Err, my english is not good, that may not be the correct word, "weak bass" could be a better one. What I mean is at neutral amp, T5P tries to produce sound as close to what is recorded in the studio. If there is bass recorded, then it will be heard, but will not exaggerate it.
At the same song, some other headphones can give punchy bass even with neutral amp. However this is because of that headphone itself has intentionally boosted the lower frequency signal. The sound produced is not exactly the same as what is recorded. I can't give good example... Sennheiser IE8 earphone may be one of them.
Some people like this type of head/earphone with boosted bass, including myself.
I have been listening to music and movie with boosted bass, so when i first heard T5P my feeling is "huh!? how come the bass is so weak? Where is the boom boom?"
Earlier I have a very wrong perception; that I think the more expensive the headphone is, the heavier and deeper bass it will produce. Now my understanding is how close it is to the recording source.