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RE: 1.7 frame damping

Posted by Satie (A) on December 24, 2016 at 13:21:59

In Reply to: RE: 1.7 frame damping posted by zulugone on December 24, 2016 at 09:49:48:

Since you have done some reading on vibration control and dissipation more broadly then you should recognize that Magnepan chose to float the magnet board frame in the
MDF as a low mass approach to keep the MDF from coupling too well with the steel driver frames. Relying on air damping of the magnet board.

There are 4 vibration issues you want to deal with in the magnepans.
1. Swaying and general MDF bending effects. Due asymmetrical anchoring of the panels at one end.
2. magnet board ringing
3. radiation on the listening axis from the MDF frame, including diffraction.
4. transverse waves in the mylar diaphragm being reflected back from the steel edges of the driver frames.

Each of the approaches to vibration damping and rigidity leave less for the others to do - as in belt and suspenders. The damping of the steel frames with damping material between the steel frame and L brackets bolted through the MDF as AndyR has done, should provide a good damping of the magnet board edges on the vertical and leave little for the CLD "razoring" to do.on the magnet board itself. It would control both ringing of the magnet board and damp the transverse waves in the mylar.

The bow and arrow mod will also provides damping at the center of the panels in an easy and reversible way by essentially installing springs. But unlike the CLD damping at the steel frame edges it would not do much for transverse waves in the mylar - the kazoo noise that bothers people who have noticed it as a separate coloration.

Though I find that the fabric itself is good enough to control diffraction, things could be improved further using felt on the MDF front surface near the tweeter and in the TIV and 20.x around both mids and tweeter.

AndyR's frame takes care of any possible rigidity issues and IIRC he used elastomer damping strategically in the mounting of the wood frames that serve also to damp self noise from panel ringing to kazoo noise. Hopefully AndyR will correct this or provide further detail if I got it wrong or missed something.

The PG bolted hardwood frames take off ringing and kazoo noise and transfer them to the hardwood frame and radiates them away from the listening axis. The cross braces add to rigidity and thus deal with all the vibration control issues on the maggies. Perhaps not completely but effectively, as many who have applied the mods or had PG build it for them have noted.

For my TIV/Neo8 I put on big feet oak on the bass panels and braced the center of their tops to the sidewalls. The mounting on the feet includes a leaf spring aspect where the 1/4 inch brackets leave the panels hanging over the feet, that is wedged to vertical orientation using hardwood shims That provides a spring damping for large vibrations. For the mids and tweeter I have not done any significant bracing, Just damping of the Neo8 mounting rails with foam weather stripping between the hardwood slats and the MDF. I also added strips of foam vertically along the sides of the Neo8 drivers to suppress ringing and diffraction. The fabric turned out to be enough on the diffraction side, and it did not control the ringing enough to matter. There will be some CLD damping along the center line and edges when I get to it. Testing temporary CLD I put together from copper strips on carpet tape and foam mounting tape indicated that the results would be very good. But required that I cut u the copper sheet into thin strips - which is both too expensive and not that easy to work with so will get automotive CLD for it as Dawn Razor had done. .

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