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HD6XX bass

bobbooo

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HE4XX is 2 dB/V more efficient so 80dB average is the max. loudness (93dB peak SPL)

The fun part is you could easily use the HE4XX directly from the AVR it could play 20dB louder. The HE4XX doesn't care about higher output resistances. It would be kind of 'current' driven.
Of course when the AVR is very noisy it could be a reason to use an attenuator.

Deafeningly loud would be around 100dB average.
Well either I have very sensitive hearing or that difference in sensitivity between the HE4XX and HD650 isn't correct, because at max volume with the Ear Buddy it's painfully loud. Where did you find measured specs for the HE4XX?

Oh and I only tested them with the Ear Buddy out of curiosity, as obviously they have flat impedance so output impedance doesn't really matter. I usually use them straight into the AVR. The Ear Buddy is for my closed-back Focal Spirit Classics (to reduce noise) and my IEMs (the latter having wild impedance swings so it's definitely required).
 
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solderdude

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Sensitivity for HE4XX can be found everwhere on the web.
93dB/mW with 35 Ohm impedance = 107.5dBV
The HD650 = 105dB/V

When the earbuddy is connected to a 500 Ohm output R amplifier that can provide 28V (200W/4 Ohm) it cannot possibly sound painfully loud unless the Rout is not 500 Ohm but much much smaller. There is something called physics.
The above situation (200W/4 Ohm) will result in 0.16V at the output = 90dB peak (in music) is well below 80dB average SPL.
This is something you can endure all day long and a long way away from 'painful'.
The math is clear about this.

The only explanation here is you are wrong about the output R being 500 Ohm. I suggest you measure it to confirm.
 

bobbooo

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Sensitivity for HE4XX can be found everwhere on the web.
93dB/mW with 35 Ohm impedance = 107.5dBV
The HD650 = 105dB/V

When the earbuddy is connected to a 500 Ohm output R amplifier that can provide 28V (200W/4 Ohm) it cannot possibly sound painfully loud unless the Rout is not 500 Ohm but much much smaller. There is something called physics.
The above situation (200W/4 Ohm) will result in 0.16V at the output = 90dB peak (in music) is well below 80dB average SPL.
This is something you can endure all day long and a long way away from 'painful'.
The math is clear about this.

The only explanation here is you are wrong about the output R being 500 Ohm. I suggest you measure it to confirm.
There's also something called patulous eustachian tubes, which I have, that could mean a volume that is painfully loud for me may not be for the average person. Denon provided the 500 ohm figure, which I confirmed with them after me initially saying this must be a mistake. Also, that's the quoted sensitivity for the HE4XX, not a measured value as I clearly asked. Tyll of Innerfidelity has often measured headphone sensitivity to be off spec.
 
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solderdude

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When you connect the HEXX to a phone is that painfully loud as well (this should be at least twice as loud as via the ifi)
When the ifi and AVR is louder than the phone than Denon provided incorrect info.

When you can't handle 80dB average and this is painful you probably can't walk normally outside near traffic. A car horn would be intolerable. I don't envy you when this is the case.
 

bobbooo

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When you connect the HEXX to a phone is that painfully loud as well (this should be at least twice as loud as via the ifi)
When the ifi and AVR is louder than the phone than Denon provided incorrect info.

When you can't handle 80dB average and this is painful you probably can't walk normally outside near traffic. A car horn would be intolerable. I don't envy you when this is the case.
The Apple dongle is louder. A car horn is around 110dB, so yes, if it's a long beep and I'm right next to it that could be a bit painful. To be clear, it's primarily with strong impactful bass though, when it seems like I can actually feel my eardrum flex from the pressure. (This may be related to the fact I can hear absolute phase - I pass this blind test every time.) Maybe 'uncomfortable sensation' would be a better term than 'pain', although if I listen at a loud volume for a period I do sometimes feel a dull ache in my ears for a short time afterwards.
 
