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Old 28th November 2011, 01:43 PM   #1
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Default Eminence Beta 12CX. Crossover help

Is there anyone here that has experience with Eminence Beta 12cx?
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)

The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
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Old 28th November 2011, 01:54 PM   #2
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Quote:
Originally Posted by rvrazvan View Post
Is there anyone here that has experience with Eminence Beta 12cx?
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)

The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
This unit is designed for a compression driver in the HF. Therefore, you're going to have a somewhat complex impedance resonance peak to deal with.
Here's some discussion:
Compression driver for Eminence Beta 12CX

I don't know about correcting time alignment with the cone driver. At least they are coaxial.
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Old 28th November 2011, 03:15 PM   #3
Pano is offline Pano  United States
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Quote:
Originally Posted by rvrazvan View Post
Is there anyone here that has experience with Eminence Beta 12cx?
I don't have direct experience with this driver, but do with other coax (Tannoy, Altec, P.Audio)
Quote:
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)
Yes. It's often easier than it seems. The acoustic center of the woofer will often fall back at the HF driver near the crossover point, anyway. With a little crossover work, you can get the phase aligned.
Quote:
The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
Not much you can do about the woofer impedance peak(s). The horn will be attenuated so it will be pretty smooth as seen by the amp.

Do you have measurement equipment?
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Old 29th November 2011, 09:38 AM   #4
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No measurement equip yet. But i have access to all i need(pc based).
But i have no experience with crossovers....none at all.
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Old 29th November 2011, 04:24 PM   #5
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Quote:
Originally Posted by rvrazvan View Post
Is there anyone here that has experience with Eminence Beta 12cx?
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)

The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
Yes,
All speakers drivers can be time aligned (you mean in phase vs not in phase?) with each other, at least in one direction in space, you will have nulls in cross directions. Look at the result of adding a cap vs inductor on the signal, not only for the (graphic) output/frq but in function of the phase/frq. A lot of people design crossovers without taking this into consideration.
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Last edited by Inductor; 29th November 2011 at 04:26 PM.
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Old 29th November 2011, 10:01 PM   #6
Helmuth is offline Helmuth  Netherlands
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Quote:
Originally Posted by rvrazvan View Post
Is there anyone here that has experience with Eminence Beta 12cx?
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)

The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
I would cross it second order then the horn driver must be + connected to - and the - to the +.

When you use the bms 4550 you have to decrease efficiency about -16dB. The voltage divider will make a perfect 8 Ohm impedance so the filter behavior can be good predicted.

Then it is the question how deep the offset is from HF-diapragm to the center of the cone of the 12". This offset lets say 10cm is the same as a phase shift lets say at 1kHz we have a wave length of 34cm so phase shift is (10/34)360degree= 100degree offset.
you need for perfect phase 180 degree difference or 0 degree difference. 180 degree for inverted + and -. Or 0 degree for in phase connection.

Or with 100 degree difference the phase difference from low unit to HF unit has to be together +100degree (so the sound-wave becomes 10cm foreward in time). The low unit will be back in time due lowpas and the HF unit will be forward in time due highpass. to gather that has to bee 100 degree at 1kHz when you cross at 1 kHz.

I use freeware german "Basscad" it has a simple tool to make XO design it is very useful for fast design and plot. It shows the phase and spl decrease with filter choice.

What beginner do not see is that the filter needs a flat impedance(8 or 4 omh) to work as simulated. Or your XO point and phase will change due the changing impedance.
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Last edited by Helmuth; 29th November 2011 at 10:08 PM.
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Old 30th November 2011, 12:54 AM   #7
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Using a Zobel on the woofer and the needed pad on the horn will do a lot to flatten the impedance and make your crossover easier to figure.
I think the hard part with a 12" coax is that you can't cross much lower than about 1Khz. And the woofer has a major peak at 2Khz. It's going to take some hard work to get that to sound right. It can be done, but will take a lot of work.
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Old 30th November 2011, 01:28 AM   #8
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Quote:
Originally Posted by rvrazvan View Post
Is there anyone here that has experience with Eminence Beta 12cx?
Can the hf driver be time alligned to cone? (without resorting to digital crossovers)

The speaker will be used with a SET amp....so the impedance must be as smooth as possible.
I have used this driver before and I wouldnt recommend it for anything other than PA or home theatre use. If you just want to rock out it's fine but dont expect accurate reproduction. The poorly designed horn / cone interface causes pretty severe frequency response anomolies -somewhere in the order of 15db nulls and overall ragged response. Also the cone breakup is substantial and pretty offensive so it needs to be crossed over quite low.

Never the less, its a cheap option and a fun speaker. If you are looking for something more accurate, beyma and B&C have good coaxial drivers.
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Old 30th November 2011, 02:09 AM   #9
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Greetings dabbler!
Shame, i was thinking of getting a couple to play with. Best thing about them is they are available in Australia at a not-too-unreasonable price.

I have also looked at the B+C and Beyma models but by the time you pay freight on them to OZ they are too expensive for me to just 'take a punt' and hope I like them. Still waiting for a reply from prosoundservice about the shipped cost of a couple of BC-8CX21.
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Old 30th November 2011, 12:56 PM   #10
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There are a few succesful commercial products using the eminence driver so maybe its my implementation.

Agree that buying just to 'take a punt' becomes a very expensive excercise if you live over here. However im pretty sure you'll be happy with B&C driver, havent heard a bad thing about them.
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