pfm Ogre I

[James]

Hi Stefan,

I've had a quick simulation on LspCAD based on the published T/S parameters of the drivers. The tweeter seems to be well behaved, but the woofer is showing a mistermination spike between 700Hz and 2kHz, which may explain what you're hearing. I think the SS woofer needs a zobel to flatten its impedance, and a higher-order electrical filter to match the 4th order roll-off of the tweeter.

I suggest the following filter for the woofer, in order from amp to driver:

series 0.75mH (low DCR)
shunt 20uF
series 0.25mH (low DCR)
shunt 6R + 30uF (zobel)

Again, this is almost speculative as I don't have measurement data. If this fixes your problem, I can finesse the HP filter to make it more complementary. But one filter at a time.

James

 

[orangeart]

Great, I'll start there then. Could you expand on the 'mis-termination spike' I've not come across that before. Is it similar to signal reflection in un-terminated video systems?

Fatmarley can help me get some actual measurements once we have a good test network figured out.

Presumably the tweeter padding resistor seemed about right then?

Thanks again.

Stefan

 

[orangeart]

OK

Are these parts OK? I'll order them up if they are.

.25 coil

scroll down to the part number AC-JA03-0205 ( presumably that is low enough DCR ? It might not be the best coil in the world but to get us going it should be OK?

.75 coil on the same page

scroll down to the part number AC-JA03-0205

I'll get some ansar supersounds for the caps as they aren't to crazy expensive while we sort this out.

Stefan

 

[James]

Could you expand on the 'mis-termination spike' I've not come across that before. Is it similar to signal reflection in un-terminated video systems?

I'm not familiar with video systems, but what I refer to is the effect of a non-linear impedance on passive components. I'll take a screenshot of LspCAD when I'm home later tonight.

Fatmarley can help me get some actual measurements once we have a good test network figured out.

It's better to do it the other way around. What I really need is measurement of the unfiltered drivers, in-situ, taken in both nearfield (for the woofer) and far-field (for both drivers) and their impedance data loaded by the enclosure. With good quality data, I can get you 95% to target.

Presumably the tweeter padding resistor seemed about right then?

Don't know, can't tell.

Are these parts OK? I'll order them up if they are.

.25 coil

scroll down to the part number AC-JA03-0205 ( presumably that is low enough DCR ? It might not be the best coil in the world but to get us going it should be OK?

.75 coil on the same page

scroll down to the part number AC-JA03-0205

I'll get some ansar supersounds for the caps as they aren't to crazy expensive while we sort this out.

Yes, they should be fine. The part number you listed for the 0.75mH coil is the same as the 0.25mH coil, but I presume they are from the same Jantzen series.

James

 

[orangeart]

Great, I'll get those parts and see what happens. I'll also try and arrange to get the raw in box driver measurements. Fatmarley has got all the requisite kit. Hopefully this filter will get me in the ballpark for weekend listening It would be great to see any screen shots you care to post. When this is all working I intend to write it all up for other folk to follow more easily.

Thanks again James

Stefan

 

[James]

Could you expand on the 'mis-termination spike' I've not come across that before.

Stefan,

This image from LspCAD should explain what I mean.

James

 

[orangeart]

Right, been a long time since I visited this thread. Since then I have changed my digital front end completely and wanted to get used to the new sound before tinkering any further with the speakers.

Finally got round to doing Your tweaks James, here are some pics of the new crossover layout.

Well how does it sound?

Part way there, when I first listened I thought it sounded boxy, that was just 'cause I was so used to the previous sound. Actually the midrange response had just lessened and after getting used to it, the balance was much better, subjectively the bass was tighter and the treble more defined with more space. Much better all round. The speaker in general still has the same problem as before though, it still sounds very hard in the midrange, especially when in busier passages, it's ragged, fatiguing and sounds uncontrolled. So to some up some gains but not where it was needed.

James thanks for your time so far, if you would care to comment further I would be most grateful. I will contact FatMarley again and see if I can arrange to get some proper measurements to work with.

Oh and worth saying that I had a friend round at the weekend who is no stranger to great sounding kit (maybe not quite in the leage of DIY room stuff) He was VERY impressed with my setup, he did comment on the raggedness of the midrange but was blown away by the tunefull bass, shimmer on Cymbals, ease of reproduction and sound staging, they all seemed like a massive step up for him!!

So nearly there.

Stefan

 

[orangeart]

oh also meant to check the polarity of the drivers for the new circuit you sent James, I assumed it was the same?

Stefan

 

[James]

Stefan,

The only way to nail this properly is with measurement data. Anything else is shooting in the dark. I'll need to check my LspCAD files for polarity.

James

 

[orangeart]

Hi James,

Thanks again, I've tried to contact fatmarley who offered previously but he's not logged in for a while. If that doesn't come off I'll find another way.

Stefan