The time domain plots clearly showed that getting some damping around the driver is a good thing. Also some vibrations in the OSB could benefit from damping. So I took 12mm bitumen impregnated softboard and glued 10mm felt to it. The sizes are 3 each of 400x120mm and 400x100mm. The final lenght of the boards were trimmed to size by 20-30 mm if needed.

One 100 wide board was glued to the cieling of the cabinet (I felt vibrations there before) The front wall was covered by one 100 and one 120mm piece ( seen far back in the picture below. One 100 wide pice was glued along the back of the closed end below the brace. Then two 120 mm wide pices was glued to the dividing baffle on the side facing the closed end. Finaly the top of the dividing baffle with the cutout was covered with a layer of felt. All gluing was done with silicone glue.

The nearfield response does not suggest any major changes perhaps a slight flattening of the dips at the harmonics.

Now for the pipe

At the pipe and large changes occur even with this very modest amount of damping material.
The sharp peak at 120 Hz is reduced by about 6 dB
The huge peak at 200 is marginaly affected
The peak at 350 Hz is reduced by 9 dB
The peak at 500 Hz is reduced by 4 dB.

I then put a damping layer in the front section by gluing a 60x40cm soft board below the front braces.  This time with ordinary wood glue as I run out of silicone glue.

If I stagger the pipe output with the orginal unlined in green, the lowest trace. Next up the red is with the lining around the driver. With the frontplate is at the top note that the brown trace, note that the trace is smoother than the other two.

If I alight the bass part of the traces on the big improvement was the felt and board lining. The added front board is icing on the cake and the knuckle rap test is much improved. The dip around 150 Hz is a bit flattend out by the front brace

So to conclude I recomend the design. Building it from scratch I would line all parts in the closed en by felt before putting it all together. The front damping is also a good thing to have.

I did some experiments with wool in the closed end but it is really tricky to get anything down there with the braces and the added panels and felt.

That 200 Hz peak is still there. The current opening is about 160cm2 I plan to block it and open a hole at the very back below the closed end. Hopefully this added 90 degree bend will reduce that 200 Hz peak... or not.

After that, it is time for an open baffle I think.

The odd men out of drivers

 This is a OEM driver from the Audio Pro 4-14 dipole speaker, A really good match for pipes and horns.
* Manufacturer:  From Audio Pro 4-40 loudspeaker
* Model:  Paper cone black=greenish color, paper surround with sticky green coating and chassie that looks like 1970s Peerless.
* Piston Diameter = 170.0 mm
* f(s)= 47.10 Hz
* R(e)= 6.65 Ohms
* Z(max)= 34.26 Ohms
* Q(ms)= 1.575
* Q(es)= 0.379
* Q(ts)= 0.306
* V(as)= 59.860 liters     (2.114 cubic feet)
* L(e)= 0.93 mH
* n(0)= 1.57 %
* SPL= 94.07 1W/1m
* M(ms)= 13.81 grams
* C(ms)= 0.83 mm/N
* BL= 8.47
Note the cleas peaks at the harmonics

Good matching with the pipe and good sound as well, the high sensitivity is noted

These are Pioneet TSE20, car speakers that I got as a gift. Fr 48 Hz and Q of 0.6. With the coxial arrangement I could not use the roll of masking tape I usually use for Mms and Vas determinations, but I expect the driver to have a high mass cone. Note the absence of peaks in impedance at the harmonics.


A good match with the pipe and a good sound as well. The tweeters does not seem to work so if I can remove them I can measure TS as well.

Last driver is a PA midrange/midbass driver the Fane Studio 8M. The magnet forced me to have the driver backward

* Manufacturer:  Fane
* Model:  Studi 8M
* Piston Diameter = 167.0 mm
* f(s)= 104.30 Hz
* R(e)= 5.77 Ohms
* Z(max)= 79.19 Ohms
* Q(ms)= 7.394
* Q(es)= 0.581
* Q(ts)= 0.539
* V(as)= 12.970 liters     (0.458 cubic feet)
* L(e)= 0.75 mH
* n(0)= 2.42 %
* SPL= 95.93 1W/1m
* M(ms)= 12.09 grams
* C(ms)= 0.19 mm/N
* BL= 8.87

The lower peak of the tuning is hard to find the 110 Hz is way higher.
Soundwise as evaluated by listening to the driver facing the wrong way. Very high sensitivity, a really brutal attach to transients, bass slam. Deeper bass is missing there is no weight to the bass

While I prefer this sound to the bass mumble of the B200 and the Seas TV-EW there are better drivers for quarter wave pipes.

