The JBL 4311 is a great speaker. I have some and the low frequency response is killer even at low levels. It's a bit exaggerated but still a nice speaker for the money they cost. Make sure the mid and high frequency drivers are working and in good condition. Also any JBL speaker with the 2435 15 inch driver has good bass response and were mostly id studio monitors with great Mid and hi frequency drivers as well.
If you have a bigger budget, the larger ATC and PMC monitors are also great.