<AUS> B3S active crossover design - Value woofer suggestions?

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Hi all,

I'll preface this by saying that I've never built a speaker system before, not even a passively-crossed one, but I think I've got a pretty good handle on the theory at this point, and I understand opamp based active filters much better than I understand passive crossover networks.

I've been mucking around with the idea of doing a triamplified design with the HiVi B3S, using an as-yet unselected woofer crossed (4th order Linkwitz-Riley) at 150hz to the B3S, crossed at 3.5khz or so to a tweeter locally available through Jaycar, which I believe may be the HiVi Q1N.

OK...so my understanding of Zaph's frequency and harmonic distortion graphs is that by crossing relatively high at 150hz, I largely avoid the harmonic distortion issues at the low end, and that since frequency issues don't show up until just past 6khz, crossing at 3.5khz is low enough to avoid those issues, but high enough to avoid distortion within the "vocal band" and the tweeters resonance.

So, the parts that I'm less certain about:

a) I think I'll still need baffle step compensation, but not the notch filter. Is that correct? Should baffle step be performed before or after the low-mid crossover?

b) I'm intrigued by the use of alternative housings. As I understand it, the main issue with an open baffle with small drivers is exceeding xmax with bass content - would crossing at 150hz alleviate this, or would OB require a higher crossover point? Is there any advantage to using a transmission line or similar bass-tuning enclosure for the mids when no bass content is being reproduced?

c) <AUSTRALIA> Can anyone suggest a decent value woofer to adequately cover the range < 150hz? I'm looking for something that is available within Australia, and at the moment, I'd prefer to stick to a single subwoofer, costing <$50, unless anyone happens to know of a driver for which a pair costs <$100 including shipping. I'm open to suggestions on size, but ideally, enclosures should be small: say 400w x 200h x 300d as a rough guide, or something that could be housed downfiring in 2 foot or so of some kind of rigid pipe.

The ultimate goal is to produce a bedroom system that can suffice as a primary system for a fairly discerning student (me), striking a balance between fidelity, size and cost.

If anyone can help out with advice on any of these points, it's much appreciated.
 
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