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The 330 Ohm is the exact output resistance of the amplifier (+/- a few percent tolerance of the resistor + a few mOhm of the speaker amp output)
When I do my calculations based on impedance plots provided by Tyll, as well as my own measurements with 120 Ohm out the (mid)bass boost is 2.2dB. Upper treble will increase by approx. 1dB as well.
There is also a small capacitor shunting the headphone driver. At low frequency it's impedance is much too high to affect the output impedance. But at 20 kHz the effect of that little capacitor will be 360 Ohms in parallel with the headphone.

As for the mild peak produced at the headphone's impedance peak at 85 Hz, I had used the impedance plot that Ken Rockwell produced for the HD650. He shows less impedance rise at 85 Hz and slightly greater impedance at 10 Hz and elsewhere, compared to the InnerFidelity curve, which shows 520 Ohms for the impedance at 85 Hz. This difference in the measured impedance of the headphone explains why my result was different from yours.

If I use the InnerFidelity curve, the baseline at 10 Hz is 300 Ohm. The baseline voltage gain factor with 330 Ohms added in series will be .476 Vout. The voltage gain factor at 85 Hz with 330 Ohms in series will be .612 Vout. If these two voltage gain factors are expressed in dB, the baseline value is -3.2 dB, and the value at 85 Hz is -2.1 dB. If you double these two dB values (equivalent to squaring the voltage factors before converting to dB) and take the difference you get 2.2 dB, thus suggesting that the 330 Ohm resistor will produce a +2.2 dB gain at 85 Hz.
 
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Alas this is not an option.

The ear buddy is 18 Ohm load.
Combined with the 330 Ohm series resistor + its attenuation this will give way too much attenuation (-40dB).
At full power there would be 0.27V avalaible on the output of the ear buddy.
This is 3x less than a regular phone puts out.

The only viable way is using the link in post #112 if you want an output resistance lower than 30 Ohm (post #111)
If a custom solution is on the table, for the specific combination of headphone and amplifier, there is probably a better approach. The best custom solution, that does not require opening and modifying the amplifier, is probably to shunt each headphone driver with a series notch filter. A series notch filter will lower the impedance at the notch frequency, thereby flattening the impedance curve such that the voltage seen by the headphones will be essentially constant in spite of the 330 Ohm series resistor.

The total shunt impedance at 85 Hz would be the value that restores the effective parallel impedance (the shunt and the headphone together) to the nominal 300 Ohm value. That is, (R x 520)/(R + 520) = 300 => R = 710 Ohms. This is the series impedance at 85 Hz for the resistor, capacitor and inductor that make up the series notch filter. The obvious question is how to distribute this amount of impedance over the resistor, capacitor and inductor.

It is trivial to come up with three values that will yield the desired value of series resistance at 85 Hz. The number of choices that will do this is infinite. But of course the slopes will be different for the different values. This little math problem can be solved as the simultaneous solution to three equations in three unknowns. One of the equations says that the impedance of the notch filter at 85 Hz will be 710 Ohms. Another equation says that the impedance of the notch filter at 35 Hz will be 1.1 kOhm. The third equation says that the impedance of the notch filter at 200 Hz will be 1.1 kOhm. [Where did I get 1.1 kOhm? (R x 410)/(R + 410) = 300 => R = 1.1 kOhm.]

R + 1/(2 pi 85 C) + (2 pi 85 L) = 710
R + 1/(2 pi 35 C) + (2 pi 35 L) = 1.1E3
R + 1/(2 pi 200 C) + (2 pi 200 L) = 1.1E3

R + 1/(534 x C) + 534 x L = 710
R + 1/(220 x C) + 220 x L = 1.1E3
R + 1/(1.26E3 x C) + 1.26E3 x L = 1.1E3

