Fit and Comfort

What you see above is the Drop x Sennheiser HD 6XX put in place on a headphone stand that is actually a set of two artificial ears complete with soft-molded human ears and a couple of different adapters replicating the top of the head. This has been mounted on a tripod, which also showcases how headphones would look on a human head with ears spaced apart ~20 cm. As with all headphones, getting a good fit and seal is crucial, and make sure to have the steel band extensions correctly matching on both sides, and use the tilt/swivel functionality of the ear cups as well. The foam supports on the headband may not be too comfortable right away, with the bigger issue for most probably the high clamping force with a rated contact force of 6 +/-1 N. Try to resist the urge to bend the steel band outward to loosen the clamp, however. Unless the fit is actually painful, the clamping force will naturally reduce as you break-in the headphones and come to a more steady-state fit you may accidentally move past if brute forcing this with your hands.

The HD 6XX weighs just over 250 g without the cable, and it felt great going to these after the comparatively monstrous Audeze LCD-XC at over 670 grams. The cables are also not going to add much mass, and them going to both ear cups means their natural resting position is in the middle of your chest and body as opposed to off on one side, which may or may not work depending on where your source is placed. Also, these are open-back headphones, meaning it is best to use them in a quiet, private environment. There is little stopping external stimuli from affecting your user experience, and others around you may not appreciate the involuntary exposure to whatever you are listening to.

Audio Performance

Audio Hardware

The actual driver in the HD 6XX isn't that detailed in itself. It even takes a cursory Google search to find out this is indeed a 40 mm dynamic driver with a ~38 mm diaphragm driven by standard Neodymium magnets. Driving the HD 650 became somewhat of a meme since it was quite hard. While somewhat valid, there are plenty of reasonably priced amplifiers that can easily power the HD 6XX or HD 650 in 2021. The primary reason behind the benefit for an amplifier is the 300 Ω voice coil—just looking at that number can scare some people off. Remember that these are reference class headphones, wherein a higher impedance will help retain the required signals more so if adequately amplified. It is somewhat worsened by the 103 dB/Vrms sensitivity, which translates to ~98 dB/mW here. This is the real crux of the issue in that even if you have a mobile device that can get past the higher impedance, it takes more power than average to get these to a reasonable listening volume. For example, plugging these directly into a 3.5 mm jack powered by a Realtek ALC3266 chipset on my laptop had me increase the volume to 100% for just ~60 dB or less even then. A portable DAC/amp, such as the Qudelix-5K, is a big step up already, and a decent compromise between portability and performance. A desktop amp or even budget stack, such as the JDS Labs Atom+ DAC and Amp+, are plenty to drive these with some headroom left, and you can then go with a better amplifier to get more headroom and breathing space for the drivers themselves depending on your budget.

Frequency Measurement and Listening

I will mention that I have a general preference for a warm neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Here we see my new headphones test setup, which has a set of two custom in-ear microphones for the two channels. These microphones closely adhere to the IEC711 class, but have been tweaked to be more reliable in the >10 kHz frequency range that was the issue with my previous setup, which is still very good and will continue to be used for IEMs and earphones. Two soft silicone pinnae are installed on the sides separated by a distance matching my head, and multiple "height" adapters have been 3D-printed to allow for further customization based on fit and head size/shape. Each set of microphones has an XLR output I separately adapted to 3.5 mm, so note that the cable setup in the first photo above is just done for cable management—it is not representative of the actual testing. I did power the headphones off a dedicated source, and the sound card seen was used for a quick test as well as for the microphone input itself. A 3.5 mm audio jack associated with the right channel also enables recording, as well as real-time monitoring, and potentially audio demos if I am satisfied with the output.

This artificial head simulator feeds into a reference USB sound card, which in turn goes to a laptop that has ARTA and REW running and the headphones connected to the laptop through the sound card and/or a separate DAC/amp if needed. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/6th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. The raw data is then exported from REW and plotted in OriginPro for easier comparison.


[Update] I have replaced some of this section, which was using a less-than-satisfactory measurement protocol, with a new graph from an updated setup. You can find the raw data to compare against on this page.

Drop and Sennheiser both market the HD 6XX as a reference class set of headphones, which is to say these are not meant to color the sound signature from the source. No bass boost, no recessed mids, no elevated treble. A smooth transition all around, and overall what should be an accurate and neutral response. A quick look at the frequency response curve above shows that this is mostly true. The HD 650 released in 2003, and it is to this day one of the go-to monitoring headphones, as well as highly recommended by audiophiles for the tuning. The HD 6XX is the same thing, and my memory of the HD 650 was jogged the second I heard Careless Whisper on these, which took me back to 2010 when I was deciding whether or not to get the HD 650.

