Fostex Factory BR alignments

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A FWIW post. When these drivers first came out I had a quick look at the various BR alignments they provide for them; as I was cleaning the HDD I ran across them & thought they might be of interest.

Some general points. This is from WinISD-pro, which I use for checking consistency of published T/S specs. Factory parameters, Vas may be slightly different as I derive it from the other values, since it's often the hardest to measure. Anechoic IB FR plots (obviously), assuming voltage sources unless otherwise stated. No damping assumed, so if the boxes are lined, then you'll get a little more LF damping. Ignore everything > 1KHz.

3in drivers = yellow
4in drivers = blue
4.5in drivers = orange
6.5in drivers = violet
8in drivers = green

One additional point. When we say the Factory cabinets were designed for the En series drivers, they're weren't. They were designed for the defunct E series units, which in several cases (officially) had somewhat different specs., but have carried over to the new drivers.
 
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FFxx5wk boxes.

General thoughts. The 85 box is likely to be irritating with that peak at Fb. The 105 box is also a bit under-damped so avoid boundaries. The 125, 165 & 225 alignments aren't bad; relatively well damped, should be fairly flexible in terms of positioning, amplifiers etc. How much of a shelving filter you'll need for step-loss (if any) will depend on the amps & placement, obviously. This isn't taking linear deflection into consideration; the smaller units will have less dynamic range for obvious reasons, although Fostex units tend to compress relatively gracefully compared to some other short VC drivers.
 

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FFxx6En boxes.

Assuming a voltage source and typical room placement, the 166 cabinet doesn't look too bad (although the data-sheet dimensions are inconsistent, so YMMV), the others vary. The 83 cabinet isn't up to much as far as I'm concerned, but it's spec. isn't ideal for BR loading in any case (the slow rise will help with step-loss, but the dip between 100Hz - 200Hz & peak at Fb aren't great); the 103 box isn't pretty either with a dip through the upper & midbass & a peak at Fb; 126 box fairly classic EBS, the 206 a slightly underdamped EBS. Again, no damping assumed to adjust expectations accordingly; ditto for room-gain & system etc.
 

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FExx6En series with SET amp (2.5ohms output impedance assumed)

What you'd expect really. The 83 box is technically no better, but arguably no worse & the initial rise may help correct for step-loss. Still hate the dip with peak at Fb, though since the room dominates < 300Hz, YMMV. In small Japanese spaces with thin-wall construction leaking LF, that peak at tuning might be brought into line. The 103 box still has a peak at Fb, so avoid boundaries & lots of damping needed I suspect. 126 box taken on a nicely damped alignment so probably not bad near boundaries with some help where needed for step-loss. 166 cabinet now near-QB3, so keep away from boundaries or increase damping & probably useable with help for step-loss. 206 box now approaching classic EBS (still slightly under-damped) so a bit more flexible. The 126 & 206 will likely do better with a slightly higher output impedance amp. or resistive speaker wire. ~4ohms perhaps.

Again, YMMV given amps, rooms, room construction, taste etc. Like the FFxx5wk, linear dynamic range = limited given the short VCs, although they overload more benignly than some others of this type.

FWIW anyway.
 

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TBH, mine too. I was trying to be generous, but my doctor has just informed me the shock to the system will be serious if I keep it up, so I shall revert to my old self from now. ;)

Yep. Some of them are 'run for the hills' in alignment terms. But then, they weren't designed for these drivers & neither the old 6E or the current En series are particularly well suited for BRs anyway without a heck of a lot of help from the amp, and that's just in FR terms. :eek:
 
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I've always thought the FFXX5WK boxes looked like fair recommendations. The response humps on the smaller units might be there to make then sound livelier before what would still be a steep cutoff. They might also assume usage with no step filter perhaps? Still, I like the 125/165 alignments most "on paper". Maybe I ought to try cheap prototypes for 85 and 225 as I have both drivers around. I'd probably prefer tuning at Fs for the 225 though. Or maybe a classic Vb=Vas, Fb=Fs (permitted by Qt~0.35) could be fun, but I have no pressing need for a box this size.

IG
 
Depends on what's called 'lively', but an anechoic peak at Fb is pretty much death from my POV in alignment terms sans any extenuating circumstances.) Possibly they're aiming for reduced need for shelving filters & possibly assuming thin-wall Japanese room construction or similar leaking LF energy, as mooted above.