One way to do this would be to subtract the 2nd equation from the 1st equation, and to similarly subtract the 3rd equation from the 1st equation. In both instances R will disappear, giving you two equations in C and L. By multiplying one of those two equations by a well-chosen constant and subtracting that result from the other one, you will end up with an equation that will give you the value of either C or L. You can then substitute that value into the other equation to obtain the other value. Then you can substitute the C and L values into any one of the three equations to obtain the value for R. Note that the DC resistance of the inductor will contribute a portion of the resistance, i.e., the actual resistor used should be less than the calculated amount.
 

solderdude

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There is also a small capacitor shunting the headphone driver. At low frequency it's impedance is much too high to affect the output impedance. But at 20 kHz the effect of that little capacitor will be 360 Ohms in parallel with the headphone.
Nope..
The capacitor = 2.2nF. At 20kHz the 'impedance' is 3620 Ohm.
The -3dB point with 330 Ohm is 220kHz so there is no consequential roll-off caused by the capacitance C133, C134 (<0.4dB not counting the cable capacitance of the HD650)
 
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Just for everyone’s information you all lost me about four pages ago.
There was a lot going on there for certain.

The gist of it is that owing to the rise in the impedance of the headphone driver at 85 Hz and nearby, the effect of the 330 Ohm series resistor will be that the headphone's share of Vout (the amplifier output voltage) will be greater at 85 Hz than elsewhere, to the tune of 2.2 dB (in power terms). This is enough to be audible but is small in comparison to the existing response variations of the headphone. The rise in headphone impedance at 85 Hz would not produce this effect were it not for the 330 Ohm resistor in series with the headphone jack (in each channel). The same kind of thing will happen if you put a power resistor in series with a speaker, if the resistor's value is in the ballpark of the speaker's impedance. It happens because the speaker driver's share of the output voltage depends on the ratio of the driver's impedance to the sum of both impedances, which ratio will be different at different frequency if the speaker driver's impedance is not constant.

It is a small concern that most people might not notice. The solution that I would prefer, if it were me, would be to use a series notch filter in parallel with the headphones (more or less a short across the headphone driver), one for each channel. The reason I like this approach is that it will flatten the effective impedance of the headphones, such that the headphone's share of the amplifier output voltage will be essentially constant throughout the frequency range.

When a notch filter is placed in parallel with the headphone driver, it is called a series notch filter because the three components that make up the filter are wired in series with one another. The resistor establishes a lower bound for the impedance of the filter at the notch frequency, at 85 Hz in this case. The capacitor is chosen to increase the impedance for frequencies below the notch frequency, and the inductor is chosen to increase the impedance for frequencies above the notch frequency. The impedance of the series notch filter is low only at the notch frequency, thereby lowering the effective impedance of the headphones at this frequency. At other frequencies the series notch filter has high impedance and the effective impedance of the headphones is little affected.

I didn't finish the solution, so I cannot rule out the possibility that there isn't going to be something problematic about the solution. I cannot rule out the possibility that there will not be any combination of component values that will simultaneously solve these three equations. Given that there are three unknowns, you need three independent equations that must be satisfied simultaneously, in order to obtain a unique solution. One of these equations is written such that the effective impedance of the headphone driver at 85 Hz will be 300 Ohms. It was trivial to calculate that the impedance of the notch filter itself would need to be 710 Ohms at 85 Hz, in order that the combined, parallel impedance of the notch filter and the headphone driver will be 300 Ohms. The other two equations were obtained similarly, using 35 Hz and 1.1 kOhm, such that at 35 Hz the parallel impedance of the notch filter and the headphones will be 300 Ohms, and similarly for 200 Hz, such that at 200 Hz the parallel impedance of the notch filter and the headphones will be 300 Ohms. These two frequencies, 35 Hz and 200 Hz, where chosen because these are the approximate frequencies where the increase in impedance is half what it is at 85 Hz. But I will say again that not having completed the solution, I am not very confident that it is possible to solve these three equations simultaneously. I have the sense that I'm overlooking something.
 
