[jagtek]

Hello, I have question. Will the Eminence Beta 12-lta work in an open baffle speaker ?
I have a couple of them sitting around, and would like to put them to use.
Also can anyone guide me to an easy to grasp site for OB design pricipals.
Thanks, Jagtek.

[iON]

Hi Jagtec! You can learn a lot by reading old threads. And if you got some time on your hands, Why not try spend a couple of hours cardboard prototyping? Fast, fun and educating!

Cheers!
J

[panomaniac]

The Beta 12LTA can make a very, very good midrange on OB.  But I don't think you want to go full range.  Unless you have a really gigantic baffle!

You'll want a (super) tweeter up top and some bass reinforcement down below.
What size baffle do you want to build?  And do you have any bass drivers in mind?
I'll bet it would mate up easily to the Alpha 15.

EDIT:  Sorry, forgot to say.  You should read these two things.  They will get you started right.

http://www.lampizator.eu/SPEAKERS/PROJECTS/P17/Endorphine%20from%20Kingston%20Kitchen.html
http://www.quarter-wave.com/OBs/OB_Design.pdf

[jagtek]

Thanks for the replies. I really like the article by Mr. King.
One more question, If I use alpha 15 for bass and a decent super tweeter,
thinking a fostex unit, can I cross over the woofer with just an inductor, considering
the sensitivity's are similar, and the tweeter with just a cap, and run the beta 12 lta
full range ?
 I can use pretty much any size baffle, but would like to keep it around 24" wide.
jagtek.

[panomaniac]

Well you can, but I don't know that you'd want to.

Have another look at the Lampizator site.    This is a simple and sensible approach that really does sound good.
The idea is to figure out where your midrange is going to start dropping off on the baffle you use.  The wider the baffle, the lower the roll-off point.  The lower the Qts and Fs of the driver, the faster it will roll off in the low end.

Once you've got this figured out (try the xl-baffle spreadsheet)  you know where to set the low pass for your woofer.  The lower the frequency, the bigger the coil.  You change the value of the cap in your 2nd order low pass filter to match the roll-off rate of your mid.  The larger the cap, the faster your woofer rolls off.   The Beta LTA is probably going to roll off at about 9dB per octave in the low end.

You don't have to do an open back box with the Alpha woofer.  Just try deep side wings like Scorpion uses on his Volks OB style baffle.

Those in the know say that you should get out of the Beta LTA quickly above about 8KHz.  Use a second order low pass with larger than normal cap.   Salt to taste with your super tweeter!

I hope that's not too confusing.   

[nullspace]

Hi Michael --

You've posted about this setup in the past, haven't you? Or am I mistaken? IIRC you had said that a Beta 12LTA was used (but the old version). Any possibility you could elaborate on the crossover and other parts used?


Regards,
John

[panomaniac]

Hey John - good memory!

Yes, that rig belongs to John Busch - I think the photo is from Sacramento about 2 years ago.
What you see is the Beta 12LTA as a mid range, twin Eminence 18s for the bottom and a Vifa or Seas dome tweeter.
The 18s are not made any longer, they are a low Qts, high efficiency model.  Lots of crossover EQ for the low end.

John B reads this forum and posts from time to time, I'll see if i can get him over here to comment.

Thanks for posting the photo!

[JBspeakerman]

Good evening Jagtek

The is some confusion about the Eminence Beta 12LTA..... there are at least two generations of this driver..... the oldest has a FS of 50 HZ...XMax of .8 mm Peak.... a second version ... the one that I have has an FS of 45 hz with the same .8 Xmax and the current spec with a 45 hz FS and a stated Xmax of 3.2 MM peak.... I have a email in to Tom James the current head of engineering at Eminence asking for some clarification.... suspect the second version and the current are the same....we shall see.

The large OB with the twin low Q Eminence 18's pictured was some thing..prototype if you will I put together as a demo for the Northern CA DIY gathering a couple of years ago.... Just trying to show that with the right engineering.. a passive crossover and cross over you can get some deep and powerfull bass out of an OB design with low Q woofers.... though.. 2 pairs of 18" woofers should be able to do something interesting!

