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Drop AKG K7XX Review (Headphone)

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amirm

amirm

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thanks! Would your EQ on the 600s/650s work well?
I always recommend using my EQs. That's like asking a cook if he likes his own food. :)
 

Robbo99999

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Thanks!! When do you say DAC I assume you mean headphone amplifier. If I understand correctly, the maximum voltage level would give the maximum spl possible. Is that correct? The maximum output voltage of my headphone amplifier is 7 V RMS, given by the manufacturer. The issue is that it has a gain setting and I have it half the way (3.5 V RMS? xD). If I set it to the maximum, I would need to set the volume knob at less tan 1/4 or so. I guess this is the result of the combination that I don't listen very loud (well, that's what I want to find out) and the amplifier has a lot of power.

I don't know how naive is this, but to have an idea of the spl I thought I could hear a some generated tone or tones, up to a reasonable volume, and then measure the output voltage with a simple multimeter.

In any case, I will try to refresh some of this electrical and sound concepts and come back to the issue. It's difficult to me to use the calculator without knowing what is doing. Thanks again!
Hi, you need to know the output voltage of your DAC and also what your headphone amplifier does to the signal from the DAC - ie is the headphone amp unity gain - unity gain is when max volume on the volume dial equals no change in voltage as received from the DAC - so in this case when the headphone amp is operating at unity gain all it will do is attenuate/lower the voltage when volume dial is set below max setting. So to keep it simple & accurate for the calculation of your peak RMS then you'd want to put your headphone amplifier in Unity Gain mode - that might be the Low Gain setting or it might be the Mid Gain Setting (you'd have to check your manuals), and then you'd run your amplifier with volume dial at max position to ensure that voltage is equal to max output of your DAC - so if you know your DAC has a max 2V output with Windows Volume at 100%, then you'd set up your headphone amplifier as I've just explained and then simply lower the Negative Preamp in something like EqualiserAPO whilst listening to some tracks you listen to a lot, and you'd adjust the preamp down until you were listening at a subjectively normal level that you'd normally listen at - you then see how big your negative preamp is and then using online calculators combined with the sensitivity of your headphone and max voltage output of your DAC you work out what your peak RMS would be - it's all explained more eloquently in my post I linked you earlier.

(I don't know what your audio chain looks like in terms of DAC/headphone amp, or whether you have an-all-in-one combined DAC/amp - depending what you have might make it harder to work out how to calculate & follow my instructions, you might not be able to find out all the fixed values you need to plug into the online calculators).

EDIT: realised just now you linked your manual for your tube amp headphone amp. It does indeed say max output of 7V. But I just spotted a section where it said "-an INPUT stage with TAPE OUT to bypass the volume control ", praps that feature is just passing through the voltage from your DAC without amplifying it - that could be one way of ensuring that only the max voltage of the DAC is being passed through without being affected - but you'd have to be careful, you don't want to blow your headphones......you gotta research your gear really. I couldn't see a classic push button Low Gain / High Gain switch on that headphone amp. You'll need to look into your gear more to work it out, but don't blow your headphones when trying to follow my instructions as you don't want to put 7V into your headphones, be careful. Also, you asked me what a DAC is, this is all probably a bit complicated for you if you don't know what a DAC is.....research that first (essentially it'll be what's connected ahead of your headphone amplifier) but still research it.
 
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xaviescacs

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Hi, you need to know the output voltage of your DAC and also what your headphone amplifier does to the signal from the DAC - ie is the headphone amp unity gain - unity gain is when max volume on the volume dial equals no change in voltage as received from the DAC - so in this case when the headphone amp is operating at unity gain all it will do is attenuate/lower the voltage when volume dial is set below max setting. So to keep it simple & accurate for the calculation of your peak RMS then you'd want to put your headphone amplifier in Unity Gain mode - that might be the Low Gain setting or it might be the Mid Gain Setting (you'd have to check your manuals), and then you'd run your amplifier with volume dial at max position to ensure that voltage is equal to max output of your DAC - so if you know your DAC has a max 2V output with Windows Volume at 100%, then you'd set up your headphone amplifier as I've just explained and then simply lower the Negative Preamp in something like EqualiserAPO whilst listening to some tracks you listen to a lot, and you'd adjust the preamp down until you were listening at a subjectively normal level that you'd normally listen at - you then see how big your negative preamp is and then using online calculators combined with the sensitivity of your headphone and max voltage output of your DAC you work out what your peak RMS would be - it's all explained more eloquently in my post I linked you earlier.

