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Abyss AB-1266 Phi TC Review (Headphone)


Staff Member
CFO (Chief Fun Officer)
Feb 13, 2016
Seattle Area
This is a review and detailed review of the Abyss AB-1266 Phi TC planar magnetic headphone. It is on kind loan from a member. The Ab-1266 comes in three different configurations with the "Lite" version costing US $4995. The one I have is the Complete configuration costing $7,995 with the $3000 extra going to a replacement cable (!).

I must say, in person this headphone looks better than when you see someone wearing them:

Abyss AB-1266 Phi TC review planar magnetic headphone.jpg

Once on your head, you may remind people of Frankenstein. :)

Unlike many headphones, the premium cable serves two purposes:

Abyss AB-1266 Phi TC Complete review planar magnetic headphone.jpg

First function is to provide sound to each driver. The second one is as a tow rope should your car get stuck in mud or snow!!! I mean good grief, this thing is so heavy and long that you are constantly figuring out how to route it as to not tug on the headphone or be a trip hazard. Sadly premium cables are sold by weight and size so I guess it had to be for $3,000. No, I did not have any other cables to test with and compare.

The headphone is naturally quite heavy at 665 grams but wears almost comfortably. There is no real spring action here. You adjust the width of the headphone so that it more or less hangs next to your ears. With some force, you can lengthen or shorten the top headband. It was barely long enough for my fixture (you can bend it to make it wider). Company -- unusually so -- recommends to try wearing them with some gap between them and your ears. I avoided that and measured the headphone with the tightest fit I could, lest there be riots in the streets due to bass response.

The cups are deep, very deep at average of 34 mm. No risk of your ears hitting the drivers. They are oval with height of 70 mm and and width of 56. Very strong magnets hold the cups against the headphone. You can pull it off and rotate it at another angle. I left it as the owner sent me (see first picture above).

Note that this unit is the forth generation one (latest available now).

The measurements you are about to see are made using a standardized Gras 45C. I searched for any and all measurements I could find online. Alas while a number of them are close to mine, none are using the exact fixture down to coupler and pinna. As you will see, I have confirmed the approximate accuracy of the measurements using Equalization and listening tests. Ultimately headphone measurements are less exact than speakers specially in bass and a few kilohertz so keep that in mind as you read these tests.

Abyss AB-1266 Phi TC Measurements
As usual we start with our frequency response:

Abyss AB-1266 Phi TC Frequency Response Measurements.png

Hmmm. Hard to imagine what target curve they were going after. There are clearly anomalies that I can't imagine are intentional or if they are, misguided to be sure. The main good news is that there is plenty of bass response and that we have more energy than we need in mid-range so we can pull that down and lower distortion as well.

In relative form, we have:

Abyss AB-1266 Phi TC relative Frequency Response Measurements.png

Company talks a lot about imaging/spatial effects of this headphone but seeing the shortfall in the critical midrange, they left a lot of money on the table.

Next comes a very scary graph:

Abyss AB-1266 Phi TC THD percentage Measurements.png

As with Abyss Diana headphone I tested, we have a ton of distortion. Company would do well to pay attention to this and work to find the cause and remedy them. That said, my listening tests at modest levels produced very clean sound prompting me to go back to this measurement and realizing that the distortion at 94 dBSPL is actually quite low. Here it is by itself:

Abyss AB-1266 Phi TC THD percentage 94 dBSPL Measurements.png

Considering how much sub-bass energy we already have, we don't need to boost much so what we see here is what we get. Cranking up the volume clearly causes much distortion though in a binomial distribution in both bass and treble (previous graph). Usually our only enemy is bass distortion -- not here. More on this in listening tests.

Here is the distortion as level:
Abyss AB-1266 Phi TC THD Measurements.png

Group delay shows the common messiness in mid-frequencies:

Abyss AB-1266 Phi TC Group Delay Measurements.png

We have a going hypothesis that this is an indication of good spatial effects as it shows interference from multiple sources, i.e. reflections. Messiness in lower range though is not welcome although audible effect of such is unknown.

