1st Open Baffles; Need help!

I have read a lot of threads and still end up with a ton of questions. I sure hope you wizards can help! (apologies for the long post)

I have been trying out SET amps and love the sound. my favorite so far is the clementine darling I received from Watt in a trade. I have a simple tombstone style OB that someone kindly gave me. Have 3 full range drivers so far: visaton B200s with phase plug mod; betsys (from opa1) and radio shack 40-1286c (from mfhale). I'm thinking about getting other drivers; eg, EV LT-12s, maybe some old Jensens. the eminence betas that poultrygeist likes might also work.

now I want to build a larger OB. per suggestions from opa1 and others I first built several baffle designs with cardboard and rigid foam board. 1st the wild burro labs betsy enclosure: http://www.wildburroaudio.com/projects.php. 2nd I made the classic JE Labs OB: http://jelabsarch.blogspot.com/search/label/Open Baffle. last i tried a smaller winged baffle design: center panel 16" x 36" and two side wings each 12" x 36".

my listening room is about 10' x 13' and my cardboard OBs are placed right now about 7.5' from my listening position.

all 3 enclosures sound pretty good. the betsy design is just huge in this room so doesn't make sense. that leaves me with the JE Labs or the smaller winged baffle. I think I had better imaging with the JE Labs enclosure but am not positive.

Questions:

1. I tried the "edge" baffle design software. I used the JE Labs baffle and a 8" driver for my modeling. I get really messy looking curves unless i move the driver to very close to the edge of the baffle. (Still kinda messy anyways.) Does this make sense? Joseph Esmilla (of JE Labs) says the drivers should be offset but seems to say that offset needs only be slight. does the edge software really fit with the slanted JE Labs baffle design? how much offset should I use?

2. Given my objectives and room, does anyone have suggestions for me re baffle design? either amongst the 2 i have narrowed it to or any other design. my cardboard building has confirmed to me that I should stick with simple designs and I don't have the competence to build crossovers, etc. I am hiring a friend to build these baffles, that is how bad I am at doing it myself.

3. I want to be able to switch drivers pretty easily. so the idea is to have a cut-out in the main baffle and several inserts that would fit in the cut-out. the inserts would have the drivers mounted so drivers could be switched. my builder suggests it would be safest to screw in the inserts to prevent vibrations. i am wondering if an easier on-off is possible. what about using mounting hardware like these trunk clasps: http://www.homedepot.com/h_d1/N-5yc...keyword=draw+latch&storeId=10051#.URqHVx27PIU
any thoughts about whether that would work?

4. any suggestions re wood, finish, or anything else would be appreciated...

Thanks for any ideas!

something like this storm door clip could also be used to keep the driver insert in place:

http://www.homedepot.com/webapp/wcs...ads-_-pla-_-202639186&ci_gpa=pla#.UR0GdB287IU

The key in offsetting the driver is to make it uneven intervals to each edge. If you move it from center to 1/4 way across then the other side is 3/4, a multiple of 1/4 and you will end up with a big comb filter effect. Try to move it to somewhere that the distance to each side and top are not multiples of each other.

As to mounting interchangeable plates, the last speaker test baffle I built had these to hold the various plates:
http://www.harborfreight.com/500-lb-horizontal-toggle-clamp-96233.html

Thanks ray
That clamp looks awesome!
How close to the edge of the baffle do you think I should go?

I believe the standard we used on NXT type panels (you want the exciter to be offset just like in an OB) was 5/9 side to side and 6/11 top to bottom. That was on a panel where the top and bottom were exposed and width/height was a set ratio which I can't remember right now. With yours, the important thing for the distance from the driver to the top is that it is not the same as, or a multiple of, the distance to either side.

So if you have a 24" wide baffle then you would want the driver center at 13 1/3" from one side (10 2/3" from the other). The distance from the top should be less than 10 2/3" or more than 13 1/3" but not enough to make multiples (i.e. not 5 1/3").

