a few points on free swinging, pleated mid ribbons.....
regardless of type, foil only or plastic backed, the size of the pleats and width or the ribbon determines the flex character of the ribbon and with some designs it can be critical to tension right. The amount of tension will change the size of the pleat and thus the stiffness and resonance of the structure. Many designs will use a trap or rake circuit to level out the response and that trap circuit has to align with these resonance so if ya just tension an old pleated ribbon a bit more, changing the size of the pleat, the frequency response will no longer align well with whatever trap circuit is used. Its best to start with a new ribbon and tension as recommended. Some people seem more sensitive to this edgy sound than others.
Or buy a cheap measurement system and play with rake and traps until it sounds good to ya. You can easily see these peaks and some work with simple traps / rakes goes miles when attempting to get the best top class sound from typical planer / ribbon designs. I know that sounds ambitious but its really not that bad once ya get set up and play a bit. These type of speakers can go from good to true top class with only 1 db changes in that mid tweeters levels. or rake Many time these speakers get a bad rap and its only 1 to 2 db from greatness
As for FO's (foil only) ribbons. These do not have the self damping that the multi trace plastic backed units do and the resonance mentioned above will be quite bad at some frequency, usually somewhere between 3 and 10kHz depending on ribbon width and pleat size. Typically the way around this is to have two ribbons ( mid and tweeter) like Apogee full range or Sintilla and crossover at that resonance. I suspect with wider 2 inch FO ribbons and larger pleats that would be around 3 khz. I suppose you could put a FO in a Diva mid BUT you would likely need to cross over somewhere between 3-6 khz to side step the strong resonance rather than the 10k cross I think they now use?
Using an pleated FO in a Duetta or any ribbon that has only one ribbon doing mid and high is asking for trouble( unless the ribbon is less than about 1/2 inch wide) as ya cant cross over from the bigger ribbon to the smaller one at the big ribbons nasty resonance and hide the resonance of that mid.
regardless of type, foil only or plastic backed, the size of the pleats and width or the ribbon determines the flex character of the ribbon and with some designs it can be critical to tension right. The amount of tension will change the size of the pleat and thus the stiffness and resonance of the structure. Many designs will use a trap or rake circuit to level out the response and that trap circuit has to align with these resonance so if ya just tension an old pleated ribbon a bit more, changing the size of the pleat, the frequency response will no longer align well with whatever trap circuit is used. Its best to start with a new ribbon and tension as recommended. Some people seem more sensitive to this edgy sound than others.
Or buy a cheap measurement system and play with rake and traps until it sounds good to ya. You can easily see these peaks and some work with simple traps / rakes goes miles when attempting to get the best top class sound from typical planer / ribbon designs. I know that sounds ambitious but its really not that bad once ya get set up and play a bit. These type of speakers can go from good to true top class with only 1 db changes in that mid tweeters levels. or rake Many time these speakers get a bad rap and its only 1 to 2 db from greatness
As for FO's (foil only) ribbons. These do not have the self damping that the multi trace plastic backed units do and the resonance mentioned above will be quite bad at some frequency, usually somewhere between 3 and 10kHz depending on ribbon width and pleat size. Typically the way around this is to have two ribbons ( mid and tweeter) like Apogee full range or Sintilla and crossover at that resonance. I suspect with wider 2 inch FO ribbons and larger pleats that would be around 3 khz. I suppose you could put a FO in a Diva mid BUT you would likely need to cross over somewhere between 3-6 khz to side step the strong resonance rather than the 10k cross I think they now use?
Using an pleated FO in a Duetta or any ribbon that has only one ribbon doing mid and high is asking for trouble( unless the ribbon is less than about 1/2 inch wide) as ya cant cross over from the bigger ribbon to the smaller one at the big ribbons nasty resonance and hide the resonance of that mid.