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.