Impedance is dead flat and low as we expect in planar magnetic drivers:
Abyss AB-1266 Phi TC Impedance Measurements.png

On sensitivity, this is the second worst I have measured:

most sensitive headphone high-end.png

You roughly need four times the voltage to drive it to the same loudness as Sennheiser HD-650 for example.

Abyss AB-1266 Phi TC Listening Tests and Equalization
Headphone measurements are approximate. The best way to verify their correctness is to modify the headphone response the way they instruct us and see if the effect is positive or not. Before that though, I listened to the 1266 by itself. I didn't find the sound all that exciting. It wasn't terrible mind you but clearly it was colored. So out came the parametric EQ:

Abyss AB-1266 Phi TC Equalization EQ.png

Note that the response curve is very odd shaped which makes matching them to parametric EQ curves is hard. I eyeballed them and fortunately the result was fantastic. Tonality improved substantially and clarity improved, likely due to reduction of distortion (my guess). Most wonderful was the spatial effects. You had this really nice halo at and behind your head that seemed to constantly delight in the way it would place instruments. Deep bass was substantial with my modest boost and clean, clean and clean! I listened for hours and didn't want to stop.

To check distortion and clipping, I turned up the volume during some instrumental female vocals. As I did the highs got a bit distorted and suddenly I was greeted with oddest buzzing sound! It literally went from paying music to playing noise. Fortunately that was pretty loud so don't expect it to be everyday problem. With music that was bass heavy, the AB-1266 can produce a ton of them until starts to make a ticking sound with bass peaks. Turn it up even more and they get louder still. Again, this is beyond normal use and onset is mild. Both of these experiences match the distortion measurements where we saw problems at multiple frequencies and not just bass. These drivers are simply not designed to be pushed hard.

Speaking of pushing, I used my Topping A90 in highest gain setting using balanced out. It had no trouble driving the headphone to highest levels per above. My RME ADI-2 DAC that I normally use doesn't have balanced headphone out so I routed its line output to A90 for listening tests.

Technically the Abyss AB-1266 has fair bit of objective faults. Its frequency response varies with no rhyme or reason and it distorts at higher volumes. The former is very correctable using equalization. The latter just requires listening at normal levels. Even putting aside the $3000 for the cable upgrade, this is one expensive headphone. Would I go out and buy one? No. If I did, would I keep it without EQ? No. But if I had had, I would apply this EQ (or a refinement thereof) and enjoy the sound. It becomes a very capable entertainer then.

Without EQ, I cannot recommend the Abyss AB-1266 Phi TC. With equalization, it becomes a delight and I recommend it, ignoring the price.

As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/


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It is almost 1:00am and I am going to go sleep. You all need to behave and not use this review as an excuse to create another riot in the street!
I heard from somewhere that the company Abyss doesn't care much about objective measurement.
Time to care! We are watching. :)
Thanks for the Frankenstein autopsy :cool:
I'm noticing a "headphones testing paradox": The more expensive a headphone is, the worse it measures without EQ :D

But seriously: Did the EQ mitigate those distortion "skyscrapers" at least a bit? Probably not, but just being curious...
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Obligatory question of how these were placed on the measurement rig, positioning of the earpad notches, clamp, and headband rotation. All those should have considerable effect on the frequency response.
Thanks for the Frankenstein autopsy :cool:
I'm noticing a "headphones testing paradox": The more expensive a headphone is, the worse it measures without EQ :D

But seriously: Did the EQ mitigate those distortion "skyscrapers" at least a bit? Probably not, but just being curious...

Yes, it would be interesting to measure them again with EQ and check the behavior.
94 dB. Actually low distortion. Oh well.

(Happy owner of several Focals here.)
This looks like just background noise to me, i wouldn't read anything into it. We saw before that it is reduced with headphones with some isolation like the hd820

HD820 Measurements for reference
Sennheiser HD 820 Group Delay Measurements.png


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Oops. Measurement wise the K371 wipes the floor with this device, for what? 2% of its price?

What really worries me is the strange peak/dip around 400 Hz * (left and right channel differ a bit). Or could this be a measurement artifact due to the very big ear cups?
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