Fostex FF225WK + FF85WK together?

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Dear all,

The German magazine Klang & Ton tested the recent Fostex FF225WK in its latest issue. It seems quite an interesting speaker, with decent bass in a simple, relatively compact BR cabinet. The waterfall diagram was nice as well, there is a kind of narrow band resonance at 4k, but it decays quickly enough (so it's not certain if a notch filter would be required). The flipside of the coin is that with its relatively heavy cone, there is not much happening above 10khz. Hence it seems destined to be paired with a tweeter.
My idea was, instead of adding a classic tweeter, rather to use its small brother FF85WK, filtered only with a decent capacitator, and put in a closed area in the box. The FF225WK would run unfiltered, at least in the initial configuration.
Having the same cone material for both drivers should improve consistent tonality, I expect.
But it's not trivial. For example, I understand that the sensitivity of the FF85WK is lower than the FF225WK, however the big one still has some output above 10k, and hence I am not sure how well they would match. Alternatively I could opt for the more sensitive FF105WK as a tweeter, but its frequency response is less benign than that of the FF85WK.
So, My question is, what do you think of this possible approach? Comments/ideas?
 
After applying baffle step, the two drivers will start to come into a little more alignment. To balance them out more you would have to use a resistor on the woofer, the plus side being a little more bass extension. I think it would be a good idea to roll off the 225wk at the crossover point myself.
 
After applying baffle step, the two drivers will start to come into a little more alignment. To balance them out more you would have to use a resistor on the woofer, the plus side being a little more bass extension. I think it would be a good idea to roll off the 225wk at the crossover point myself.

Thanks for the info! Duly noted. Regarding rolling off the 225WK, yes, that is definitely possible but I would first want to try it unfiltered, and then add complexity in the filter.

I would employ a small Karlson open ended waveguide with an inexpensive compression driver for the high frequency augmentation. Here's one of Carl's test couplers with a laminated maple veneer tube in an eight inch K-coupler.

Also thanks for your feedback. However, I was never interested in Karlson alignments. Sorry about that !
 
frugal-phile™
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The concept is sound, but i expect (having heard it) that getting the cutoff much lower on the FF85 would pay big benefits (i'm gonna guess that best mid/top of the entire series is from the FF85). I'd take it down to 300-400 Hz.

2 WEs ago at diyFEST, we cobbled together FE138eSR in FH3 (this has great bass, but FE138eSR is not a full range, taking the classic shout to a scream), and FF85wk in uFonken, biamped at 100 Hz (a PPXL of said frequency was handy) and ended up with something quite special even thou far from optimized.

236414d1313907037-8th-annual-vancouver-island-diyfest-2011-backdeck.jpg


The fly in the ointment of your scheme is the much lower efficiency of the FF85 vrs FF225, you might get away with passive XO if you crossed at the baffle-step, up high not so much.

dave
 
Funny that Dave didn't mention a similar idea of MTM with 225/85/225 was floated a couple of weeks back - done right that could be very interesting


The new 85WK is silly good - even run full-range at moderate SPLs - IMHO easily as good as the previous "stealth Sigma" 85K. As Dave suggests, it would be a bit of a waste not to take advantage of its performance from lower midrange on up. We've used the older unit quite successfully XO'd "around" 300Hz in both a PLLXO/ biamped FAST ( Tysen),

An externally hosted image should be here but it was not working when we last tested it.






and a MTM with Mark Audio EL166 (Woofer6) passive series.

195454d1289116224-marks-proto-6-5-woofer-1-silk-tweet-combo-el166-mtm-front.jpg





Circa 300 seems to be a nice sweet spot for this size Fostex
 
How much db loss does a BSC filter have? Isn't that around 6db? In that case I have the impression that an FF225WK with BSC would be aligned in sensitivity to the FF85K. Also, if I would filter the FF85K with only a capacitator, how much db loss if any would that cause?
Otherwise the FF105WK (filtered high) might be interesting for the tweeter role. Does anyone have experience with that one?

The MTM solution could be good but then I'd rather prefer a better single driver for the price of two FF225WK.
 
The fly in the ointment of your scheme is the much lower efficiency of the FF85 vrs FF225, you might get away with passive XO if you crossed at the baffle-step, up high not so much.

dave
I've always appreciated the beauty in simplicity of this approach; but the fact is Talaerts, if you go this route then buying the FF225wk is probably not necessary. I mean, it wouldn't hurt, but you might get equally good results with an equally sensitive but less exotic and cheaper 8" woofer.

