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Old 28th February 2005, 02:43 AM   #1
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Question Suggestions for High Efficiency system - BetaCX?

Hi Guys,

I could use some suggestions..I'm a little out of my element a bit here. I have always just built simple boxes.

I need to build an efficient system. I will have a 'decent' (read-low) amount of power but I also enjoy the occasional concert level listening..well almost. I have an Aleph 30 in progress and plans for a mini AX or zen or something like that. That gives me ~30 watts for a woofer and ~10?(15, 20??..whatever) watts for a HF horn in an active system.

I intend to augment the system with a sub as there will be occasional movie watching and I feel I won't be able to squeeze the low lows out of my mains. Maybe one of Bill's Tuba's? Maybe a long throw as I have a couple of 555's kickin' around. Dunno yet.

I intend on using 'pro' drivers and yes, I am on a WAF budget both monetaraly(sp?) and spacewise. I don't have a figure on the monetary part.

I am looking at the Eminence Beta 12CX:
Specifications: * Power handling: 250 watts RMS * Voice coil diameter: 2" * Le: 1.01 mH * Impedance: 8 ohms * Re: 5.57 ohms * Frequency range: 45-20,000 Hz (with PSD2002 driver and pxb2-1k6 crossover) * Magnet weight: 38 oz. * Fs: 43 Hz * Vas: 5.66 cu. ft. * Qms: 6.69 * Qes: .51 * Qts: .48 * Xmax: 3.0 mm

I know there are a few threads on this driver but I have more than a couple of questions. This driver seems to model pretty well as long as the cabinet is huge ~4cuft.I need to avoid that . Getting to 50Hz or so would make me reasonably happy, lower would be nice too. What do you guys think about open baffle for this driver? With what I have read, a Qts of .48 should work(??). Can I build a shallow open backed box? If so, how low do you think it would play? How big does the baffle have to be and how deep the open box (if it would work at all)? Can I expect that "snap" in the midbass that I love so much that 'pro' drivers have given me in the past? I had line arrays planned but I couldn't get away with the height...multiple 'hifi' drivers are out.

Heck, maybe I am modeling it all wrong and I have no problem here. If so..HELP!! I would consider 2cuft to be probably too big.

Regarding the HF driver, I am open to suggestions. Actually I am open to suggestions on the whole deal. //aperiodic, maybe???//hmm

These are kinda long range plans and I am probably going to change them 100's of times. Hopefully with your help, I could use it!

Thanks a lot.. Marc
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Old 28th February 2005, 02:48 AM   #2
DonoMan is offline DonoMan  United States
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How much space do you have? <2cuft seems a little tough, but how much less are we talking?
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Old 28th February 2005, 03:01 AM   #3
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dunno man? But the smaller the better. The form factor is a factor too. I am in the very early planning stages so any input/idea is welcome.
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Old 28th February 2005, 04:50 AM   #4
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I've been eyeing the 12CX for OB once I go active. I have 6 of the Adire HE8.1's which were a bit sterile until I got them out of the box and went OB. The 8CX needs a lot of bass support due to the low Qts, but the 12CX is going to get you down to 50hz or so with a minimal backless box. You may not even want to go that low due to the limited excursion, but they'll definitely go down to where a mono sub can take over or just add an IB15" or one of Ascendant Audio's new drivers to the bottom of each speaker and forget the sub. That would give you a fine set of OB speakers in a very compact size. Experiment with the box depth with cardboard mockups first and don't make the sides at 90 degree angles to the baffle to avoid resonances. If speaker placement has to be near the back wall you can adjust it with some foam or polyfill behind the driver and avoid cavity effects while retaining much of the OB benefits of openess and natural sound.

I'd definitely go with the Adire tweeter over the one from Eminence.
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Old 28th February 2005, 08:03 AM   #5
joensd is offline joensd  Germany
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Have you seen the different Prometheus speakers?
They are OB speakers with a Beyma CP21 tweeter and subs to go with it(URPS). They say the drivers are modified Eminence 12CX.

Have a look here:
They also have an international forum.
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Old 28th February 2005, 03:43 PM   #6
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Thanks guys,

II just noticed that Eminence is recommending a different compression driver for the cx.

The apt50 was rated down to 3.5k.....the psd2002 is rated to 1.5k with higher pwr handling. Also they are spec-ing the 1.6k x-over. This could be good! Does anyone have any experience with this new driver? I wonder if the horn in the cx can handle the bandwidth..anyone?
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Old 28th February 2005, 04:58 PM   #7
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JohninCR gave you some good advice WRT HF drivers and Saurav has posted here in a previous thread that he swapped HF drivers in his Adire 12.1 kits to the Selenium DT150 with good results, though there was a peak at ~4500Hz that needed EQing out. Regardless, you need Adire's XO to make them work well at a low XO point.

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Old 28th February 2005, 05:06 PM   #8
tiroth is offline tiroth  United States
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Default Autotuba

I have yet to try this, so take it with a grain of salt. I am also working on a hi efficiency system, and my guess from preliminary listening is that a pair of Autotuba will match very well from 80Hz down. I was originally planning to cross lower, around 50Hz or so, but I now think the Autotuba won't really get a chance to sing with such a low LP crossover.

The Autotuba seem to have that livelieness that I associate with high efficiency. They don't go super-low without EQ though. I am trying out a 16" version to see if I can squeeze a couple more Hz of low-end out of them.
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Old 28th February 2005, 05:17 PM   #9
usekgb is offline usekgb  United States
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The PSD2002 is a great driver for mid-priced PA systems, but I would NOT use it for home listening. The sound is somewhat harsh compared to other drivers of that size. You may want to take a look at the B&C DE250. It's a great 1" compression driver that would sound great for home use.

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Old 28th February 2005, 06:21 PM   #10
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Thanks all,

OK, it seems that no-one is complaining that a Beta 12cx is a problem open baffle.

I am gathering that the clincher is the horn. I suspected as much. I need to keep the costs down, which is why I am looking toward eminence cd's. The general theme is that they sound pretty crappy...this means I'm gonna have to check them out myself somewhere. I think B+C's are too expensive..I'll look at the selenuims.

I've seen your posts and I have a feeling you are quite talented in speaker design. I intend to go all active. Your comment RE: my needing adire's crossover leads me to believe that you may think this a bad idea? Am I mis-understanding?
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