In article .com,
wrote:

How, I don't know - perhaps adding a little more weight to
the cone? Sounded highly dubious to me, anyone else here heard of this
and /or can verify that it was a con??

If you make the speaker cone heavier you will move the speakers
resonence frequency down. This will enable the speaker to produce lower
frequencies. The downside is that the efficiency also goes down. Just
gluing weights on speaker cones at random will most likely not produce
better sound.

23 years ago I used paint on the speaker cone to adapt two 12" speakers
to a sub woofer enclosure. Paint was applied until the speaker resonance
frequency was low enough for the enclosure. As a student I found this
cheap method superior to buying two expensive speakers. I would never
try anything like it today though.

--
Göran Larsson http://www.mitt-eget.com/