Difficult to find 'original wheel' information [ie speaker/driver building info].
Initial results using strong, small magnets and coils indicates to me that unless I'm missing something, making a ''working'' speaker isn't all that tricky.
I didn't notice that the north and south poles in one diagram were 'inside/outside' of the magnet slot.
The speakers I've made have the magnet inside the coil only, N/S poles along the coil-line.
C o i l
N Mag S
C o i l
While this works quite well, It seems counter intuitive that the poles, according to the diagram with N being the polepiece and S being the surround...how north south on the coil could be pulled N/S when the magnet is "West/East" so to speak.
Just wondering how the magnetization of pole/surround magnets get the direction 'installed', how much am I missing by using round magnets as pole with North being ''toward the diaphram'' and South being 'toward the back'.
(http://i.imgur.com/pKNHO.gif)
PRR's drawing says a lot. Also, for a good speaker you want the magnetic field to be as uniform as possible (density and direction) across the coil's entire travel. If not, this will result in non-linear distortion (hey, might actually be cool if you're not going for hifi)
Highly recommended: Vance Dickason's books on speaker design. Lots of info and background, focusing on enclosures but also goes into the design of an actual driver. Should be available at a well-stocked library.
I'll probably just fiddle around with it some more.
Mostly tone is what the ideas are about, probably easier to just buy drivers, but perhaps I'll continue messing with coils/magnet assemblages [ie small magnets make the mag-field structure.
I likes my speaker/cabinet choices and intend to keep using them.
I'm not sure I'll be able to make anything worth haulin' around or even plugging in, I have ideas but testing them would be easier with a lab/shop.
Of course the field will be 'better' [stronger at least] when surrounding the other field as shown in the 'good' pic.
I wish I could find the page again now, it shows "N" in the center-pole, and "S" [on both sides of a cutaway magnet/coil structure diagram] SNS instead of
N
S
...as the 'good' pic shows.
Doesn't seem as directly understandable as to how that'd work, and so to just have a devils advocate pose the question:
Is it feasable to have the mag-poles radial instead of up/down, and what'd be the most common mag-pole orientation.
I guess the 'good' picture shows it.
I've never known or seen a magnet with North in the center of a magnetic rod, or that it was even possible.
So it seemed to me to be one of the following: a misprint or alternative design.
The pic I can't find now showed East/West fixed magnet orientation to the N/S coil. The pole being "N" and the surround ring being "S".
Speaker designs seem to segue from basic-est possible drawing from 4th grade science book, to sketchy patent texts of long-scatter-train-descriptions about missing diagrams.
What you're describing is exactly what's in the "good" pic - a Ntop Sbottom magnet, with a metal (iron) structure which *channels* the magnetic flux so the S-pole is "directed" straight through the ring surrounding the N-pole of the magnet and the coil. This, if you look at an arbitrary cross-cut through the heart of the speaker, leaves a S-N-S configuration like you mention.
Ferrous metals can channel magnetic flux quite well. The design, size and shape of that specific structure and the ring (bevelled edges or not, etc) have a pretty large influence on speaker behaviour.