(I don't know what your audio chain looks like in terms of DAC/headphone amp, or whether you have an-all-in-one combined DAC/amp - depending what you have might make it harder to work out how to calculate & follow my instructions, you might not be able to find out all the fixed values you need to plug into the online calculators).

EDIT: realised just now you linked your manual for your tube amp headphone amp. It does indeed say max output of 7V. But I just spotted a section where it said "-an INPUT stage with TAPE OUT to bypass the volume control ", praps that feature is just passing through the voltage from your DAC without amplifying it - that could be one way of ensuring that only the max voltage of the DAC is being passed through without being affected - but you'd have to be careful, you don't want to blow your headphones......you gotta research your gear really. I couldn't see a classic push button Low Gain / High Gain switch on that headphone amp. You'll need to look into your gear more to work it out, but don't blow your headphones when trying to follow my instructions as you don't want to put 7V into your headphones, be careful. Also, you asked me what a DAC is, this is all probably a bit complicated for you if you don't know what a DAC is.....research that first (essentially it'll be what's connected ahead of your headphone amplifier) but still research it.

Hi @Robbo99999. Thanks for your reply and effort. The gain selector of this amplifier is continuous and therefore isn't easy to know where it has this 0db gain spot, so maybe I'lll use the bypass as you suggest. Or maybe I'll grab another amp I have in a box and use it for this job because it's a studio amp and has a clear indication to set it to 0db gain. What I really thank you is that warning with the output voltage, as I wasn't aware of the risks involved.

I'm not aware of having asked what a DAC is. :rolleyes: I'm not a native speaker so perhaps I made some inaccuracy, sorry for that. I hold a physics degree so I have some academic background to more or less understand what a DAC is, in fact, I remember building a very simple one in an electronics practice at college. That was some time ago thought and all this electronics and electrical notions are quite blurry in my head. Also, I try to be cautious because I have the feeling that everyone in this forum has a great deal of academic and practical background.

I feel you have spent too much time on me, now it's my turn to work on this thing. Thanks again.
 

Jimbob54

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Hi @Robbo99999. Also, I try to be cautious because I have the feeling that everyone in this forum has a great deal of academic and practical background.

Hang around a while longer and you'll realise its a classic 80/20 split. Social scientists pointing this out have been double blinded and been subjected to the most rigorous of testing procedures.
 

phoenixsong

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Yeah, I'm here precisely because I have close to zero academic knowledge in this field and am keen to learn, to relate what I hear with what can be proven through measurements and the knowledge of expert others. I can relate about the being cautious part though- tbh I still believe cables potentially can make a difference but hey, I think it is perfectly fine for learners like myself to harbour some differing opinions from my teachers and peers, as long as due respect is exercised and the core values of the site remain uncompromised. Ironically, it's because I do not have anything at stake in the audio industry (reputation, business etcetera) that this tightrope could be traversed without much acrimony imo :D
 

Eldus

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I wonder if the distortion is because of the high SPL causing the housing to rattle. It wouldn't surprise me if that was the case.
 

phoenixsong

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I wonder if the distortion is because of the high SPL causing the housing to rattle. It wouldn't surprise me if that was the case.
I've driven many headphones to rattling levels. If others can rattle without similarly high distortion in their measurements, I don't see why this one can't :)
 

phoenixsong

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Nah, if anything from experience closed-back headphones rattle more. This one sounds like a driver issue
 

NoSnakeOil2

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I always recommend using my EQs. That's like asking a cook if he likes his own food. :)
what I mind was whether your EQ for the 600 or 650 was the correct EQ to use for the 6xx. ah, language can be confusing.)))
 

Robbo99999

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Hi @Robbo99999. Thanks for your reply and effort. The gain selector of this amplifier is continuous and therefore isn't easy to know where it has this 0db gain spot, so maybe I'lll use the bypass as you suggest. Or maybe I'll grab another amp I have in a box and use it for this job because it's a studio amp and has a clear indication to set it to 0db gain. What I really thank you is that warning with the output voltage, as I wasn't aware of the risks involved.

