[panomaniac]

By boost I mean boost the gain of the sub amp.  Since you'll be filtering out so much of the upper bass/ low mids, you'll need to boost the volume on the plate amp a bit to make up for it.  That will give you the correct acoustic volume.

[Telstar]

By boost I mean boost the gain of the sub amp.  Since you'll be filtering out so much of the upper bass/ low mids, you'll need to boost the volume on the plate amp a bit to make up for it.  That will give you the correct acoustic volume.

Yes, I will adjust in room depending on measurements and my tastes.

I though you referred to the "bass boost" of some plate amps, that is very bad for the sound.

[panomaniac]

Right - NOT bass boost - just overall level. Sorry. The P.E. plate amps I used don't have bass boost anyway.

[Badwater]

i am finally getting around to building my project and have several questions for the group.

I will be using an Alpha 15A in an H frame driven with a small PE 70 Watt plate amp as discussed earlier in this thread.  An EV SP12B wide band will be on top and will be mounted on the back of the baffle.  I plan to use a Fostex T90A tweeter to fill out the top end.  The T90A will sit on top of the baffle above the EV. 

The plate amp and crossover components will be mounted in a separate box on top of the H Frame.

Pic's of a dry fit of what I plan to do:

http://gallery.me.com/marilynladieu#100295

I have done several simulations using MJKs worksheets and it looks like the EVs will be fairly flat to about 100 Hz at 95 db.  I plan to use the plate amp to level match the Alphas and the EV. I will use a single 2 uf cap on the T90A and a level pad.  It will be tuned by ear.

Questions:

1.  Should I leave the top and sides on the baffle?  From the front of the baffle they are 5 1/4" deep and effectively form a U frame for the EV. 

2.  Should I add a high pass on the EV or should I let it run full range?   From a previous build I have the components for a 200 Hz 12 db crossover.

3. Any benefit to adding a low pass on the EV?  What about a series inductor as has been suggested elsewhere. 

4.  Any benefit to adding felt or damping material to the back of the baffle?

Thanks for the help.  I will post progress pictures of the build.  I hope to have it done by the end of the year, but probably not in service till the xmas tree comes down.

Bill

[Magnetar]

I have done several simulations using MJKs worksheets and it looks like the EVs will be fairly flat to about 100 Hz at 95 db.  I plan to use the plate amp to level match the Alphas and the EV. I will use a single 2 uf cap on the T90A and a level pad.  It will be tuned by ear.

Questions:

1.  Should I leave the top and sides on the baffle?  From the front of the baffle they are 5 1/4" deep and effectively form a U frame for the EV. 

2.  Should I add a high pass on the EV or should I let it run full range?   From a previous build I have the components for a 200 Hz 12 db crossover.

3. Any benefit to adding a low pass on the EV?  What about a series inductor as has been suggested elsewhere. 

4.  Any benefit to adding felt or damping material to the back of the baffle?

Thanks for the help.  I will post progress pictures of the build.  I hope to have it done by the end of the year, but probably not in service till the xmas tree comes down.

Bill

The SP12 will probably be good to 200 cycles on that baffle. You should always high pass a cone driver on an open baffle.  A preferred way of doing it is prior to the amplifier with either a simple RC network at the input of the amp or an electronic crossover. This will free up more amplifier power and clean up your midrange because the EV won't need to be driven where it's inefficient plus the driver will have less excursion and lower distortion.

I'd leave part of the top on the mid baffle - curve it around and leave enough to sit the Fostex on. If you leave the wings on the mid baffle use 3-4" thick of foam glued or stapled to the inside walls.

A low pass on the EV might be a good idea, start out with around a .68 inductor and unwind it until it sounds correct.

[panomaniac]

Yeah, I agree with all of the above.
Tho I have run the FR driver in rigs like that with no hi-pass.  It did not seem to hurt.  Up to you to try it and find out.

Felt or foam does help.  I've even covered the entire baffle face with felt.  Seems to smooth things out and take away some of the midrange bite that bare wood can have.

[Badwater]

Thanks you both for the information. 

