On the H6s parts in general, Ed Chapman of University of Wisconsin commented:

I have some information/corrections for you . . .  for example, I just
talked to SEAS and they said the "H3310" is not the name of the bass
driver in the H6 - that number is just a number for the rubber surround
used on many of the different 6.5" drivers that SEAS
manufactured.   I see the "H3310" on the rubber surround of my bass
driver in my Lalis,  but this specific stock driver is actually called
the "CA17RC".  SEAS no longer makes it.  So, under "H6" on your web
page, it is incorrect to call the driver the "H3310", if the
H6 is really like the Lali, then the driver is the SEAS "CA17RC".

The Kevlar tweeter (from Focal) is not longer made and always eventually
dies; mine did.  So, I reluctantly put in a titanium tweeter from Focal
- one must widen the opening a tiny bit to get it in.  But, it sounds
even better than the Kevlar - what a relief.  I used the Focal TC 120
TD5 tweeter.

One more thing - I also changed the Solen to a Hovland cap - the Hovland
works magic with the new Focal tweeter.  Pricey, but a worthwhile
upgrade.

The crossover is set at about 4KHz. You don't need to play with it at all, and in any case on mine the cap and inductor were very difficult to get at, being soldered to the back of the terminal panel. If you must have at it, and habitually listen at high levels, an air-core type inductor is probably a good idea so long as the series resistance is kept low (less than 0.4ohms here).

The original tweeter is very similar to the (Kevlar inverted dome) Focal TD90K. This tweeter is no longer produced but the TD120 series use the same baffle cut-out and will drop in place ((if you can find a pair - Focal no longer sell their drivers to others) You'll have to adjust the L-pad substantially because the TD120 is about 2dB/W more sensitive than the TD90K.

At the top of the page I've drawn the original arrangement I found in my pair. Below that is the equivalent series connection. There's loads of information on the web about series crossover design - try browsing the Madisound forum especially - but a few quick note here:

As you can see, the series arrangement is a kind of 'telescoped' connection of the standard parallel crossover with the proviso that the capacitor, inductor and one bass and tweeter terminal are all soldered together at one point. So electrically the inductor is also in parallel with the tweeter, and the cap is also in parallel with the bass driver. This is a 'subtractive' network - it means that the signal applied to the tweeter and bass unit must add up *exactly* to that applied by the amplifier. Always a good thing - and one that's not true for most crossovers! An incidentals result is that series crossovers have the unique property of being able to accurately pass a square wave - not much use when it comes to music, but interesting nevertheless.

The principal gain is that the cap damps the out-of-band motion of the bass driver, and the inductor does the same to the tweeter., just as a second order crossover can do. This is why I think H6owners might find the series arrangement worth trying - to help suppress out-of band, break-up products from the bass/midrange unit.

The key to success and long tweeter life is a low resistance value for the inductor, because it's the inductor which protects the tweeter from bass by 'shorting' bass frequencies across the tweeters terminals. At low frequencies voltage appearing across the inductors resistance is applied to the tweeter - so the less the better! 0.4 ohms or less is the minimum really - in this implementation the tweeter still is forced to endure bass signals only 40dB down from the main level. The Focal unit can survive this fine, and the standard ferrite inductor has a suitably low R value.

Re-using the existing component values) will give a 'zeta' value of 1.0 for the series crossover. Zeta is a measure of peaking at crossover - you can see that the inductor and cap are now in series across the amplifier terminals. As such, they will have a series resonance, where the series impedance falls to a very low value; note this doesn't necessarily coincide with the acoustic crossover point. Don't worry, it won't blow your amp up, because the resonance is damped by the resistance of the inductor, and the drive units and resistors also across this L-C tank 'steal' energy from the resonance, damping it. 'Zeta' is a measure of the damping; higher values (1.2+) lead to greater output from the units at the crossover point, which is definitely what you don't want to cure that 'hardness'. Lower zeta values are overdamped and also open up a gap in the driver overlap.

As I've shown, and tried, the standard values work fine and in fact give zeta =1. Increasing the cap value to 3.9uF (by adding a small680nF cap in parallel) give a better match to the driver parameters in use theoretically, and might be well worth trying. You can still fiddle with the L-pad on the tweeter to tweak relative levels; quite small alterations have quite large effects on spectral balance.

Remember to test the crossover for shorts between terminals before plugging-in the amp. If you want belt-and-braces protection before committing to solder, use 1A fuse wire in series with the crossover input; this will protect both the amp and speakers in the case something does get hooked up wrong. Remove the fuse when all finished.

"finished the crossover and everything last night at about 10pm, I had to try it out 
so listened to Wish You Were Here quite loud, what a fantastic lp that is, loads 
going on and I found myself thinking how do people write such fantastic music, 
hang on aren't I supposed to be listening to the speakers, I forgot whilst I got lost in 
the detail, smoothness, controlled bass, crystalline treble (especially Mr Gilmour's guitar), 
clear midrange and loss of the hardness and overblown bass.  The new drivers, 
new crossovers, and new internal wiring aren't even run-in yet.

I guess you can tell that this was a fantastic success!!!

I ended up using a 10R in series with the tweeter and another 10R across the tweeter 
terminals to tame the higher efficiency of the new focal tweeter, and it seems to have 
worked straight away.  
(...)
the new crossover layout is excellent, in fact I don't know how I listened to it before, 
they are the same speakers but even more so, if that makes sense."

www.acoustica.org.uk (opens new window)