Sealed Bipole with Fostex FE12(6/7)E

Hello everybody!

I am finally going to build a better pair of full ranges after I heard the simple bass reflex design of the FE126 that a friend of mine built, and I am vastly fascinated by the sealed bi-pole design found here
http://diyaudioprojects.com/Speakers/FE127E_SB/FE127E_SB.htm

but as usual, there was some uncertainty.

1. I don't care if the driver is shielded, can i simply use the 126E, and get more efficiency out of the speaker? as I am going to be driving them with an EL34 SET (~5 watts).

2. as far as wiring goes, if I wire the two in parallel vs series, I have a 16 vs a 4 ohm load, however, If I mess with the wiring, switch the positive, and negative terminal on one driver, will the two fire OUT of phase and become a Di-Pole instead of a Bi-pole?


3. Is bi-amping practical at all with these? I know I would have to make a second EL34 amp to be able to bi amp them, however, would using the exact same amplifier be close enough to get them to act as a bi-pole, or do they have to be plugged into the same amplifier?

4. could I power only one driver and use one as a passive radiator? and what would the consequences of this be?


any help on any of these questions would be appreciated,
Thank you

-Moose
 
1) No. Specs & alignments are different. Sealed is relatively fogiving compared to other alignments, but even so, you want to be designing a box for the driver. Qt of the 126 is much higher than Fostex claim, but it's still lower than the 127, so you'll have even less LF than with the driver it's designed for (which will itself be marginally less than nothing).

2) You can run them out of phase, but if the sealed box is of the acoustic suspension type (which it is), you'll loose the advantages of it because as one driver moves out, the other moves in, so there is effectively no air displacement / pressure in the box.

3) I wouldn't bother. You'd probably get more benefit upgrading your output transformers or putting the money elsewhere.

4) Yep, although it wouldn't be ideal. You're moving away from sealed into effectively a vented type of alignment there though, so ideally, you'd need to design it from scratch, & have a proper PBR designed for the purpose, rather than a second driver (bit of a waste of the second driver really).
 
alexmoose said:
http://diyaudioprojects.com/Speakers/FE127E_SB/FE127E_SB.htm

1. I don't care if the driver is shielded, can i simply use the 126E, and get more efficiency out of the speaker? as I am going to be driving them with an EL34 SET (~5 watts).

4. could I power only one driver and use one as a passive radiator? and what would the consequences of this be?


Hi alexmoose, it seems that Scottmoose has answered the questions but I will add a bit.

1. This design will need a sub. The FE126E will result in a higher XO and as a result the bass may become directional. I suggest the 127 unless you will have two subs.

4. Using the rear driver as a passive radiator works. The result is more bass. I tried it just for the sake of trying it. I did not play with it too much as the bipole sounded much better. It will need a BSC to balance out. So as Scott mentioned, it is a waste of a second driver plus you need a BSC. To me, the big advantage of a bipole is eliminating the BSC.

Just in case you missed it, here is Alex's build of the DIY Fostex FE127E Sealed Bipole Speaker and his comments and experience.

Let us know how you make out or if you have anymore questions.

Cheers.
 
Re: Re: Sealed Bipole with Fostex FE12(6/7)E

gmilitano said:



Hi alexmoose, it seems that Scottmoose has answered the questions but I will add a bit.

1. This design will need a sub. The FE126E will result in a higher XO and as a result the bass may become directional. I suggest the 127 unless you will have two subs.


The original design featured a 20" open baffle sub? I assumed I would still need a sub even if I went with the 127 design.

I have two subs with 120wpc to push them with, and an extra crappy receiver to drive them with. should I need my good receiver to drive the bipoles with 127, or the good receiver on the subs, and the SET on the 126 bipoles?

As long as I don't have to re-work the box, I am going to buy the lumber tomorrow, and assemble them sometime this week.

as well, my roomate is looking for a good speaker design that is smaller, is there anyway I could literally shorten this project (shorter tower, less stuffing?) with the same sound?