Yep, the 225 box would work OK Fb = Fs. Slightly less damping of course, but decent. Off the top of my head, Vb = Vas, Fb = Fs should give something vaguely approximating a EBS alignment, albeit with less of a shelf. Personally I don't much like EBS style alignments except for v. low tuned subs ( < 16Hz or so assuming appropriate driver), but YMMV as always of course.
 
Here are a few FF225WK plots:

Yellow: WinISD recommended QB3
Blue: Fostex recommended
Green: Fostex recommended tuned to Fs
Pink: Vb=Vas + Fb=Fs

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The Vb=Vas/Fb=Fs box is indeed a sort of EBS, shelved by only 1dB though. I never built an EBS in any case. It might sound bassier and bigger, but probably will have lower power handling and compromised transient response? I like the WinISD recommendation, though I'd be tempted to re-tune to Fs once again and bring it somewhere in-between the Yellow and Green traces.

Giving each combination a bit of power, 8W, it's easy to see that the 28L@39Hz handles power better and breaks Xmax noticeably lower than any of the others. Pick your area of compromise, nothing new here. :)

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I conisdered the FF125WK for a good while before deciding to try the TB W4-1320SIF instead. I kept coming back to 9L@55Hz when simulating, very close to the factory recommendation.

IG
 

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Pretty much as expected then; 28 litres to Fs with slightly less LF damping & Vb = Vas Fb = Fs quasi EBS with less of a shelf. Right, not much new in the world of vented boxes. ;)

Yeah, EBS alignments work for v. low tuned subs, but for other duties / higher tunings where Fb is likely to be within or near (say) the average BW used in most musical genres & I'm less than convinced.
 
The 83 cabinet isn't up to much as far as I'm concerned, but it's spec. isn't ideal for BR loading in any case (the slow rise will help with step-loss, but the dip between 100Hz - 200Hz & peak at Fb aren't great);

I used to have a pair of the old FE83 in factory BR. Like you, I modeled them in WinISD and was somewhat aghast at the result. However, I had an empty pair of boxes of the correct volume just sitting around. At that point, I had not tried any of the Fostex suggested alignments, and I figured it was about time.

Actually, they were quite nice. The peak was lower Q than the sims indicated, and I didn't have a dip. The slight rise at the bottom subjectively made up for their limited Fc, and overall they sounded very balanced and listenable. I concluded that Fostex knew what they were doing, and the highish Q was intended to give these tiny speakers a semblance of full sound. In my view, it works. Sure, they could be put in something that looks better on paper, but who listens to graphs...
 
I was screwing around in WinISD with FF225WK once more. I never much looked at the "Port Gain" plots before. It seems like the port output Q-factor (-3dB bandwidth to peak ratio) is decent at ~0.75 on the factory box. The tuning I prefered "on paper", at Fs=44Hz, has a higher Q at ~0.9.

One thing I noticed just now, when Fb=Fs, peak port output is at Fb, as I'd rightly expect. But, as Fb is shifted away from Fs, peak output then becomes correspondingly lower or higher than you'd think based on Fb alone. This is happening in WinISD simulation, which I assume gets it fairly correct, but is it so in real-life box measurements? Can't say I ever noticed much myself, as most BR I've built so far were tuned to Fs or very close. What is the reason behind this then?

Impedance minima does not seem to be such affected, usually landing pretty much on Fb, regardless of relation to Fs, maybe unless tuned ridiculously far from it... I also wonder exactly where excursion minima and cone null line-up with all this. Seems like it's be good for me to have a sit-down with my measurement gear and the deceptively "simple" BR enclosure... First-hand experience is how I learn best. :)

IG
 
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Not that surprising but not often noticed. :) Traditionally (i.e. prior to Small and also Novak's unfortunately overlooked work which pre-dated it by some years) BRs would be tuned to Fs for maximum system efficiency. Of course, what Novak, Thiele & especially Small demonstrated in terms of mathematical filter equations (and what was regularly done via simpler formulas and / or empirical testing & tuning before that) is that you don't necessarily want maximum system efficiency at Fb. ;) Certainly not in the large / efficient boxes that were used as a matter of course until the late '60s rather than the ducted types popular since the ready availability of cheap power.
 
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I'm guessing maximum system efficiency at Fb might have been desirable when most amps had higher output impedance and matching the load was a concern. Not so much today indeed.

I'm tempted to build that 28L box. It looks like it'd have decent tuning flexibility depending on one's taste and might even work sealed if corner-loaded, Qt~0.63, f10 in the upper 40ies. I'd probably make a few people cringe though, were I to implement the BBC-slot I've wanted to try for a long time. :) I'm not supposed to be building more speakers for now anyway... :D

IG
 
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