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Re: Crossover Frequency vs. Slope Question for Ribbons

Posted by andyr (M) on October 23, 2006 at 16:36:39

In Reply to: Re: Crossover Frequency vs. Slope Question for Ribbons posted by JP van Son on October 23, 2006 at 11:23:53:

Hi JP,

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.

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.

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 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.

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?

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.

Please let me know! :-))

Regards,

Andy

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