The Superlux HD 668B are great-sounding and affordable critical listening headphones. They let in a lot of ambient noise and leak enough to be distracting to those around you, so they won't perform as well for other use cases. They're also a bit bulky and cumbersome to carry around. However, when it comes to sound, they deliver an almost unmatched audio reproduction at this price range.
The Superlux HD 668 look like a budget version of the AKG K240, with minor changes to the headband design. They have the same semi-open ear cups that make them a bit cumbersome to carry around since they don't fold or lay flat. They're also not the best headphones to use outdoors as they're a bit bulky and not stable enough for sports. On the upside they're lightweight, they have a detachable cable, and they can be comfortable depending on your head size.
The HD 668B look very similar to the AKG K240. They have paddles instead of a fabric strap to cushion the headband and an odd-looking male audio jack in place of a more traditional female port for the detachable cable. However, the rest of the HD 668's design, including the large semi-open ear cups, look like a cheaper version of the K240s. Overall, they have an understated and utilitarian appeal but they're not headphones you would use outdoors for their style.
The Superlux HD 668 are decently well-padded but a bit too tight on the head. They're lightweight and the ear cups are large and fit well around most listeners ears. Unfortunately, the headband doesn't extend to accommodate different head sizes, so they tend to feel a bit tight. That and the paddles that act as a cushion for the headband put quite a bit of pressure, which will get fatiguing after a long listening session.
The Superlux HD 668 are cheaply made and plasticky. They feel like a budget version of the AKG K240, which shows in their build quality. They have a plastic design with no metal parts, and all the materials used in their build quality feel slightly low grade. They won't break if they accidentally fall once or twice, but they don't feel like durable headphones. The paddles, especially, are weak points that will wear over time.
The HD 668B are tight on the head which make them decently stable. They won't fall during casual listening sessions and may even be tight enough for a light jog but they are not sports headphones. The earcups are a bit bulky and move a lot under physical activity so they won't be the ideal headphones to go running with. On the upside, the detachable audio cable will disconnect if it gets hook on anything
The Superlux HD 668B are a great sounding pair of headphones with a balanced Bass, excellent Mids and good Treble. They perform quite consistently on most people and have good Imaging and Distortion performance. However, they lack a bit of thump in Bass, and the Treble could sound a bit sharp on overly bright tracks. Also, they don't have the most open and immersive Soundstage due to their relatively closed and shallow earcups.
Excellent Mid-Range performance. Low-mid is reproduced flawlessly. There is a small but broad dip surrounding 1KHz, which tends to push vocals/leads to the back of the mix. However, at about 1dB this effect will be very subtle.
Good Treble Range performance. Low-treble and treble are a bit inconsistent. Additionally, treble and high-treble are overemphasized by a couple of dBs, making these headphones a bit bright and sharp on certain tracks.
Good consistency. The Bass Range of our Over-Ear and On-Ear headphones are measured on 5 different human subjects, 5 times each. In the graphs, each line represents an individual's average Bass response. The variance in the Bass range is very little, except for one of our test subjects who wears glasses, which gets about 3dB less Bass at 40Hz. In the Treble Range the variance is about +/-3dB is which is decent.
Good harmonic distortion performance. The overall level of harmonic distortion is low for the most part. However, high-bass shows a bit of excess distortion, especially under heavier loads. Additionally, peaks at 8KHz tend to make the sibilant frequencies a bit brittle and harsh, but at 1% of the test signal this effect will be subtle.
The HD 668B are not intended to block a lot of ambient noise. They have a semi-open design that gives them a more immersive Soundstage but also means they leak and let ambient noise seep into your audio. They're headphones best used in isolation where there isn't much noise to ruin what you're listening to and the leakage level won't bother anyone.
Poor Isolation. Given the semi-open design of these headphones, poor isolation is natural. These headphones don't block any noise below 1KHz. Above that, they achieve about 20dB of reduction which actually is above average.
Poor Leakage performance. The semi-open HD 668B leak less than some fully open-back headphones, but more than the ones with a closed-back design. The significant portion of their leakage is between 400Hz and 10KHz which is a relatively broad range, and the overall level of the leakage is also fairly loud.
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