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..
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!
Good luck!
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.
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.
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.
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.
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.
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?
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.
A 31-band graphic EQ is not very helpful, you should have a full-parametric EQ with 10-15 bands at least.
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! 🙂
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...
you are right, very weak motor and the super high Qts acts as a very crude equalization, compared to a low qts woofer equalized actively. but they are cheap and fun!!
Cheap ? Not really anymore, at least not in Europe. Fun, certainly not when you know the alternatives. In Europe the budget-choice for OB would be A&D R1524 from: A&D Audio Datenblatt costing 65 EUR today from HIGH-TECH-HIFI. I have compared A&D R1524 to Eminence Alpha15 and Acoustic Elegance IB15 which I have all three and the Alpha15 is by far the worst performer of them. The A&D R1524 was used in my: 'Volks-OB' without EQ and went down to about 40 Hz level.
Played side by side it is striking how similar AE IB15 and A&D R1524 sound giving a tight, clean bass of exellent quality.
/Erling
Well appreciated your comments and suggestions.. One point, though.... Since I already have 4 of the alphas, buying other bass units is not an option, or at least until I really beat them up!!! LOL!!! so, I have to work with these for the time being.. But I can say is that having 2 ,of them gives great bass (at least for me and based on what I have put on together)... Now a variation to this project... Since tha BG Radia panels are not actually capable of mating with the Alphas, I decided to go with my original idea.. 3 way OB using 2 alphas, a SB Acoustics SB17NRXC35-8, 6.5" midbass unit and either a Vifa DX25TG05-04 dome tweeter, a D25AG-05 6ohm aluminum dome or a BG NEO8 PDR per channel, which I already have available... since the active XO is 2 way, I am planning to use it to filter the bass and mids and build a passive XO to filter the midbass and the tweeter.. Opinions, suggestions, recomended crossover points??? the baffle measures 20"wide by 34"high in the bass area, then reduces to 8" wide by 7.5"high for the midbass and a small plate to support the tweeter.. all vertically aligned. I have pictures, but do not know how to post them here..
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Cut the top off ... lay the 15's down, turn one around magnet facing out ... extend the sides for either "U" or "H" frame ... fab another intermediate baffle with a vintage 10-12" driver and set it on top ... replace the cut off mid/tweeter section above that.
Limit the alphas to 125hz ... cross over to the midbass (10-12) <--- a good one could play quite high in frequency. A guy would have to fiddle with this transition to the top section.
Limit the alphas to 125hz ... cross over to the midbass (10-12) <--- a good one could play quite high in frequency. A guy would have to fiddle with this transition to the top section.
OK, puppet... let me get this straight... You mean eliminating the 6.5"midbass and both mid and high cutoff and extend the main bass baffle to accomodate a 10"- 12" fullrange driver? and extending the baffle backwards more than the 4 inches it already has?
OB Fan,
your setup looks perfectly ok to me. I would recommend to use the Alphas up to 200 Hz and cross to the SB from there. Xover between the midbass and the Neo8 could be anywhere from 1-1,5 kHz. Both dome tweeters seem to be a worse match to the SB17 than the Neo8.
your setup looks perfectly ok to me. I would recommend to use the Alphas up to 200 Hz and cross to the SB from there. Xover between the midbass and the Neo8 could be anywhere from 1-1,5 kHz. Both dome tweeters seem to be a worse match to the SB17 than the Neo8.
I got curious and looked a bit deeper into this project - using the MJK U frame worksheet from www.quarter-wave.com
A first look with Edge hints at a very early roll-off of the midrange driver on its small baffle:
This demands a higher crossover frequency of the system:
Note how the SPL of the U frame is consistently higher than the level of the mid driver. The dipole peak is still visible as a small hump.
The level difference between U frame and midrange may not look too serious. But if we include the bass boost by the floor, things become worrisome:
By making the midrange baffle as wide as the U frame we can boost the lower part of the midrange somewhat:
Note how the wider OB leads to more diffraction ripple.
All sims above are with the Alphas in parallel. We can reduce their combined sensitivity by connecting them in series:
Now the combination is lacking a bit of SPL in the woofer region. The series connection raises the woofer resistance to 12 Ohm, which could be too much for some amplifiers. And it asks for a hefty 18 mH inductor in front of the woofers.
It is a nice example why most people prefer to feed dipole woofers with their own amplifiers - it makes life a lot easier. 😉
A first look with Edge hints at a very early roll-off of the midrange driver on its small baffle:
This demands a higher crossover frequency of the system:
Note how the SPL of the U frame is consistently higher than the level of the mid driver. The dipole peak is still visible as a small hump.
The level difference between U frame and midrange may not look too serious. But if we include the bass boost by the floor, things become worrisome:
By making the midrange baffle as wide as the U frame we can boost the lower part of the midrange somewhat:
Note how the wider OB leads to more diffraction ripple.
All sims above are with the Alphas in parallel. We can reduce their combined sensitivity by connecting them in series:
Now the combination is lacking a bit of SPL in the woofer region. The series connection raises the woofer resistance to 12 Ohm, which could be too much for some amplifiers. And it asks for a hefty 18 mH inductor in front of the woofers.
It is a nice example why most people prefer to feed dipole woofers with their own amplifiers - it makes life a lot easier. 😉
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