Steve hi
I find the'' speaker tip'' paper very helpfull and i thought why not trying some of the tips modifing a Visaton W130s 8ohm driver to ged rid of the 2 nasty peaks at 4khz and 6.8khz.
So i completely removed the dust cup and i replaced it with a home- made wooden phase-plug.
The 4khz peak completely went away but the 6.8khz peak still persists.
What can i do to get rid of the 6.8khz peak?

Theodoros Paschos
Preveza -Hellas

Removing the phase-plug makes no difference to 6.8khz peak so it has not to do with the shape of the phase -plug.
The wavelength of 6.8khz is shorter compared to 4khz peak so if the problem with 4khz peak was the dust -cup then the origin of the 6.8khz peak should be something between the voice-coil and the dust-cup.
The only i can think is the voice-coil former that protrudes of the cone by 3-4mm.
The problem is that is not easy to trim the voice-coil former ''as Steve Ssuggests because of the wires of the voice-coil that are glued at the top edge of the voice-coil former.
Probably Steve with his experience could help.

Thanks for the help