Partially true. The effect of burn in should principally be reduced frequency of the fundamental resonance of the driver, by making the suspension a bit softer after burn in. Other resonance(s) reamain of course the same. All the process will be documented to allow for reproduction.
I had actually much different post than this in mind, but what I hoped to be able to present with JVC HA-S770 unfortunately works correctly only with earspeakers requiring no pads at all ( Jecklin Float, AKG K 1000 ). As I have no intention of becoming a chain headphone buyer, I will try to use this new pair also to document burn in effects - something I hoped to pull off with the above that proved unusable with anything requiring earpads.
Luck has it that the Bruel & Kjaer representative for our country has his premises 15 min walk from my place. I will try to use "long eyelashes, high heels, fishnet stockings & any other charms imaginable" a guy in his early 50s can pull in order to try to get a quick measaurements confirming the effects of burn in "before"" and "after", that normally co$ts dearly, for free. IF they can do it at all - three months ago I was the first person in 30+ years history of B&K in ex Yugoslavia/now Slovenia, who inquired about artificial ear pinnas - no demand, no supply, those who are familiar with B & K prices will surely understand.
Otherwise, I will have to construct my own DIY ear coupler of some sort to be able to measure 770s with anything like even approaching correct results. Which means 770s have received zero playtime after recent unpleasent discovery and that is how it will remain until further notice pending the development of the events.
So, wish me luck for tomorrow's visit to B & K !