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RE: TAS Steel BB tweak from Decembers issue.

Posted by stehno (M) on November 16, 2014 at 03:06:12

In Reply to: TAS Steel BB tweak from Decembers issue. posted by dcuhl on November 14, 2014 at 07:04:03:

I read portions of that article. Personally, I think the PhD author was trying to make the phenomena far more complex than need be and they are reading too much into what's happening. Something PhD's seem wont to do.

IMO, the authors are describing and experimenting with nothing more than simple mass loading methods and on a very small scale at that. In some cases, mass loading simply works while in other cases mass loading works quite well, and in extreme cases mass loading works extremely well and is frickin' incredible.

Why? Because our vibration-sensitive components attract unwanted resonant energies. Primarily air-borne and internally-generated.

In simple cases, like what the authors were experimenting with in the article, the mass loading of boxes of BB's on the top plate, is nothing more than damping.

Damping in and of itself generally brings little but positive benefits. For example, top plates on many components are comprised of flimsy, unsecured stamped sheet metal. When excited their behavior can be a bit like a cymbal.

For better or worse, a vibration-sensitive component is a roadmap for mechanical energy to travel. Once vibrations are captured within or without the component, the mechanical energy travels along the more rigid paths until they can exit or attach themsevles to less secure objects like tubes or chassis top plates.

Once attached to less secure objects, since the mechanical energy has nowhere else to go it starts to dissipate their energy there. And since the object itself is insecure, it becomes excited by the vibrations dissipating and will actually vibrate in sympathy with the vibations already dissipating. Thereby, making a bad situation worse.

In the examples by the author, simple damping techniques like boxes of BB's on a top plate, the damping in essence damps or minimizes the abiity of the vibrations from releasing their energy at the top plate and subsequently minimizing the top plate's ability to vibrate in sympathy with those captured vibrations.

In essense, the added weight of the BB boxes makes the top plate more secure or rigid so that it takes more energy to excite it. However, that in itself may not be such a good thing because shoring up or securing one object of the component is really just forcing the mechanical energy to travel elsewhere so that it may attach itself to yet another unsecured object and dissipate its energy there.

In other words, so long as there is no exit path for the unwanted mechanical energy, it simply travels the road maps within to attach itself to an object and release its energy there.

Why smart fellers always choose little things like BB's is beyond me. A brick or a steel or lead plate of the same weight should always invoke greater results. Simply because a solid metal plate is less vulnerable to mechanical energy than a bunch of tiny little BB's, even if they are steel or copper.

You might have noticed that the author also placed boxes of BB's between the bottom plate and the shelf underneath. And it looked like the BB boxes there were resting on 2-high CD jewel cases. Obviously the author didn't realize that he was trapping all mechanical energy within the chassis so there was no hope to escape. Which is exactly what soft or loose footer do.

So in essence the PhD was fumbling with simple damping or mass loading techniques and realizing some minimal positive benefit in the process.

Now where he could have really opened things up and made the experiment fun for himself and the reader, would be if he attached a secure metal objects (cones, points, etc) in place of the soft stock footers. Because then for the first time, he's provided at least some type of exit path for the mechanical energy to escape the component chassis altogether. Rather than force all mechanical energy to dissipate within. In other words, the damping begins to take on a new purpose. When a component is anchored securely to its shelf using hard materials, you've now created a mechanical conduit between normally disparate objects so mechanical energy is now more free to travel from the component to the shelf. In this case, damping the top plate with boxes of BB's, you're installing the mass loading with the thought, I know you're going to vibrate and perhaps even vibrate in sympathy with the mechanical energy you capture so I'm going to place these boxes of BB's to minimize your excitations with the hope that the mechanical energy will continue to travel until it finds the exit path I've provided before you start to release your energy.

With an exit path installed, the boxes of BB's or mass loading also helps to improve the mechanical conduit connections between the chassis and the shelf. The more secure the connections, the more superior the conduit.

So the damping helps to redirect the unwanted mechanical energy to a location other than here (e.g. the top plate).

With regard to your own simple damping experiments and your concern about potentially greater negative sibilance. I'm not surprised that your results were less than impressive. Primarily because every component is different. It's built different, assembled differently, different materials, loose mechanical screws and connections, some have tubes, some capacitors, motors, op-amps, etc. etc.

In other words, simple damping and without providing an exit path for the unwanted mechanical energy will provide indeterminate results because in essense every component is like a box of chocolates. Hence, you never know what you're gonna' get.

Edits: 11/16/14 11/16/14 11/16/14

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