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Nope..
The capacitor = 2.2nF. At 20kHz the 'impedance' is 3620 Ohm.
The -3dB point with 330 Ohm is 220kHz so there is no consequential roll-off caused by the capacitance C133, C134 (<0.4dB not counting the cable capacitance of the HD650)
You are correct. Rather than using a regular calculator I used one of those purpose-specific calculators on a web site and I probably did not correctly set the range, or else it ignored my selection and just assumed microfarads, or something like that.

Why do you suppose that capacitor is there?
 
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Thread Starter #132
There was a lot going on there for certain.

The gist of it is that owing to the rise in the impedance of the headphone driver at 85 Hz and nearby, the effect of the 330 Ohm series resistor will be that the headphone's share of Vout (the amplifier output voltage) will be greater at 85 Hz than elsewhere, to the tune of 2.2 dB (in power terms). This is enough to be audible but is small in comparison to the existing response variations of the headphone. The rise in headphone impedance at 85 Hz would not produce this effect were it not for the 330 Ohm resistor in series with the headphone jack (in each channel). The same kind of thing will happen if you put a power resistor in series with a speaker, if the resistor's value is in the ballpark of the speaker's impedance. It happens because the speaker driver's share of the output voltage depends on the ratio of the driver's impedance to the sum of both impedances, which ratio will be different at different frequency if the speaker driver's impedance is not constant.

It is a small concern that most people might not notice. The solution that I would prefer, if it were me, would be to use a series notch filter in parallel with the headphones (more or less a short across the headphone driver), one for each channel. The reason I like this approach is that it will flatten the effective impedance of the headphones, such that the headphone's share of the amplifier output voltage will be essentially constant throughout the frequency range.

When a notch filter is placed in parallel with the headphone driver, it is called a series notch filter because the three components that make up the filter are wired in series with one another. The resistor establishes a lower bound for the impedance of the filter at the notch frequency, at 85 Hz in this case. The capacitor is chosen to increase the impedance for frequencies below the notch frequency, and the inductor is chosen to increase the impedance for frequencies above the notch frequency. The impedance of the series notch filter is low only at the notch frequency, thereby lowering the effective impedance of the headphones at this frequency. At other frequencies the series notch filter has high impedance and the effective impedance of the headphones is little affected.

I didn't finish the solution, so I cannot rule out the possibility that there isn't going to be something problematic about the solution. I cannot rule out the possibility that there will not be any combination of component values that will simultaneously solve these three equations. Given that there are three unknowns, you need three independent equations that must be satisfied simultaneously, in order to obtain a unique solution. One of these equations is written such that the effective impedance of the headphone driver at 85 Hz will be 300 Ohms. It was trivial to calculate that the impedance of the notch filter itself would need to be 710 Ohms at 85 Hz, in order that the combined, parallel impedance of the notch filter and the headphone driver will be 300 Ohms. The other two equations were obtained similarly, using 35 Hz and 1.1 kOhm, such that at 35 Hz the parallel impedance of the notch filter and the headphones will be 300 Ohms, and similarly for 200 Hz, such that at 200 Hz the parallel impedance of the notch filter and the headphones will be 300 Ohms. These two frequencies, 35 Hz and 200 Hz, where chosen because these are the approximate frequencies where the increase in impedance is half what it is at 85 Hz. But I will say again that not having completed the solution, I am not very confident that it is possible to solve these three equations simultaneously. I have the sense that I'm overlooking something.
Thanks, I really appreciate you taking the time to break that down for me. I’m guessing this is what you love doing, it shows!
 

bobbooo

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Just for everyone’s information you all lost me about four pages ago.
Honestly, if you've only just received your HD6XX's, my advice would be to return and exchange them for the HifiMAN HE4XX also sold at Massdrop/Drop (they do free no questions asked returns/exchanges). A complicated modification of your NAD frankly seems a bit ridiculous just to get it to work better with your headphones, when you could simply get the HE4XX that not only have a flat impedance and so won't be adversely affected by any source's output impedance, but also have more extended bass and better soundstage (which it seems you prioritise for gaming/movies), a higher sensitivity and less bass distortion so will get louder and be able to be EQed with more headroom, and will save you $60 over your HD6XX's. Seems like the obvious, simple solution to me.
 
