Beta 12LTA + Beta 12A-2: is this open baffle concept viable? - diyAudio
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Old 18th September 2011, 03:17 AM   #1
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Default Beta 12LTA + Beta 12A-2: is this open baffle concept viable?

I've been nursing this idea for a little while and decided to run it past you folks.

Put the Beta 12LTA on an open baffle and allow it to run full range. cross the Beta 12A-2 in at around baffle step. Some super tweeter could be used for the top end; take your pick. I'm expecting that this arrangement would still need EQ to get a decent balance, as well as extend the bass (neither is a particularly high-Q woofer). But I have two questions: since the combination of two 12" drivers will have more surface area than a single 15", will these drivers be capable of decent SPL levels, despite one of them being used full range? And with EQ, will they be capable of reaching 40hz without too much distortion?
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Old 18th September 2011, 03:49 AM   #2
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I'm running a pair of 12A-2's to meet a Beta8A at 240Hz in a 2x4' baffle. The 12's have current feedback in the amplifier to set the total Q to around .7. There is also 6dB oct baffle compensation on the 12's. The output below 47Hz with q=.7 is of course limited by driver resonant frequency but it really doesn't sound like it. There's good 40Hz available. I'm sure it depends a lot on baffle and room. I never did get outside yet to get good low frequency response measurements.

This is only a temporary arrangement for me as subs will eventually be added and the 12's will only go down to 70 or so. Distortion all depends on how loud you need it, although I must say, they do rock pretty good with just 25 watts. I started with the 12A2's going up to 400Hz and I didn't appreciate the sound at all.
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Old 18th September 2011, 04:18 AM   #3
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You were thinking of running them both full range, no crossover? Andrew's post indicates that while it might work, it won't sound great. That would be my take on it, too.
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Old 18th September 2011, 04:29 AM   #4
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I think I said the 12A-2 would be crossed in at baffle step; I figured it should be rolled off with the help of an inductor at least. So in effect I'm proposing a 1.5 way.
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Old 18th September 2011, 04:35 AM   #5
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OK, got it. Since we are here on the fullrange forum I was thinking no crossover. Sorry
Running the 12A-2 as a helper woofer should work OK once you figure out the inductor needed. It may be bigger than you suppose because there is such a rising response on OB.

I've only heard the 12LTA as a wide bandwidth OB midrange. It was very, very good at that job.
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Old 18th September 2011, 05:04 AM   #6
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Quote:
Originally Posted by Pano View Post
I've only heard the 12LTA as a wide bandwidth OB midrange. It was very, very good at that job.
That's always good to hear! What was handling the low end in the system you heard?
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Old 18th September 2011, 06:05 AM   #7
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found it. it was john busch's system you heard, right? what a monster! lots of good info in that thread.

Beta 12-lta question.
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Old 18th September 2011, 06:44 AM   #8
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There's no question the 12lta is a great wide range midrange on an open baffle in my mind... I am currently building a powered sub using a 12" driver in a sealed box. I hope it mates well. Getting the bass right is critical with any system.
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Old 18th September 2011, 01:40 PM   #9
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Yes, that was the one. Good find! John's not afraid to use double 18s for bass.

If I were trying this double beta setup, I'd run just the LTA on the baffle and measure how it drops off in the bass. That would give a good idea of how much the low end needs to be filled in. Since the 12A-2 is going to have a similar response that gives you a good idea of how big an inductor is needed to restrain the 12A-2 to the "fill in" range. Then start fine tuning coil and cap.

It may never be a perfect match, but having that extra driver down there to help the LTA will sure make it sound more balanced. Just my 2 cents.
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Old 18th September 2011, 04:15 PM   #10
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I also wonder how the open baffle hump might be used to help balance the response of the 12LTA when run full range. According to MJK's graphs baffle hump is around 3db, which if centered around 500hz could fill in the 12LTA's response quite a bit. The phase plug mod would smooth out the top end even more. After that, maybe the best idea is just to buy a sub plate amp and cross a pair of woofers in around 100hz. Thoughts?

For that matter, I have a pretty decent sealed sub in storage. While it's my impression that open baffle bass is at least half the reason to go open baffle in the first place, it might allow be to get started using 12LTAs right away...
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