[mgalusha]

OK all you OB guru's and junkies. I may undertake a little experiment and welcome any help I can get.

In this thread: http://www.audiocircle.com/index.php?topic=53098 where I obtained a pair of Mark & Daniel monitors that had been destroyed by UPS, DMason suggested that I try the drivers in an OB setup.

I remember reading the label on the back of the drivers that they have 10mm of XMax, so hopefully bass won't be entirely terrible. I have a Woofer Tester II, so I can get the parameters. I have downloaded MJK's documents and will be giving them a good read so I can at least have an idea of where to go next. The existing M&D monitors use this woofer: http://www.mark-daniel.com/Dir_En.asp?Proid=15 and this tweeter: http://www.mark-daniel.com/Dir_En.asp?Proid=10 - which is basically a Heil AMT. The tweeters are open backed, so I'm hopeful they will be happy with an open baffle.

I have a DCX2496, so actively crossing them over will be easy to do. I would likely drive the tweeters with an OTL amp using some Speltz Zero Autoformers to raise the impedance up. The OTL wouldn't care for the 2.8R load at all. 

To start with I'll just use some cheap plywood I have on hand. I have a couple of pieces that are currently 24 x 96 inches.

I do have a semi decent measuring microphone, a Behringer ECM8000, not great but not completely horrible either.

I mention all this in hopes that some of you might offer some pointers before I fire up the power tools and make sawdust.

I realize that bass will be limited but I can build something to augment that if I can get the main portion sounding good.

Thanks for any info or tips that you can offer.

mike

[Dmason]

Now you're thinkin'...turn a lemon into a lemonaid..

Can you not use the existing crossover? If it is glued to the floor of the cab, it could be pried off delicately I would think. Or saw it out. The cabinet looks like some blow-moulded composite stuff, should yield nicely to a jigsaw. Failing that, if you were to actively XO and biamp, I would bet $ that you would be astounded by the result. These are evidently quality drivers being freed, the Prisoners of Acousta, will thank you for being released to the care of static air masses. My guess is you are in for a winner..

Two of the best drivers I personally have ever heard on OB were the stock Pioneer paper 6X9's I pulled out of the rear of my Honda Accord. So, how can you go wrong?

My recommendation is to look at this as a one- 6 Pak job. Hope that puts it into perspective.

[mcgsxr]

Welcome to the madness Mike!

Not sure if 24 inches of width will support significant bass, but it also comes down to the FS of the driver in question, and of course the QTS.

The best thing to do, to get started, is to cut some holes, and mount those drivers, and fire them up and see what happens.  You might find that experimentation with duct tape, and cardboard to extend the baffles, and/or play with wings, may take you in a direction quickly - then you can formalize in more significant material.

Have fun!

[scorpion]

Mike,

Yes, go ahead and retrive bass parameters, then we perhaps can go on discussing design !

/Erling

[markC]

My first attempt would be to migrate the x-overs, cut the plywood to around 42" high, mount everything and have a listen. Do you know what the x-over freq. is? You'll likely want to mount the midbass unit fairly low with the tweeter on top almost touching and tilt the baffle back a few degrees to fire close to ear level.
My MB driver is 26" from baffle bottom to centre. Baffle is 30" wide and 40" tall. Don't know if I just lucked out, but after only a few baffle size experiments they produce suprizingly good bass.
There are pics in the Toronto and area audio society circle under the thread "northern exposure meet" -last couple of pages IIRC.

[mgalusha]

Thanks for the input gents, most appreciated.

I was able to extract the XO's without a problem and nothing appears to have been damaged, at least just looking at everything. I'll connect them up and make sure all is well.

Since the XO's appear to have survived I'll give them a try. I haven't drawn a schematic yet but they look to be 2nd order.

Looks like a trip to orange depot is in order tomorrow to grab a larger piece of plywood. The weather is supposed to be nice, so that'll make it easy. Don't have to cover the trailer. 

Had some fun with what was left of the cabinets. The material is supposed to be synthetic marble but looks more like the ceramic your toilet is made from. It's amazing what happens when you smack a brittle material with a ball-peen hammer.  I've never beaten a speaker to death before and I have to say it was kind of fun.

I've just printed Martin King's OB documents out and I think I'll listen to a little music and give them a read.

