Look at stock T50RP measurements. Would you expect something with that kind of frequency response to have great bass? I sure wouldn't. Some of the modified ones are really good though, even if that usually goes along with a drop in sensitivity. (The stock unit clearly sacrifices SQ for sensitivity.) A standard cMoy may be a little low on oomph for one of these, but either going to dual 9V supply (i.e. real ground) or changing the circuit topology to inverting should help there, with an NJM4556A (can run w/o output series resistor) much recommended.