I have ordered a 0.68 mH inductor.  I was considering the U-Frame to deal with WAF issues.  She isn't happy with the project anyhow so I will leave them off and just add a shelf for the T90A. Hopefully the sound will win her over. My wife really likes my Fostex FE166 ESR factory recommended horns, which these will replace.

I will keep you posted.

Bill

[Badwater]

I haven't done anything yet and I am still considering my options.  I am wavering between doing a flat 3/4" baltic birch baffle and a flat baffle with shallow sides and top.  Any opinions, on using  multiple layers of insulation board (blue board)  to fill in the back so that is is more or less flush; if I decide to go with the sides and top?  An added benefit is that the insulation board may help to damp the baffle.

Thanks for the help and opinions.

Bill

[tubamark]

I haven't done anything yet and I am still considering my options.  I am wavering between doing a flat 3/4" baltic birch baffle and a flat baffle with shallow sides and top.  Any opinions, on using  multiple layers of insulation board (blue board)  to fill in the back so that is is more or less flush; if I decide to go with the sides and top?  An added benefit is that the insulation board may help to damp the baffle.

Thanks for the help and opinions.

Bill

I say this with love (not just to Bill, but all OB starters): You're overthinking it for this stage of your journey!
I would recommend doing some mock-up baffles before ever cutting the birch.
In the OB world it's bad practice --even with modeling software and all-- to think ahead too much to final configuration before hearing lots of variations for yourself.  No modeling decently captures the way the OB will actually sound, how it will image, tonality, etc. becuase OB's always interact with the room very differently --and unpredictably-- than the ol' monkey coffins.  Modeling (which I do advocate) at best gives a starting point, never ever an optimum design.

I would recommend doing mock-ups with drywall scraps, OSB scraps, or cardboard first.  Despite all the hoopla about construction methods, resonances, etc, the baffle configuration and room placement itself will always dominate the sound.  Even Siegfried Linkwitz --who crunches numbers with the best of them-- Prototyped the $$Orion with cardboard, because it gets you 96% of the way there, while allowing you to really find what works best.  You may love a squat JE labs configuration.  You may love a tower, or even a baffleless "stop sign" configuration.  All are valid with the right driver in the right room for the right listener.

If you comb the threads over the years, there are a suprising number of guys that end up chopping up thier finely-crafted photo-ready prototypes that just didn't meet their expectations.
My two cents. Try before you buy!
-- Mark

[mcgsxr]

mdf - the experimenter's friend.  It will give you most of the rigidity of baltic birch, with 1/10th the cost (locally anyway).

Of course, my OB's are still in mdf... so be careful what you build, you may find it tough to find the time to actually finish them if you love how they sound!

The most important part of the Open Baffle experience, is to be sure to bring an open mind.

[Badwater]

Mark,

Thanks you for the thoughtful reply and great advise.  Protoyping is reallly very helpful and can save a lot of false starts. 

I am not running entirely blind on this project.  I ran a test baffle using the EVSP12B, EVT35 and one Alpha 15 per baffle for several weeks to see if I would like it. The design I used is based on the work of Martin King.  Check out:

http://www.audiocircle.com/index.php?topic=52058.0

I was very happy with result despite a small room and sub-optimal placement.  My current project, at least to my way of thinking, is an evolution of that project. Planned changes:


1. H-frame for the Alpha 15 driven by small plate amp to gain more extension on the low end. This plate amp will allow me to level match the bottom end and ditch the L-Pad on the SP12B.  I used Martin's worksheets to design the H-frame.
 
2. No subwoofer.

3. Using a Fostex T90A super tweeter in lieu of the EVT35.  I have both and plan to experiment to see which I like better.  The tweeter will be high passed using a 2.7 uf cap and will include an L-Pad to level match.

4. The baffle is slightly narrower (17.5" versus 20") than my test baffles and are sized to match up to the H-frame.

The narrow sides and top were an attempt to make them more aesthetically appealing to my wife. She really doesn't want these babies in her living room.  I doubt very much that they will have very long run in my system. You should have heard the comments I got when I was running the test baffles.

I recognize that this probably is not the best that I could do.  I don't have the patience to do extensive prototyping.  I am more into building and trying different ideas to see where it takes me and to learn more about this great hobby.  The next evolution of the project will be to try a CD and WG, which really fascinates me.

