Picked up the Duetta Signatures today, as expected they buzz at higher volumes at certain frequency and the frames have seen better days, they're a nightmare to lug around though....we barely managed to get them upstairs through a spiral staircase.
At least they're usable for now and man do they sound good! I've sent Henk an e-mail to see if he can help me out, I will probably just restore and repaint them, not being crazy about modifications.
You think yours were bad mine have to move on March 12 and they weigh quite a bit more than standard Duettas.
It is just plain scary.
You could use a simple web based signal generator to find out what frequencies they buzz at, but it won't help you at the end of the day.
In all honesty they can be made quite a bit better than stock but if budget is a limiting factor just sort out the bass panels with Henk. It will still be a killer speaker for not much money.
IMHO even standard Duettas will trash the large majoirty speakers out there to this day.