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Old 3rd November 2007, 05:41 PM   #1
bigwill is offline bigwill  United Kingdom
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Question Eminence Beta 12LT system

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?
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Old 3rd November 2007, 05:52 PM   #2
bigwill is offline bigwill  United Kingdom
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Upon further consideration the Fostex FT17H is also a good candidate for tweeter duty
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Old 3rd November 2007, 10:29 PM   #3
tinitus is offline tinitus  Europe
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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
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Old 3rd November 2007, 11:31 PM   #4
John L is offline John L  United States
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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.
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Old 4th November 2007, 02:50 AM   #5
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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.

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Old 4th November 2007, 10:58 AM   #6
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by John L
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.
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..

Quote:
Originally posted by planet10
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
Good luck, hopefully it sounds good!
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Old 4th November 2007, 10:59 AM   #7
bigwill is offline bigwill  United Kingdom
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I think the first thing I shall do is order a single Beta 12LT and maybe some passive components and just listen to it on a baffle. That way I can hear what needs to be done and experiment with filters.
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Old 4th November 2007, 01:30 PM   #8
freddi is offline freddi  United States
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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/img240/8...orn515bwh5.jpg


here's a couple of on-axis graphs of 12LTA - ignore those lower F dip
http://img341.imageshack.us/img341/8...2vs12ltnu7.jpg
http://img245.imageshack.us/img245/9466/onoffwim9.jpg
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Old 4th November 2007, 03:08 PM   #9
bigwill is offline bigwill  United Kingdom
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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.
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Old 4th November 2007, 03:49 PM   #10
BHD is offline BHD  United States
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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.

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