Here are the article in HFN &RR that inspired me to buildning the DCH (Decca Corner Horn)

As I hade low expectations I built them in 11mm OSB, now I have found veneered ply at quite good price. So perhaps, perhaps!

The Voight pipes I have seen have had a cross section area at the closed end from 0 to perhaps 50% of the surface area of the drivers cone. In this case it is 150%, then the negative taper around the driver and the final constriction of the opening that is both a 19mm high slot around the sides and read but also a 100mm long facing the flat front? I have been told that this DIY version is a simplifacation of the commercial Decca speaker, but as far as I can tell the images of decca speakers in the net looks like mine,

They are quite wide and high but as they are shallow and fit in a corner or flush to a wall they are less dominating than sheer size suggest.

I will get back with posts on various 8" drivers, With Fr from 30 to 100 Hz and Qts from below 0.3 to above 1.0. The DCH was intended for a fullrange driver but one could equally well use a conventional 8" unit and tweeter/tweeters. Perhaps even a 10" unit.

The Decca corner horn is the second to the left.

I have lagged behind in updating the blogg

This is how the finiched box looks like there is a cutout to clear the magnet in the internal baffle. Note that there is no damping material att all added to the cabinet. The cabinet is not flush with the floor but stand on 19mm high feet.

Turned the right way with the driver facing the wall or corner it looks like this

And now for some measurements. I started with a Philips 9710 fullrange driver. It has a 10 dB lift above 1-2 kHz on axis and sound really bright and piercing in that position.

Black is with driver facing forward measured 1 m away at driver hight. Some of that lift can be seen around 1 kHz but the angling upwards tames it (Black trace) facing the wall (red trace) is more even if I would apply third octave smoothing.

In the corner boost below 200 Hz. Both positions give good output to about 40 Hz.

I fully expected a terrible boxy sound from that flimsy cabinet with no damping material. To my surprise it sounded really good. Sure the lower half of the front vibrates a lot, as can be felt by hand, when playing loud. The rest of the cabinet vibrates less.

If I look on the time domain, with the driver facing forward, with two sets of near field measurement of frequency of amplitude and time domian respons it look like this:  The 9710 has a double cone and seem to be sensiteve to the precise location of the microphone, that is the reason for very different frequency response in the top end.

 This is the pipe output from empty pipe and from having the first section of the pipe filled with rolls of BAF fibers

Near Field response of the Philips 9710 in empty pipe

This is two ways of looking at time domain response the lower one is decay in milliseconds the upper one is the same data set but decay is expressed in cycles instead of ms. This slant the graph to the high range as there are more cycles per millisecond the higher the frequency. It is not a pretty sight but not so bad either. The slow decay is quite evenly spread.

Next I added 3 rolls of BAF (Biltema) of 82 grams each. Two rolls were put into the closed end on each side of the center brace. The third roll was cut up to fit covering the the back and side walls behind the driver ( when driver is facing forward)

At this slightly different measurment position I got a peak in the 8 kHz range compared to previous measurement.

Time domain wise it is huge improvement. This rather crude sets of measurements suggests why it can so good even without damping material with good supression of the third harmonic of the pipe and decent higher harmonics. Adding bulk damping up to the driver improves the time domain response a lot but was a let down with regard to the harmonics. The optimal placement of damping material should be at pressure minima/velocity maxima of the pipes fundamentals.

I will try to get some decent images to post the drawings of the orginal article by Ralph West in HFN &RR about the Decca Corner Horn.

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.