I'll post the results of testing the drivers and crossovers. Hopefully they are OK and I can build something with the parts.

Do you know what the x-over freq. is?

Supposed to be 800Hz.

Failing that, if you were to actively XO and biamp, I would bet $ that you would be astounded by the result.

I've been using an active XO for about 16 months and astounded is a good term for what I heard. While my current speakers, Meadowlark Blue Heron 2's, don't even resemble an OB they are a TL and I very much like how they sound using an active XO and biamping. Hence my thoughts about using the active xo and amps for the OB project. The XO is a much modified Behringer DCX2496 and of course allows me to adjust XO point, slopes and baffle step very easily.

mike

[oracle309]

Well here I rant again.

please spend some money on some good BB plywood. Take your time. Cheap ply and good drivers are a terrible mix.
Somehow you will need to hold the baffles up, so use some leftovers from the plywood purchase and make "uprights.
Cant the baffles back about 10 degrees.put a full width "shelf" between the uprights. You may also want to put a sheet of material behind the bass driver, at least as wide as twice the diameter of it. This will help a lot with bass, and hopefully will result in not requiring active correction.

do a search for the "no-box" a Visaton design, to get an idea. Personally I own, use and promote the "JE Labs" style of OB, 31" tall, 35" wide.

[markC]

I absolutely agree with the BB ply. That's what I use.
Mike's just getting a "taste" here, thus the recommendation to go on the cheap to experiment. When and if it works out, then spend money on quality materials.

[mgalusha]

Oracle - Thanks for the input. I fully intend to use decent wood if the initial results are promising. I much prefer quality over quantity.


Anyway, for those who might be interested, the results from Woofer Tester 2.

;==================================================================
Q test completed: Sat Apr 05 14:18:36 2008
Q drive current  3181.82 uA
;------------------------------------------------------------------
Revc=    3.1256 ohms
Far =   50.7571 hz
Zmax=   26.8817 ohms
Ro  =    9.1662 ohms
F0  =   39.0045 hz
F1  =   72.8562 hz
Fmin=  193.5672 hz
Qms =    4.3972
Qes =    0.5785
Qts =    0.5113
Le  =    0.7719 mh @1kHz
XLe =    7.3357 impedance @1kHz
PLe =   41.3856 phase @1kHz

;==================================================================
Vas test completed: Sat Apr 05 14:33:13 2008
Vas drive current  3181.82 uA
;------------------------------------------------------------------
Revc       =    3.1256 ohms
Fs         =   50.7571 hz
Zmax       =   26.8817 ohms
Qes        =    0.5785
Qms        =    4.3972
Qts        =    0.5113
Le         =    0.7719 mh  (at 1Khz)
Diam       =  123.0000 mm  (  4.8425 in  )
ConeArea   =11882.2893 mm^2( 18.4176 in^2)
Vas        =    8.9686 L   (  0.3167 ft^3)
BL         =    6.1201 N/A
Mms        =   21.7391 g
Cms        =  452.2763 uM/N
Kms        = 2211.0378 N/M
Rms        =    1.5767 R mechanical
Efficiency =    0.1954 %
Sensitivity=   84.9096 dB @1W/1m
Sensitivity=   88.9912 dB @2.83Vrms/1m

[Bob in St. Louis]

Hey Mike,
The general OB guidlines have been covered pretty well here so far.
Personally, I'd start "too" large on the baffle size and trim width as you deem nessesary.
{have jigsaw near by}

Baffle too wide; You'll lose clarity, openness, soundstage, imaging. --UNFIXABLE
Baffle too narrow; You'll lose bass. Easily fixable. You've got the equipment to augment missing bass already, I'm sure.

Good luck. May the force be with you. Enjoy your OB journey. 

Bob

[Dmason]

Qts = .51 = 

These little mid-bass drivers are In The Game. They likely will make more than "alittle" bass.

Pretty cold and hungry little buggers. My rationale these days goes in the opposite direction: the $$ I would spend are directly proportional to system SPL.

[Bob in St. Louis]

Yea, sensitivity is a little low, but it's still high enough that a couple watts will still make the old folks happy.   

