maty
Major Contributor
One of the mods is the use of this Spanish visco-elastic damping material inside: two layers of Tecsound SY70 as first in my main loudspeakers (sandwich with fiber-glass) many years ago.
[PDF] https://lotus.soprema.fr/www/reftechsop.nsf/($AllByUNID)/5E5A87A76E0804A1C125871E00545B0E/$File/TDS_INSES0002.d.ES_TECSOUND SY.pdf
en.wikipedia.org
[PDF] https://lotus.soprema.fr/www/reftechsop.nsf/($AllByUNID)/5E5A87A76E0804A1C125871E00545B0E/$File/TDS_INSES0002.d.ES_TECSOUND SY.pdf