[mcgsxr]

Here is where I am.  I have built 2 or 3 iterations of the OB with the b200, and am currently looking to reduce the overall size of the baffles, but retain the sound I enjoy.

Source – Bolder SB3
Sub Amp – BASH 300w with 12db/oct Xover, variable from 50-150Hz
Main Amp – Magnavox EL84 single ended console pull
Sub drivers – Mach5 12 inch
Main drivers – b200 Visatons

Currently, the signal passes from SB3 to sub amp, and Xover at 80Hz to subs, and out to Maggie.  The b200’s share the main baffle with the Mach5 12’s.  The baffles are currently winged (14 inches, and 7 inches, main portion 15 inches) with piano hinge (that rattles on one side, with loud bass notes) and are quite wide.



I seek guidance around the idea of redesigning these, to use a much smaller main baffle with the b200’s in it (roughly 14-16 inches I hope) and have the 12’s in an isolated U shaped baffle, fire through the main baffle, but not attached to it.

Math not being my strong point, could someone help me understand what FR I am likely to see from the b200 attached to a flat 12-16 inch baffle?

Any other advice?

Ideas on what else I should consider, or what to watch out for etc?

[Bob in St. Louis]

Since nobody has posted yet, let me give you the wacked-out, idea I've been wanting see somebody try.
You've probably seen the wooden bowl treatment on the front of a driver?...Well, how about the back of an OB driver with some form of magnet mount??

Whatcha' think?

Bob

[guest42212]

16" baffle using factory driver specs:

[goo]

Here is where I am.  I have built 2 or 3 iterations of the OB with the b200, and am currently looking to reduce the overall size of the baffles, but retain the sound I enjoy.

Source – Bolder SB3
Sub Amp – BASH 300w with 12db/oct Xover, variable from 50-150Hz
Main Amp – Magnavox EL84 single ended console pull
Sub drivers – Mach5 12 inch
Main drivers – b200 Visatons

Currently, the signal passes from SB3 to sub amp, and Xover at 80Hz to subs, and out to Maggie.  The b200’s share the main baffle with the Mach5 12’s.  The baffles are currently winged (14 inches, and 7 inches, main portion 15 inches) with piano hinge (that rattles on one side, with loud bass notes) and are quite wide.



I seek guidance around the idea of redesigning these, to use a much smaller main baffle with the b200’s in it (roughly 14-16 inches I hope) and have the 12’s in an isolated U shaped baffle, fire through the main baffle, but not attached to it.

Math not being my strong point, could someone help me understand what FR I am likely to see from the b200 attached to a flat 12-16 inch baffle?

Any other advice?

Ideas on what else I should consider, or what to watch out for etc?

You will love the B200's in the smaller baffle. Mine sure have opened up.
Also mount the drivers off center, and stiffen the baffle as much as possible (if you are not using a magnet mount)
Q

[goo]

Since nobody has posted yet, let me give you the wacked-out, idea I've been wanting see somebody try.
You've probably seen the wooden bowl treatment on the front of a driver?...Well, how about the back of an OB driver with some form of magnet mount??

Whatcha' think?

Bob

Bob I think John in CR has already tried that and is know going for a Horn (wave guide) approach. Is that what you were talking about?

[Bob in St. Louis]

goo, I thought John did the front wave guide, didn't he?
I kinda, sorta, maybe, remember??

I'll search for it
Bob

[Bob in St. Louis]

Damn, I was wrong twice this week!

[JohninCR]

Actually that one is now acting as a rear waveguide, because I was too lazy to swap it out for the rear WG on that side.  I'm staying kinda tight lipped on this both the rear only and dipole until I have measurements on both the waveguided dipoles and the edge diffraction rings, but both show some real promise.  BTW what I'm working on are not horns, just waveguides, so I still consider them OB's since there is little or no cone loading and they are dipole.  There's no horn loading, however, there is a significant gain +/- about 40 degrees of axis with less beaming due to the controlled directivity.  Here's a sneak peak of the raw construction before damping.

