I was just wondering if someone could give me some advice on choosing crossover components for the MJK open baffle project. I have never built a crossover before, but want to ensure I buy high crossover quality parts (willing to pay more if it will have an audible effect).
THe MJK open baffle requires the following:
I'd like to purchase the crossover parts from the store below.
Can anyone please offer some suggestions? I have no clue!
Thanks!
http://www.soundlabsgroup.com.au/c/Components/Electronic+Components.html
THe MJK open baffle requires the following:
An externally hosted image should be here but it was not working when we last tested it.
I'd like to purchase the crossover parts from the store below.
Can anyone please offer some suggestions? I have no clue!
Thanks!
http://www.soundlabsgroup.com.au/c/Components/Electronic+Components.html
Wixy,
I built the crossover using most of the components on Martin's list. I substituted a cheaper cap for the 68uF on the low pass because in that position I don't think the cap quality is critical. The 24 uF cap on the high pass is more critical. I used a 22 Solen and a 2.2 Hoveland in parallel because I had them. You may want to look at other options for that cap but Solens are good. The Erse inductors are very good, I have used them on other projects.
You can see a picture of my crossover on Martin's design gallery. Scroll down a bit..
MJK Design Gallery
Make sure you keep the two inductors away from each other and at right angles to each other.
It's a great design, good luck with yours.
I built the crossover using most of the components on Martin's list. I substituted a cheaper cap for the 68uF on the low pass because in that position I don't think the cap quality is critical. The 24 uF cap on the high pass is more critical. I used a 22 Solen and a 2.2 Hoveland in parallel because I had them. You may want to look at other options for that cap but Solens are good. The Erse inductors are very good, I have used them on other projects.
You can see a picture of my crossover on Martin's design gallery. Scroll down a bit..
MJK Design Gallery
Make sure you keep the two inductors away from each other and at right angles to each other.
It's a great design, good luck with yours.
I agree with Dave. MDF is heavier, but isn't nearly as stiff and would require braces to even come close. Dave (and others) might even add that Ply sounds better and results in a far more harmonious outcome. The fact is that ply is far more pleasant to work with, as well as being able to give you a baffle that is stronger, usually better looking, and when you're finished, you can face the world with the calm confidence of a born-again Christian holding four aces 
Best Regards,
TerryO
Best Regards,
TerryO
avoid mdf if possible
Wixy,
Mdf is a convenient material but has nonlinear sound characteristics, esp about 300hz, so you will get "strange" lower mids which are just as audible with OB, as box designs.
You don't get this problem with ply, as Dave, Terry, (and others) have advised. It's not as convenient to find, esp void free, but much better result.
Also, the glue that holds mdf together is not good for you at all!
The "form ply" and/or marine ply are much better than mdf, but more difficult to glue and finish off.
Suggest you find a "ply shop" in your area and just try your first one to get you started - can dampen rear faces, if required - not expensive.
The "lighter" ply will often give a "lighter" sound, silly as that seems!
I initially used two different layers of ply glued together with a non-hardening liquid adhesive ("liquid latex", I think) and pressed overnight (wheel of car, bricks,etc.)
If your budget allows, suggest ICW 'Clarity caps' for Xover, available from 'Lede Electronics' (in Catherine, NT) at about $1/uF, I think.
Hope this helps.
Wixy,
Mdf is a convenient material but has nonlinear sound characteristics, esp about 300hz, so you will get "strange" lower mids which are just as audible with OB, as box designs.
You don't get this problem with ply, as Dave, Terry, (and others) have advised. It's not as convenient to find, esp void free, but much better result.
Also, the glue that holds mdf together is not good for you at all!
The "form ply" and/or marine ply are much better than mdf, but more difficult to glue and finish off.
Suggest you find a "ply shop" in your area and just try your first one to get you started - can dampen rear faces, if required - not expensive.
The "lighter" ply will often give a "lighter" sound, silly as that seems!
I initially used two different layers of ply glued together with a non-hardening liquid adhesive ("liquid latex", I think) and pressed overnight (wheel of car, bricks,etc.)
