The Sennheiser HD 599, like the HD 598, deliver a comfortable critical listening experience. They're lightweight, not too tight on your head, and have a well-balanced audio reproduction. However, like most open headphones they're not suitable to use outdoors or in noisy environments.
The Sennheiser HD 599 are the updated version of the HD 598 with essentially the same design. They have a few cosmetic changes to the headband and ear cups, but it won't affect the fit and feel of the HD 599. They're still relatively lightweight and super comfortable headphones you can wear for hours, but they're also not ideal for outdoor use.They're not stable or portable, and their build quality feels a bit weak at the hinges.
The Sennheiser HD 599 do not change much design-wise from the HD 598. The headband has been slightly improved with a better padding and a more premium look and feel. The ear cups also have some minor changes, with more metal around the cups but a cheaper plastic grill when compared to the HD 598. However, apart from the silver branding on the HD 599, it's difficult to distinguish them from the HD 598 at first glance due to the similarity in their design.
The Sennheiser HD 599 are incredibly comfortable headphones to wear for long listening sessions. They have large oval ear cups that are well padded and fit comfortably around most listeners ears. The padding is coated with a microfiber fabric that's soft and feels nice on the skin. The headband is also amply padded and not too tight on the head. You will rarely feel any fatigue even after having the HD 599 on for hours.
Like the Beyerdynamic DT 770, the Sennheiser HD 599 are bulky and don't fold. Therefore, they're not portable and they're a bit cumbersome to carry around on your person without a bag. Unfortunately, they don't come with a good carrying case so they may get scratched or damaged if you just throw them in your bag with all your other things, which is slightly disappointing.
The build quality of the Sennheiser HD 599 is about the same as the HD 598, with minor changes to the headband. The headband is now covered with a more premium leather coating and there's a bit more metal used on and around the ear cups. However, the frame still feels a bit weak when compared to some other headphones especially at the hinges.
The Sennheiser HD 599, like the HD 598 and the Audio-Technica ATH-M50x, are not stable enough for sports but should be fine for casual listening. They also have a detachable cable that will disconnect if it gets hooked on something unless you lock it into the ear cups. However, they're not made for sports and aren't as tight as some of the other models from Sennheiser so the ear cups will sway a lot and slip off your ears if used while running.
The Sennheiser HD 599 are very good sounding open-back headphones with an extended bass, good mid-range, and a well-balanced treble (see our recommendations for the best audiophile headphones). They also perform consistently across multiple individuals and have a relatively open and spacious Soundstage. However, their Distortion and Imaging performance can be improved, and like most other Sennheiser headphones, they tend to sound a bit muddy in the low-mid/high-bass area.
Very good Bass Range performance. Low-bass, which is responsible for low-end thump and rumble is slightly lacking. Also, high-bass is overemphasized by an average of 4dB, making the sound of these headphones noticeably boomy. See our recommendations for the best headphones for bass.
Very good Mid Range performance. Mid and high-mid are reproduced nearly perfectly. However, the bump in low-mid, which is the continuation of the high-bass overemphasis will make the Mid Range slightly muddy.
Excellent Treble Range performance. Low-treble is reproduced consistently and is within 1dB of our target which is very good. The small bump around 9KHz however, could make the sibilant sounds slightly sharp.
Excellent consistency. The Bass Range of our Over-Ear and On-Ear headphones are measured on 5 different human subjects, 5 times each. The Sennheiser HD 599 shows very good consistency in the Bass Range, since their open-back design allows them to rely less on an air-tight seal to create their low-end. The Treble Range also shows good consistency, but depending on the positioning, there could be up to 3dB of variance at 3KHz.
Average Harmonic Distortion performance. The amount of harmonic distortion in the Treble Range is very low, regardless of the level, which is excellent. However, high-bass and low-mid show excess distortion, especially under heavier loads.
The Sennheiser HD 599 are open headphones that are not expected to do well in loud environments. They let in a lot of ambient noise and won't be the ideal headphones for your commutes. Their open design also makes them quite leaky, which may be distracting to those around you in quieter settings. The HD 599, like other open headphones, are best used in isolation, where you can appreciate the benefits of having an open design without leakage and noise being an issue.
Poor Isolation. Due to their open-back design, it is natural for the HD 599 not to isolate well. They achieve no reduction up to 2KHz, and above that, they only achieve about 10dB of isolation, which is poor.
Poor Leakage. The significant portion of the leakage is from 400Hz to 20KHz which is a broad range. The overall level of the leakage is loud too, which is a consequence of the open-back design of these headphones.
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The Sennheiser HD 598 and the Sennheiser HD 599 are both very good critical listening headphones, but the HD 599 are marginally better. Though they look pretty different, they’re nearly identical in terms of comfort and build quality. The HD 599 do sound a bit better, with less underemphasized bass, but the difference will likely be negligible for most. The HD 599 also seem to isolate the wearer better than the HD 598, but neither of them isolate very much since they’re both open-back headphones. They’re very similar headphones and your personal preference will matter most in your decision.