Speaker res. freq. lowered by age

[Tubiflex]

I contacted Celestion to get the correct speaker res. freq. for G12K-85. Have been told that it is identical to G12K-100 but was´nt sure. This was confirmed by the company, and they also told me that my speakers that are 15-20 years old are likely to have 10-20 Hz lower res freq than a new speaker (85Hz)

I have never heard about this factor before and will now try to change my settings in the advanced amp menu.