The Superlux HD 681 are very similar to the HD 668B in shape and sound. They're a bit more comfortable thanks to the different headband design that's not as tight on the head. They also sound better than a lot of pricier headphones, but they're not very versatile. They're cumbersome, they don't block a lot of noise and leak quite a bit so they're best used in isolation.
The HD 681 are best used for critical listening and won't be the most versatile headphones for other use cases. They're good-sounding and affordable headphones but they do not block a lot of noise, they leak and they're bulky and cumbersome.
The Superlux HD 681 are a good, budget option for neutral listening. They have slightly more extended bass than the HD 668 and deliver a satisfying audio reproduction that caters well to instruments and vocals. They have a relatively flat mid-range but tend to sound slightly sharp because of the bump in the high-mid/low-treble, especially with tracks that are already a little bright. Sadly, they don't have a Soundstage as immersive as some of the other fully open-back headphones, but overall the sound quality of the HD 681 like the HD 668B is good for both casual and neutral listeners.
Poor for commuting. They're not intended for this use case as they don't block a lot of ambient noise, they're not portable and do not have the most durable build quality.
Not made for sports. They're bulky and impractical to use outdoors. They're a bit more comfortable than the HD 668B but they're less stable and won't be ideal to use while doing physical activities. They also, they don't have any controls, which makes controlling your music source while exercising a bit more of a hassle.
Subpar for office use. They let a lot of noise seep into your audio and also leak a lot which might be distracting to your colleagues.
The Superlux HD 681 look very similar to the HD 668B. They have practically the same ear cups but a different headband design. This makes the HD 681 look even more like the AKG K240 MKII. The color scheme is pretty bland but this model stands out a bit more compared to the HD668 thanks to the red accents on the ear cups and headband. Unfortunately, their plasticky build quality makes them look cheap and not durable.
The Superlux HD 681 are more comfortable than the HD 668. They're just as lightweight and have a better headband design that doesn't feel as tight on the head and extends a bit further than that of the HD 668. They also have large ear cups that fit well around most listeners' ears. Unfortunately, the padding on the ear cup feels a bit stiff and may cause a bit of uneven pressure. It's not particularly uncomfortable but it is noticeable after wearing them for a while.
The Superlux HD 681 are lightweight but bulky and cumbersome headphones. The ear cups do not fold or lay flat, making them difficult to carry around on your person if you do not have a bag.
Comes with a somewhat, rugged pouch that will shield the headphones from scratches and minor water exposure. However, it will not protect your headphones against drops and impacts.
The Superlux HD 681 like the HD 668B 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 HD681 are not as tight on the head as the Superlux HD 668B and are slightly less stable overall. They won't be the best for sports since they have big ear cups that sway during physical activity but they don't move much during casual listening sessions. Unfortunately, this model does not have a detachable cable so the headphones will get yanked off your head if the cable gets hooked by something.
Good Consistency performance. The Bass Range performance is very consistent across our human subjects, except for our subject who wears glasses as he gets 3dB less Bass than others at 20Hz. The Treble Range consistency is also very good, especially below 10KHz.
Excellent Bass Range performance. Low-frequency extension is at 14Hz, which is great. The entire Bass response is virtually flat and within 1dB of our target.
Very good Mid Range performance. Low-mid and Mid are virtually flat, but under our target by about 2dB. This pushes vocals/leads slightly to the back of the mix and giving more emphasis to Bass and Treble Ranges. High-mid shows a small tilt favoring higher frequencies, but the effect will be very subtle.
Decent Treble Range performance. Low-treble is well-balanced but slightly inconsistent. Treble has a 10dB bump between 7KHz and 12KHz which makes the sound of these headphones noticeably sharp and sibilant.
Poor Isolation performance. Due to the semi-open back of the HD 681, they don't isolate at all in the Bass and Mid Ranges. In the Treble Range they reduce the outside noise by about 20dB, which is decent.
Poor Leakage performance. The significant portion of Leakage on these semi-open back headphones sits between 500Hz and 20KHz which is a broad range. Additionally, their overall level of Leakage is also relatively loud.
No compatible app.
Wired connection negligible latency (see our recommendations for the best wired headphones).
The Superlux HD 668B and the Superlux HD 681 are both very good headphones if you like a neutral sound, but the HD 681 have a slight edge. While they both can sound quite harsh and sharp, the HD 668B also lack thump and rumble, on top of sounding a bit muddier. The HD 681 are also much more comfortable.
The Superlux HD 681 and the AKG K240 MKII are similarly designed headphones, but the Superlux have an overall better-balanced sound profile. The Superlux produce much deeper bass with less clutter in the mid-range but sound a bit harsh, and even piercing, in the higher frequencies. The AKG have a smoother treble and feel better-built.
The Superlux HD 681 are better critical listening headphones than the Audio-Technica ATH-M20x. The Superlux semi-open headphones are more comfortable and offer great audio quality, especially for their affordable price. Their design also makes them more open-sounding, although their build quality is pretty cheap and fragile. On the other hand, the Audio-Technica will be better headphones to bring on the go since they are closed-backs, which means they block a bit of ambient noise and don’t leak as much as the Superlux.
While the Superlux HD 681 and the Superlux HD 681 EVO are similarly performing headphones, the HD 681 are better for neutral listening. They have a more balanced sound and a better passive soundstage. However, the HD 681 EVO have a slightly better build quality and they're a bit more stable on your head.
The AKG K712 PRO and the Superlux HD 681 are both great audiophile headphones if you like a neutral sound. They have fairly similar profiles overall, though there are a few differences. The Superlux get quite a bit more bass, and they also sound brighter in the treble range, which gives them a slightly more excited sound profile. They're also less comfortable than the AKG and feel a lot more cheaply made.