[guest42212]

If you use a 'helperwoofer' it only makes sense to have the
drivers magneticly connected

[goo]

Damn, I was wrong twice this week!

Your never wrong Bob, no one ever is anymore. All you need to do now is check into Rehab

[goo]

Actually that one is now acting as a rear waveguide, because I was too lazy to swap it out for the rear WG on that side.  I'm staying kinda tight lipped on this both the rear only and dipole until I have measurements on both the waveguided dipoles and the edge diffraction rings, but both show some real promise.  BTW what I'm working on are not horns, just waveguides, so I still consider them OB's since there is little or no cone loading and they are dipole.  There's no horn loading, however, there is a significant gain +/- about 40 degrees of axis with less beaming due to the controlled directivity.  Here's a sneak peak of the raw construction before damping.

John was too lazy....impossible
The tools we learn when trying to build horns are losely applied correct?
Goo on the otherhand is the lazy one. Which starting me on the past of OB's. If I was a little more industrious. I'd be listening to a stack of Horns right now. ...yet another plus about OB's
q

[Bob in St. Louis]

Your never wrong Bob, no one ever is anymore. All you need to do now is check into Rehab

It's all my parents fault....right?

John, how did the round rear wave guide sound?
And how does the:
"Costaricain Three Dimensional Dual Wave Guided Baffleless Drivers"{CTDDWGBD 1.0} sound?

Bob

[Russell Dawkins]

Now that the design of some of the OBs has arrived at this "stopsign" configuration, that is, almost no baffle, I wonder if anyone had tried for the effect that Gradient (that OB neo-pioneer) took advantage of all those years ago in an attempt to minimize floor bounce.

Their thinking was that floor bounce, the first reflection off the floor right in front of the speaker, is the strongest and most negatively influencial of all the room reflections.

Their response, since their midrange was a naked 12 inch cone driver, was to tilt the driver back so that the null off the edge would be aimed at the spot on the floor where the bounce would occur.

This largely took the floor out of the equation and helped make the speaker notable for its relative insensitivity to room acoustics.

Can't remember the model name/number, but it had the vertical array of cone tweeters above and behind said 12" mid. A refreshingly original re-think of many of the design elements in domestic speakers.

In the case of the minimal baffle OBs I see in this thread, it would be a matter just of tipping the driver back about 40 degrees from the vertical. Many widerange drivers sound more palatable at that angle anyway!

[JohninCR]

Bob,

I'm approaching 2 different problems with the rear only and the dual.  The rear only one (see the edge diffraction ring thread) was an attempt to reduce the effects of edge diffraction using minimal circular baffle, and I wasn't concerned much with the waveguide effects on the rear wave.  I thought the first attempt sounded pretty good with the main benefit being a much more focused point source sound.  I really need to do measurements to see how much that shape helps with diffraction.  The rear shape has to affect rear dispersion over some frequency range, so in all likelihood damping is needed in the rear.  In the no baffle thread Rudolph predicted that your circular 15's won't have a significant diffraction problem, so some kind of smallish rings to dress them up shouldn't be a problem. 

With the front + rear dipole waveguides I am trying to create an OB with constant directivity.  If you walk from in front of your OB's to the side while they are playing, the tonality changes pretty drastically with the bass and treble all but gone leaving only the midrange.  This means that the reflections originating from off axis radiation will have the same tonal imbalance resulting in a less natural sound.  With the waveguides I am limiting the dispersion of the midrange, creating a much better balance in the sound off axis.  This increased directivity also makes the direct sound a higher percentage of the overall sound to you hear, taking reflections more out of the equation.  With my test baffles, I'm already hearing these benefits.  I just need to make some adjustments to deal with diffraction and reflections which color the sound, since these effects are magnified due to much higher pressures involved because the waves are constrained within the waveguides instead of launching into open half space from a flat baffle.

I forgot to mention that since the dispersion is controlled to project within a smaller angle, they are much louder with the same power input.  It's like the difference between having your sub outside on the ground vs putting it in a corner in your room.

