Crossover help required

[zebra100]

Hi all,

I have acquired a large pair of floor standing speakers with a view to rebuilding them. One of the previous owners had them as a development pair and never really got round to finishing them. At some stage, the cabinets have been bashed and will need re-finishing, probably filling and re-spraying over the veneer. They are marked up as "DIVINI LARGO10-F" but I think the original model is this beast from China (http://www.madeinchina.com/415511/P5...r-System.shtml)

It is listed as a 4 way, 5 driver, front slot ported speaker with an ambiance rear firing tweeter. The rear tweeter is no longer fitted (removed by previous owner). The 2 rear facing bass drivers are supposed to drive the front slot port, but don't seem to work well at all. The front firing 5" mid driver is boxed in with the rear tweeter (no longer fitted) in the top 1/4 of the speaker. The rest of the box holds the 2 rear facing 6 1/2" bass drivers and the 28mm front firing soft dome tweeter. Also in the bottom box is the terminal plate and the crossover. The mid range and the front tweeter are half decent drivers. The 2 bass drivers are fairly poor quality (thin pressed steel basket).

I'm not sure if the crossovers are the original items. The PCB's are marked "Unichina Electric, UC-001. They have been extensively "bodged" and will need replacing. The board has 2 ferrite cored inductors. One large, and one about half the size. I don't know the value, but I will try and get hold of an inductance meter from somewhere. A couple of nasty radial electrolytic's(150uF & 6.8uF), 4 half decent polypropylene caps (33uF, 3.3uF & 2 1uF) and a big resistor (3ohm, 5W) finish the board off. They're cracked, bent, warped and dented. I think they're wired up as a 4 way x-over, but I can't be sure.


I have some new PCB's for the crossovers (from Wilmslow Audio). My intentions are to rebuild the speakers using the original components for now (due to the cost). The drive units have no markings on, so aside from putting a multimeter across the terminals and getting a DC resistance, I don't know what the nominal impedance is.

The crossover is a bit of a puzzle also. I am rebuilding the speakers as a 3 way instead of the original 4 way. There are 2 separate outputs for HF drivers on the original PCB. One for the dome tweeter, and one for the ribbon (which will not be refitted). I can't work out which is which. Any ideas?

Does anyone have any experience of the large crossover PCB's from Wilmslow as I can't work out where to start?

[sreten]

Hi,

Somethings about your treble section seem to be wrong.

The bass section seems correct, 2nd order lowpass.

The midrange inductor is correctly in series with the mid but should
not be in series with either treble unit, which in the diagram it is.

The 68uF capacitor should be in series with the midrange.
The 33uF capacitor appears to be too big, unless its actually
in parallel with the 68uF capacitor, which makes some sense.

If the all the above is true, then 2 is the hf ribbon and 1 the tweeter.

Re check the HF wiring.

/sreten.

[zebra100]

Thank's Sreten,

Like I said in the original post, the crossovers appeared to have been extensively bodged. In this configuration, they are very bass light, and the mid/treble don't seem to intergrate very well. That could be down to the cabinet design, but I don't think that is the case.

I may have to have a complete re think with the design. Do you have a "Textbook" Crossover design that I could use as a starting point?

[sreten]

Originally posted by zebra100

Do you have a "Textbook" crossover design that I could use as a starting point?

Hi,

You mean the "the spawn of the devil" for the totally clueless ?

The bass crossover point is somewhere around 200Hz, which it
would have to be as the drivers are rear facing. 68uF||33uF is
also ball park for in series with the midrange as the high pass.

Assuming the midrange inductor is also a ballpark value this
also goes in series with the midrange as the low pass.

Ignore the 1uF ribbon connection HF1 could work with your
tweeter, i.e. use 3.3uF / 3R / 1uF as shown in the diagram.

If the above sounds really bad I do not think a textbook c/o
will help much at all, you would need to do it properly IMO.

/sreten.

[tinitus]

Strange schematic...are you sure you have it drawn the way it is...is it a kind of hybrid series/paralel filter

[zebra100]

That's exactly how it was. Never seen anything like it before.

I think the guy who had them as a developement project didn't know what he wanted them to be, although some of the caps are decent quality.

I did say they were bodged!

[zebra100]

This is the front!

Sreten,

Doy you have a diagram for the "Spawn of the devil" textbook crossover? I need a starting point, as the only crossover experience I have is modding a 2 way.

Thank's

[sreten]

Hi,

It seems I misread 6.8uF as 68uF, in this case the diagram
looks "correct" with a 2nd order low pass on the midrange.
But the 33uF midrange 1st order high pass looks too high.

The only strange thing is the HF(2) output after the inductor.

Try this :

Big inductor in series with your bass units.

150uF (parralelled with 33uF if you want) in series with the midrange.
Smaller inductor in series with the midrange. 6.8uF in parallel with mid.
3.3uF + 3R in series with the tweeter. (add the 1uF to taste.)

http://www.diyaudioandvideo.com/FAQ/XOver/
It tells you nonsense most of the time, unless you understand that.

/sreten.

[zebra100]

Thank's,

I'll give it a try.

[zebra100]

If I understand correctly, something like this?

As the bass drivers are rear firing, should they be connected reverse polarity?