I will have to do some damping to the walls around the driver so the time to fiddle with damping material is coming up.

The two worst drivers for the DCH I have found so far.

Two closed box drivers from well respected manufacturers. Both of them  good drivers in such closed boxes.
* Manufacturer:  KEF
* Model:  B200 SP1014
* Piston Diameter = 172.0 mm
* f(s)= 37.68 Hz
* R(e)= 7.52 Ohms
* Z(max)= 59.42 Ohms
* Q(ms)= 5.965
* Q(es)= 0.864
* Q(ts)= 0.755
* V(as)= 56.650 liters     (2.001 cubic feet)
* L(e)= 1.20 mH
* n(0)= 0.33 %
* SPL= 87.34 1W/1m
* M(ms)= 23.89 grams
* C(ms)= 0.75 mm/N
* BL= 7.02

* Manufacturer:  Seas
* Model:  21TV-EW
* Piston Diameter = 170.0 mm
* f(s)= 34.99 Hz
* R(e)= 5.99 Ohms
* Z(max)= 70.15 Ohms
* Q(ms)= 7.519
* Q(es)= 0.702
* Q(ts)= 0.642
* V(as)= 52.260 liters     (1.845 cubic feet)
* L(e)= 1.88 mH
* n(0)= 0.30 %
* SPL= 86.93 1W/1m
* M(ms)= 28.65 grams
* C(ms)= 0.72 mm/N
* BL= 7.33

The B200 has some inconsistent mode of measurements compared to the other drivers. The black reference trace is the 9710 (lowered by 10dB) and red for the B200. Note the 5 dB peak driver output at 65 Hz and pipe peaking at 60 Hz. This is how it sound boomy and booring.

 Cast chassi Alnico magnets and a rubber suround, and a lower Q than the KEF it looks like it would be an improvements, does it not

Frequeny wise the it is a similar story to the B200 but with a less pronouced peak of the driver at 65 Hz. Soundwise the difference in bigger. The Seas sounds much worse than the B200, the bass lines that stands out at all times brings a smile for a couple of minutes but after a couple of tunes it really start to become irritating. If I wanted to learn to play bass and wanted the bass lines to stand out at all times it would be OK but otherwise...

I have also tested drivers with similar high Q but with higher Fr and they fare better. They are not good but the combination of low Fr high cone mass and high Q really bring out the worst in the construction.
* Manufacturer:  Seas   
* Model:  21F-GW
* Piston Diameter = 175.0 mm
* f(s)= 57.87 Hz
* R(e)= 4.76 Ohms
* Z(max)= 15.09 Ohms
* Q(ms)= 2.971
* Q(es)= 1.369
* Q(ts)= 0.937
* V(as)= 42.030 liters     (1.484 cubic feet)
* L(e)= 0.70 mH
* n(0)= 0.57 %
* SPL= 89.64 1W/1m
* M(ms)= 14.62 grams
* C(ms)= 0.52 mm/N
* BL= 4.30

As I said not good but not to bad either.

* Manufacturer:  Philips
* Model:  AD8001W4
* Piston Diameter = 168.0 mm
* f(s)= 59.22 Hz
* R(e)= 4.16 Ohms
* Z(max)= 17.17 Ohms
* Q(ms)= 4.058
* Q(es)= 1.295
* Q(ts)= 0.982
* V(as)= 39.440 liters     (1.393 cubic feet)
* L(e)= 0.76 mH
* n(0)= 0.60 %
* SPL= 89.90 1W/1m
* M(ms)= 12.64 grams
* C(ms)= 0.57 mm/N
* BL= 3.88 

 Familiar octagonal chassi front, very common in high volume low price speakers in the 1970s

 Not a pretty sight with that lift 70-100 Hz. And while it's sound is not to good it is substantially better than the first Seas.

