this is what it looks when I connect crossover built as this. I use a 2.5 mH coil and low resistance in series with the bass driver.  All caps are plastic not electrolytics.

This is the result for the tweeter section, how it will work I have to measure.

This is the woofer and woofer plus crossover, there is a minor rise in system Q from 0.95 to 1.05

The work will be to match the woofer and tweeter, I am pretty confident that the woofer section will work, but not so sure that the tweeter section will tame the T27. Time will tell.