Kofi Annan in: "206EnABLin' the Mamboni"

[Kofi Annan]

So, I have recently finished a 1.5-year journey to complete my Monkey 300b DRD (thanks Thorsten, 2wo, Sheldon, et. al.!) and I have been running them through my Fostex 206Es in the 208EZ backhorn.

The detail and bass response are fantastic, however the dreaded shout remains, along with some noticeable shhibilanche.

Here are the modifications I've made to the driver / cabinet so far:

1. Installed Dave's (Planet 10's) phase plugs (is there anything they can't do?)
2. Damped the magnets with wool felt
3. Grounded the - terminal to the basket
4. Added a good hunk of polyester batting to the back wall of the compression chamber

All these modifications have helped, to some degree, kill the shout, but I still spend many evenings changing sources, moving speaker cabinets and various furniture items to try and rid myself of it all, but to no avail.

Don't get me wrong-- they sound really good, but I believe that they can sound better.

Now, I've been reading up on the EnABL process and I'm interested in giving this a shot. Of course, this is scary to me, given the permanence of this change, but I think I should go for it. Nothing ventured blah blah blah...

Anyway, I see that there has been a successful EnABL modification of what looks to be a Fostex 206ES-R , but not the 206E outright.

So, here are the questions:

1. Would the pattern for the 206ES-R work for the 206E? If so, is there printable pattern available?

2. Would the fact that I have installed the phase plugs change or eliminate the effectiveness of EnABL?

3. There has been some discussion of taping the pattern on to the cone to allow removal of the blocks. Has anyone tried this?

4. Also, one of the threads I have attached above mentions that if acrylic paint is used, the blocks may be removed with alcohol. Has anyone successfully removed them this way?

I'm also reading up on the Mamboni process, but I'm not done yet so I'll hold off on questions.

I would certainly entertain other 206E tweaks, but the EnABL process seems interesting. I'm still reading up on this, but any recommendations for additional tweaks and / or guidance on this process would be much appreciated.

Kofi

[t-head]

Kofi,

I cannot speak for your drivers...I had BudP EnABL my set of FR4.5C drivers from Hemp Acoustics...love the sound. After, I EnABLed a set of Fostex FE126E drivers and the resulting sound is worth the effort/cost IMHO. I do not regret the process. It will not take away from the sound of your stock drivers, just remove certain distortion caused by standing wave issues and smooth out the sound as well as 'clarifying' the sound. BudP may EnABL your 206s. Contact him directly. (He charges a fee...worth every penny IMHO). BTW, I read/enjoyed your build posts...I don't have the cahones to do such myself...

Richard

[Jim Shearer]

Kofi,

If by 'shout' you mean the excessive high freqs that result in overly detailed sound causing fatique, then I would try a baffle step correction circuit. Worked wonders for me w/ Fostex FE108E(sigma). You can read up on it at Martin's quarter-wave.com site. He even has a calculator to help you pick the parts you need; look under 'speaker related articles.' The FE108 didn't need the zobel network--don't know about the FE206. If you try it, be sure to vary the resistor values a bit to see how you want the BSC tuned for your room & preferenes.

Cheers, Jim

[ultrakaz]

The driver in your link is a Fostex 168 Sigma old style with whizzer. It was treated with genuine C-37 lacquer which resulted in the dark brown color. The acrylic blocks were easily removed because of the lacquer. An untreated cone will likely absorb the acrylic paint.

Bud has a pattern schema for phase plugs. Or you can enAbl the the pole piece or dust cap. I've tried all and they do make a difference to varying degrees. Taping the pattern may add too much weight and affect the conformal coating that needs to be applied. Read Bud's account of the drivers he's been "enAbling" and you will find that he tunes the drivers with the coating, which is often overlooked but a key part of the process.

The best way to rid the shout is with a notch filter or a huge (Beauhorn style) mushroom phase plug. The other tweeks will not pad down the peaks enough and are for making a good driver better and not making a shouty driver listenable.

[planet10]

Originally posted by Kofi Annan
Here are the modifications I've made to the driver / cabinet so far:

1. Installed Dave's (Planet 10's) phase plugs (is there anything they can't do?)
2. Damped the magnets with wool felt
3. Grounded the - terminal to the basket
4. Added a good hunk of polyester batting to the back wall of the compression chamber

You have not listed a quite crital (and reversable) mod. The basket/magnet junction needs to be damped & streamlined to provide a smooth exit for the backwave, Ductseal is the easy way. It is effective too. A step further would be to apply a stiffening agent at the apex of the juncture -- epoxy, Silent Running SR500 or metal-weld (last recommended by Ron C)

1. Would the pattern for the 206ES-R work for the 206E? If so, is there printable pattern available?

I will be generating a pattern shortly for the 206/207 (i have a couple pair of 207s to do). I may also have some extra tricks from the FE127 research we are evaluating now.