Is that making any sense?

ray,

i think i can figure out the avoid multiples thing. i am more interested in the results i got using the "edge" software that seemed to indicate i would get a much smoother response curve if the driver was located near the edge of the baffle (for that run i used the JE Labs baffle).

does that make sense? in all my research i have yet to see someone build a JE Labs baffle with the drivers way off the center. so, i'm wondering if the edge software properly models the JE Labs enclosure which is placed on the floor for additional bass response and is tilted back 20 degrees.

thanks!

What does the bass response look like as you get closer to the edge? It should be creeping up to the point where there isn't much when you get right to the edge. The closer you are to the center, the lower the bass cutoff will be. What you have to work out is the balance between how much bass you can stand to lose and how smooth you want the response to be.

Does the edge software allow you to load the actual response of the speaker? It might be enlightening to look at that superimposed on the baffle response.

Is there a reason why people messing with these simple sorts of OB speakers aren't using absorption on the baffle? Seems to me that if if you just offset the driver a bit (like the odd ratios Ray mentioned), you'd preserve the most bass response you can get for your baffle size, and then you could just knock down the virtual sources from edge diffraction with thick strips of insulation.

P.S. somebody should move this to DIY.

That is helpful. I think the edge program just models a generic speaker. You supply the diameter.

You can also input speaker source density and # of edge sources. I wasn't quite sure how to use these and the web site is not too helpful. I used 3 or 4 for speaker source density (for a full range driver?) and used a high # for edge sources.

I can do more runs looking at the bass cutoff but as I recall it didn't move much as I moved around the source location.

Do you have confidence in this software?'

Increased source density increases accuracy and slows down the program. I think you're generally just suppose to experiment with increasing it to where you see no major changes. The program is just fine for what it's supposed to do: let you experiment quickly with baffle edges and sound source locations focusing purely on effects from those things.

The wild burro labs design calls for cork backing. I think poultrygeist has used ikea cork placemats for backing.

That wouldn't do much, except probably damp the panel a bit. I was talking like 1-3" thick by 3-5"W strips of highly absorptive material (fiberglass, mineral wool, denim insulation, specialty products, whatever) on the front, all along the edges.

Why don't you try no-baffle? I ran OB for a year, but recently hung the driver from wire inside a frame. Poor man's electrostat, if you will. Unbelievable improvement over OB.

Maybe that is in my future. But don't you need a really good driver to pull that off?

Most any driver that works in OB should work without any baffle, but it will roll off at pretty high frequency. You can simulate that rolloff in the edge - just set the baffle size a couple mm larger than the driver, and add a bunch of corners.

One extra question. I have run across some 12 inch jensen extended range alnico drivers. A bit pricey for my current budget, but how do you all think they would do in the OB designs I'm looking at? I got to hear them briefly and they sounded pretty good with some guitar music.
I'm also thinking about some EVs.

I had to experiment with the Dayton full-range to get it to really sing...

added fiberfill behind the surround (just the surround) to eliminate an upper mid - lower treble shoutiness, and I am using a coil/cap notch filter also. But that's it.

Dumptruck- what rolloff? I get response up to 25K. Best top end I've ever had.

Two pieces of bad news for you, I apologize in advance.

1. A single full range or extended range driver mounted on an OB is not going to produce much in the way of bass output. The midrange will be fine but the overall sound will be very light weight. You need a helper woofer and the simplest set up will have a woofer with an fs of about 40 Hz and a Qts between 1.1 to 1.3.

2. If you buy into the idea of a helper woofer and want to use a single amp with a passive crossover, your tube amp is probably not going to be happy. A simple two way woofer / full range driver OB will want to have a passive crossover at about 200 Hz and my experience is that most tube amps will not perform well with the big impedance swings this produces.

The good news is that this type of system is easy to design with available software tools and if done right sounds really amazing. Easy to design, easy to build, low cost -----> great performance.

Martin

meh.... I run it 500Hz & up. Using 2 x 12"ers in 2 ported boxes for bass.

truly the cleanest, most detailed system I've owned.

I listen to all kinds of music but mostly jazz. With the visatons on the tombstone baffles and now the betsys on my larger cardboard mock- ups I get acceptable bass.
I am listening in a small room so don't have to fill a large space.
Using my set amps is a bottom line for me. Guess I could add an active sub if necessary.