Have a great day and Merry Christmas.

Bill

[tubesguy2]

Those that have interest in the original topic of this thread might be pleased to know that Martin has posted the recommended passive crossover configuration in the corresponding thread at DIYaudio.  Thanks again, Martin.

[-Richard-]

Hi Tubamark, I really like your sober insights and suggestions to everyone in the AC community that feels the urge to explore what the OB sound can teach them... and of course for the sheer pleasure of hearing music unfettered by the evils of the "box".

When I was working with my own OB designs I got together with Jim McCarthy, a fantastic designer in his own right who creates original furniture designs for his clients here in Ojai, and we did a great deal of experimentation together. For example we spent several hours working with "wings" for the side of my OB baffles using various sizes that we took on and off a simple flat baffle. We would play 3 different types of music for perhaps 2 minutes... and listen intently. Jim also happens to be a professional musician, composure and engineer... so he comes from a professional audio background. Which means his listening skills easily match my own... and it turned out that we both had different kinds of things we listened for... which made our experiments together very interesting... we learned a great deal working and sharing insights with each other.

Jim actually built my baffles for me and his design input was original and very effective... and that is why my baffles look as good as they do. That is something some of you might want to consider... working with a master designer in wood... especially if your skill level is modest like mine.

But most important... we both learned what worked and what did not work in terms of using "wings" in various configurations. So I also urge everyone who is interested in designing their own OB speakers to do some critical listening and to find out for yourselves... that is the key here... find out for yourselves... and what you learn will help you to grow exponentially as an listener. After that kind of experimentation you will know exactly what a speaker sounds like... it is amazing how much you can learn. It is also great fun!

With Warmest Regards ~ Richard

[Badwater]

i finished the speakers....sort of.  I used the Alpha 15A in an H frame powered by a 70 watt PE plate amp.  The EVSP12B is high passed at 200 hz 2nd order.  No low pass as of yet. i may not bother as they sound very good as is.  The baffle for the EV sits on top of the H frame.  The fostex T90A is high passed using a single 2.7 uf cap with an L-pad.  It took a while to get them dialed in.  Very nice rich balanced sound. They really fill a room and image very well.   

They are kind of ugly and probably won't have too long of a run in the living room.   

I will post some pictures next week when my wife gets back with the camera.

Bill

[Badwater]

Follow the link below to some pictures of the open baffle.  No too sure about the H-frame.  The plate amps are picking up some hum from my ST-70 which normally isn't noticeable. I want to try a solid state amp to see if it cuts down on the hum or try to design a passive with a fixed L-pad to level match the top end with bottom.

I really like the EV with the Fostex T90A. They really sing.  The top baffle is loose and can be moved to suit. The sound stage these project is massive. They are a very easy speaker to listen to.

http://gallery.me.com/marilynladieu#100295

Bill

[opnly bafld]

Nice Bill. 
How tall are the speakers?
Have you tried it with the mid driver and tweeter lower?

Lin

[Badwater]

Thanks. They are about 42" tall. The EV is about 34" to it's centerline. If can figure away around the hum they are real keepers.

[cboy168]

Hello everyone. I am new here but I am learning a lot on the discussions you guys are posting.

I am very interested in this OB based on Jordan and 18inch woofer. I think the approach is very creative and could be the answer to many OB's woes in the past. One question, can this design be used with a passive crossover??? TIA

[MJK]

I am very interested in this OB based on Jordan and 18inch woofer. I think the approach is very creative and could be the answer to many OB's woes in the past. One question, can this design be used with a passive crossover???

I have a passive crossover design built, measured, and running. I finished the first pass write up last night and added it to my site this morning. I got tired of looking at it so let me know about any typos. The passive crossover works very well.

[-Richard-]

Hi MJK ~

You did it!!!!! You built a great looking Open Baffle speaker with a minimum of electronic clutter and fussing. A real minimalist gem. Congratulations.

And thanks so much for sharing all of your work with us. I admit that I am tempted to try this design myself... someday.

Please let us know how you feel about the sound as you get better used to it... I am very interested to hear any insights you have.

Warmest Regards ~ Richard