Thank you all so much

-Moose
 
Re: Re: Re: Sealed Bipole with Fostex FE12(6/7)E

The OB 20" sub and active 24dB XO was one setup that was tried over at a friends place. It worked very good, but I'm not allowed to have speakers that big.

I use mine with a HT amp with built in XO (12dB) and a single ported sub. It works well too.

With an active XO, you can get some very good SPL.

It will also work fine running fullrange with say a tube amp.

I'm a bit confused, will you be using the FE126E or the FE127E?

Yes a smaller sealed box will also work well, just a little loss on the low end. As Scott mentioned sealed enclosures are very forgiving.




alexmoose said:


The original design featured a 20" open baffle sub? I assumed I would still need a sub even if I went with the 127 design.

I have two subs with 120wpc to push them with, and an extra crappy receiver to drive them with. should I need my good receiver to drive the bipoles with 127, or the good receiver on the subs, and the SET on the 126 bipoles?

As long as I don't have to re-work the box, I am going to buy the lumber tomorrow, and assemble them sometime this week.

as well, my roomate is looking for a good speaker design that is smaller, is there anyway I could literally shorten this project (shorter tower, less stuffing?) with the same sound?

Thank you all so much

-Moose
 
There isn't all that much difference in sensitivity between the two, and given that it's designed specifically for the 127, logic says that's the one to go for. As well as the fact, as Dave points out, there's a difference between subs & woofers. You need the latter if you wanted to go with the 126, which really isn't a good choice for sealed box loading.
 
I have my bi-poles with the 127Es built!

let me tell you, the sound rivals my Magnaplanar SMGs, and they leave nothing to be desired in the efficiency department, they scream off of my SET, and have exposed alot of flaws in that little amplifier that now need to be addressed.

Despite the amazing sound, is it at all possible to mod the drivers to make the sound amazing-er! I know some people mod the drivers of the 126, i was wondering if people do the same with the 127?

over all, project was an amazing success, small speakers that really pack a punch, I am just now starting work on the active XO... which leads me to another question.

80hz seems to be the Freq to go with, however, how should I adjust the order of the active XO to accommodate the natural roll-off of the design?

I'm thinking these speaker's very own amp is going to be PP 2a3, sound good?

-Moose
 
Hi Alexmoose,

That is great and I am glad you like them. Sealed is my preference for this driver. It goes deep enough to integrate well with a sub. It plays pretty loud and even louder if you have an active XO and limit the bass.

Can you share some pictures of you build? I would love to see them.


As for tweaks, you can try phase plugs. They should tame the upper end at the expense of off axis response. Also there is this very long thread on the enable process:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=100399

Cheers
 
gmilitano said:
Hi Alexmoose,

That is great and I am glad you like them. Sealed is my preference for this driver. It goes deep enough to integrate well with a sub. It plays pretty loud and even louder if you have an active XO and limit the bass.

Can you share some pictures of you build? I would love to see them.


As for tweaks, you can try phase plugs. They should tame the upper end at the expense of off axis response. Also there is this very long thread on the enable process:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=100399

Cheers


messrs Moose et al - due to the physical location of the voice coil lead-ins, installation of phase plugs on the FE126 & 127 is bit trickier than any other Fostex we've tackled to date, but certainly well worth it. It should also be noted that the Planet10 treatment to these drivers includes a couple of features not part of Bud Purvine's Enable process alone.

We listened to quite a few variations last year before settling on what we found to be a quite synergistic combination.

In the case of bipoles, I'd suggest that treatment to the front drivers alone might well be enough to effect substantial improvements.


If you want to really step things up a notch (even with a monopole) , actively XO the FE127 to a pair of woofers between 100-120Hz, and hang on for the ride. When well implemented for seamless integration, the first things you'll notice is substantially improved dynamics and midrange.
 
chrisb said:
If you want to really step things up a notch (even with a monopole) , actively XO the FE127 to a pair of woofers between 100-120Hz, and hang on for the ride. When well implemented for seamless integration, the first things you'll notice is substantially improved dynamics and midrange.

Here is the current state of that experiment... push-push SDX7 FonkenWoofTL prototypes, 100 Hz active XO (a real surprise pulled out of my antique collection), and the new CSS RT1 XOed with a cap @ ~ 25k.

