Driver Burn IN and Aging

[davecandialex]

We all know that drivers can go through some parameter changes when first used. But what about over a long time?
About 10 years ago I built an MTM using 4 of the well known Vifa P13WH. These speakers never got much use often going unplayed for a year at a time. Recently I decomissioned them to make some prototypes. After some stange results I measured them and the Fs was in the 150 to 160Hz range vs 65 to 70. I've run them overnight with a low frequency and only had maybe a 10 Hz drop.

Does anybody have suggestions as to what I might do? Or they destined to be midrangers forever.

[chris661]

Strange - I would have thought the mech. Q would have changed, not Fs.

[Ron E]

Just some observations, no direct experience with such a dramatic parameter shift. First, the Vifa woofers' Fs usually measured a bit higher than spec, 20% or so, IIRC. Drivers with rubber surrounds can have a strong temperature dependence, and while the rubber may look good, it can harden over time. Usually the surround doesn't dominate on suspension stiffness, though...

[Moondog55]

David Weems mentions in one of his books on speaker design that the suspension on the P-13 is known to stiffen with time and does recommend using it as a mid-range