If your budget allows, suggest ICW 'Clarity caps' for Xover, available from 'Lede Electronics' (in Catherine, NT) at about $1/uF, I think.
Hope this helps.
low Qts drivers
I was doing some experiments on a woofer with a Low Qts of about .27 and Fs of 28 Hz on an 18 inch wide open baffle. The in room response measured about 10 to 11dB/octave up to 400 Hz. I was thinking a 12dB lowpass x-over at 25 to 30 Hz would work to bring the response in line. It turned out that this was too much of a slope and there was too much bottom end for my purposes (upper x-over of 400Hz). If you were only using this at 80 to 100 Hz this setup would work, but I needed to extend the upper roll off to 400 Hz.
This got me thinking of the article Nelson Pass wrote on Current Source amps. So, I started trying different resistor values on the output of my voltage amp and discovered that 47 Ohms in series with the amps output resulted in a response (before X-over) of 6dB/octave on the open baffle. This made it very easy to 6dB lowpass the driver at 25 Hz and now I have a flat response from the 20s to over 400Hz in room where the woofer crosses over to the midrange. If you passively x-over, the inductor is going to be large, but an active Bi- amp setup is easy to x-over. The surprising part to me is that contrary to popular belief the bass is very controlled and effortless with the series resistor.
If you need the bass to go low and you have a low Qts driver on hand you can experiment with different values of resistors and x-over slopes to get your desired results. X-max is important if you want significant output on the low end.
BDP
I was doing some experiments on a woofer with a Low Qts of about .27 and Fs of 28 Hz on an 18 inch wide open baffle. The in room response measured about 10 to 11dB/octave up to 400 Hz. I was thinking a 12dB lowpass x-over at 25 to 30 Hz would work to bring the response in line. It turned out that this was too much of a slope and there was too much bottom end for my purposes (upper x-over of 400Hz). If you were only using this at 80 to 100 Hz this setup would work, but I needed to extend the upper roll off to 400 Hz.
This got me thinking of the article Nelson Pass wrote on Current Source amps. So, I started trying different resistor values on the output of my voltage amp and discovered that 47 Ohms in series with the amps output resulted in a response (before X-over) of 6dB/octave on the open baffle. This made it very easy to 6dB lowpass the driver at 25 Hz and now I have a flat response from the 20s to over 400Hz in room where the woofer crosses over to the midrange. If you passively x-over, the inductor is going to be large, but an active Bi- amp setup is easy to x-over. The surprising part to me is that contrary to popular belief the bass is very controlled and effortless with the series resistor.
If you need the bass to go low and you have a low Qts driver on hand you can experiment with different values of resistors and x-over slopes to get your desired results. X-max is important if you want significant output on the low end.
BDP
I don't see any reason that what you have done would not work or is not predictable by simulation.
But what kind of efficiency did you end up with when you had the bass to your liking? I bet you had to use a lot of power to get decent volume levels to match the midrange driver.
Do you think that there is an advantage to using a more expensive low Qts driver (bigger magnet = higher cost) and then a series resistor to raise the effective Qts by lowering the mid bass efficiency, instead of buying a lower cost higher Qts driver and retain the driver manufacturer's stated efficient?
I think you could end up in about the samer place sonically with either method. I see other people doing this but I guess I just don't see many advantages in particular if all you are only looking bass below about 200 Hz.
But what kind of efficiency did you end up with when you had the bass to your liking? I bet you had to use a lot of power to get decent volume levels to match the midrange driver.
Do you think that there is an advantage to using a more expensive low Qts driver (bigger magnet = higher cost) and then a series resistor to raise the effective Qts by lowering the mid bass efficiency, instead of buying a lower cost higher Qts driver and retain the driver manufacturer's stated efficient?
I think you could end up in about the samer place sonically with either method. I see other people doing this but I guess I just don't see many advantages in particular if all you are only looking bass below about 200 Hz.
My sharing was to show that there are varying degrees of ways to reach similar results, meaning that you dont always need a driver with exact Qts for proper results.