I'm not aware of having asked what a DAC is. :rolleyes: I'm not a native speaker so perhaps I made some inaccuracy, sorry for that. I hold a physics degree so I have some academic background to more or less understand what a DAC is, in fact, I remember building a very simple one in an electronics practice at college. That was some time ago thought and all this electronics and electrical notions are quite blurry in my head. Also, I try to be cautious because I have the feeling that everyone in this forum has a great deal of academic and practical background.

I feel you have spent too much time on me, now it's my turn to work on this thing. Thanks again.
Me, I've just learned pretty much everything I know about audio from this website over the past year and a half, but I do have a scientific background (University) in areas of Microbiology/Chemistry/some Physics, and I've always been interested in any topics involving science of any level.....so I don't have any academic background in audio apart from some overlaps.

That's a good idea re hooking up an amp that you know you can set to Unity Gain, so I'd do that and then you should be able to work it out from my initial post I linked you. Good luck
 
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amirm

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what I mind was whether your EQ for the 600 or 650 was the correct EQ to use for the 6xx. ah, language can be confusing.)))
Oh, I have not tested the 6XX so don't for sure. Members can advise if these are similar or not.
 

solderdude

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HD650 vs HD6XX consider unit to unit variances as well. I think it is safe to say, based on these measurements they require the same EQ.
Light blue and grey = HD650

HD6XX vs HD650.png
 

Aperiodic

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Ah, the infamous speaker killer K700 series headphones from AKG. To this day, I still cannot understand why the original K701 got such rave reviews. Exhibit A above, and case in point shows why they shouldn't. I found the K700 series family to have always had a plasticky tonality to them and this is bonafide evidence of the aural anomaly. I would not be the least bit surprised if this spike in distortion is common among that product family.
Loved the widely copied self-adjusting headband and the comfort. Other than that they didn't float my boat either. HD650 was maybe a little more 'colored' but a lot more 'involving' (YMMV).
 

Robbo99999

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One practice I would like to see adopted here is the ability to overlay and compare FR from two (or more) different cans, like you could in Innerfidelity's heyday (before it was sold and ruined).
I would have done that, but K702 Anniversary is not on Oratory's Headphone Grapher, but he does have it included in his pdf's. Here's the headphone grapher where you can overlay different headphones:
https://headphonedatabase.com/oratory/headphones?ids=37,271
That's just the standard K702 graphed at the link above, not the Anniversary Edition.
 

Maiky76

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This is a review and detailed measurements of the Drop AKG K7XX Limited Edition Red, open back headphone. It is on kind loan from a member. I can't find the price on it. If someone knows, please post and I will udpate the review.

I must say, I like the look of this headphone. It is both serious and playful:

View attachment 139236

The giant cups are comfortable and the headphone itself is light for its size at 300 grams:

View attachment 139237

Inside cup dimensions are 66 by 23 mm (diameter x depth).

Note: The measurements you are about to see are made using a standardized Gras 45C. Headphone measurements by definition are approximate and variable so don't be surprised if other measurements even if performed with the same fixtures as mine, differ in end results. Protocols vary such as headband pressure and averaging (which I don't do). As you will see, I confirm the approximate accuracy of the measurements using Equalization and listening tests. Ultimately headphone measurements are less exact than speakers mostly in bass and above a few kilohertz so keep that in mind as you read these tests. If you think you have an exact idea of a headphone performance, you are likely wrong!

The large cups made an easy job of mounting them on my fixture and getting good measurements on first try.

Drop AKG K7XX ohm Measurements
Let's start with our usual frequency response measurements:

View attachment 139238

As we see the only area that more or less hits our target is 100 to 500 Hz and then again above 8 kHz. Everywhere else there is a shortfall. We can see the differential better for the purposes of equalization:

View attachment 139239

The big news is in distortion:

View attachment 139240

Ouch, ouch, OUCH! If you are going to have distortion, please don't have it where our hearing is most sensitive in the 2 to 5 kHz. Unfortunately that is the area of frequency response we need to boost as well. Let's pray "measurements don't tell the story" here or we are toast.

