Two things that you have to worry about here. That is, the weight of the speaker causing the top of the chassis to sag and the vibration from the speaker causing the TV to go out of alignment. Here's a simple plan to get around both problems.
Take and place a layer of construction grade styrofoam insulation on top of the TV. On top of the styrofoam, use a 3/4" thick board, something along the lines of plywood works fine. The foam and the board should be as wide as the TV is i.e. 49.6 inches in your specific case. Using this approach spreads the weight across the entire width of the television AND takes advantage of the extra structural support of the side walls of the TV chassis.
On top of this board, use the isolation device of your choice i.e.
Vibrapods,
sorbothane, etc... Make sure that you have enough of these of the proper weight rating to do the job. If in doubt, you are better off using a few extras. Not using enough will end up compressing them due to the weight. This will end up negating their isolation characteristics due to increased rigidity and the resultant increase in coupling.
On top of the isolation / damping device, place another board that is of the same appr dimensions as that of your speaker. The use of a 1/2" thick low mass board ( something like Pine ) will work well here. Between the speaker and the top board, use the
cone footer of your choice.
When laying out the various footers on the two support boards, you want to stagger them. In other words, you don't want to have one footer stacked right above another footer. By staggering their locations and spreading them apart, any energy transferred from the speaker has to travel through each footer and then into and through each of the individual boards before being passed onto the support structure below it. By making the energy take a longer path, the boards themselves will end up dissipating some of the energy through mechanical and thermal losses. The more energy that we can dissipate in the boards and damping material, the less vibration that the TV chassis itself is going to have to deal with.
Not only does this approach reduce the amount of energy transfered into the TV, this also elevates the speaker up off of the TV chassis somewhat for better dispersion / less problems from reflections. If you want to play with angling the speaker up or down for better focus at your seated viewing position, you can either shim the bottom board accordingly or use different height footers in the front & back of the speaker.
Obviously, you can make this as fancy or plain looking as you would like. Depending on your interior and if you have a wife that is "fashion conscience", you can even come up with various cloth or fabrics that match your interior in order to "hide" the support structure. This can also be a good thing, as it will help to damp reflections from the speaker bouncing off of the top of the TV chassis.
This approach couples energy from the speaker cabinet into the cones. The cones then feed this to the low mass board that they are mounted on. Due to the low density of the wood used here, much of that energy is disippated in this board, which makes it an "energy sink". Any energy that this board can't dispose of by itself is then coupled into the Vibrapods or Sorbothane, which are also "lossy". Anything that makes it past these "soft" footers is fed into the Plywood, which due to its glued and layered construction, is also lossy. Anything that the gets past this is now fed into the styrofoam, which is also very lossy.
All of the items that are mechanically lossy are quite low in mass and spread out across the spectrum in terms of resonance. This reduces the potential for "mud" or "bloat" to creep into the system, which would reduce the intelligibility and articulation of the spoken words that the center channel tends to reproduce.
Where most people make the mistake is that they try to mass load devices, which only lowers the point of resonance. In doing so, they create a situation where energy is not only disippated in a slower fashion, but also makes it easier to be excited by high energy bass passages that are of the same appr frequency. By using "spread spectrum technology" and staggering the resonant frequencies apart, and keeping mass to a minimum so as to avoid the high energy bass regions, there are no tell-tale individual sonic signatures to clutter up the signal.
I hope this helps and gives you and anyone else interested in such subjects something to think about : ) Sean
>
PS... My center channel speaker is built like a tank and is as wide and as deep as my Mitsu TV is. I'm strictly guessing at the weight, but it is probably close to 75 lbs. The above approach worked like gangbusters for this speaker, which is about twice the size and over two times as heavy as your PSB.
