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AKG K371 Review (closed back headphone)

amirm

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This is a review and detailed measurements of the AKG K371 closed-back headphone. I purchased this last summer and it currently costs US $149 on Amazon including shipping.

Note: our company, Madrona Digital, carries various Harman brand products although not the AKG products.

The K371 is made out of plastic but has a nice finish which belies its cheap structure:

AKG K371 Review.jpg


I especially like the feel of the pads. They are not huge but big enough to fit around my ears. Inside height of the pad is 2.51 inches. Inside width is 1.62 inches. With no depression, the pad depth to the driver is 0.8 inches. Outside diameter of the pad is 4 inches by 3 inches.

Three different cords are supplied which terminate into a 3-pin mini-XLR:

AKG K371 Review closed back headphone.jpg


Let me warn you about something I hate about these headphones: the headband adjustment mechanism. It either gets stuck and doesn't move at all. Or all of a sudden moves a bunch of notches. I also see reports of the mechanism failing which means you have to send them back to Harman/AKG for repair (you pay shipping even under warranty).

Clamp pressure is a bit much especially if you wear glasses at first but gets better with some use. When I take them off, the pads are quite warm so likely in summer, they will not be comfortable if your room is not cool.

Note 1: The measurements you are about to see are preformed using standardized GRAS 45CA headphone measurement fixture. Headphone measurements require more interpretation than speaker tests and have more of a requirement for subjective testing as a result. In addition, comparison of measurements between different people doing it using different configurations requires fair bit of skill. So don't look for matching results. Focus on high level picture.

Getting the K371 seated did not require much work and indeed, measurements track some of the others I have seen using same fixture as I use.

AKG K371 Measurements
As usual we start with frequency response of K371. They are said to follow the Harman target. Let's see if that is the case:

AKG K371 Measurements Frequency Response.png


This looks to be closest we have gotten to the target. Indeed in sub-bass where vast majority of headphones fall off, the K371 actually overachieves a bit. Then again the Harman fixture is a bit different than what the rest of us use so maybe in their fixture that was right on the money. Either way, during equalization and listening tests we will investigate this further.

Following down the curve, we have a dip around 3.8 to 3.9 kHz. It is a shame as past that the response envelop more or less follows our target.

We can subtract the response from the target and see the deviations:

AKG K371 Frequency Response Measurements.png


Distortion is better than average:

AKG K371 Measurements distortion Frequency Response.png


The 94 dB line in blue shows extremely good performance. That keeps up even at 104 dBSPL.

Edit: forgot to include the absolute measurements:

AKG K371 Measurements THD distortion Frequency Response.png


Group delay gives us some clues to things going wrong with manifested in frequency response graph:
AKG K371 measurement group delay.png


We get similar clues in impedance versus frequency:
AKG K371 Measurements Impedance vs Frequency Response.png


This is a very sensitive headphone so don't need much horsepower to drive it:

Most sensitive efficient headphone review.png


AKG K371 Headphone Listening Tests & EQ
First impression was a very good response albeit, with a tad too much bass and a bit of exaggerated highs and harshness. You really had to listen to find these though. I also found the vocals to be a tiny bit recessed. Overall, you could listen to these headphones and be perfectly fine without any equalization.

But we, at least I, want perfection so let's apply a bit of touch up as instructed by the frequency response:
AKG K371 headphone eq equalization.png


I first boosted the lower treble and while that opened the sound up and nicely increased detail, the sound became somewhat bright. So I went after one of the peaks at 6800 and pulled that down. That fixed most of that. I initially had the bass pulled down some as you see in Band 1 crossed out above. I turned that off as it nicely countered the slightly sharpness that was left. Once there, this headphone was absolutely delightful to listen to. I could only find the slightest amount of harshness left (which could be magnification of what is in the music).

It was such a pleasure to listen to music with deep bass with and without EQ and hear those notes resonate in my ear even at very modest playback levels. Tracks like
Nachtschwärmen, by Regen:Tropfen were stunning in their impulsive bass notes:


And so was the rest of the spectrum. Notes come from every end of spectrum at no time do you say, "oh, why is that too high or too low." It is all balanced to near perfection.

Spatially without EQ the experience is fine. My boost of the lower treble however helps a lot here to get very good "soundstage" and layering of instruments. Mind you, it is not crazy nice like that if Sennheiser HD800s and such but it is "correct" and satisfying.