The little boxes on the side of the cabinet are the µFonkenWoofs (single sealed SDX7)

dave
 

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planet10 said:


Here is the current state of that experiment... push-push SDX7 FonkenWoofTL prototypes, 100 Hz active XO (a real surprise pulled out of my antique collection), and the new CSS RT1 XOed with a cap @ ~ 25k.

The little boxes on the side of the cabinet are the µFonkenWoofs (single sealed SDX7)

dave


Thanks, Dave - I wasn't sure if this was yet ready for publication.

This system is amazingly well integrated, and has no problem filling Dave's large space with very clean bass and huge soundstage. With the ribbon XO set this high (and "presbyopic" hearing :angel: ) it's hard to hear much contribution from the ribbon.

"Nights at the Alhambra" never sounded this big at my place - you never want the concert to end.
 
alexmoose said:
80hz seems to be the Freq to go with, however, how should I adjust the order of the active XO to accommodate the natural roll-off of the design?

alexmoose,

Vary the XO point depending on room, amplifier and taste. Ball park 75-120 Hz. 80Hz worked best for my setup.

As for the XO, a sealed box rolls off at 12dB (2nd order). So you can use a 2nd order on the low pass and let the FE127E roll off naturally. My best results were 4th order on both low and high.
 
gmilitano said:


alexmoose,

Vary the XO point depending on room, amplifier and taste. Ball park 75-120 Hz. 80Hz worked best for my setup.

As for the XO, a sealed box rolls off at 12dB (2nd order). So you can use a 2nd order on the low pass and let the FE127E roll off naturally. My best results were 4th order on both low and high.


and in the case of the system Dave pictured earlier, the XO of 100Hz was simply the fixed setting on a "heritage"* unit from his collection

*read stuff forgotten in the basement for 20+yrs, some of which still works (perhaps not so ) surprisingly well compared to current fare
 
Dave,

Please tell us more about the "heritage" XO that worked so well. What LP and HP slopes were employed? Was the XO active on both the LP and HP legs? Given its age, any chance that the active stages used those "nasty sounding" AD711/712 opamps ;)?

I've added woofers to full range speakers in the past, but, in my experience, good integration with the fullrange has been difficult to achieve.

Dean
 
dhieber said:
Please tell us more about the "heritage" XO that worked so well. What LP and HP slopes were employed? Was the XO active on both the LP and HP legs? Given its age, any chance that the active stages used those "nasty sounding" AD711/712 opamps ;)?

I'll let you know when i figure it out... Its an Ace Audio XO, and with a dinky PS i didn't expect much of it.

I've added woofers to full range speakers in the past, but, in my experience, good integration with the fullrange has been difficult to achieve.

That has mostly been my experience too...

dave
 
dhieber said:
Please tell us more about the "heritage" XO that worked so well. What LP and HP slopes were employed? Was the XO active on both the LP and HP legs? Given its age, any chance that the active stages used those "nasty sounding" AD711/712 opamps ;)?

I got it reverse engineered last night. One thing i have to say is that it is minamilist. Signal passes thru 2 opAmps, an input buffer followed by a 2nd order high or low pass filter. opAmps had already been swapped out (OPA2134) and are being used as straight buffers (i had also installed new RCAs & a couple small poly bypass caps on the PS elcos). Fixed C, variable R (an 16-pin DIP plugin). R & C values don't seem to fit the usual schemes, i'm going to guess that the filter Q are somewhat different than usual.

Only has level controls on the HP. Only one pair of power supply decoupling caps. No regs in the PS (and althou the trafo seems to be center-tapped, the ground reference is established virtually with a pair of Rs. And i have a question about ground reference for the input of the LP cheip (i'll ask once i get the map drawn)

I'm going to try swapping out some electrolytics on the output, and maybe a couple others. Also decouple all the PS pins, and graft on a regulated power supply (in a separate box) and see where it goes.

Next experiment will be to build up something similar but use JFET buffers instead of opAmps.

dave