I have a Gotoh 201 bridge on my J. It is a medium weight, die-cast bridge made of some type of zinc alloy, I guess. For grins, I tried a lightweight, bent-plate vintage style bridge on my guitar (same hole spacing, so no big deal). Yikes, an immediate loss in tone! The dead spots that were just barely there with the Gotoh just jumped out and there was an overall "smearing" of the notes. The amount of punch decreased and the low E string was just barely there. Needless to say, it only lasted about 15 minutes on my bass. This got me thinking about what a huge impact the bridge can have on the tone of a bass. Any of you players out there experimented with various bridges? Brass v.s. aluminum, heavy v.s. light, and particularly the ABM single-style bridges with lockable saddles and the Hipshot type B. Is the Badass II made of brass or die-cast? I have read someplace that a heavy bass does well with aluminum and a light bass does well with brass, but this seems overly simplistic.
Once you got one that's better than the Fender-style excuse for a bridge, the differences become pretty minor. Higher mass is not necessarily better, the construction matters more IMO.
I have no evidence to support this theory, but I suspect the difference is not because of weight, but because of stiffness. More rigid bodies (or in this case bridges) will have higher resonant frequencies. As a result, you won't have the a dampening effect that causes dead spots. It is just a hypothesis, but if you think about it, it makes sense.
I have an interesting experience with this. YEARS ago, my brother (also a bass player) bought a Hohner B-bass as per my recommendation. It had a massive Steinberger brass bridge with a D-tuner (on the E-string saddle). The tone was fantastic -- both unplugged and through its inexpensive EMJ Select J pickups. A few months later, I bought the five string version of the same bass (same woods/finish and all), which had a thin die-cast run-of-the mill bridge on it. WHAT a difference in the two basses! My brother's bass had much more fundamental, more punch and more balls to it...whereas mine sounded thin and insignificant. I'm not going to say that the bridge was the only reason for this, since obviously there are many factors involved in bass construction, but I really do believe that the weight/mass did play a significant role in his the better tone. Just my $.02. -Aram