[Bob in St. Louis]

John, I actually followed all that. But it seems you toned down your explanation for me a little bit. Thanks!!
Regarding this:

I just need to make some adjustments to deal with diffraction and reflections which color the sound, since these effects are magnified due to much higher pressures involved because the waves are constrained within the waveguides instead of launching into open half space from a flat baffle.

We'll continue with you using the big words and me coming up with the radical ideas. One of these days, I'll come up with a good one.
Like maybe this one:
How about some holes in the "bowl"? Not small one's, but holes about 2" in diameter, maybe with some form of damping in the holes, or wrapped around the outside covering the holes.

Whatcha think?

Bob

[mcgsxr]

Interesting ideas there with the wave guides, but well beyond my woodworking capacity.

I will probably do this, for the sake of experimentation - pull the wings off my current baffles, and see what has to be done, to make the sound bearable.  If it cannot be done simply, I can reverse the process, and live with the visuals a little longer, it is closing on 2 years now...

Thanks guys,

[JohninCR]

Interesting ideas there with the wave guides, but well beyond my woodworking capacity.

I will probably do this, for the sake of experimentation - pull the wings off my current baffles, and see what has to be done, to make the sound bearable.  If it cannot be done simply, I can reverse the process, and live with the visuals a little longer, it is closing on 2 years now...

Thanks guys,

Use your sonotube idea, but just on the bass driver.  Put some polyfill and/or open cell foam rubber in the cavity to damp the TL resonance and make the U function properly.  If you cut that pipe terminus at an angle making it 2-3" longer on one side, and add a Karlson slot, curved "V" at the shortest point that will further reduce resonances.  You can start with fairly long, eg a 24" average length will net you an Fequal of about 50hz.  It really depends on where you roll the woofer off.  I've used something similar in shape for a Hawthorne coax with good full range results using a pipe length with the longest point at 16", for which I estimated an Fequal in the 70's.  Some lengths can sound terrible for some reason, so just cut a couple of inches off if it sounds bad.

[JohninCR]

John, I actually followed all that. But it seems you toned down your explanation for me a little bit. Thanks!!
Regarding this:

I just need to make some adjustments to deal with diffraction and reflections which color the sound, since these effects are magnified due to much higher pressures involved because the waves are constrained within the waveguides instead of launching into open half space from a flat baffle.

We'll continue with you using the big words and me coming up with the radical ideas. One of these days, I'll come up with a good one.
Like maybe this one:
How about some holes in the "bowl"? Not small one's, but holes about 2" in diameter, maybe with some form of damping in the holes, or wrapped around the outside covering the holes.

Whatcha think?

Bob

Bob,
Those holes would release pressure (containing the pressure is a good thing) and their edges would cause diffraction.  Smooth expansion, especially at the mouth, is what's needed.  Also, I'll use foam rubber to absorb the reflections.  That will eat up some of my efficiency gains, but if I can get rid of the coloration without attenuating the top end I'll be doing great. There's no way the end result can be pretty inside the waveguides, so once finished grill cloth will stretch over the mouth, maybe with added triangles of a darker material along the perimeter of the flat sides to enhance the star shape. aa

[Bob in St. Louis]

Dammit John, after the third time I read this:
"I just need to make some adjustments to deal with diffraction and reflections which color the sound, since these effects are magnified due to much higher pressures involved because the waves are constrained within the waveguides instead of launching into open half space from a flat baffle."
I NOW understand. I thought you were looking for a solution to the wave being "constrained".
Yea, drilling holes would send your diffraction issues through the roof. I was trying to help the wave be less constrained.

Ok, now that I understand:
How about the individual panels having an outward bow to them. Like laminated sections of a very flexible 1/4" wood?
More flower like:

[JohninCR]

Then it becomes a horn too, and that's not what I want, because horns beam in the higher frequencies.  I only want to guide the waves within a given dispersion pattern.  Not to mention straight sides are simpler.  Remember this is still the experimental phase.