One Enthusiasts Take on Top-of-the-Line Headphones: The State of Flagships
In a recent reddit post here, SanjiWatsuki has unleashed his impression of current flagship headphones from various manufacturers, grading them on the basis of measurements and his interpretation of them. I found his methods and evaluations laudableeven though I would add other factors and weight them a bit differently. If you want to read along, you'll find the document here: "The State of Flagships". My comments follow...
Page 2 - "Most of them suck at designing flagships."
Ha ha ha! Pretty funny...I've been trying to figure out how to say the same thing recently.
Page 4 - Flagship Characteristics
I think these are pretty good benchmarks for headphone with the exception of #9. After hearing quite a few good sealed headphones lately (NAD VISO HP50, Focal Spirit Professional, Sennheiser Momentum), I'm beginning to think it just might be possible to make a sealed headphone that is world class. Personally, I'd much rather EQ for frequency response on a Focal Spirit Professional or Viso HP50 than any of the headphones mentioned in the article.
Page 12 - Why This Metric? #7
Wiggles in the impedance response between 300Hz and 1kHz can be caused by a rocking voice coil I suppose, but I tend to think impedance blips in the range between 300Hz and 3kHz as coming from not dealing properly with the small volumes trapped, or nearly so, around the driver and diaphragm. These are usually dealt with by using various damped ports in and around the driver. I do agree however, that a bunch of small wiggles in the impedance response can be an indicator of poor design. On the other hand, methods used by designers trying to flatten the diaphragm response will often turn into bumps in impedance, however, these bumps indicate something that is actually flattening the FR.
Page 14 - Why This Metric? #7
Here again is the statement that open headphones are inherently superior. One thing that's fairly easy to see is that sealed headphones are better able to control what's going on in the bass. It seems to me that open cans have a harder time keeping the air compressed around the ear for the long bass excursions, and as a result, sealed headphones often outperform open headphones in bass distortion.
I've also heard some sealed cans lately that are particularly good at treble resolution (HP50, B&W P7). These cans do deliver a sense of space similar to that of an open can. It also seems to me that some of the sense of space from open cans might be that you remain aware of some outside sounds, which may tend to create a sense of space that's not actually coming from the audio, but rather your ongoing acoustic sense of the room you're in. I'll admit the open cans are more likely to deliver good imaging and soundstage, but I'm beginning to thing it's not a foregone conclusion.
No mention of time domain signal analysis.
In his reddit postings he claims, "Square waves don't tell you much at all, especially not more than the frequency response. Making judgments based on the square wave is a poor decision, in my opinion. Tyll talks about trying to determining damping of the signal -- frankly, I'm not entire sure I buy it. I've never seen a study at AES come to his conclusion, but I'll accept it once someone else who has done more scientific rigor has said so. Edit: It's also worth noting that the tizziness appears whenever there is a lot of treble, particularly if it is a spiky treble."
It's true that the square wave is largely just another way to look at frequency response, but it can also tell you some things about the phase response. The 30Hz square wave is particularly good at this to observe bass phase: If the waveform rapidly drops to the zero line and stays there, you have no bass. But if it undershoots the zero line substantially it means there's bass there, but it's gone out-of-phase.
Also, the reason why the treble goes "spiky" is because of resonant interactions, and this phenomenon is more directly observable in the impuse response, or better yet the cumulative spectral decay plots derived from the impulse response. Music is an extremely random signal; reproducing it requires a system that reacts well in the moment. I think time domain information is important.
In the 300Hz square wave responses at left, it seems to me capture the nature of the various treble response of the headphones shown in a more meaningful way. (Grade received in paper is shown next to model number.) The HD800 is truly a great headphone, it's clean impulse gives it unparalleled imaging. SanjiWatsuki says in the HD700 section, "There's brightness near 6kHz, but nothing to suggest horrible resonance." I'd say the square wave response makes it pretty clear. The K812 and the T1 have a very hard time reproducing a clean instantaneous edgeswhich is a lot of what music is. And the K701 response is exactly why one needs more factors and additional metricsthis headphone should get a better grade against the flagships.
More Emphasis on Listening
I think analyses without significant listening to verify the audibility of measured features an incomplete attempt at a true evaluation. I'd like to have seen a bit more listening comments in this paper.
A Good Attempt Overall!
On the other hand, an evaluation based on measurements alone does provide a significant amount of information. I applaud SanjiWatsuki for this valiant attempt to grade headphones based on an objective measurements. I found it very interesting, and no doubt many others will.
I do think the difficult thing here is identifying the actual relavent factors and how they add up. Also knowing the target response in absolute terms is very, very difficult. None the less, I think it's efforts like this one by SanjiWatsuki, acting as models for ongoing modification by the larger headphone enthusiast community, that provide an avenue forward for real learning in the hobby.