How can one learn from poor teaching evaluations? I teach at a large R1 state university, and I just received my teaching evaluations for Fall 2013. Usually I get excellent evaluations, but this time my evaluations for Calculus II were an unpleasant surprise. My numerical scores were mediocre, and representative student comments included: "Answers were obscure"; "can sometimes be cryptic when answering questions"; "didn't really answer questions".

These comments do not appear to be sour grapes, as the same students didn't complain heavily about the workload or grading of the exams. Moreover, I got excellent teaching evaluations when I taught Calc I a year ago, at the same university, with the same philosophy and style, with similar course policies, and with a comparable workload. Clearly, I did something wrong with regard to this course in particular.

I e-mailed both of my TAs, and only got encouraging comments ("I thought you did a good job"). I then e-mailed the class, and explained that my teaching evaluations were poorer than I expected, and asked students to offer criticism and suggestions for the benefit of future Calc II students. No responses.

So, apparently my teaching left room for improvement but I have no idea what to improve. This is quite uncomfortable -- is there anything useful I can do here?
Ben Norris's answer is excellent but I would add one additional point to it. When you are asking for constructive feedback from the students, you must do so in a way that students feel completely comfortable that their honesty is not going to come back to bite them.

At the end of every semester, I email all of my students a web-based survey with some open and some closed questions specifically so I can get their honest opinion. Again, the key is that all responses are anonymous. I believe if I asked them to email me (not anonymous) I would get nothing but praise, which does not help me improve at all. While I do still get many positive comments, there are usually some small gems in there which help me improve.