Well definitelly with an amp the sound is glorious with the CD3000, but I disagree in that the sound is not good unamped, all depends on which portable are you using, to feed it. Out of my D-34 and D-33 the sound is still very good, and it does not lack puch or impact, just that the bass is a little weak, but if you use the bassboost on the first setting, this is completelly different animal, the sound is very loud, and very good.....again an amp make it sound it's best, but this apply to any headphone in the market too, IMO...with the difference that many of them out of the portables sound really crappy....