I was only joking about the diagrams .... are you thinking of a driver that needs to go up to 300 or 400Hz ?
Meanwhile, I've been applying the
Salt Test to the 8FE200 :
This with a signal generator feeding a small amp and scanning through frequencies above 1kHz to see if I could determine anything about resonant areas.
Now at first I thought I could just rely on the salt to move away from the areas of max amplitude and identify the clear(ed) bands .
However after a few minutes I realised that the whole cone is slightly convex radially, so you can see salt move away from different zones depending on exactly how you tilt the driver. So the above pic & markings proved to be wrong.
So my further work was done by tilting the driver back & forth and watching the salt run across zones of the cone at a frequency of interest, and see where it was bouncing up & down most as it drifted across. This gave me more believable & repeatable data.
I identified a few frequencies of interest from listening and from looking at the datasheet for peaks . What I found in terms of location on the cone is as follows :
1.25kHz : Most of cone together but interestingly outer 20% hardly moving
1.6kHz : outer edge of cone & border into accordion surround
2.5kHz : Near outside , about 80% of cone radius
3.4 to 3.5kHz : about half-way out or a bit more - 50 to 60% cone radius
4.8 to 5kHz : join of dustcap to cone inner
So my plan to use an annular ring mask to kill some spikes is not so good - too many areas contributing different peaks.
I think I will hang a phase-plug ( being made soon , rapid prototype based on previous one used in horn ) in front of the dustcap & join , which will blend the dustcap & cone movements together in that area ( should still capture midrange output ) , then take a razor blade to the cone & try & apply some of those ScanSpeak-style slices diagonally from approx the 50% to the 90% region. if something terrible happens, the driver only cost £47 so I can get another couple. I think I'll try two slices 180 deg apart and do them and let the glue ( most likely PVA ) dry, before trying some more.
"Once you find out ... the Circumstances ; then you can go out"