View attachment 139241

Group delay is fuzzy across the full spectrum which I had not seen before:

View attachment 139242

Impedance is pretty constant and on the low side:

View attachment 139243

Sensitivity is slightly worse than average:

View attachment 139244

Drop AKG K7XX Red Edition Listening Tests and Equalization
Instant impression was dull tonality so out came the EQ tools and quick:

View attachment 139245

Bass boost worked very well. As did the the other two boosts until I listened a bit more to my reference vocal tracks. At times, I started to clearly here a secondary distorted version of the female vocals. Turning off the filter in pink reduced most of it. I originally had it at 1.3 kHz and at higher amplitude. With that setting the headphone sounded great at times, and horrible because of distortion other times. I adjusted the levels of that filter down and shifted it to 1 kHz. Added that other notch. It reduced the magnitude of the distortion some but still very problematic. Once you heard it, you also couldn't "unhear" it.

Shame the distortion is so bad as spatial qualities were pretty good (B+).

Conclusions
The tonality of the AKG K7XX is wrong out of the box. This is the case for many headphones but what was rather unique here was severe distortion in the 1 to 2 kHz. This stops you from correcting the response in that all important region. Even without correction, the sound is not quite right as distortion is high even before you boost it. This is a clear defect in design which should have been caught and fixed. Maybe there was too much cost pressure from Drop and they reached for the cheapest drivers they had; I don't know. What I do know is that they screwed up a headphone that otherwise could have performed very well with equalization. And be comfortable to boot.

I can't recommend the Drop AKG K7XX with or without equalization.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Hi,

Here are some thoughts about the EQ.

Notes about the EQ design:
  • The average L/R is used to calculate the score.
  • The resolution is 12 points per octave interpolated from the raw data (provided by @amirm)
  • A Genetic Algorithm is used to optimize the EQ.
  • The EQ Score is designed to MAXIMIZE the Score WHILE fitting the Harman target curve with a fixed complexity.
    This will avoid weird results if one only optimizes for the Score.
    It will probably flatten the Error regression doing so, the tonal balance should be more neutral.
  • The EQs are starting point and may require tuning (certainly at LF).
  • The range above 10kHz is usually not EQed unless smooth enough to do so.
  • I am using PEQ (PK) as from my experience the definition is more consistent across different DSP/platform implementations than shelves.
  • With some HP/amp combo the boosts and preamp gain need to be carefully considered to avoid issues

Good L/R match.

I have generated one EQ, the APO config file is attached.

Default Harman Target Curve:
Score no EQ: 45.2
Score with EQ: 82.1

Code:
Drop AKG K7XX APO EQ [email protected] 96000Hz
July082021-112613

Preamp: -10.1 dB

Filter 1: ON PK Fc 36.06 Hz Gain 4.54 dB Q 0.68
Filter 2: ON PK Fc 240.98 Hz Gain -2.51 dB Q 0.92
Filter 3: ON PK Fc 1431.18 Hz Gain 6.17 dB Q 0.60
Filter 4: ON PK Fc 1986.81 Hz Gain -4.40 dB Q 1.71
Filter 5: ON PK Fc 3071.31 Hz Gain 8.07 dB Q 2.13
Filter 6: ON PK Fc 6705.42 Hz Gain -2.00 dB Q 1.77
Filter 7: ON PK Fc 11733.39 Hz Gain 5.88 dB Q 0.89
Filter 8: ON PK Fc 4718.36 Hz Gain 1.38 dB Q 7.59

Drop AKG K7XX Dashboard Flat@HF.png


Default Harman Target Curve [email protected]
Score no EQ: 56.7
Score Armirm: 81.5
Drop AKG K7XX Dashboard -1.5dB@HF.png
 

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Robbo99999

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Hi,

Here are some thoughts about the EQ.

Notes about the EQ design:
  • The average L/R is used to calculate the score.
  • The resolution is 12 points per octave interpolated from the raw data (provided by @amirm)
  • A Genetic Algorithm is used to optimize the EQ.
  • The EQ Score is designed to MAXIMIZE the Score WHILE fitting the Harman target curve with a fixed complexity.
    This will avoid weird results if one only optimizes for the Score.
    It will probably flatten the Error regression doing so, the tonal balance should be more neutral.
  • The EQs are starting point and may require tuning (certainly at LF).
  • The range above 10kHz is usually not EQed unless smooth enough to do so.
  • I am using PEQ (PK) as from my experience the definition is more consistent across different DSP/platform implementations than shelves.
  • With some HP/amp combo the boosts and preamp gain need to be carefully considered to avoid issues

Good L/R match.

