Thanks Rudolph,
NSB was supposed to be a joke taken from a reference to the 49 cent wonder Pioneer 4" that
became called the NSB's for No Stinkin Badges, although I'm unsure of that origin. Later someone
used NSB to mean No Stinkin Boxes, and I took it a step further.
I believe I understand the pressure release from half space containment to full space, or baffle step.
It's ok if you want to only talk in terms of pressure, but with OB's there's a greater pressure differential
resulting in more happening at the edges. I'm not thinking there is some audible wind turbulence, but
Olsen's work demonstrates clearly that the shape of the makes a difference. The Edge gives no
consideration to this. All it shows are the dipole ripples which are based solely on the phase relationship
of the front and rear waves combined. The Edge better reflects the ripples than the peaks and sharp
nulls shown by Linkwitz. I believe SL's graph is more indicative of folded shapes with the worst case
being a pipe with drivers on each end wired as a dipole. I'm used to ear tuned OB's, so 2db is something
I can live with (maybe not at the wrong frequencies though, since they appear to be harmonic ripples).
If nothing else, a change in the edge geometry will result in a change in how the pressure is released at
the edge. That's what Olsen's work tells me. A smooth and more gradual change in pressure has to be
better than an abrupt one.
Before I brought this topic up, it was generally accepted that we should avoid circular baffles like the plague.
Now you're telling me it's not that big a deal, or that it matters for small drivers but not big ones. Come on,
the only difference is wavelength.
For now, I'm sticking to the idea that the edge geometry makes a difference, and more of a difference for OB's.
My real concern is that at these lower frequencies need a transition distance greater than the 3-4" that I'm
willing to commit to trying.
As support for my way of thinking, here are a top and front view of my small baffles for my Fostex FE108Esigma's.
First I built just a 3 piece squared edge baffle. I wasn't satisfied with the somewhat boxy sound, which I
attributed to the squared backside, so I filled those inside corners for a smooth expansion of the well rounded
driver cutout. That cured the boxy sound, which I believe to have been reflections off of the inside of the
wings disrupting the rear wave. Still not satisfied with the sound, I edges of the front corners as seen in the
top view, which really sharpened the focus of the audio image. I made the changes to one baffle at a time so
I had a direct comparison of before and after changes I made. I've tried roundovers on boxed speakers before,
and was unsure of much, if any benefit. With these little OB's the difference was more than just subtle. Please
explain how those results fit into your interpretation of theory, and why trying something similar but round from
the front is a waste of effort with the NoBaffle idea. Are you sure I'm missing the boat, or is there maybe more
to edge diffraction than just the baffle step effects due to the pressure release?