Calling these completely neutral would not be wholly true; after all, the frequency response and tuning is not a flat line even in the lower frequencies. Note that the small bumps in the sub-bass seem to be measurement artifacts, I certainly didn't feel any discrepancy on my ears, and using the IEM testing setup showed a smoother slope heading down. This very slope is where people would claim there isn't much bass response, and I get what they mean. The headphone world has changed drastically even since the HD 6XX was released, let alone the HD 650. There are planar magnetic headphones available in this price range now, as well as beryllium-coated dynamic headphones which change the meaning of what a neutral bass response and elevated bass is. These will feel lacking in energy if you've just come off listening to a V-MODA Crossfade M-100, but that is one of the furthest removed headphones from a neutral tuning you can get. There is detail galore here to where you can distinguish various notes and hums in the sub-bass and mid-bass accurately. See what I did there? This is especially where pairing the HD 6XX with a capable source is handy, as you may otherwise even feel things are low resolution when it is anything but! Either way, if you are an avid listener of the likes of EDM, house music, or hard rock, you may want to look elsewhere.

Let's get the negatives out of the way early, shall we? The HD 6XX is not your typical pair of dynamic driver headphones. The Technical performance with dynamics/slam/punch is not high on the agenda here. The soundstage is also relatively lacking for open-back headphones—it's tall and follows the oval pattern of the ear cups, but there just is not enough width or depth to appreciate it wholly. It gets dark early on in the highs, and depending on your unit, a subtle shift up and down around 9–10 kHz may take you aback if you are not expecting it, with some string instrument resonances coming in hot! Imaging is decent for music, but I can't recommend these for gaming as with a few other such recommendations I have seen online.

That's about it. Everything else is all good in my books. The tuning throughout is really good with the reference mindset considered. This is all the more valid from ~100 Hz onward, with the upper bass to lower mids effectively a continuous transition. I could swim in the range the mids are given and not run out of room. This is where some of the speaker-like sound comparisons come up, since the HD 6XX can resolve so much when it comes to male vocals and most instruments that this alone makes it worth considering for monitoring. As mentioned before, Imaging is fairly decent for music, but the compact soundstage makes it a non-issue. As long as you can pin point the sound in the 3D space, you can visualize where it is coming from. Funnily enough, the mids are also not what I would call completely neutral, as they are instead slightly warm, which benefits the casual listener by providing energy on top of the range and the detail not to make things one note. This is something to be aware of for the monitoring use case, admittedly, but the overall benefits far outweigh it. In fact, this combination makes the HD 6XX quite pliable for everyday listening too, although more for calls and movies than gaming.

I might disappoint some of you, but I never really got the "Sennheiser veil" critique when it comes to the treble response. Sure, the tuning looks like someone put a weighted blanket over the frequency response, but I am not sure why that is bad. The linear and total harmonic distortion is low enough to where you can just add a peak and/or shelf filter bump in your favorite EQ software and call it a day if looking for added presence. When I was getting into this hobby, I admittedly listened too much to what others said and started having second thoughts about my HD 600 I had bought to complement the HD 598 a year prior. This is what prompted me to try out the HD 650, having heard things were far more amenable. It's 2021 now, and I have no qualms changing the tuning as I would also like to see if the headphones can handle it. The HD 6XX does well most of the way, including in the bass region, by the way. Going back to the out-of-box tuning, the fast treble response you see here helps avoid overly bright music, sibilance, high-pitched clipping, and the like. This helps with accuracy while still being extremely enjoyable to listen to. The HD 600 tunes things further in that vein, and now you know why I did not get the HD 650 when I had the HD 600 already. If you do not have either, I can wholeheartedly recommend the HD 6XX unless you absolutely cater to my specific tastes of music and sensitivity. As it stands, the HD 6XX is excellent for the likes of pop and jazz too, with classical music somewhat testing the tuning and transient response, and the darker response making some instrument classes come off as step-children you only love 90% of the time.


This is what I am referring to—not only is the higher frequency response recessed, there is also longer decay on the order of a few hundred milliseconds. The Y-axis is resonance time in milliseconds, by the way. Blame REW for making it difficult to grab the actual raw data here. The two don't work together against the listening experience; rather, the darker treble somewhat mitigates this to begin with. When it comes to the competition, the obvious one is the Sennheiser HD 650 which comes in at a much higher price, so I am hard-pressed to recommend it at all knowing all the changes here are for the better. There are some alternatives from the likes of beyerdynamic, AKG, and Audio-Technica to consider also. Of all those I have listened to in the price range of the HD 6XX, I really can't think of any that do it better overall. The DT1990 Pro gets there, but it also costs much more than the HD 6XX. The value offering is what makes this special, but let's find out how exactly as we collect our thoughts on the next page.