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Re: Crossover Frequency vs. Slope Question for Ribbons

"Thanks for the explanation and the schematic .... unfortunately, though, without the driver resistances and the inductor values, I can't model the Flatline XO in lspCAD for you."
Thanks for trying. I don't know the inductor values due to my lack of documentation for these speakers. I suppose I could measure the DCR of the drivers if I can find the time to spare, but the need for the values isn't particularly pressing just yet.

"Now, just to correct a few things you said:

1. Your 69" ribbon is not "planar magnetic". I suspect you've been reading some Magnepan marketing blurb here ... the true ribbons on the 3-way Maggies are not planar magnetic either! :-)) They are folded (pleated) ribbons like I suspect yours are.

It's only the smaller/cheaper Maggies which have what Magnepan call a "quasi-ribbon" which are planar magnetic."
I made a point to mention "(not planar magnetic)" as I've seen how often marketing hype claims planar magnetic/magne-planar designs to be ribbons when they're not. It's a bit of a pet peeve of mine when that happens. Technically, the ribbons on the Flatlines could be called "quasi ribbons" as they appear to be Kapton backed, but otherwise they're only attached at either end and suspended between two powerful columns of rare earth magnets. (Funny story about that how when I brought these speakers home, I had trouble prying the ribbons up due to their attraction to the metal in my truck bed.)

"2. Re. filter slopes ... the ribbon, yes, is a 1st order HP slope. From what you've drawn, though, the mid-range seems to have a 2nd order LP slope (where it crosses over to the ribbon) and and no HP slope where it takes over from the woofer. So the speaker relies upon the natural acoustic roll-off of the mid-range driver for this crossover point?

The woofer has a 2nd order LP slope."
As I mentioned in my other reply just a little bit ago, the review made a point to note that these were 1st order crossovers. Looking at the crossovers and the schematics, they look to me to be 1st order with a Zobel network behind to correct impedance changes over the frequency range. That lack of an HP on the midbass does bother me, but as I said I kind of hope that it's accounted for with the cabinet geometry (tall 6' cabinet with a narrow baffle and side firing woofer).

"As you say, monopoles don't match well with dipole ribbons but I'd have to say you are entering into a difficult integration exercise to rework your speakers into something that sounds good. Yes, if the ribbons currently go down to 350Hz with a 6dB slope then you should be able to take them down lower with a 12 or 24dB slope but whether this sounds any good or not ... you'll have to see!! And 100Hz is probably pushing it"
Well, that'd the fun of it for me. I typically do tweak my speakers both to learn and to make them perform better with my system in my room. I'm just too picky, I suppose and am rarely happy with stock form. The thing about 100Hz was that figuring theoretically perfect slope, provided I'm not totally wrong about the basics (and this thread is to check my assumptions), the output of the ribbon with the 6dB slope, down 3dB at 350Hz (making the beginning at 470Hz) should be down 24dB at a mere 29.375 Hz whereas with a 24dB/oct slope it'd be about the same at a xo freq of a mere ~60Hz. Now, this is figuring an ideal driver and I doubt the ribbon would have much usable output down that low (even though being so long it already has a very low resonance frequency). So, why couldn't it be possible to put a steep slope down low and still have great results? (Ignoring the nastiness higher order crossovers can create in the response.)

"I suggest if you really want to do this experimentation you should:
a) buy a cheap digital crossover which enables you to easily change crossover points and slopes ... and then simply listen to different setups to find the one that sounds good.
b) try using the bass and mid-range drivers in a dipole arrangement (ie. no back to the cabinet). This might mate better to your ribbon?"
I'm strongly considering one of the Behringer offerings for A, but for me that's a bit expensive. I'm a budget scrounger by necessity, not choice meaning I really lucked out with these speakers. Meanwhile I am in the process of building a tubed crossover kind of like a poor man's, featureless Marchand XM126 (first DIY electronics projec in a few years, so I have much to relearn). It'd only require the swapping of a few resistors and capacitors to change the xo frequency. I could use it once I get it built to experiment with. I'll admit that ideally, it'd be awesome to be able to use just the ribbon with a subwoofer base, which might be possible with my smallish room and low listening levels.

For option b, I could try that, but I'm just not that big of a fan of cones. I did try something similar to that by jury rigging my old pair of Magnepan MG-Is in place of the midbass driver and it was an astounding improvement. So it'd be hard to convince me now to stick with the cones.

"Finally, you say you might be able to get hold of a pair of Magnepan Tympani bass panels ... do these by any chance also come with their mid panels? I'm keenly interested in getting hold of a pair of Tympani IV or IVa mid-range drivers, to add to my IIIAs."
I believe that they may be 1Ds, in need of a lot of repair I might add, so I'm afraid they might not have what you need. Sorry.

Whew, I have such ambitions, but such a terrible amount yet to learn.

- JP


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