As for the Beta LTA... the version I have is great on a larger OB  ... say 28" wide.....from around 100 hz up to around 4K... about then the whizz-er kicks in and even though it does extend the output up to a bit over 8K... it requires a lot of crossover work to tame.... so in the design pictured I got out of it around 3,500.   The LTA is about 96 db really..... and it is very clean... great transients in the mid range... a cow bell ... sounds and feels like a cow bell... very few drivers have the combination of low distortion and attack to pull this off.  BTW... the pictured system was about 92 db/watt and flat to 32 hz thanks to wide baffle and extensive front and rear wings.

If you try to mate it up to any OB woofer...or woofers... you have to decide if you will go passive or active... dedicated sub woofer with passive for the mid and tweeter and so on before you try to use the LTA.... Likely you will have to bring down the LTA any where from 3 to as much as 12 db to get it to match up with your OB woofer...

So.. curious as to what your current plans are.... and keep in mind ....the LTA has a nasty rising response... like 5 + db or so starting just above 1K.. and one way other you have to deal with that....

Gives it great clarity in the PA roll it is intended for ... but in a hifi application it will sound very hot if not corrected....

Look forward to your comments.....

John

[nodiak]

Glad to see this thread. I am looking for a 12" for ob that would roll off just under 100 hz, and mate to a powered sub. Would try with different 5-8" widerange drivers from ~ 300 hz up, (ex. FE127, Hemp 8"). The LTA midrange quality sounds great, better than some others I was considering.
Don

[jagtek]

Hi, Thanks for great for the great replys. eclosed is an idea of what I was thinking. Not sure if
 it will even work. I was hoping to try first order on all drivers, but looks like I may have to do
 an active crossover (would it be easier ?).
 
I'm sure I have the later version of driver, thet are only 6 months old (was going to do an "afterburner" project).

 Be honest with me, I'm not a math person ,past basic algebra. If it will to difficult to integrate the
 Woofers, I could just use an external sub. Anyway let me know what you think.
Thanks ALOT.  David.




if the image doesnt work heres the link= http://www.flickr.com/photos/29356240@N00/2661885629/

 

[panomaniac]

Hi David - I like the sketch. =)

Yeah, that should work.  Getting the LTA to mate with the woofer shouldn't be hard, but I would do second order. After all, it will work better and all you need is to add a cap

Getting the LTA to play nice in the top end may be harder.  But It can be done.  I've heard John use it and it's a damn good driver. (I'm picky about that stuff).  John says he got out of it at about 4K.  John, do you remember what values you used?

I've been trying to computer design a crossover for the LTA to be used in a big Voight pipe on another forum.  Can't really do better on virtual paper than the Hammer Dynamic crossover.  But I use a Selenium slot tweeter with just a 2uF cap.   I guess you could start with just the Hammer 1st order + Zobel and add the notch filter later.  See the Hammer crossover here:
http://www.enjoythemusic.com/magazine/equipment/0600/super12.htm   Does not matter if you use this in a box or not, the LP filter is going to be much the same.  So the Afterburner would need the same thing.

Bottom line.  I think you can make a great sounding speaker that you will really love following your sketch.  Taming the LTA top end is going to be the only tricky part.  But that will be the case no matter what you do with the LTA.

[jagtek]

 Thanks for the reply and confidence, I'm going to give it a try freehand first (that means no math)  and see what happens.
david

[panomaniac]

Cool!  Let us know how it goes.

My guess is that you will be crossing the Alpha to the Beta at about 90Hz.  Easy to do with an active filter, such as those on plate amps, not so easy with passive (big inductors and caps).

If you do it right, the baffle peak in the low end of the Beta response might just match the rising response of the Beta circa 1K.  That would be nice.

[jagtek]

OK, let me get this right. Your saying to use a seperate active crossover/amp (plate amp) for the woofer, and then a passive for the mid/tweeter combo, I like it   Why didnt I think of that ! I was thinking Behringer and
Tri-amping. This sounds much cheaper and simpler DUH! I even have a Jolida Passive preamp with two
variable outputs, to make things easier. (now I just need a smiley with a light bulb over its head LOL)
THANK YOU !!

[panomaniac]

Your saying to use a separate active crossover/amp (plate amp) for the woofer, and then a passive for the mid/tweeter combo...

Yes indeedy!   If you can do it, you should.  A plate amp on each side is the easy way. (works for me)
If you have the DCX2496, by all means use it.  I have one and quite enjoy it.

Passive should be easy enough for the mid/hi, but active can work too.