Now that I have gotten the ergonomics and aesthetics out of the way, it is time to move on to review the sound of both headphones. The AD700 has one definite edge compared to most sub-$100 headphones. There are great headphones that can be had for the money, such as PX100-II, MS1, Grados, and Mike’s favorite AIAIAI; however, their soundstage is definitely on the small side when compared to real full-size headphones. The AD700 doesn’t stop at giving you a decent-sized soundstage; it gives you a really big one, which shows through even unamped. If you pay attention to the headphone drivers, you will notice that they are angled, which might partly contribute to this big soundstage. With the big soundstage, music seems more to revolve a little bit more around you, instead of playing strictly in the middle of your head. This soundstage is particularly useful for classical music or music that requires expansive ambiance. Even with the big and diffused soundstage, the AD700 still manages a good positioning and good spaces between the instruments. On the flip side, the overall imaging can be a bit soft and diffused, so some people can perceive them as a little fuzzy-sounding.
The HD668B also has a good soundstage in its own way. Size-wise, though still fairly wide, the soundstage is definitely smaller than AD700’s. What the HD668B loses in size, it gains in a clearer delineation between instruments and sounds. The soundstage is focused, with a more focused imaging than the AD700. The soundscape also maintains a clean and black background, enhancing the imaging. When I played a recording of an instrument playing against a quiet background, it was easier to hear the nuances of the instrument, and when it starts playing and when it stops, as the sound faded slowly into the background.
Already different in their soundstage presentation, the HD668B and the AD700 are even more different in their sound signature. Generally, the AD700 is a very open and airy-sounding headphone with an overall warm balance and a forward extended treble. The bass is light on impact. Quantity-wise, it is decent but the bass somehow dissipates rather quickly before it can deliver that punch down to the gut. The mid is colored, low mid is adequately represented; however, the upper midrange is comparatively laid-back when compared to headphones like Grados and my Beyerdynamic DT531. This resulted in vocals that tend to be on the warm side, but on the other hand, still has some of that ethereal airy quality contributed by the extended yet relaxed treble. The AD700 is not a neutral headphone; the transition from low mids-upper mids-treble is not very flat. However, if you are not aiming for neutrality and bass impact and just take the colored sound signature as is, the AD700 is still a very nice-sounding headphone at this price point. It also sounded good out of any setup I have tried. So, people concerned about the quality of their source or amp don’t have to worry much when using the AD700. To nitpick, the AD700 can sound a bit grainy when compared to better headphones.