Yes of course the changes would show up in FR but if they’re disproportional and non linear depending on frequency then you in fact cannot extrapolate all extra information from FR alone, you’d need additional information to find the unknown variables. Without a valid min phase assumption there’s too many unknowns to solve. 20-50hz is for sure in most people’s audible spectrum, as is alot of the hf content susceptible to it. Again, not saying this is inherently a bad thing, but it is true. Please see my other comments below for more discussion