WaveTheory
100+ Head-Fier
Interesting review, however I disageee with the part about the "bass frequencies making their way out of the headphone and back in through the gap."
It actually makes perfect physical sense. As frequency goes up, sound waves become more directional. With speakers/subwoofers, the bass driver(s) are almost always built into an enclosure because low frequency waves are nearly omnidirectional. Since the driver pushes air in both directions, the back wave is 180 degrees out of phase with the front wave and of the same magnitude. Thus, below ~100 Hz you get near-perfect phase cancellation. Building a box around a woofer allows for trapping and controlling the back wave so that such cancellations don't happen.
It's actually quite common with open-back headphones to get a bass bump - the bass peak Lachlan mentions and measures in his review - when the seal is broken. The same happens with HiFiMans and Audezes when their seal is broken. Why? Diffraction, ie waves bending around obstacles. The back wave can escape through the outside of the headphone cup but it also has to bend around the enclosure of the headphone and the pads before it reaches your ear. This bending around messes with the time alignment of the front wave and back wave enough that they no longer perfectly cancel. Instead, a tight range of frequencies will get a noticeable bump through constructive interference and then outside of that there will be decreased sonic energy due to destructive wave interference.
The reason that headphones have "minimal bass" as you put it comes down to physics again too. Low frequency sounds require more energy than middle and high frequencies to reach the same sound pressure levels. One way to increase that energy is to increase the area over which a vibration happens, thus pushing more air. This is why in speakers woofers are bigger in area than mid and high drivers. The problem with headphones is that there are practical limits to driver size lest you get into comical Jecklin Float territory. Headphone bass still sounds quite strong though because of how close the driver is to the ear. You can get away with less energy pushing bass frequencies when the bass only has to travel a couple of cm.
That said though, the sound going out of the TC and coming back in certainly applies to the mid and high frequencies. If you can hear the headphone playing music when it isn't on your head, then every sound that you CAN hear from this point will make its way back in when you do wear it. He totally got that backwards. Every open headphone does this, including speakers.
Yes, but I think there is another misconception here too. As frequency goes up, more and more of the back wave content that returns to the ear is going to be due to reflections. Especially in the treble, which gets very directional especially above 10KHz, some portion of the back wave will reflect off the inside of the grille on the backside of the driver and be directed into the ear. This is going to create wave interference again. Back to speakers again to help us understand, sometimes this reflected back wave is desirable. Some home theater enthusiasts swear by using dipolar surround speakers. Those intentionally let the mids and highs travel both forward and backward 180 degrees out of phase so that the back wave reflects off the walls and reaches the listening position a little while after the front wave. The result is a more diffuse soundfield with less pinpoint imaging. Fans of this approach say that the position of the speaker becomes less detectable this way and the overall presentation becomes more enveloping. Some speaker makers have used similar approaches or bipolar designs (sound completely in phase going forward and backward simultaneously - which requires an enclosure and multiple drivers) for speakers made for music listening because some listeners like the effect.
I applaud Abyss for trying something different. Leveraging the bass bump Lachlan measured is a unique approach in headphones. It has advantages. The Abyss bass presentation can be loads of fun. They arguably - within a specific frequency range - bring an unmatched combination of bass quantity and quality. But there are tradeoffs to their sound. Lachlan covered many of them. I personally find their midrange resolution and timbre to be WAY behind similarly priced competitors. That alone is a deal breaker for me. Add in that the 1266 series does not stay on my head hardly at all unless I sit there as still as a headphone stand and then they just get generally uncomfortable quickly and I find them hard to recommend. But that's just me.
Cheers