I have generated one EQ, the APO config file is attached.

Default Harman Target Curve:
Score no EQ: 45.2
Score with EQ: 82.1

Code:
Drop AKG K7XX APO EQ [email protected] 96000Hz
July082021-112613

Preamp: -10.1 dB

Filter 1: ON PK Fc 36.06 Hz Gain 4.54 dB Q 0.68
Filter 2: ON PK Fc 240.98 Hz Gain -2.51 dB Q 0.92
Filter 3: ON PK Fc 1431.18 Hz Gain 6.17 dB Q 0.60
Filter 4: ON PK Fc 1986.81 Hz Gain -4.40 dB Q 1.71
Filter 5: ON PK Fc 3071.31 Hz Gain 8.07 dB Q 2.13
Filter 6: ON PK Fc 6705.42 Hz Gain -2.00 dB Q 1.77
Filter 7: ON PK Fc 11733.39 Hz Gain 5.88 dB Q 0.89
Filter 8: ON PK Fc 4718.36 Hz Gain 1.38 dB Q 7.59

View attachment 139759

Default Harman Target Curve [email protected]
Score no EQ: 56.7
Score Armirm: 81.5
View attachment 139758
Your Harman Curve EQ looks good Maiky (first set of graphs), I bet that would sound good. I like that you've not boosted the bass all the way to the Harman Curve below 30Hz as doing so probably wouldn't suit this headphone given my listening experience with my K702 which is similar design (although don't know if actual drivers are different). I also think choice of using peak filters on the bass allowing some natural roll-off rather than Low Shelf is a positive move on this particular headphone given my experience with my K702.

One thing to note, I'm not really a fan of your 2nd set of EQ's where you EQ to your modified Harman Curve - I believe you've modified the Harman Curve to reflect where Amir normally ends up on average with his EQ's. To be honest, given what his EQ ended up doing to this headphone as seen in your second set of graphs I'm not surprised he didn't like it - bass is a long way off the Harman Curve and his treble is also below the Harman Curve....to me I think that would sound boring. Note to the readers, in the second set of graphs even though Amir's treble follows the Target spot on, that happens not to be the Harman Curve, it's the modified Harman Curve I was talking about in the first sentence of this paragraph - therefore Amir's EQ result in the treble is actually below the real Harman Curve Target. All-in-all, I'm not surprised Amir found the K7XX uninspiring with that EQ he ended up at. I suppose his assessment in listening tests of detectable distortion remains, but to me that flies in the face of the measurements (94dB blue line in the distortion results in review), so I don't have enough faith to go against the measurements in this respect.
 

Foulchet

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I bought the K712 Pro one year and half ago.
When I first tried them, I found that they had a weird sound which was somewhat disappointing.
I tried to convince myself that my brain would become used to it but even switching to AirPods Pro made me feel relieved.

Last week, I decided to purchase the Sennheiser 560S. I tested it yesterday and I never thought the difference would be so huge : I rediscovered a clean and balanced, even pleasing sound.

I do not know what is wrong with this AKG, afterall the deviation is not that big, but the sound is just hollow (especially voices, is this the distortion ?). Plus the voices seem « devoured » by the rest of the spectrum, especially high mids. The soundstage also feels weird. Are FR and distortion enough to explain that ?
For the price and for « reference » headphones, maybe it is a bit exaggerated and of course subjective, but the 712 Pro is a disaster. I even prefer sometimes a dollar pair of IEM for some aspects of sonic enjoyment.
 

Grumpish

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I bought the K712 Pro one year and half ago.
When I first tried them, I found that they had a weird sound which was somewhat disappointing.

Glad it is not just me - I bought a pair about three years ago, having read lots of good things about them over on one of the headphone forums (the one that is infested with cable sniffers) but sold them on very quickly, I was totally underwhelmed by them. They got replaced by a pair of HD650's.
 
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