Fostex FF225WK + FF85WK together?

[talaerts]

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?

[freddi]

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.

[chazdrumzalot]

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.

[talaerts]

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 !

[planet10]

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.



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

[chrisb]

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),







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






Circa 300 seems to be a nice sweet spot for this size Fostex

[talaerts]

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.

[chazdrumzalot]

Originally Posted by planet10

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.

[planet10]

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

[talaerts]

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...