I do not know why the Seas TV-EW sounds so particulary bad. It has the highest cone mass and it could be that the cone that is twise the mass of the Philps exacerbate som vibration mode in the the lightweight cabinet, but this is speculation.

Some really good drivers from Peerless for the DCH
They are not the current stock but they are quite similar to other current Peerless drivers. Data is measured using Dayton Woofer Tester 3.
* Manufacturer:  Peerless
* Model:  850126
* Piston Diameter = 175.0 mm
* f(s)= 48.45 Hz
* R(e)= 6.00 Ohms
* Z(max)= 58.76 Ohms
* Q(ms)= 4.488
* Q(es)= 0.511
* Q(ts)= 0.459
* V(as)= 43.160 liters     (1.524 cubic feet)
* L(e)= 1.91 mH
* n(0)= 0.92 %
* SPL= 91.72 1W/1m
* M(ms)= 20.31 grams
* C(ms)= 0.53 mm/N
* BL= 8.52
*PP cone inverted dome looks like the CC line expected +/-5mm, rubber surround.

Impedance is pretty straight forward, tuning to 50 Hz.

The downward slope in the nearfield of the driver below 100 Hz indicated the low Q of the driver resonance and the good radiation resistance offered by the pipe. The dip in driver near field response (black) is centered at 50 Hz the irregularity is due to a room resonances.

This drver sound really good in the DCH, a very natrual easy balance in the music with both weight and slam in the bass when called upon.

The next one is also good but for some reason not quite as good to my ears at least.

* Manufacturer:Peerless
* Model:  831862
* Piston Diameter = 170.0 mm
* f(s)= 35.66 Hz
* R(e)= 3.19 Ohms
* Z(max)= 22.41 Ohms
* Q(ms)= 2.101
* Q(es)= 0.349
* Q(ts)= 0.299
* V(as)= 60.770 liters     (2.146 cubic feet)
* L(e)= 0.70 mH
* n(0)= 0.75 %
* SPL= 90.87 1W/1m
* M(ms)= 23.72 grams
* C(ms)= 0.84 mm/N
* BL= 6.97
Noninverted fabric dome and foam surround on this one.

The frequency response is exellent very flat up to 2 kHz, it also sound good, but not as good as the other one, why that is and if it will change with some decent amount of damping material in the pipe I do not know, presently.

The near field dip of the drivers in the DCH has had a strange shape, I had suspected that standing waves had something to do with it. Today I took measurements in an other room with the speaker standing on a low table in the middle of the room. Much better! A sharp symetric dip, textbook style

The tip of the dip is further 2 dB down off the scale in this graph. The difference in sensitivity between the 9710 and a Stridbeck/Tyrland is supposed to be 10 dB but it really sounds like 20 dB.  I have to get to work in that 5th harmonic at 200 Hz. But that will have to wait for a while.

Time to test a driver almost as old as the DCH. The Goodman Axiette, you can really tell it comes from the 1950s.  Designed by Ted Jordan.

I put a MDF rim around it to get a smoother surface than the OSB. Still the seal is really hard to get as the Axiette is made to be mounted from the rear of the baffle only.

This is the Thile Small parameters of the driver, I have included the curve to show those wiggles in the curve that are intrinsic to the driver. A high Q of 1.0 and a very low moving mass of only 8 grams.

Then the frequency response as measured in nearfield of the cone and at the opening of the pipe.

What I see is a pipe output that peaks well above 50Hz the tuning frequency and an output that is 4 dB below that and sloping around 50 Hz. There is also a hump in driver output at 100 Hz. The 100 Hz hump add some "bassyness" but it lack weight and impact. This is a bad combination.  I am not totaly sure that I got all leaks so some of the flaws might be reduced by having the Axiette properly mounted but I think the high Q will allways lead to a peak around 100 Hz, at least if the DCH is damped close to the original.

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.