The stiffest and heaviest brace on a guitar is the bridge. Changing the mass and/or the design of this important element will have discernable effects on the sound of the strings.
- A relatively heavy bridge will cause the attack to be slow compared to a relatively light bridge, which conversely will allow for a faster attack. This results in a duller sounding attack.
- A relatively heavy bridge will also reduce the overall volume as it takes more energy to move a heavier object than a light one. Thus a heavier bridge makes for a less responsive guitar.
- However the law of inertia implies that it will also take longer for the heavier bridge to stop vibrating (An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.) So the heavier bridge augments sustain. How much that matters with the weights involved here is debateable.
Taking all this into account, my approach is to go for maximum attack and volume by using relatively light weight woods for bridges. When using heavier woods like rosewood, my target weight is 20 grams for the bridge, not including the saddle, but this is an elusive target and can result in very thin bridge wings. Using a lighter wood like sapele, I usually get a bridge weighing 14 grams, which includes a tie block overlay of a very dense wood like ebony or gidgee. I also save a few grams by making the saddle from a dense wood like african blackwood or snakewood. The end result, when used in conjunction with properly built composite soundboard with diamond bracing is a very loud and responsive guitar. No one has complained of lacking sustain on these instruments.
Note: About the Kasha bridge design.
I have a few things against the Kasha bridge design, which I have used in the distant past. The primary issue is weight. In order to create the large surface area of the bass side of this design, that side at least must exceed my weight target(s) significantly. The treble side is not that much smaller than a traditional bridge, and I can equal or better the weight of that side by using a lighter material. I don’t actually believe that the two piece bridge concept has any appreciable positive effect when mounted on a top that is not separated. The whole top vibrates regardless of the number or size of the bridge sections. I understand the rationale for the design of this type of bridge and how it relates to the overall Kasha system, but my experience is that complete adherence to the overall design is not necessary to benefit from the insights contained in the concept.