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testarossa2k 28th October 2006 05:46 PM

tweaking the Fostex 206E
I built the a 45 liters bass reflex cabinet with 8cm diam and 7,5 long port. Is there any way to fill the hole in frequency responce around 100hz?

Here's what I thought to do:

1) equalizer

2) passive equalizer circuit

3) adding mass to the cone. How?

how these affects the group delay and the phase response? because I'm using it with a sub with cross frequency at 100hz so I would like to have a synchronized sound....

Now I'm making some experiments with the length of the port

Scottmoose 28th October 2006 06:32 PM

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Are we talking about the Fostex 45 litre box here? According to MathCad, and I've just modelled the box in the latest version of Martin King's worksheets to four decimal places, there, er, isn't a hole at 100Hz (or at least, not in 1/2 space). There is a hole at 150Hz in the horn, but IMO, the 206 horn isn't up to much. Ugly too.

Predicted response of the 45 litre reflex cabinet is attached; as you can see, it almost exactly matches what Fostex state: slowly decreasing bass with a peak (not sure if I'd call it 'controlled' though!) at 55Hz. If there's a big hole in the system response at 100Hz, then I'd say it's being cause by a room effect like floor-bounce, not a driver / cabinet characteristic. I don't like the reflex cab myself -you'd be much better off building Martin King's MLTL, or paying for Bob Brines's slightly more refined plans for a similar cabinet. They're an easy build -no harder than a reflex cabinet, won't be costly in materials, and you're unlikely to need a sub, except for frequencies below 40Hz. Alternatively, get them into a horn -again, a decent one will not require a sub except to support it below 40Hz.

I wouldn't advise adding mass to the cone -you might as well have bought a different driver in the first place; and there's a lot of potential for damaging the driver, which would be a shame. Adding some phase plugs will work wonders for the midrange and treble though -well worth doing. Damp the basket and the rear of the magnet with something like Ductseal. You could even try adding another magnet -just rip one off an old scrap pair of speakers out of a skip. Not a common idea, but might be worth a shot.

Crossing over to a single sub at 100Hz is a bad idea -anything over 70Hz is directional, so you'll be hearing frequencies between these two points coming from there, and everything else coming from your main speakers. Not so good. Two subs are needed if you want to XO over 70Hz IMO.

Get a BSC circuit on it too, if you want some more bass performance -you'll be loosing at least 3db through baffle-step diffraction. Depending on your amplifier, you might also want to add some series resistance. It'll lower the efficiency, but provide a more balanced response. Again, Martin's circuit, or Bob's, should do the job.

Hope this is of use

Bob Brines 28th October 2006 06:35 PM

There's a severe dip in the FR because 35l is way too big for the 206E. You might try an EBS alignment with a 20l box tuned to 50 Hz. As always, my recommendation for a ported box is the 207E, not the 206E. It can be done, by why accept all of the compromises.


testarossa2k 28th October 2006 09:21 PM

there's the hole, look at my graph using winisd and also other prog is the same. Ok it stays in the -6db limit and so you can hear it, also because the room will boost that frequency.
Could you show me your frequency responce but to 20k?


Damp the basket and the rear of the magnet with something like Ductseal.
what it does this to the sound?


Adding some phase plugs will work wonders for the midrange and treble though -well worth doing
I like the treble of fe206e


You could even try adding another magnet
and this? I've seen some people adding addition magnet to lower the qts, right?


anything over 70Hz is directional
it isn't 80hz?
anyway yes it is a bad idea for the most cases. But I place the sub beetween the two fostex, and I really don't notice the sound coming from there. Before I was using the sub at 150hz to completly fillup the hole:D I'm mad eh:smash: just in one song with a sax I could locate the sound, but the main problem was the resonce of the room at that frequency in few cds, you know at 150hz the sub it has a strong output. the quality was good aspecially the voices were so full, you know like pavarottii whoooooooooooooo but with a great cavernous voice.


Depending on your amplifier, you might also want to add some series resistance
I'm using a DB technologies MT530 amplifier, do you know it? anyway I think it will drive anything...


There's a severe dip in the FR because 35l
you mean 45l, right?


my recommendation for a ported box is the 207E
yes but the last year when I built the speaker I was seeing a lot of people using that driver and saying it soud good in BR... infact it sound fantastic, it's just light on bass( it's one of the compromises you told?), but it deepends a lot of what you listen and especially from the records quality. I had them 30/40cm from the wall and was good until one time I tried with sub. Also the previous speaker I had had a good extension in bass region but man when the last day I tried they had not great bass.

thank you thank you

hm 28th October 2006 11:33 PM

2 Attachment(s)
did you saw this:

Scottmoose 29th October 2006 09:41 AM

MathCad only goes up to 1Khz as it models the driver / enclosure combination, and above that point, the only function of an enclosure is to provide a solid mounting point for the driver. With all due respect to WinISD, it's not in the same league as Martin's MathCad worksheets. However, you can still see the similar shape in the response, which drops away from 120Hz to a peak at ~55Hz. The graphs have different values which makes them look somewhat different.

