B&G RD-75 dipole - baffle and or waveguide?

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Awesome I really appreciate your help StigErik. I have a lot of ideas that I want to try in the next couple of months. I am going to try a Gilmore audio raptor which is ice power, because I have heard a few people that owned Atma-Sphere otl thought the ice power amp was on par with the otl's, but with none of the tube draw backs. Right now I have Transcendent Sound Otl which I intended to run with the Beyma tpl-150h and a 12 inch driver all actively crossed over with a marchand xm-44. I haven't heard them yet because I haven't built boxes for them. I followed your past posts on the Beyma tpl-150 so when I saw that you switched to the Rd75 Drivers that really piqued my interest because I have always wanted to try them, but haven't because I haven't found any solid state amplifiers I like yet. I'm always willing to give new things a try. I am going to order in the gilmore amplifier and try it on a 30 day trial. In the end I will probably only keep one set up, either the beyma or the bohlender.
 
Hopefully I am not steeling this informative thread, but I also did benefit from the work done by Rudi Blondia and John Whittaker. And much like Carl Huff, I also built an airfoil baffle for RD-75. Here are the pictures.

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and

An externally hosted image should be here but it was not working when we last tested it.


I then shamelessly borrowed ideas from Linkwitz and utilized his Phoenix W-woofers with Peerless XLS 830500 12-inch drivers wired in parallel. The midrange array consisting of 4 Scan Speak 10-inch drivers, the 25W/8565 in copy of Phoenix baffles.

Over the years I used a several crossover ideas, ranging from an analog circuit, to what is currently a DCX2496 digital implementation. Right now I am looking at Minidsp 4x10 or even 10x10 stand alone box. It seems like a way to go; particularly that it has an integral volume control. I do not like the DCX, as is, too flaky and I have no desire to mod it. Minidsp looks better to me.

Anyway, I would love to hear and learn what others have done in the cross-over area.

Best regards,
Vadim
 
SpinMonster,

Thank you for the kind words. My room is not great these days, - it is about the same as yours, a bit longer but also a bit narrower. My screen is 'only' 104 inches wide. I have been using Front Projectors for the past 20 years and next year will be the last. Went from 9-inch CRT to DLA RS-2 over the years. I am going to to go with a 80-inch wide LED screen and concentrate more on audio.

Right now I am setting out to start build new amps soon and am re-thinking the crossover for my front dipoles, -hence I am looking at the MiniDSP.

It seems that the 10x10 box is a good deal here, but I have yet to hear from anyone who has used it. I need to integrate my right and left 3-way dipoles with a single stand alone subwoofer. It is a DIY sealed sonosub with two 15-inch Avalanch drivers. I also have centre and rear channels, but at least I do not need a crossover for them. My only active speakers are the 3-way dipoles in the pictures I posted.

All in all, I have 10 channels to worry about. So, - the question is can this MiniDsp 10x10box do it all? Volume control is really attractive there. It seems like it can, but I am not sure. I have this crazy idea of simply using my DVD player with a built in decoder and avoid a need for a separate processor. I am doing it now, but its a cludge and am trying to improve the set-up.

Sorry for taking this thread off topic.
 
Vadim,

Your loudspeakers are a beautiful piece of art. They are much nicer than mine. Mine are black enamel paint! Great job and kudos to you.

As to crossover I originally used the custom active crossover designed sold by Rudi Blondia specifically for the RD75. However most recently I swapped that out for the active crossovers and EQ that are in the Datasat RS20i. Both solutions worked very well form me.
 
Carl,
Thank you...yes, I heard of rs20i. It cost as much as one of my cars! Naturally MiniDsp is a lot more economical. I had build an analog crossover for my dipoles years ago. It was a rather big circuit. The problem is, it is a pain to tweak. Well, - currently I am thinking of a part DIY and part commertial implementation.

Ideally I would like to have a digital in-digital out crossover, so that I can do my own DACs. It seems that the MiniDsp just has the DSP engine and will serve me well in interim until I figure out how to get to the output digital signals inside it. I was going to do the same with my dcx2496 unit, but it was way to flaky for me.

Both the 10x10 and 4x10 units from minidsp look very promising to me and overall look better then the dcx.
Question, does Rudi publish schematics for his crossover? I'll be interested to see his implementation and possibly follow his circuit digitally.

My analog crossover had a requsite 5-6 db notch at 5k and a high frequency boost of about 12 dB at near 20 kHz. I used gurator configurations. Crossover was around 450 Hz to midrange, L-R 4th order. Now I want to change those parameters to see what happence , so DSP approach is a must.
 
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With a short listening distance I found that a baffle is really not necessary, and I XO at 180 Hz. With greater distance, the level below 1 kHz will roll off, and to compensate a baffle will be necessary.

I run an all-digital computer-based XO and EQ solution, and the digital output is fed to a multi-channel DAC.

