OB consisting on 2 Eminence Alpha 15"s and B&G Radia RDxx - diyAudio
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Old 21st August 2012, 01:39 AM   #1
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Default OB consisting on 2 Eminence Alpha 15"s and B&G Radia RDxx

Hello everyone. I would like to get some imput on buulding an OB using 2 Alpha 15 and one B&G RD40 or RD48 using active XO. My room is 13.5 feet wide by 23 feet long by 8.5 feet tall an has acoustic ceilling, carpeted floor and carpet up to 4 feet around side walls. Any input, opinion, idea or criticism will be very welcome..
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Old 22nd August 2012, 02:48 PM   #2
woof is offline woof  United States
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The Alpha's are good up to about 200 hz. If you can get the BG's to play down to close to that OB, you should be OK. You'll probably need EQ as well. You will have to experiment with the planar high pass to account for the OB characteristics. Some recommend 200 low pass & 400 high pass. Seems to blend well with the dipole hump you get.

Good luck!
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Old 22nd August 2012, 03:21 PM   #3
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I have build a system using the biggest RD ribbon, RD-75. I run the RD-75 dipole with no baffle at all, and I XO at 200 Hz. Below 200 there are several H-baffle woofers.

You will need EQ for the woofers for sure, and the RD will need EQ as well.

To make it work you should measure the response and set EQ based on that.

And if you do that, you should have a system better than almost anything else.
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Old 22nd August 2012, 11:52 PM   #4
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Than You both for your response...I am using a Pioneer Elite A/V Receiver that incorporates the use of MCACC, which adjust the sound based on the readings of a mic that I set where I will be seating and it adjusts for eq (10 band per ch), standing waves, distance, channel level, etc.. the output goes via preamp outs to an electronic analog 2 way XO and then to a Parasound Multi channel amp. To be honest, I already built a prototype which is basically a clone of the Jamo, using the 2 Alphas, an SB Acoustics mid-bass unit and a NEO8 PDR combined with a DCX2496. I sold the DCX to eliminate the extra A/D D/A conversion and the reduction from 24/192 to 24/96 that it was doing to my HD files in that process (I do not know if You knew this), and decided to go into the active analog XO. What do You think about this? The question goes out for both who kindly responded to my post as well to others.
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Old 23rd August 2012, 12:58 AM   #5
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Stig, I went to the trouble of looking up a picture of your system, and all I can say is, WOW!!
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Old 23rd August 2012, 11:29 AM   #6
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Crossover and EQ for the RD ribbon the way you describe should probably work. I'm more concerned about the woofers. The sensitivity will be much larger than the ribbon at the XO point, so you need to lower the level of the woofer a lot. Preferably, the woofer should be level matched and the dipole EQ should be placed at the active (analog?) XO. Also, 10 EQ points may not be enough, and the EQ in A/V receivers is usually not possible to tune with enough accuracy.

It would be better to use a dedicated digital XO with parametric EQ in my opinion. DCX2496 is the cheap option, although not the best in sound quality.

I have used the Hypex AS2.100 plate-amp in one set-up with RD-75 and H-baffle woofer, and it worked very well. It has digital 3-way XO and DSP. Highly recommended! But you will get an additional AD-DA conversion of course.
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Old 23rd August 2012, 02:21 PM   #7
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The Hypex seems an excellent choice, because it even let me go digital, right out of the preamp into the plate and has everything on it!! But maybe it has the limitation of 24/96..and I do not know if it is sold in the USA.. and last, but none less, my budget is somewhat limited.The XO I already have offers level controls, phase polarity switches and variable XO points for each output and still analog Then I can switch the receiver to direct mode and add an analog dual 31 band EQ between the XO and the power amp. What do You think about this?
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Old 23rd August 2012, 04:18 PM   #8
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You can buy the AS2.100 directly from hypexshop.com

A 31-band graphic EQ is not very helpful, you should have a full-parametric EQ with 10-15 bands at least.
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Old 30th August 2012, 12:15 PM   #9
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mmm I actually have 4 Alpha 15 left from a previous project, they are ok down to about 40hz.. I will follow your progress closely!
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Old 30th August 2012, 01:16 PM   #10
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I once cloned the Emeralds Physics CS2 just to find out that the Alpha 15a not are that good... Search for Alpha here: http://www.troelsgravesen.dk/OBL11.htm to see my comment. Check the Super V at GR Research, might be a path for you...
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