Eminence Beta 12LT system

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bigwill

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Joined 2004
#1
Here is my plan

I wish to use a B12LT for fullish range duty, most likely with a simple correction circuit or "honk" filter.

The B12LT only manages to reach around 8Khz, so a super tweeter will be needed. The Eminence ATP-80 looks suitable. I'm not entirely sure how I will cross this over to the B12, it seems that a simple 1st order filter may be too shallow - or it might be just right, who knows.

I want to temporarily mount these on a damped U-frame OB. Eventually I hope to augment these with something along the lines of the Alpha or Beta 15, but a U-Frame will hopefully provide enough bass for now.

My goal is to have a nice efficient dynamic speaker to pair with my 15W tube amp. Ruler flat frequency response or super deep bass not needed, just a NON FATIGUING tonal balance and hopefully nice imaging.

Basically, my questions are:

  • Is the Beta 12LT a pleasant driver with a correction filter?
  • Would the usual 1st order tweeter crossover be sufficient?
  • Are there any alternative drivers to recommend that may offer better value/performance and are EASY to get in the UK?
 
#3
According to measurement on Strassacker there is a 10db dip between 2.5khz and 5.5khz
Well, it appears to be so, but its actually a rise in FR
Strassacker measurements doesnt show that, but only the dip centered around 4khz, but otherwise smooth
PartsExpress(Eminence?) measurements on the other hand show a rise from 700hz to 2.5khz, meaning that its only just above 90db below 700hz, which actually makes sense
I suppose that 2.5khz is the point where the 12" diaphragm gives up and the whizzer cone sets in around 4khz, hence the dip

I have thought about this driver and concluded that I would use two drivers in a 2.5way

Maybe I would remove the whizzer cone and cross it around 3.5khz, but not sure about that

The US version is called LTA and EU version only LT, but specs are exactly the same so I suppose they are identical drivers

There i another Eminence, the 10" bass driver, Legend B102
It might be of better quality, but I havent heard any of these
 
#6
John L said:
I would suggest that before you do anything, that you go to The Afterburner Files and read about the project involving this Emenance Beta driver. I remember it because I copied and printed it out years ago, when it was on the Single Driver Website, I believe. It is no longer there, but a Google search brought it up for me.

I think you will enjoy reading it. 😉
Click to expand...

Ah yes - The Afterburner. I also remember reading about this a long while ago and it is probably what inspired me! I will try the filter values shown. They might not be perfect but they're a starting point. I might use a variable resistor instead of R1 so I can attenuate the upper mid band to taste..

planet10 said:
I'll be following your project with interest. I have a pair of the 12LYAs and will be putting them in a Chang-family BVR. I have a number of possible tweeters to use including the aforementioned FT17.

dave
Click to expand...

Good luck, hopefully it sounds good!
 
#8
I think you could get music out of 12LTA - I put on in an old one-fold t-line then opened the vent by ear until it sounded like it was alive - -

for reflex, RCA-Fan's v-vent type with maybe 140-170 liters might work - the edge of the v is gapped aobut 1.5" from rear of box to form a lowpass choke

Eminence's old B102 made a good fake Druid - maybe the new one would work too - who knows if Zu's custom woofer has lower qes (?)

12LTA probably has better tone and somewhat more extension than B102 plus are $50 in US - it extends about as far as EV SP12 (alnico)

I'd like to hear Planet10 BVR for 12LTA - I'd like one for Eminence c12cx

here's a messed up t-line and picture of RCA-fan's v-vent type box - I think this is the one whose plans appear in RCA-fan's high efficiency gallery and I have one loaded with coax.

http://img136.imageshack.us/img136/3488/si1xl0.jpg
http://img240.imageshack.us/img240/8308/vventhalfhorn515bwh5.jpg


here's a couple of on-axis graphs of 12LTA - ignore those lower F dip
http://img341.imageshack.us/img341/8360/arb102vs12ltnu7.jpg
http://img245.imageshack.us/img245/9466/onoffwim9.jpg
 
#9
A question - does a tweeter with a high crossover point damage imaging?

I'd hazard a guess myself and say "not much", as I've found that above a certain frequency it becomes harder to localise a source (much like as you go lower down in frequency below 100Hz or so)

Is this a sensible line of reasoning?

If I had more money I'd just go for a coax but I want to keep this relatively affordable.
 
#10
A Demetri style cabinet for the 12LTA would be cool, I'd guesstimate it'd be about the size of a Klipsch Cornwall, you could mount the Fostex FT17H in a pod on top of the cabinet. I bet it'd sound pretty darn good.

I can't wait to see the drawings for a BVR for the 12LTA, though.

🙂
 
#14
that's a US stamped APT80 clone I bought new off Ebay for US$8 each - the magnet's back plate was thinner than regular APT80 and IIRC resonance was somewhat lower- with the styrofoam coffee cup it was firing forwards and pattern could be rotated by rotating the cup.
 
#15
I am at present listening to a pair of "afterburners" using the LTA driver. It is my office system, driven by 2a3 set amp. They sound much better than the price point would indicate. I did most all of the mods TL suggested, modeling clay on the basket (rings like a bell!), dammar on cones and whizzer. One addition is a set of planet 10 phase plugs (remember these Dave?) I am using FT17 tweeter with 1.5 uf cap as only crossover. The notch filter is a must - there is too much rise in the upper midrange without it. I house them in cabinets that are around 5 cf, with a simple port cut on the back near the floor. Bass performance and dynamics are very good, especially at low levels (I mainly use them for background music.) Biggest complaint is, being a 12" fullranger, they are quite beamy, the sweet spot is very well defined. Off axis they sound muted.
Jim
 
#16
JimW said:
I am at present listening to a pair of "afterburners" using the LTA driver. It is my office system, driven by 2a3 set amp. They sound much better than the price point would indicate. I did most all of the mods TL suggested, modeling clay on the basket (rings like a bell!), dammar on cones and whizzer. One addition is a set of planet 10 phase plugs (remember these Dave?) I am using FT17 tweeter with 1.5 uf cap as only crossover. The notch filter is a must - there is too much rise in the upper midrange without it. I house them in cabinets that are around 5 cf, with a simple port cut on the back near the floor. Bass performance and dynamics are very good, especially at low levels (I mainly use them for background music.) Biggest complaint is, being a 12" fullranger, they are quite beamy, the sweet spot is very well defined. Off axis they sound muted.
Jim
Click to expand...


Good to hear that they sound good.

Could you tell me what you're using as a notch filter?
 
#19
Idea behind it is to smooth the impedance curve of the driver to make it an easier load to drive, and to make crossover functions a little more predictable. I did listen to the driver with no notch/zoeble - kind of harsh. I added the zoeble at the same time as the notch and never tried without. One thing, these drivers have thin paper cones - they are sensitive to internal reflections in a big way. I tuned the sound of the speaker more by messing with the cabinet damping materiels than I would have thought possible. I found I liked them best with the upper part of the cabinet highly damped, the bottom much less. Read the fullrange driver form for an article on the hammer dynamics 12 - a very similar driver.
Jim
 
#20
I 've heard the 12LTA used as the mid driver in a big open baffle rig. I thought they sounded quite good.

They were actually crossed to a dome tweeter, but I don't know the filter topology. They have a great, lively feel to them and go a long way toward the "delicate lighteness" that real acoustic music has. Nice driver.
 
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