Sound Deadening

A little late to the party, but wanted to address a comment made early on. Not all dampers are made of the same stuff. Butyl (or stuff claiming to be butyl) is not all formulated the same way. Across brands you'll find variations in heat tolerance and viscosity. You'll also find variations in the constraining layer (both thickness and material). There are better combinations and they tend to cost more.

All of them will be effective to some degree, and as probably suspected, some will be more effective than others. The big concern with dampers though is their heat tolerance. Some will downright melt on you and can cause a ridiculous mess that will never come off. Think headliners. Put a cheap damper on the roof, let it get hot, and just use your imagination. Cheap is not worth it here.

There's a great facebook page going on right now called 'The Deadening' where Chris Purdue and a few others are [again] putting a lot of these dampers to the test. Don from SDS also did some testing where he demonstrated diminishing returns from using 100% coverage with CLD. The Cliff's notes from that - using a GOOD damper lets you get away with ~25% strategic coverage. MLV requires as close to 100% as possible coverage, as it's a barrier layer, but not required for a good damper when it's used to alter resonant frequencies in resonant panels.