2. Would the fact that I have installed the phase plugs change or eliminate the effectiveness of EnABL?

No, but you do need to EnABLE the plugs as well.

3. There has been some discussion of taping the pattern on to the cone to allow removal of the blocks. Has anyone tried this?

i don't think this would be as effective and you might well tear the paper surface.

4. Also, one of the threads I have attached above mentions that if acrylic paint is used, the blocks may be removed with alcohol. Has anyone successfully removed them this way?

Not off the banana paper you won't

dave

[Kofi Annan]

I would try a baffle step correction circuit

I built Martin's BSC circuit some time ago, putting them in cigar boxes so I could switch the circuit in and out as desired. It really does make a difference and I tried different resistor values, but it dulled the image and reduced the sensitivity too much for me, so I had generally left it out.

So this weekend, I found I had a leftover 3.3uF Obbligato cap from the DRD build (sounds worse than it is-- the cap didn't make it in due to size and was substituted) so I used it as the shunt cap in place of the Solen 3.0uF. There's really a sizable difference in the sound-- it's a good bit smoother, but I wonder if this is due to the quality of the cap or the additional .3uF rolling things off earlier (later?).

I'm getting closer-- the shout is almost gone and the sibilance is improved, but there's still some shhibilanshe on male voices in particular. I have the day off, so I' headed out to grab some modeling clay for basket damp-er-in'.

Also, I wonder if I don't have too much polyester batting behind the driver. The magnet is damped with wool felt, so could I now remove the batting along the back wall of the compression chamber in favor of a thin layer just to absorb reflections?

Well, I know I could, but would that help?

Also, am I really screwing up the BSC by using the increased cap value?

Kofi

[Jim Shearer]

I probably don't know enough to comment, but I'll say something away, just take it w/ a grain of salt & get other's feedback too.

The cap is part of the zobel network to fix the issue of the driver's rising impedance at high freqs. I have no idea how sensitive the circuit is to changes. As I understand it: the inductor will control the hinge point of the BSC and the resistor will control the magnitude of the BSC effect. Martin's Excel calculator for the BSC gives a range of values for both parts, depending on what your situation may require. If the stuffing in the box is too much, that can certainly kill the sound--as I found out in building my Metronomes. I needed much advice from Steve C, Scottmoose, and Dave D to get that right! Then the BSC gave me the final tweek.

Cheers, Jim

[Ropie]

Originally posted by Kofi Annan I have been running them through my Fostex 206Es in the 208EZ backhorn.

Kofi, there's probably a whole thread on this out there somewhere but why did you put the 206Es in the 208EZ back horn cabinet?

[Scottmoose]

I can't speak for Kofi, but I can say that the 206 works a whole lot better in there than in its own cabinet, which is not one of Fostex's finer moments. Similar extension, much better LF gain & far less ripple. Doesn't have the big hole in the midbass the 206 box suffers from either.

[Kofi Annan]

If the stuffing in the box is too much, that can certainly kill the sound--as I found out in building my Metronomes. I needed much advice from Steve C, Scottmoose, and Dave D to get that right! Then the BSC gave me the final tweek.]

Yep. Started messing with the stuffing today. More on that in a minute.

the 206 works a whole lot better in [the 208EZ cabinet] than in its own cabinet

...and how! Really incredible bass response in the 208EZ cab.

So, here's what happened today:

1. Removed most of the polyester batting from the back wall in the compression chamber.

2. Replaced the shinola-ton of wool felt on the magnet with a simple disc of felt sticky-taped on the back.

3. Added modeling clay to the magnet/basket junction like Dave said.

4. Kept the BSC correction circuit in with the 3.3uF shunt cap.

This really sounds great. There's no more shout at all and while the presentation is rather relaxed, I'm really enjoying it. The instruments are really individualized and I can listen without any fatigue at all.

One thing I've noticed, however, is that the louder the better, meaning that the bass just blankets you and the whole thing sounds liquid when it's almost at full blast, but doesn't seem as balanced with the volume down.

This could have something to do with the "room gain" concept I've seen referenced on the boards. Also, I distinctly remember not doing too good of a job sealing up the gaps when I built the 208EZ cabs, so it may be that the bass becomes correct once the air flow inside the cabinet is so intense that the air crowds the gaps and pushes out the mouth, resulting in increased bass response.

However, it may just be that I like it motherfather loud.

I need to rebuild these cabinets in baltic birch and seal them tight, so I'll work on that. Right now, these sound good to my ears, but then, the seven-or-so scotches may play a factor...

Kofi