[scorpion]

Mike,

Here is a simulation with MJK's Math Cad models of your basspeaker in an OB 40 x 40 inches. I suggest you build this like MJK's in his project 7  Lowther Open Baffle System (16 " wide main baffle and two 12 " wings 90 degrees to the main baffle). Speaker was placed 30 " high and 4 " off center. You should have no problem compensating for the bass roll off and sensitivity should match the tweeters. I haven't ordered Jan Diddens kit yet, but I probably will.



/Erling

[mgalusha]

Thanks for all the input. Since this is just a first effort I'm going to give Erling's suggestion a go. I made a lot of sawdust on Saturday and cut all the panels. I will cut the holes and get the hinges mounted this weekend (hopefully) and get them up and running. I'm looking forward to it.

mike

[mgalusha]

Yea, sensitivity is a little low, but it's still high enough that a couple watts will still make the old folks happy.   

Not that old... Hell, I'm only 47. The OTL will do 70W/4R and 100W/8R and the LNPA's are good for 150W/4R so that should be enough for most purposes.

And if the whole thing fails I have a pair of EV SP12C's that are something like 97dB sensitive and since there is a thread on using a pair of SP12B's, I have other folks to bug.

[mcgsxr]

Any update Mike, on how this is coming together, or am I rushing you?

 

[mgalusha]

Mark,

Didn't have a chance last week and this past weekend I made an alignment tool for my Morch arm. The weather is going to be very nice today and tomorrow, so I'm hoping to get some garage time in the evenings. All the panels are cut, just have to cut in the driver openings and mount the hinges, drivers and XO parts.

[mgalusha]

Well it took a long time but I finally got these up and running yesterday. I'll snap a photo tomorrow but my initial impression is positive. I can see why so many folks like the OB sound. Bass is actually better than I thought it would be. The downside the the Mark & Daniel drivers are really low impedance. I have a pair of Speltz Zero auto formers and connected those up today. With the R.E. Designs LNPA 150's and the Zero's on 3x they sing very nicely.

Photos tomorrow. Big thanks to Erling for getting me going again.

Mike

[Bob in St. Louis]

Good to hear you've got OB in the house Mike.  Welcome to the club.
Yea, OB bass gets such a bad rap it generally end up suprising most folks when they finally hear it.

Can't wait to see the photos.  aa

Bob

[mgalusha]

As promised, a few photos.



View from the listening chair.  aa

Rereading the thread I didn't make them quite to spec. Erling mentioned using 12" sides. I made 12" wings and about 9" sides. But since the wings are hinged I can use them both ways tho they don't lean back when the wings are folded. Unfolded they tip back 10*. The front panel is 1/3 of the way into the room, about 80" (203cm).



Folded vs open.



XO and Zero Autoformer. You can see the extra cheap wire I used. Until I heard them I wasn't going to go to any trouble to mount the XO and use any kind of fancy wire. The woofers are wired with some old 12ga monster cable from a long ago HT project and the tweeters are wired with some 20ga stuff off a spool. As plain jane as it gets.



Drivers. You can see the pleats in the tweeter, so in this case they are really open baffle, front and rear.

The XO is 1st order, just a coil on the woofer and a series cap on the tweeter and a notch filter across the tweeter.

As for sound, I like them better with the wings folded. Bass is a somewhat better and imagining is much better. Funny, I received my new $tereophile today and Sam Tellig was talking about a C-J preamp and his basic premise was it didn't so much conform to the audiophile adjectives as it just allowed the music to flow. I was reading this while listening to the system and that description seemed very appropriate to what I'm hearing with the OB speakers. They don't have "slam" and "air" but they are sure fun to listen to.

I did note a bit of brightness so I put in a 6db/octave shelf filter from 1K up of about -4dB. I have not measured anything yet, this was a total seat of the pants adjustment. I tried a bit more and a bit less but this seem to produce a nice balance.

One thing that does surprise me is how loud they will play. Given the low sensitivity they seem to have the ability to play louder than I want to listen. I heard these when they were in the original Mark & Daniel cabinets and my amps ran out of gas trying to drive them. With the Zero's in place I don't have any sense of running out of power, so this seems to be the right choice. I was on the verge of packing up the Zero's and loaning them out but he's gonna have to wait.

Thanks for all the help and to DMason for the suggestion. Well worth the effort and so far I'm enjoying the ride.

mike