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Thanks, I really appreciate you taking the time to break that down for me. I’m guessing this is what you love doing, it shows!
Well, it was an interesting exercise, but it turns out that it can't be done, as I suspected but didn't know for certain. Now I am certain. The required inductor value turns out to be very large, 910 mH, almost a full Henry. And the resistor turns out to be negative, -250 Ohms. The inductor needs to be this big so that the impedance of the notch filter will be high enough above the notch frequency, at 200 Hz, to keep the effective impedance of the headphone high such that its share of the amplifier voltage will be as high as it needs to be to avoid excessive attenuation at 200 Hz and at higher frequency. The impedance of the inductor at 200 Hz needs to be about 1140 Ohms. The reason the solution includes a negative resistance value is that the series impedance at 85 Hz of the capacitor (4 uF) and the inductor, without the resistor, is greater than the required 710 Ohms. (I didn't confirm it, but apparently it will be 960 Ohms).

This happens when the desired notch is too narrow and steep to be achieved without a more complex filter. It is somewhat likely that an ideal or near-ideal transfer function could be achieved by additionally using a parallel notch filter, in combination with a series notch filter that partially flattens the impedance of the headphone driver. The parallel notch filter is placed in series with the headphone driver and consists of a resistor, capacitor and inductor in parallel with one another. The resistor lowers the headphone driver's share of the amplifier output voltage, and is more effective at doing this than it would be without the partial impedance-flattening effect of the series notch filter. The capacitor bypasses the resistor for frequencies higher than the notch frequency and the inductor bypasses the resistor for frequencies lower than the notch frequency.
 
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Thread Starter #135
Honestly, if you've only just received your HD6XX's, my advice would be to return and exchange them for the HifiMAN HE4XX also sold at Massdrop/Drop (they do free no questions asked returns/exchanges). A complicated modification of your NAD frankly seems a bit ridiculous just to get it to work better with your headphones, when you could simply get the HE4XX that not only have a flat impedance and so won't be adversely affected by any source's output impedance, but also have more extended bass and better soundstage (which it seems you prioritise for gaming/movies), a higher sensitivity and less bass distortion so will get louder and be able to be EQed with more headroom, and will save you $60 over your HD6XX's. Seems like the obvious, simple solution to me.
Nah, think I’ll keep them, the bass extension wasn’t what I expected but overall the HD6XX’s are magnificent and I’d rather train my ears to appreciate them than swap them for something different. KaiserSoze raised some interesting points so I thought I would academically explore them being I have a very nice classic integrated already. I think I lean more toward well engineered colored sound as apposed to a perfect reproduction of a recording but I think it’s valuable to use something like the HD6xx to see if I really do appreciate one vs the other. Not sure where I’m going but I’m enjoying the rabbit hole for sure.

I really want to try some Parasound gear, I think I would really like it. That said I think I like coming here to learn what perfect reproduction should sound lie, a base line if you will but then find my preferred sound from there. It’s truly abound enjoying the sound, not analyzing it but the analysis is important.
 
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solderdude

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Why do you suppose that capacitor is there?
Probably HF filtering.
Anyway.. the position on the PCB can be used to mount resistors instead and lower the output R drastically.

Nah, think I’ll keep them, the bass extension wasn’t what I expected but overall the HD6XX’s are magnificent and I’d rather train my ears to appreciate them than swap them for something different.
Good decision. The HD650 has been a flagship for tens of years and still is a very capable headphone today where the HE4XX is entry level and colored. Better bass extension but also has a treble peak (which can be removed) and is a little bit less 'forward' sounding as the HD650.
 
