[Rudolf]

... I'm with Rudolph that much of the edge diffraction with OB's doesn't net to zero and is directional in nature. JohnK may be right regarding an infinitely thin baffle with a driver with equal front and rear radiation, but it's also theoretically possible to cross a continent on a gallon of gas.

I believe JohnK took great pains to explain where and how baffle thickness affects diffraction:
http://www.audiocircle.com/index.php?topic=34205.20
And he did adress the real world problem of different front and back radiation. So I don´t see any contrast between him and us here.

Regarding edge geometry: Of course it is an issue. But for most fullrange drivers on a 2" thick baffle any variation in edge geometry will basically adress frequencies from 2 kHz upward, while the position on the baffle will adress frequencies from 2 kHz downward. So it is different solutions for different problems.

wonder if MJK’s worksheet models this?

Yes it does. But the beauty of MJK’s worksheet lies in showing to you, how minor those modifications are compared to changes in wall and listening distance. 
So you really better look at EDGE for optimising the driver to edge distancies.

[mcgsxr]

Rick57 - yes, that is the end result of the journey I was talking about - he started out with a design, and refined it along the way, fielding questions etc as he did so.

In the end, he is as happy as I am, but with completely different speakers.

In the end, the best teacher is experimentation - I was warned that adding the subs to the baffle would muddy the mids, and I did it anyway.  The warnings were absolutely on the money. 

When I rebuild the panels, I will poach JohninCR's magnet mounted, isolated bass solution, and build smaller baffles for the b200, but with U baffle for the lower area for bass.

Just another compromise.

Best of luck, great thread here!

[Rudolf]

As I’m likely to have a “top to toe” driver length (15” woofer, 6.5” mod & 8” ribbon in a row) of 30” ~ 75 cm, how much extra should be allowed, say 5” ~ 12.5 cm either end, for a minimum height of 1 metre?

This is easy! 
A 8" ribbon will beam vertically quite much. It does not "know" where the top edge of the baffle is. So you can put it as high (or low) on the baffle as you want.
The midrange dip you want to equalise with the driver-to-edge distance is anywhere between 500 and 1500 Hz, depending on baffle width. You can´t equalise that if you place the mid driver below the ribbon. You would have to be less than 8" away from the top edge. But you should at least try to make all three distances to the baffle edges quite different.

The better strategy would be to place the mid driver on top and the ribbon below. The mid should be crossed below 3000 Hz, which will be no problem. That way you could move the mid driver as far up as you want. And you want it as near to the top baffle edge as possible.

[JohninCR]

Rudolph,
I didn't mean that any of us are at odds with anything JohnK has posted.  I prefer to
understand the theory.  That's why I ask you and JohnK as many questions as possible.
I need that understanding in order to reconcile theory with real world results, because
the alternative is trial and error for which I don't have the patience. 


Mark,
Anything I post is meant to share or stimulate discussion, so don't think of it as poaching.
I now have a few versions of separate woofer support structures which are relatively
simple and work well.  I'll be posting a lot of new stuff soon.  My thirst for building new
stuff should be satisfied, at least for a while.  Then I can dive deeply into measuring a ton
of stuff that should be very useful to anyone building OB's.

[JeffB]

Don't you lose a lot more lower frequencies with the midrange driver close to an edge.

I have sort of settled on a 17" wide baffle.  This is all the room I have. 
At the moment the board is 48" tall, as it avoids me having to cut it.
I mounted a B200 such that the center of the driver to the top of the board is 14".
This put the driver at about ear height when seated (34" from floor).

I mounted dead center because my baffle was so narrow I figured I needed as much room on both sides of the driver as possible in order to keep the bass frequencies.

If I stick to a 17" wide baffle and mounting of the driver such that the driver is 34" from the floor, how tall should my baffle be and how close to the inner edge should it be.

I also have a 15" warrior that I was going to mount to the board.
After reading that this is not a good idea, and since I don't think I can easily make a magnet mount,
could I put another shorter board just in front and cut holes through both boards.  The boards being separated by a slight air gap.

[rick57]

Rudolf, Mark . .

very busy with work & christmas (bah humbug)

Thanks for your suggestions ~   

Cheers