How much db loss does a BSC filter have? Isn't that around 6db? In that case I have the impression that an FF225WK with BSC would be aligned in sensitivity to the FF85K

Theoretically baffle step loss is 6db, but most people agree that about 3db of BSC is enough in real-world (in-room) situations, the exception being open baffle systems.
 
frugal-phile™
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To expand on chaz's post.

If you are crossing low enuff to use bafflestep to align levels, most of what the FF225 does would be wasted (you really only need something that reaches up to about 1kHz), and for the same cost, you can very likely find something with better bass. The MTM above is meant to be an example project, there are many good midbasses out there, their problems are usually at the top of their bandwidth.

Bafflestep has a maximum magnitude of 6 dB, rarely is that much needed. Room, placement, and taste all play a big role.

dave
 
I guess there's nothing stopping you from trying your idea, however popular opinion says that in a generic woofer crossed low to the 85wk or a generic tweeter crossed high to the 225wk would be more appropriate solution. But there's no saying for sure. No matter what, I don't think it could hurt to buy two pairs of very good drivers and experiment a bit!

I've always been tempted to try the fullrange/generic woofer solution ala the FAST speakers. But I have one holdup: everyone here talks about how bad multi-way systems are because they cross in the sensitive midband region. But judging by the fact that many more instruments and voices cross the 3-400hz region than, say, the 2 khz region, is this really better than making a typical 2-way? I don't know, to be honest.
 
Yes, meanwhile I already thought that if I cross low, then I can take a more generic woofer. Still, my original idea was to run the FF225WK full range (with BSC), and add the 85WK in from say 8khz. Decisions, decisions...

No matter what mid/bass driver is used, I'd opine that it'd be a terrible waste of the BW over which the 85WK works so well to cross it over that high.


Chaz: that's why we started playing with our XO for FAST /etc in the 250/ 350Hz range - sure you'll restrict the ultimate attainable SPL, but as I consider sane listening at under 80dB average, that's generally not an issue for me.
 
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Thanks all for the good feedback. I begin to realise that it will make more sense to use the FF225WK with a generic matched tweeter, or the FF85WK with a generic matched woofer.
Of the two options, crossing high to a tweeter seems the cheapest option. Isn't it correct that it's not evident to cross with good audio quality at say 200 hz with passive components?
 
I consider 200 Hz to be the transition point (ie less than 200 Hz should be active). To cross that low you would need to have a cabinet on the order of 60 cm wide to incorporate baffle step into the woofer/mid-tweeter transition.

dave


not to forget the cost and size of quality passive components required to achieve even a simple 1st order XO at that low a frequency (assuming 8 ohms each, that'd be approx 100mf for the HP and 6mH for the LP)
 
My unfashionable suggestion is that they be crossed over at approximately 1000-1200Hz. This way, there is enough bandwidth available from both drivers that a true first order crossover could be utilized, and the freq is low enough (within ~ 1wl) that good integration should be attainable.

Also, the little FF85 will have some hope of keeping up dynamically with the 8" driver.

Separate BSC will need to be employed on the FF225, but the loss in efficiency is approximately equal to the SPL difference between it and the FF85, so it all works out.

A simple cap and coil is not going to cut it, but it could still be done with a fairly simple crossover. Consider putting the FF85 in a stuffed tube or aperiodic to flatten the Z curve.

If going the full range + supertweeter route and crossing at 8k or whatever, I think a horn supertweeter will sound better, or perhaps a ribbon or even mini K-tube (as suggested previously).
 
My unfashionable suggestion is that they be crossed over at approximately 1000-1200Hz. This way, there is enough bandwidth available from both drivers that a true first order crossover could be utilized, and the freq is low enough (within ~ 1wl) that good integration should be attainable.

Also, the little FF85 will have some hope of keeping up dynamically with the 8" driver.
there is some precedence for this approach in the old SDX7/alpair5 combo. Crossover points anywhere from 500hz to 1.5khz were suggested, and I remember at least one person saying that the higher crossover point worked out much better. While that was just one opinion, and of course a very different speaker, it's at least one example of a full range drive being used successfully as a tweeter.
 
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