Speaker voicing and capacitor types used

[DaveD]

I have been told by two members of the AudioAsylum Vintage Asylum that classic speakers- which were voiced by the designer with eletrolytic capacitors- will sound brighter and less well balanced if the old capacitors are replaced with metallized polypropolene types of equal value. So, high quality modern electrolytics sould be used. They did not render an opinion on film and foil capacitors or the Danish Jensen mineral oil impregnated film or the Jensen metallized paper capacitors.

I would appreciate any experienced comments on this issue, and recommendations for capacitor type to use.

The speakers in question are KLH 17, but the question would apply to all classic designs with electrolytic capacitors. My goal, aside from protecting the tweeters from damage, is to make the sound as pure as it can be without changing the voicing, or tonal balance, of the speakers.