Dali 8008 Up-Grade
Copyright 2008 Troels Gravesen
CROSS-
OVER
AS-IS
CROSS-
OVER
NEW
MEASURE-
MENTS
CROSS-
OVER
KIT

As mentioned in the HES-I article, my friend Michael has a pair of Dali 800s, making good partners for his Joplin 2A3 PP amplifier. This amp delivers some 8 watts per channel and has an unexpected firm grip on the Dalis. Having two bass drivers, presumably tuned differently, our main suspicion was that the Dali800 had an unusual even impedance profile, in particular in the bass region despite an overall 4 ohms impedance.

One of the ribbon tweeters thought time was up and we decided to install new Vifa XT25TGs in replacement of the Foster cone tweeter and Foster planar super-tweeter. MDF inserts were made for the new tweeters and time was ripe to take a closer look at this Dali 800 speaker.

Taking the Dalis onto the test-bench proved to be slightly embarrassing, because we had both found the Dali 800 a fine and easy-to-listen-to speaker with properties that would easily compete with many modern designs. We both miss the classic Vifa M21 bass drivers (with the light-weight paper cones and narrow suspension) in current Tymphany driver range. This bass driver has punch and drive and the frequency response has a smooth roll-off making crossover work very easy for diy'ers.
Same thing for the M13MG mid driver, where the only current substitute is the SEAS MCA15RCY mid-driver. Smooth and extended. We both love (good) cone tweeters due to the large membrane area and easy integration with other paper cone drivers. I may be old-fashioned by not thinking the classic dome tweeter is the best thing sice sliced bread, but from working with the
Peerless CT62H pp cone tweeter and the JBL LE26 tweeters I've kind of rediscovered the classic cone tweeter. Not that many around anymore now the Peerless CT62H has been discontinued.

 

The Dali 800 crossover turned out to be quite a mess. I can't believe Dali ever launched a speaker with a crossover like this. The choice of drivers is excellent, the combination of an 8" and 6" driver for bass is not a bad idea at all (with the lower bass close to the floor producing significant amounts of bass due to room-gain), but the crossover must have been made at the desk and never put on the test bench.
Due to height these Dalis are not easy speaker to measure and from examining the crossover in LspCAD, it turned out that we have the P17 - close to the floor - doing well into the upper-mid area, thus blending with mid-driver at tweeter, producing serious crossover lobing unless we measure at long distance. Ideally we should measure at 3+ meters distance, thus my examination of crossover performance is based mostly on LspCAD simulation, which seems well in accordance with a few measurements at 2 meter distance. More on this later.

What was expected to be a couple of hours work on tweaking the tweeter crossover turned out to be a completely new crossover for the Dalis, so here we go.


Dali 800 with new tweeters installed.


Left: Dali 800 drivers and crossover. Right: Dali 800 crossover close-up.


Dali 800 crossover, as-is.


Dali 800 crossover as-is.

Dali 800 measurements, as-is:
(planar super-tweeter not included)

Red and blue was what was seen on the screen the first time I measured the Dali 800 at tweeter height, 1 meter distance. I thought something was wrong with the CLIO.....
Moving the microphone up and down didn't change much, so initially I though the mid was connected with wrong polarity but changing the polarity of mid (and tweeter) didn't make things better. "Hmm....we'll deal with this later", I told Michael. I wanted to see the impedance profile of this speaker to know why 8 push-pull watts is more than enough to drive this speaker.

(Disregard green graph = one of the new crossovers tested)

Above the impedance of the Dali 800, as-is. Indeed an easy load! Flat in the entire 100-20000 Hz range and with modest phase angles in the bass region. No wonder the Joplin doesn't complain when driving these speakers excessively loud. 4 ohms minimum.
Measuring the impedance of the P17 and M21 revealed same vent tuning, around 32 Hz. Hmm.... I had expected different box tunings to smooth the impedance well knowing this may impact the impulse response negatively, but don't expect commercial speakers to fit in with all nice math associated with speaker building.

Frd* and zrd* files were created for all drivers to start simulation and see what this speaker was all about.

*: frd and zrd files are raw data files of frequency response (including minimum phase) and impedance of drivers driven without any crossover attached. These files are imported into LspCAD for crossover simulation.

Above simulated frequency response at 1 meter distance. Not too well in accordance with actual measurements due to P17 and M21 being connected in parallel for creating the response files. Having the P17 some 25 cm lower than the M21 probably makes crossover lobing more severe than seen here.


Simulated response at 2 meters distance.


Simulated response at 3 meters distance.
This starts looking like 1 meter readings at tweeter height.


Simulated response at infinite distance.

The rationale behind this exercise is to see what this crossover does to the overall performance at different distances. Except for the tweeter all drivers are run from 1st order crossovers and as said, crossover lobing is expected to be severe - and indeed it is.

As can be seen, the tweeter response is way too high and I wonder how this would have looked with the planar included. We know that treble sells, but this seems a bit over the top.


Dali 800, new crossover


Low-budget renovation. Some of the original coils were un-wound to suit mid and tweeter section.
Two new low-ohm coils were used for bass drivers.

New Crossover Kit


Complete crossover kit available at
Jantzen Audio.
Price approx. 850 DKK/114 EUR incl. VAT + shipment.
Vifa tweeter not supplied.


New crossover made for client from the Jantzen kit.


Response from another client:

Hei Troels. Takker for fine delefiltre. Lyden ble utrolig mye bedre med ditt oppsett.   Mvh. Arne/Norway


Measurements, new crossover:


Left: Summed response and response from individual drivers. Points of crossover around 800 Hz and 4 kHz.
Right: Impedance of system from new crossover. Not as smooth as the original, but Michael's 2A3 PP didn't object.

Conclusion

First of all the Dalis need to be lifted some 10-14 cm from the floor. Having the M21 handling most of the midrange the overall performance is improved from lifting the whole speaker (- sorry, forgot to take a picture).

Setting up the speakers again was a pleasant experience. The level of transparency is vastly improved and there's an overall balanced sound from the modded system. These Vifa drivers have so good qualities I don't hesitate to recommend a full renovation; that is:

1. remove all drivers, crossover and damping material.
2. add bracing to the rear panel.
3. add bitumen pads to the M21 cabinet. (the cabinet is mostly made from decent 25 mm chip-board materials.
4. use cored, low-resistance coils to the bass section to maintain sensitivity.
5. good caps would take 2 x 0.47 uF, 2 x 4.7 uF, 2 x 8.2 uF and 4 x 10 uF and possibly set you back some 200 US $ excl. VAT depending on brand and supplier.
6. re-install damping material and add another role MDM3 to the M21 driver enclosure, half at top of the cabinet and the other half right behind the driver - on top of the crossover.
7. Buy a pair of XT25TG-30-04 tweeters and you have a speaker that will outperform most modern 2-2-way systems.

Enjoy!


The Foster cone and planar tweeters

Left: SPL response/2.8V from the two cone tweeters (red and blue). Planar tweeters: Green/purple. Right: Impedance plot of cone tweeter (red) and planar (blue).

Now, this planar is marketing gimmick and the best you can do is disconnect it. Throw it out! It's a phzzzz-thing supposed to caress you eyes more than your ears.


Disconnect the planar and use the cone tweeter like this.


Simulated response from Foster cone tweeter set-up.
Not tested and won't be, but I'm sure this will work fine.

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