FE206E Recommended Enclosure

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Just getting ready to build the fostex enclosure for the FE206E and had a question about the internal bracing. If someone has built this already I thought they might have some insight.

Link the the PDF of the enclosure

My question is regarding the braces labeled 9, 11, 2, and 6 in the drawing. I can't tell exactly where they are to be positioned by the drawing. Are they on edge in the center line of the speaker? The picture of the built speaker almost makes them look staggered inside.

Thanks for any info

Tim
 
frugal-phile™
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A natural inclination would be to put them in the middle (the drawing is not clear). This is -- from a bracing point of view -- the worst place for them. I'd offset them at least a bit (ie draw the centre line & put the edge of the brace on the centre line. This should dramaticaly reduce the 1st major bending mode of the panel.

dave
 
FE206 in my DIY Voigt Pipe

Hi, Last year I built a pair of DIY Voigt Pipes using a pair of Fostex FE206 drivers and like the combination very well. Am using them with a tubed amplifier. Note that my 206 drivers were purchased from Decware, they modify them by replacing the dust cap with a phase plug and treating the paper cone with stiffening ink. On the good side, at least the Voigt Pipes are fairly easy to build if you get the angles right, they dont take much wood and have relatively few pieces and require few cuts. I built mine of one 4 x 8' sheet of maple plywood for the front, sides and bases, and two pieces of select pine for the back pieces, which isnt too expensive.
 
I know that the so-called 'traditional' Lowther Club of Norway Voigt Pipe is a very popular enclosure, and can sound quite entertaining, but I would personally advise against it. It has a number of problems, none of which can be fixed though simple tweaks such as adjusting the suffing. The greatest problem is the absense of any top surface-area: the top comes to a point. This means that the cut off of the pipe is higher than necessary. There isn't enough area at the base either for that matter, the driver isn't positioned correctly, and the vent's too large. All of this is cabinet related, and deals with issues below 1Kz by the way; above that the cabinet doesn't / shouldn't really affect the response as at higher frequencies, its only job is to provide the driver with a nice, solid mounting.

Below, you'll see the frequency response of the Lowther Club of Norway cabinet using the FE206E calculated in MathCad, assuming 0.25lbs to the cubic foot of stuffing from the top to just below the driver. The FE207E in this enclosure looks almost identical, give or take a db or two. If you really must, I'd advocate the FE207E however, which is more suitable for a responsnat enclosure like a TQWT because its response curve above 10Khz is substantially flatter than the rising response of the 206, and it will therefore require less correction. You can still use the 206, but you'll need larger values in the correction circuit, which will increase the cost, and why make life more expensive than it has to be, I say.

if you want to use these drivers in a TL, go for either Martin King's MLTL project, pay the small asking price for Bob Brines MLTL plans, or design your own in Martin's MathCad software. If you want a TQWT taper (and why not?), try something around these starting values:
Line length: 60"
Driver mounted at 1/2 line length
Top area (So) = 1Sd (driver surface area)
Base Area (Sm) = 5Sd (or more if possible, though this will mean a big cabinet)
Vent or port: circular, 4" up from the base 3"x2" (width x length).
These are rough starting values -they're probably not great in themselves, I haven't tried it, but they'll give you somewhere to start, and the response will be a lot better than the 'Voigt pipe'.

Regards
Scott
 

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Greets!

planet10 said:
Yes, 207 is better suited to a Voigt than the 206... the Q of the 206 makes it like horns best.

dave

OK, I've seen this stated by numerous folks in even more threads on several forums, so I posted a rebuttal on a similar Fullrange Forum thread awhile back, and since no one pointed out any faulty reasoning on my part...........

I recommend you use a bit of common sense. ;^) If you do a couple of sims where each driver has enough series resistance to raise Qts to 0.403, then Vb = Vas and Fb = Fs. This is a good alignment WRT trading effective efficiency for LF cutoff, though you could just as easily compare them at any other alignment the 207 can handle. Since the Fs/Vas for both drivers are near identical, they will both work well in the same cab. Also, since they both have the same Xmax and power rating, This also means that for all intent and purpose they have the SAME effective efficiency and dynamic range. The ONLY difference between them WRT will it/won't work in a BR/ML-TL is the resistor rating required.

Since the 206 is 'faster' due to being a more highly damped resonant system than the 207 above the cab controlled BW, and why it has a rising HF response that yields more 'micro detail' (as some folks refer to it), unless you need a shielded driver and/or your amp can't handle the high effective speaker impedance, then the 206 is the hands down winner IMO in this decidedly unfair (for the 206) comparison.

WRT to its rising response being the 'deal breaker', that's what toeing in the cabs is for, which you need to do with any driver whose polar response shrinks with increasing frequency, and if the HF roll off is a problem you can either 'lift' it with a cap in parallel with the series R, or better still, add a real super tweeter since no driver this big is going to do this BW well anyway.

As for horns requiring low Qts drivers, this only applies to high compression ratio and/or ones driven with a high output impedance.

GM
 
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