[Angelo Campanella[_2_]]

wrote:
Here is one example. Very educational reading if you're interested in
noise reduction.
http://www.ultraquiet.com/

Apparently, a well-developed company in these arts...

I'm interested in the "active tuned vibration damper". As I noted, I
developed, with the ad of an fellow analyst, the tuned vibration damper.
We found (theoretically) that two or three fequency ranges were needed,
the findamental, 2nd and thord harmonics of the prop blade fundamental,
about 130 Hz. In theory, one set per skin panel was required about the
circumference of the fuselage, and for several panels fore and aft of
the propeller plane. That was 1983-84 (time flies!); one conclusion was
that clock spring steel was best as damper spring material... That work
went from Fairchild to SAAB and now to Ultra, so it seems. The apparent
news is that passive is not good enough , since they speak of "active
tuned dampers", but that could mean just that the weight is slid along
the spring by a servo to find the best noise reduction... one never knows...

Angelo Campanella