I am amazed at the lack of bass of my new Energy C5s. The specs show a frequency response of 36-23Khz. My old Energy C4s only go down one more notch to 35 Khz, but the difference in bass is ridiculous. The C4s' bass is rich and pleasurable, while the C5s' bass leaves me totally unsatisfied. Granted, I only bought the C5s on Thursday. Aside from two pairs of Paradigm Titans I bought a couple of years ago, I have never bought new speakers that had to go through a break-in period. I always thought break-in was a myth, but now I am hoping it is true. Otherwise, my C5s purchase was a really bad decision.