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The Sundara actually sounds quite nice. I was on a loaner tour, but the unit arrived late for me when I was smack in one of the toughest terms in my program so I only had a few short listening sessions, but I was pretty impressed. I would also suggest that anybody who really wants to listen to a very well done headphone where the bass is very well integrated into an overall well balanced headphone should consider the Verum 1. My friend loaned me his for a few weeks and I was suitably impressed. I did prefer my Edition X V2, but the Verum got very close overall and I think I would give it the nod where bass was concerned. Not just quantity, but also the quality of the bass. And I have owned the HD800S/700/650/600 so I have that frame of reference and I would still strongly suggest somebody who likes the general strengths of the HD600, but still yearns for more and better extended bass consider the Verum.
 

solderdude

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Well, it was an interesting exercise, but it turns out that it can't be done, as I suspected but didn't know for certain. Now I am certain. The required inductor value turns out to be very large, 910 mH, almost a full Henry. And the resistor turns out to be negative, -250 Ohms. The inductor needs to be this big so that the impedance of the notch filter will be high enough above the notch frequency, at 200 Hz, to keep the effective impedance of the headphone high such that its share of the amplifier voltage will be as high as it needs to be to avoid excessive attenuation at 200 Hz and at higher frequency. The impedance of the inductor at 200 Hz needs to be about 1140 Ohms. The reason the solution includes a negative resistance value is that the series impedance at 85 Hz of the capacitor (4 uF) and the inductor, without the resistor, is greater than the required 710 Ohms. (I didn't confirm it, but apparently it will be 960 Ohms).
A practical, expensive, large footprint and prone to pick up hum, parallel to the HD6XX (series) notch filter, that would work with other output resistances as well, would be:
1.5H inductor: Mouser 553-C85X (choke used in tube amp designs)
3.3uF capacitor: Mouser 505-MKS23.3/63/5
1k1 resistor: Mouser 594-5063JD1K210FT

Replacing the 330 Ohm and 2.2nF by 2 different resistors would be cheaper and a much better solution that works with all headphones though ;)
 
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bobbooo

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Good decision. The HD650 has been a flagship for tens of years and still is a very capable headphone today where the HE4XX is entry level and colored. Better bass extension but also has a treble peak (which can be removed) and is a little bit less 'forward' sounding as the HD650.
They're both 'colored', just in different ways. In terms of overall spectral tilt though, the HE4XX is very neutral, whereas the HD6XX/HD650 has a warm/dark tilt, due to the overly boosted mid/upper bass and rolled-off treble. The HE4XX has better bass/sub-bass and treble extension, and no egregious treble peaks - maybe you're thinking of the HE400i, which is not the same headphone and has quite a different frequency response (I see the HE4XX isn't on your website, so maybe you haven't even heard it). The HD650 has slightly too forward mids / lower mids, whereas the HE4XX has a bit of an upper-mid dip. All in all, the HD650 is a warm, dark, mids-focused headphone, whereas the HE4XX is a better all-rounder with a more neutral overall tonality. The majority of people will judge the HE4XX to reproduce music in a less 'colored' way with higher overall sound quality in blind tests, as evidenced by its predicted preference rating of 88/100 to the the HD650's 78/100, from Dr. Sean Olive's headphone formula (which has the same high 0.86 correlation between predicted and actual preference as his speaker formula). Then there's distortion, which is lower in the bass on the HE4XX, where it matters if EQing the bass of both headphones up to the Harman target, in which case distortion could become audible on the HD650. Oratory also said frequency response unit variation of the HE4XX is very low, one of the best he's seen. There is nothing 'entry level' about it except the price; it's a common fallacy to equate price with sound quality of headphones (in part due to sighted cognitive pricing bias), for which it has been shown there is little to no correlation between the two.
 
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solderdude

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Yes, there is no 1 to 1 relation between price and sound quality.
I don't care about preference ratings and research by others to be honest. I do my own research on my own way with my own results by measuring and above all listening and EQ'ing headphones and simply have come to different conclusions than the one you adhere to.
Over 200 headphones anlyzed, owned, heard EQ'ed and 35 years of experience in electronics (audio) can make one it so one develops his own opinion instead of quoting other other peoples research they found on the web.
 
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