[djn]

Hi All, I just aquired a pair of OB horns with Fostex FE126E drivers and a pair of "H" boxes with Alpha 15A in them.  I am now going to work on the crossover and need to figure out the right place to cross for the "H" boxes.  The FE126E rolls off at 200hz so I know I need to be around or above that.  The "H" boxes are 22"w x 22"h x 11.5"d with the baffle board in the center of the 11.5" depth.

I am not so start when it comes to the computer programs used to figure this out.  Can anyone help me with this?  Thanks so much in advance.

ps, the back of the FE126e is open so technically it is OB, but kind of neither fish nor fowl.

[JohnR]

You could have a look at MJKs published project :

  http://www.quarter-wave.com/OBs/OB_Design.pdf

If you can get access to a mic and a USB mic preamp you might want to measure them before spending on the crossover parts, as values in that range are fairly large (i.e. expensive). Is active an option?

[djn]

I read through MJKs paper but still don't under stand it all.  I just talked to a friend that has a spare Active Xover.  We try that this weekend.

Are "H" boxes any good?  I can see in MJK's paper that they can work down low, but how is the sound?  Any issues there?

[JCS]

I have only heard MJK's H-frames with the 18" Goldwood woofer.   Used with several different full range drivers running OB on top of them.  In fact, I will be going over to MJK's tomorrow to listen to FE126e and FE126enabled (by Dave of Planet 10) to see if I can hear any differences and whether I prefer one or the other.

But I digress.  IMO the H-frames sound FABULOUS!  clean, detailed, nuanced.  They do it all.  You would never know that you are listening to a bargain priced driver.  For me, it's bass done right.  The one thing that might help them is to add weight on top of them.  At least with the 18" drivers, the simple H-frame made from 0.75" plywood needs a little extra mass to hold it in place when the driver really starts kicking.

As to the XO, I would start around 125 Hz on the H-frames.  You may need to drop it a bit lower, but that's a place to start. Explanation can be found in MJK's project papers.  If you set it higher, I think you will end up with a hump in the response. 

Cheers,  Jim

[djn]

Thanks Jim.  I am running may subs up to 150hz at the moment and it seems a little thin in the lower mid region.  Hopefully I will get the active crossover going this weekend and play with the xover point.  I've never heard OB woofs but from what you said, they might work very well.

I sure do like the looks of them and would hate to muck that up with bags of lead shot on top.

[scorpion]

Maybe Jim is a bit too short in his his arguments. For crossover you will rely on the frequency response of your H-baffle with the Alpha15. MJK shows in his examples variations for passiv crossing with 12 dB/octave Linkwitz-Riley characteristic where the actually chosen crossover frequency results in an effecient  crossover frequency that is higher. For your setup I would say that crossing at 125 Hz 12 dB/oct L-R will result in an effective crossover frequency around 275-300 Hz. Reaching 200 Hz for the resulting crossover I would suggest starting at 150 Hz 24 dB/Oct L-R crossing and meeting this with a similar 200 Hz crossing for the FE126 horn. Interesting combination ! Good Luck !

Let's see if Jim will confirm MJK's no hearing any 'Enabled' effects.

/Erling

[djn]

I will be hooking up the active tomorrow and playing with the crossover point.  I've also been reading up on the Planet 10 Enabled FE126Es.  They are great drivers as is, but they do tend to be shouty.  I'd like to hear from others that have gone the Enabled route.

[djn]

Hi All, yesterday two friends came over and we hooked up the QSC active crossover.  Well that did not work so well.  For some reason, it was not crossing over and allowed the "H" frames to run wide open....which by the way sounded very good.

John brought over an active (which I can't remember the name of) that used plug in chips for the crossover point but only had a 90hz chip with him.  That sounded good but as you might suspect was not high enough and resulted in a thin midrange.

The up shot though was INCREADABLE bass.  The most open and detailed I'd ever head.  At first the "H" frames were back near the back wall and really came alive at 31hz but had a huge bump at 63hz.  We pulled them out two feet from the back wall and they came alive at 41hz but were then flat up to 500hz or so.   I am really impressed with them.


