2x4s don't have enough depth to make a substantial difference. Maybe 2x8s would make a nice test model.:thumbsup:Upon further review, I think this "test" is flawed. In the real application, the joist would be supported on both ends as well as being tied together. How about a side by side test. Build 2 mini floor systems out of 2x4's and install bridging in one system. Then add the weight and see how much differently they perform.