audio-talk

Can anybody explain in general terms what the difference might be in presentation between the 2 sections shown.
I can't beleive I've never thought about this before. I've trawled through all the books I've got(Olson, D'Appolito etc) and can't find any references at all.
I'm currently listening to type B, and quite like it. Unfortunately I don't have any type A to form any kind of comparison.

It's a good question, and one I'm sure that James has some opinions on. I remember a brief exchange between us on this subject, years ago ... long enough ago that I don't remember the comments.
The Supravox 285 is definitely of exponential form ie. 'B'.

Depends on the exact details of the driver as you can't isolate one aspect like profile & generalise too much. Ted Jordan was (very) good on this; he, RCA and W.E. / Altec did the bulk of early research on curvilinear profiles from the '40s - '60s.

All other things being equal (they never are, entirely) straight sided cones tend to have good rigidity in the LF region, but the response will typically start to become more uneven as frequency rises due to the concentric modes, and potentially transverse cancellation effects (hence one reason for pole-piece extensions / 'phase plugs [not really, but we go with it]). Curvilinear cone profiles tend to have more progressive decoupling / distributed TL modes so may allow you to get to a higher frequency without obvious high Q resonances. They also tend to have a smoother off-axis response, especially higher up as the general tendency is toward a shallower cone (or a VC coupling further forward if you prefer).

That's about 'it' as far as generalising can go -the cone materials, thickness, mass, how the coil is coupled to the neck & at what angle, the presence of plugs, direct-bonded central caps, decoupling rings, coatings or strategic mass / acoustic damping etc. all have a major effect too.

Scott has the reasons for an exponential cone correct at least according to Supravox but I can add a little more historical detail...

Pre WWII i.e. in the 30s S.E.M. in France started manufacturing an exponential cone loudspeaker and the only other company doing so was University Audio in the USA. S.E.M. greatly expanded their range after WWII was over and in the 50s became Supravox. University Audio in the USA didn't survive the war economy and WE, RCA & Altec picked up their research and became the premier USA makers of exponential cones.

Interestingly S.E.Ms original work showed that their exponential cones were more ridged than straight sided cones but that might have been the result of their thickness profile as well as geometry...

ciao

James