Using Eminence Beta12 LTA - crossover questions - diyAudio
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Old 14th August 2008, 01:52 PM   #1
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Default Using Eminence Beta12 LTA - crossover questions

I'll admit it up front - I'm a speaker design newbie. I understand the basic concepts, but not really the application. This specific request is tied to a post I made in Musical Instruments that I now think is misplaced...

What I'm trying to do is build an inexpensive and small integrated amp/speaker for instrument use. I have found the Afterburner project, and the dimensions of the box he uses are appropriate for what I'm going to be doing - 75cm X 48cm X 30cm outside with 22mm ply. Approx 80L.

This design uses the Eminence Beta 12LTA, which is cheap and there are reports that it sounds good for vocals, so it should lend itself well to the violin I intend to use this for. Low frequency response is not too important, so I will stick with a sealed box, but I need to add a tweeter to the design. I'm looking at the Eminence APT-80 for that duty.

My questions mostly relate to the crossover. I plan to do an active cross, but could easily be convinced to go passive. First, where to cross these drivers? The APT-80 recommends a 3500Hz high-pass, which seems to look good to my uneducated eye based on the FR charts. Can/should anything be done about the 12LTA's 'honkiness'? Assuming I want an inexpensive active crossover, any ideas the best way to implement a crossover for these drivers?

Oh, finally, a simple question that I can't seem to find the answer to anywhere - is it possible sim the high frequency response of drivers/networks? I've tried WinISD and speaker workshop and it seems they give an upper frequency response that's only affected by Le. How can I sim a crossover network with an approximate response curve to get an idea of what the actual response will be without 'eyeballing' the curves?
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Old 14th August 2008, 02:13 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

For a sealed box you can halve the box volume.

If you are adding a proper tweeter a twin-cone driver does not make sense.

try pi-speakers : http://www.pispeakers.com/

/sreten.
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Old 14th August 2008, 02:31 PM   #3
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Can you perhaps suggest another woofer (or combination) that would work well in the same price range ($100 for both)? I couldn't find any that had reasonable response past 2K except for this - and then finding a matching tweeter would be tough since most of the decent (not $10) ones don't seem to go very low. It didn't make sense to me to try and run a 40-2K woofer crossed with a 2K-20K tweeter, so I figured I'd just roll the 12LTA off early. It sounds like that approach was successful in the Afternburner project. Is it a bad idea? If I can halve the volume that would be great, and actually I was planning to make the enclosure shallower. My goal is to make the enclosure approx 48-60cm wide, 48cm tall, <30cm deep.

I've seen the pi speakers mentioned before, there are two reasons I didn't think they were a good idea. One, I'm not really looking for a Hi-Fi, sit in the living room speaker - I need a good form factor for a portable instrument amp, and I think these designs are too deep and need to swap the height and width. It doesn't look like a speaker that would be easy to carry with a handle on the top. Two, I can't seem to find the enclosure plans anywhere.

Thanks
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Old 14th August 2008, 03:10 PM   #4
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In this thread - BBBIB Bigger Badder BIB Speaker - I think they had settled on the Beta12LTA. There is discussion of crossover and tweeter stuff (later) in the thread, tho you probably don't want to use the box.

BBBIB Bigger Badder BIB Speaker
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Old 14th August 2008, 03:27 PM   #5
sreten is offline sreten  United Kingdom
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http://www.audioroundtable.com/PiSpeakers/

For the plans. Again for sealed you can half box volumes. /sreten.
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Old 14th August 2008, 04:49 PM   #6
Pano is offline Pano  United States
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Quote:
Originally posted by sreten
If you are adding a proper tweeter a twin-cone driver does not make sense.
Normally I would agree - but this driver is a little different. Get out of it by about 4KHz and you will have a very sweet sounding midrange.

For an example of a higher crossover for this driver - see here:

http://www.enjoythemusic.com/magazin...00/super12.htm
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Old 15th August 2008, 08:17 AM   #7
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Okay, so here's the plan thus far, I'm on a bit of a tight timeline so I'd like to either place orders for everything by the end of next week, or decide the project isn't feasible.

Enclosure: ~50-60L sealed, 1/2" Baltic Birch, 1 5x5' sheet + hardware - I haven't made a cut list or design yet but I think this is enough material - $45 locally

I'd like to use 3/4", but the extra cost and weight changed my mind. I will add additional braces instead.

Drivers: Eminence Beta 12LTA + Eminence APT-80 - $90 from PE

Power Amps: Either LM4780 or LM3886, depending whether AudioSector will sell me a single stereo set of LM4780 boards or not... ~$70

Crossover: ESP Project 09, 24dB Linkwitz @ ~3kHz - I wish I could find a single channel crossover board... Elliot's boards are pricey enough when you're not going to be wasting half of it...Any ideas? I'd get something fabbed myself, but either the price is too high or the lead time is too long for this project. - ~$50

I will use the Zobel from the Hammer project, and omit the notch filter unfortunately, unless I can find another crossover to build that includes it.
Preamp: ESP Project 27 preamp - I don't really want to pay $18 for this simple board, but I can't find anything else, so so be it. $45 for this + components.

By the time I add carpet, handles, knobs, pots, switches and so on I'm about $100 over budget. What do you guys think of this design, before I put down the cash? Will it work fairly well?

Thanks for your help.
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Old 15th August 2008, 11:00 AM   #8
sreten is offline sreten  United Kingdom
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Hi,

TBH if it was me I would slow down a lot.

There are small PA / keyboard combo's with a lot a features
you have not mentioned that makes them very useful and
there is always some sort of used market for music gear.

e.g. : http://www.behringer.com/K900FX/?lang=ENG

Click the image to open in full size.

"This 3-channel PA/keyboard amplifier enclosed in a bass reflex
cabinet has a special, beefed up 12" BUGERA woofer and a
custom-made 1" tweeter, delivering clear, clean sound that’s ideal
for larger gigs. We’ve included an internal 24-bit digital FX processor
with 100 awesome presets including reverb, chorus, flanger, delay,
pitch shifter and various multi-effects. Our revolutionary FBQ
Feedback Detection System immediately indicates any feedback
frequency and lets you combat feedback at your finger tips. Full
3-channel operation with separate volume and FX Send controls,
plus there is an additional XLR mic input on channel 1 for direct
connection of dynamic microphones. Dedicated 5-band graphic EQ
....


/sreten.
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