Yes, the amplifier is required to output more to drive the woofer. In my case I'm using a First Watt F3 clone driving the mid and Tweeter and an A75 driving the bass.
I think one of the advantages in this approach is that I get usable output down in the mid 20s. This would be difficult to achieve with a box alignment and at a similar size.
I can't comment on the sound difference between a high Qts and low Qts and series resistor because I have'nt built or listened to both. I can say that the bass on this open baffle setup is more effortless at lower volumes than a comparable bass relex or sealed alignment.
I am by no means trying to undermine the work you have presented, in fact if I had'nt already had the available drivers on hand I would have followed your recommendations on the driver selection. This type of thread is what keeps me coming back to DIY Audio. It makes you think about applications in different ways. So, thanks again for your work and ideas that you have presented here.
BDP
Yes, the amplifier is required to output more to drive the woofer. In my case I'm using a First Watt F3 clone driving the mid and Tweeter and an A75 driving the bass.
I think one of the advantages in this approach is that I get usable output down in the mid 20s. This would be difficult to achieve with a box alignment and at a similar size.
I can't comment on the sound difference between a high Qts and low Qts and series resistor because I have'nt built or listened to both. I can say that the bass on this open baffle setup is more effortless at lower volumes than a comparable bass relex or sealed alignment.
I am by no means trying to undermine the work you have presented, in fact if I had'nt already had the available drivers on hand I would have followed your recommendations on the driver selection. This type of thread is what keeps me coming back to DIY Audio. It makes you think about applications in different ways. So, thanks again for your work and ideas that you have presented here.
BDP
I figure around overall 89-90 db. But i am using the Fe 87.
If you are into tubes a good PP around 30 watts. I am using a Marantz re-built 2238 and it sounds very good. I have no need for high SPLs as i really dont get above around 85 Db at the couch and i live primarly in an apt.
Why do i have OBs ? Well i enjoy the open spacious sound, the simplicity of the design and the very realistic bass at lower volumes.
Drawbacks, well i havent put a meter on them but i figure a low end of around 55 hz. All i did was build and enjoy not try to break down all the physics/math.
One thing i do want to try is to mount the 87 in a seperate smaller OB at 90 deg to the LF OB and wall/floor load them. If this works then you have a much smaller front profile and increased LF performance.
Any ideas Martin?
ron
If you are into tubes a good PP around 30 watts. I am using a Marantz re-built 2238 and it sounds very good. I have no need for high SPLs as i really dont get above around 85 Db at the couch and i live primarly in an apt.
Why do i have OBs ? Well i enjoy the open spacious sound, the simplicity of the design and the very realistic bass at lower volumes.
Drawbacks, well i havent put a meter on them but i figure a low end of around 55 hz. All i did was build and enjoy not try to break down all the physics/math.
One thing i do want to try is to mount the 87 in a seperate smaller OB at 90 deg to the LF OB and wall/floor load them. If this works then you have a much smaller front profile and increased LF performance.
Any ideas Martin?
ron
BDP,
I did not mean to give you a hard time about your design, I hope it did not come across that way. People constantly e-mail me about using a low Qts driver in my design because they have been conditioned to think boomy inaccurate bass with a high Qts and quality tight bass with a low Qts driver. That may be true for a boxed speaker but in my opinion for an OB one needs to reverse this perception unless they want to biamp and equalize the system. It is amazing how many people try the low Qts route with a narrow baffle and passive crossover then want to know where the bass went and how to get it back. What I wanted to emphasize is that you made it work but it took some effort with a second amp with some extra power.
Thoose numbers sound about right. With one of the other Fostex drivers on my list you might get 90 to 91 dB/W/m. If you go with a much higher efficiency full range driver the bass will start to sound a little recessed unless you pad it down a few dBs.
Ooohhhhh ... that is an interesting idea. By mounting the Alpha 15A near the floor you are getting 3 or 4 dB of bass reinforcement and avoiding a floor bounce issue. If you were to mount the Alpha 15A along a side wall, perpendicular to the wall or even tilted towards the listener a little, you would pick up a few more dB of reinforcement. The only down side would be if you could not sit far enough back you would start to loose dB if you were more than 45 degrees off axis due to the dipole figure 8 radiation pattern. Definitely a very interesting idea.
