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Old 8th January 2012, 09:18 PM   #621
holdent is offline holdent  Canada
diyAudio Member
Join Date: Nov 2005
Location: Ontario
Originally Posted by woody View Post
I am considering biamping. This design calls for a 12db/oct crossover but could
I use 24db/oct on the woffer and 12db/oct on the full range driver or failing that
anyone know how to modify my Behringer cx2310 for 12db/oct slopes and still
use the same xover points?
Hi Woody:

I built both passive and active versions of MJK's OB with a Alpha 15A and Fostex FE103E and really enjoyed them. I've used a Behringer cx3400 for the active version.

You can biamp using your cx2310 but you need to change the crossover points and invert the phase of the woofer. Since that xover limits you to 4th-order LR filters, I would suggest that (using the cx2310) you either:
a) set the crossover at 275 Hz for both the woofer and fullrange and perhaps boost the bass by about 2 dB or
b) set the crossover at 350 Hz for both - this perhaps provides the best modelled response but I found that this wasn't as satisfactory for nearfield listening because I could locate the woofer.

It isn't worth having someone modify your Behringer to have 12 db/octave filters -- its much cheaper just to buy a MiniDSP or Behringer DCX2496.
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Old 4th August 2012, 04:30 PM   #622
RKH is offline RKH  United States
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Join Date: Sep 2002
Location: Colorado, USA
Default Another pair

I've been listening to these, 'unfinished' for 3+ years. I just got around to the wood work and router work behind the Fostex.

There are a few mistakes in the finish. I guess that adds to the character. I sure do enjoy how they sound.

Attached Images
File Type: jpg OB Front.jpg (137.7 KB, 572 views)
File Type: jpg OB Back.jpg (140.9 KB, 543 views)
File Type: jpg OB Fostex.jpg (84.4 KB, 541 views)
Lighten up while you still can ...
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Old 5th September 2012, 11:47 PM   #623
carcass is offline carcass  Portugal
diyAudio Member
Join Date: Oct 2006
Originally Posted by holdent View Post
Hi Woody:

I built both passive and active versions of MJK's OB with a Alpha 15A and Fostex FE103E and really enjoyed them. I've used a Behringer cx3400 for the active version.
Care to share your cx3400 settings?
I'm just finishing mine and have the exact same behringer!


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Old 7th September 2012, 12:51 AM   #624
holdent is offline holdent  Canada
diyAudio Member
Join Date: Nov 2005
Location: Ontario
Hi Bruno:

You're stuck with 4th-order Linkwitz-Riley x-overs with the CX3400. However I got very good results with it set to 350 Hz for both the low- and high-pass filters. When I initially modelled it with MJK's worksheets I though it would be best to back off the Alpha 15A by 3 db. However in practice I thought the sound was much better balanced in my room with the level set flat.
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Old 26th November 2012, 09:58 PM   #625
drongo is offline drongo  Australia
diyAudio Member
Join Date: Apr 2004
Location: Sydney
Default Many Thanks to MJK

I too have just built a pair of MJK open baffles. My implementation has used Lowther DX3s, Alpha 15s and miniDSP as an active crossover. I drive the DX3s with a Trends T-amp and the Alphas with my old Rotel 40 watt amp (a little small I know but just fine my for modest volume needs) I used Martin's crossover points of 200 and 400hz and no equalisation.

Result: fantastic - if you're reading this you've probably read the other posts about MJKs OBs - they're all true. I was in the fortunate position to already own a pair of DX3s, however I'm sure any one of many other wide rangers would fit the bill.

I would recommend the miniDSP - it gives you the choice to run the driver of your choice and its a breeze to configure.

Just a note on the bass sound - it is articulate, sounds like about 40hz and its a "big natural" sound. "Normal" 6.5 - 7inch polypropylene mid bass units (to my ears) have a more "authoritative drier slam" - not bad but different. I'm very happy with these - I can't imagine building anything better.
Attached Images
File Type: jpg alpha_DX3_OB.jpg (638.7 KB, 289 views)
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