My other friend George listened to them for an hour then got online and ordered two 15As.


In total we spend 5 hours messing with them.  Theey are 22" by 22" baffles and 11.5" deep so that is a bit larger than MJKs but still work very well.  I have a pair of Steve Bench tube crossover boards that I will now build for the crossovers.  I think thay are 6db.







,

[JCS]

djn,

Sounds like you are on your way to a really sweet sounding system!  I'm sure you will love it when you get the XO dialed in.

-------------------
Scorpion,

I listened to FE126e, std. and Enabled, over H-frames w/ 18" Goldwoods at MJK's on Sat.  The 126's were on 20 x 20" OB.  They sounded very nice! 

I did hear subtle differences between the std. and Enabled drivers, but mostly attributable to the std drivers not being fully broken in.  I think I have enough experience w/ Fostex drivers to know the sound of new and old drivers and how it changes.  Concerning Enable, my view is: I can't see what all the fuss is about.  Whatever it is that the proponents of Enable are hearing, I just don't get it.  Chalk it up to personal preferences.  I really enjoy the sound of OB speakers, but I know there are folks who hate that sound.  If we all heard things the same way, then we wouldn't need all those different speaker manufacturers!

Cheers,  Jim

[djn]

You are right, we would all buy Bose

I am wondering if I need a crossover.  They sound pretty darn good as is.  Maybe if I really crank it, there might be some break up or distortion, but with just a "Y" coming out of my preamp into two amps, I like it.

Later today I will mess with baffleing the driver a bit on one or two sides just to see if that eliminates some of the cancleation that MUST be going on as the drivers are centered.

[djn]

Just for kicks, I took out the "H" frames with the Alphas and hooked up my JBL Scoops.  Man those things kick like a mule.  BUT, I find I did not like it after a half hour.  I guess I am getting old.

[rjbond3rd]

Hi djn, what a beautiful setup.

Is your right-side horn really that close to the wall, as shown in the picture?  I have a similar horn, where the driver is open-backed, and it definitely needs to be out from the wall.  I'm sure you already know this though!

P.S. my design is very similar and in my opinion, a crossover is so beneficial that I would say it's practically required.  I've heard only one design where it wasn't required (a BLH with a tapped horn but the tapped horn was low-passed with an inductor, so half a crossover).

[chlorofille]

djn,

Maybe you could consider using a passive, acoustic LR-2 (2nd order) crossover at around 275Hz.
What amp are you using?
I think a good SET valve amp would bring tremendous musical pleasure with that set up.

[djn]

Actually those are pix from the guy I got them from.  Below are pix of my room.  They have plenty of room to breath.  I agree with the need for a crossover.  The Steve Bench tube crossover I am building will be set at 300hz or so.  I friend of mine is bringing over his Rane active and we will adjust to the best xover and build to that.

Hi djn, what a beautiful setup.

Is your right-side horn really that close to the wall, as shown in the picture?  I have a similar horn, where the driver is open-backed, and it definitely needs to be out from the wall.  I'm sure you already know this though!

P.S. my design is very similar and in my opinion, a crossover is so beneficial that I would say it's practically required.  I've heard only one design where it wasn't required (a BLH with a tapped horn but the tapped horn was low-passed with an inductor, so half a crossover).

I am currently using SS amps but have four tube amps on my bench to complete  This system will be driven by an GM70 SET amp.  I will most likley do a passive just to see how it sounds.

djn,

Maybe you could consider using a passive, acoustic LR-2 (2nd order) crossover at around 275Hz.
What amp are you using?
I think a good SET valve amp would bring tremendous musical pleasure with that set up.

Here is my room.

[chlorofille]

What a gorgeous room! Warm, cozy and inviting !!

[djn]

Thanks C.  The guy who built the house was the Cheif audio engineer for Ford Motor.  The room is built to Paul Klipsch's specs.  The guy had Khorns in the corners and Mac gear up on the shelve.  From the gear, there is wiring in the walls to the khorns.

Lucky to have it.