Quick edit a minute or two later :
I have added updated OB worksheets in the past week or two. I have made the OB article the default design in the two driver worksheet. I have updated the three driver worksheet to reflect a Fostex FE-167E driver with two Alpha 15A woofers on a similar size baffle. It is kind of the bigger brother model of the FE-103E design. A little deeper bass and higher efficiency with similar crossover requirements. You can look at the designs by opening the pdf's of each worksheet on my MathCad Models page. I am just finishing revisions to the U and H frame sheets which will produce a few more interesting results and I think a new article comparing OB with U and H frame geometries.
I did not mean to give you a hard time about your design, I hope it did not come across that way. People constantly e-mail me about using a low Qts driver in my design because they have been conditioned to think boomy inaccurate bass with a high Qts and quality tight bass with a low Qts driver. That may be true for a boxed speaker but in my opinion for an OB one needs to reverse this perception unless they want to biamp and equalize the system. It is amazing how many people try the low Qts route with a narrow baffle and passive crossover then want to know where the bass went and how to get it back. What I wanted to emphasize is that you made it work but it took some effort with a second amp with some extra power.
ronc said:
Thoose numbers sound about right. With one of the other Fostex drivers on my list you might get 90 to 91 dB/W/m. If you go with a much higher efficiency full range driver the bass will start to sound a little recessed unless you pad it down a few dBs.
ronc said:
Ooohhhhh ... that is an interesting idea. By mounting the Alpha 15A near the floor you are getting 3 or 4 dB of bass reinforcement and avoiding a floor bounce issue. If you were to mount the Alpha 15A along a side wall, perpendicular to the wall or even tilted towards the listener a little, you would pick up a few more dB of reinforcement. The only down side would be if you could not sit far enough back you would start to loose dB if you were more than 45 degrees off axis due to the dipole figure 8 radiation pattern. Definitely a very interesting idea.
Quick edit a minute or two later :
I have added updated OB worksheets in the past week or two. I have made the OB article the default design in the two driver worksheet. I have updated the three driver worksheet to reflect a Fostex FE-167E driver with two Alpha 15A woofers on a similar size baffle. It is kind of the bigger brother model of the FE-103E design. A little deeper bass and higher efficiency with similar crossover requirements. You can look at the designs by opening the pdf's of each worksheet on my MathCad Models page. I am just finishing revisions to the U and H frame sheets which will produce a few more interesting results and I think a new article comparing OB with U and H frame geometries.
I see it as a U shape with the extensions aiming at the wall in an off axis direction to help control the radiation pattern and provide control of the reflection from the reflecting wall with the smaller OB on a swivel mount to aim the higher frequencies, It would no longer be a true U shaped(cartoid) produced shape due to the reflected energy pattern.
If i had the time i would sim this.
Just an idea.
ron
If i had the time i would sim this.
Just an idea.
ron
I'm just wondering, instead of building a crossover is it possible to use something like the Behringer CX3400?
http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=248-668
If it is possible, are there any disadvantages?
http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=248-668
If it is possible, are there any disadvantages?
wixy said:
You'll need to have 2 power amplifiers and a single pre-amp. You could get away with a CX2310, but I'd do it for development purposes only as I think some of the Behringer crossovers generate a fair bit of hiss. Maybe there are modifications for them to stop this - I've got three, and the one I'm using seems OK (maybe I'm lucky).
ronc said:
Hi Ron!
After reading Martin article about 2-way open baffle project, which I enjoy so much, I've been doing 'homework' eversince - including searching some experience from the people here before building it.
Your reason of choice using FE87 for mid & hi freq is interesting to me. If you don't mind, I have a few questions here regarding your system using FE87 & Alpha 15,
- Do you use exactly the same baffle dimension as in Martin article? (38"x20"...etc).
- Do you put any wings on it?
- What is the xover setup and value?
Thanks in advance!
Joshua
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