Conclusions
Some of you have been asking, even demanding to see a headphone that does the job without EQ. Well, the AKG K371 is it. My equalizations of it are subtle (but worthwhile) so you could indeed live without it. I do however highly recommend that you deploy EQ if you can.

You could say I am rubber stamping the Harman research and approach to headphone tonality. But such was not the case. I went into this review critically and thinking hard about what rating to give the headphone. I almost notched it down one step to avoid accusation of bias. But at the end, the truth is the truth. Years of research by Harman has resulted in creating headphone tonality that matches what I dream about getting out of best speakers in the world. To the extent their research goes after that sound (tonality of a good speaker in the room), it is natural that Harman and I land in the same spot.

Note that my strong positive recommendation for AKG K371 is for sound only. Physically, this headphone may not do it for you. It may get too hot around your ears, and the adjustment mechanism may annoy you or break. I leave that to you to decide.

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

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Gurkerl

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Very interesting, thank you a lot!

So what would a Dan Clark Aeon RT offer more, if EQ'd roughly to the same tonality - aside from fit, comfort, build quality? Detail and Soundstaging maybe?
 

Vini darko

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Very interesting, thank you a lot!

So what would a Dan Clark Aeon RT offer more, if EQ'd roughly to the same tonality - aside from fit, comfort, build quality? Detail and Soundstaging maybe?
I was wondering the same. One big difference is the akg can be powered by a gnat fart and the Dan Clark needs a nuclear reactor :D
 
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amirm

amirm

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So what would a Dan Clark Aeon RT offer more, if EQ'd roughly to the same tonality - aside from fit, comfort, build quality? Detail and Soundstaging maybe?
I briefly compared the two and I find the highs cleaner on AEON RT. It may be due to its ultra low distortion.
 
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amirm

amirm

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I was wondering the same. One big difference is the akg can be powered by a gnat fart and the Dan Clark needs a nuclear reactor :D
You are not kidding. Testing them side-by-side, I had to crank and crank my RME ADI-2 DAC to the same level as the K371.
 

sweetchaos

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sweetchaos

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sweetchaos

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For Canadians...

Finished going through my list of 100+ headphones resellers/dealers...
Found 3 resellers/dealers that sell K371. => Currently CDN$215, but was CDN$150 in Sep 2020 on amazon.ca
Found 10 resellers/dealers that sell K371-BT. => Currently CDN$280.
 
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solderdude

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I have measured it pretty much the same and can 'confirm' Amir's measurements and findings.

1611381953874.png


fr-stock.png


The kink one sees at 100Hz (most obvious in the GD) is caused by the pads. It loves to absorb and release 'energy' at that frequency. Most pads do b.t.w. it is not a driver thing. When changing pads on headphone I often see it shift higher or lower.

CSD shows the 5kHz part to be a resonance.
For those that want to address the small treble peak passively:
k371-filter-schematic.png


fr-filter-1.gif


It is a good sounding headphone. Too bad about the mechanical issues and comfort of the pads as well as the microphonic cable. Otherwise I would have kept it.
 
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JohnYang1997

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The channel imbalance will drive me crazy. Recently I purchased a new pair of HD6XX and a new pair of srh840. The 6xx got exact 1db difference from 100hz to 2khz. Not much but big enough to got me mad and just give it to my colleague. Same for the srh840, but nice and matched over 300hz but 2db difference down below. It sounds really weird, feels like one of my ears is stuffed when listen to them.
So maybe having some attention on this is a good idea.
 

DivineCurrent

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Somehow, despite what the measurements suggest, I don’t find these to sound all that full in the bass. Yes, sub bass is excellent, but maybe I’m used to headphones like the HD650 that boost the 100-200 Hz area, adds a bit of warmth. These actually dip in that area. Also, the mids do sound slightly off, perhaps due to that 4 kHz dip. It could also be the closed back design and I’m used to open backs, and of course pad fit and seal factors in.
 

solderdude

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It could also be the closed back design and I’m used to open backs, and of course pad fit and seal factors in.

These, indeed do not have the 'warmth/midbass hump'.
Also there is another thing to consider with closed headphones and that is seal
Below the K371 with the seal being different
seal.png

perfect seal, thin armed glasses, thicker armed glasses and a 6.3 plug wedged between the earpads and rig.
 
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