Sealed Bipole with Fostex FE12(6/7)E

[alexmoose]

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.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

[Scottmoose]

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).

[gmilitano]

Originally posted by alexmoose
http://diyaudioprojects.com/Speakers.../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.

[alexmoose]

Originally posted by gmilitano



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

[Scottmoose]

I'd stick your reciever on the subs. Give your main units (with 127s) the higher quality power (assuming it is of course. )

You want small FR based speakers? 'ere you go: http://www.planet10-hifi.com/fonken.html

[gmilitano]

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.

Originally posted by alexmoose


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

[alexmoose]

I am trying to decide which driver to use. I want the added sensitivity of the 126, but most logic points to the 127, but I have two subs, and the equipment to drive them

[planet10]

A sealed FE126 might be good down to 250Hz. It won't need subwoofers, it will need a woofer that goes up to about 1k or higher to get a decent mesh.

dave

[Scottmoose]

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.

[alexmoose]

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