I also have a dip around 5 kHz and 12 dB boost at 20 k.
 
"Question, does Rudi publish schematics for his crossover? I'll be interested to see his implementation and possibly follow his circuit digitally."

To the best of my knowledge Rudi never made public a schematic of his Clearview CXR crossovers.

However I can tell you that they were well done and a very dense circuit with many OP275 opamps in it.

I only abandoned my Clearview xover after I had access to a more flexible digital technology.
 
With a short listening distance I found that a baffle is really not necessary, and I XO at 180 Hz. With greater distance, the level below 1 kHz will roll off, and to compensate a baffle will be necessary.

I run an all-digital computer-based XO and EQ solution, and the digital output is fed to a multi-channel DAC.

I also have a dip around 5 kHz and 12 dB boost at 20 k.

Yes, I understand and I agree that you can do without a baffle, as long as you are willing to live with rather high roll off. I wanted to use 10-inch drivers for my mid-range, so at most I needed to place the crossover around 500 Hz and my baffle can support that. You probably are using 8-inch drivers.

Erik, I wonder if you could describe your PC-based crossover in some detail. I would like to know what software you are using and what are the computer requarements? Also, - how many channels are possible? Am I to understand that you are running multiple SPDI/F outputs out of your PC? Can you do AC-3 5.1 format? I just might go the same route. Thank you.
 
"Question, does Rudi publish schematics for his crossover? I'll be interested to see his implementation and possibly follow his circuit digitally."

To the best of my knowledge Rudi never made public a schematic of his Clearview CXR crossovers.

However I can tell you that they were well done and a very dense circuit with many OP275 opamps in it.

I only abandoned my Clearview xover after I had access to a more flexible digital technology.

Carl,

I can imagine what Rudi did. Actually it was not all that bad. I had a similar circuit, I am sure of it. But, yes, it was rather large and all digital solution is preferable. I am now thinking PC-based approach, - will see...
 
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Yes, I understand and I agree that you can do without a baffle, as long as you are willing to live with rather high roll off. I wanted to use 10-inch drivers for my mid-range, so at most I needed to place the crossover around 500 Hz and my baffle can support that. You probably are using 8-inch drivers.

Erik, I wonder if you could describe your PC-based crossover in some detail. I would like to know what software you are using and what are the computer requarements? Also, - how many channels are possible? Am I to understand that you are running multiple SPDI/F outputs out of your PC? Can you do AC-3 5.1 format? I just might go the same route. Thank you.

At my listening distance, RD-75 is flat to 200 Hz even with no baffle. I XO at 180 Hz. The real attraction with the RD-75 is that you can make a 2-way.

I am using 21" woofers in large H-baffles together with the RD-75.


My PC XO is based on a midi routing software called "Console", which can be used as a host for VST-plugins. I use a high-quality parametric EQ plugin for both XO and EQ. Such a system can do multi-channel, provided you have enough outputs. A three-way 5.1 system will require 16 channels. Some pro-audio interfaces can support that through AES-3 or ADAT interfaces. How powerful the computer needs to be depends entirely on what EQ plugins you will use. Some are quite CPU-intensive, and some are not.
 
Questions

Hi StigErik I have a few questions I would like to ask you. I just ordered the Bohlender Graebener RD75, they should be here in a week. My questions are at what frequency on the top end do I need to start EQing from. I know it's 12dB at 20khz but were does compensation start at. Also at what exact frequency do you need to compensate with a notch filter and how wide of band, I guess that is the Q. I am using a active crossover Marchand xm44, so not digital. I need to order the frequency modules for this crossover. Thanks alot.
 
I was wondering if you could change the q figures into frequency response for me. I don't know how q works. Is a q of 10 one octave. Also if I give you a baffle width of 20 inches could you calculate the notch filter frequency for me, I don't have any measuring software or hardware and probably won't for another 6 months.
 
Q is the inverse of octave width.
For which definition of bandwidth? With the usual -3dB points it's

Robert Bristow-Johnson said:
The relationship between bandwidth and Q is
1/Q = 2*sinh(ln(2)/2*BW*w0/sin(w0)) (digital filter w BLT)
or 1/Q = 2*sinh(ln(2)/2*BW) (analog filter prototype)

You can find the Bristow-Johnson cookbok here.

Most software implementing digital filters takes analog values as input and uses the same definitions as Bristow-Johnson. So generally one wants the analog translation for converting from Q to bandwidth in octaves to find the values to plug into the UI:

BW=2/ln(2)*asinh(1/(2*Q))​
 
Double check

Stig Erik are these frequencies correct. A notch filter frequencies of 5800hz wit a q of 1.6 gives me a starting frequency of 3625hz and an ending frequency of 9280hz. Is that correct? That seems like pretty big range for a notch. Just figured I'd double check. Thanks alot StigErik.
 
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This is how such a notch looks like in a parametric EQ.
 

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