The Fostex box is actually closer to being a short, mistuned MLTL than a reflex cabinet IMO. It's not a great design, as Bob points out & I agree 100% with everything he says. For reflex loading, it's too big, for QW loading, not really large enough, with a port that isn't tuned too well. Not too uncommon an alignment, if you can call it that, to have a decreasing bass down to a slightly high Fc, which peaks. Not one I'd ever suggest though.

70Hz. Actually, according to the latest findings, it's 72.874Hz, but we won't split hairs. ;) To each their own!

Damping the basket will kill resonances in the structure of the driver. Worth doing, especially as it costs very little and is completely reversable. The phase plugs will smooth the 206s treble and midrange; you won't loose any detail; in fact, you'll gain some insight if anything as they also remove the resonance caused by the hollow centre pole-piece under the dust-cap, which rings like crazy at about 3KHz or so. It takes away a little of the artificial brightness, but you'll find them a better driver in the long-term.

The 207 is indeed the better natural driver in a reflex or otherwise resonant cabinet, primarily because it's a higher Q (relatively -0.26 still isn't much), giving it better bass, but also it lacks the rising response of the 206, which was nominally intended to be re-balanced by horn loading. You can also bring it into line with a circuit, but you loose some efficieny that way. The plugs, as mentioned, help here too. The massive magnet of the 206 might give a whisker more detail, but it needs larger values in a compensation circuit, and more cabinet fettling to get working right.

Do yourself a favour: get them into a better cabinet. I know it's a hard thing to face up to, especially if you've put a lot of work into the enclosures. Believe me, I've been there, and it's a real pain.
But, you are not hearing your drivers at anything even remotely approaching their best at the moment, and there is very little you can do to improve your existing boxes. Martin's or Bob's MLTLs would be the automatic choice for an easy, relatively compact build.

Alternatively, if you have the space, get them into a horn. There are a few options here. The Factory horn design for the 206 isn't up to much, and looks horrible. However, their design for the FE208ESigma is much better, and the 206 will work quite well in it. I've just done a double-horn for the 8in Fostex speakers which should be nominally flat in-room to 30Hz or so (Bruce V1.1 -see the Spawn of Frugelhorn thread). Or a BIB -I suggested some dimensions for the 206 on the zillaspeak site:

Any of these, MLTLs or horns, will allow your drivers to perform as nature intended; and they'll be transformed. You'll get more enjoyment out of your music in the long term -promise.

All the best

testarossa2k 31st October 2006 07:28 PM

mhh ok I accept your tips. Now I'm gonna try the free tricks and then if I'm not satisfied I will build a horn.
But could I use the sub with the horn for very low frequencies? are there some problem with delay with horns in the low end?

blumenco 2nd November 2006 04:55 AM

its really really hard to sub a horn.

meaning that the speed of bass that comes out of a full range horn loaded is the sole reason to build a horn for it. to get a sub to catch up with that is very difficult indeed. it realistically does not happen, except in cases of good EQ and biamping, etc. lots and lots of money and fussing for a few octaves that the driver will put out better all on its own anyways.

the martin, bob boxes, I have not heard. seem to look solid for the driver.

the fostex recommended enclosure I think would perform well probably. I have not heard it, but have heard alot of good things about it. it might not be pretty, it is a tough build, but it is a nice orthodox squared off BLH megadynamic and nicely coloured sonically. something to consider.

there are alot of other nice options though. simpler, (lighter), for all practical purposes just as good.

I like the treble distortion from the dust cap too. it is fun and crazy sounding. admittably, these are not my only speakers i do not have to live with it. some day I will get around to phase plugging a few of my drivers.


Scottmoose 2nd November 2006 05:40 PM

The Factory 206 BLH has a horrible response up to 200Hz. Not one of their best. OTOH, dropping them into the 208ESigma horn would be a heck of a good move. Now that one really is a great cab. Massive bass heft, looks far better, and a much smoother response too. The 206ES-R cabinet is an alternativbe of course -response falls somewhere between the two camps.

hm 2nd November 2006 06:09 PM

alternative with bass
2 Attachment(s)
the SAXOPHON has bass:

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