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published: Jul-7-2017

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NO SMOOTHING is applied to the shown plots. Most measurement sites have some smoothing applied which ‘irons flat’ sharp peaks and ‘wiggles’. I do not use smoothing because some info about sound quality is lost when plots are smoothed.

Aside from a small correction of the microphone itself also some correction in the lowest frequencies is applied to the plots to compensate for the perceived loss of bass when using headphones. This is described HERE in more detail.
A ‘horizontal‘ frequency response curve on the shown frequency response plots on this website thus indicates a perceived ‘flat’ tonal signature.

ALL measurements are made with a good SEAL on a flatbed measurement rig.
The shape of your head, bone structure, pad size, pad ‘softness,  (compliance), hair or no hair and or wearing glasses may (drastically) change the frequency response of some headphones, so… your personal experience may differ substantially from these plots.

Frequency response (tonal balance) is the most sound-determining aspect of headphones. A horizontal line shows audible neutral response in the plots on this website. Deviations in different severities at different frequency bands have an effect on the sound character.
The bigger the deviation the stronger the effect.

Below an aid to help determining the sound character of headphones with relation to the frequency response.


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Denon AH-D600

The Denon AH-D600 is a closed dynamic headphone.  It feels bigger in your hand than it appears to be on the picture. The up – down and left – right swivel of the cups is quite limited. Because of this not every head size may have optimal wearing comfort or fit.
The price point was on the high side with its €400.- price tag (around 2012, no longer available).  The earpads look like leather but are fake leather pads. They start to flake after some time as evidenced by this used pair I measured. The pads are quite soft to the touch and compress and give a good seal. This is essential for deep bass.
It comes with a long and shorter cable with 2x 3.5mm TS (mono) plug with color-coded rings for the left and right cup.
The cable is covered with cloth and quite microphonic. You can hear the cable rub against clothes etc. The headband is soft but has a small contact surface area which takes away some of the comfort.


Type: Over ear, closed
Usage: Portable, commuting, office and home.
Driver type: dynamic with bio-cellulose diaphragm (Foster brand)
Pads: pleather
Foldable: No
Headphone connector: 3.5mm TS (mono)
Cable entry: dual
Cable: 3m 3.5mm TRS (+ 6.3mm adapter) to 2x 3.5mm TS and 0.9m 3.5mm TRS  to 2x 3.5mm TS with inline mic/remote.
Driver size: 50mm
Max power rating: 1.8W
Max. S.P.L. > 135dB
Impedance: 25 Ω
Efficiency: 108dB / 1mW
Weight: 365 g.
Clamping force: medium low.
Accessories: Soft carrying pouch with Carabiner hook, 6.3mm adapter

Sound description:

The sound signature seems designed for use with portable devices given the considerable, yet tastefully, boosted lows on most music. The overall sound signature is on the bassy and warm side with a splashy and exaggerated treble. Cymbals are over accentuated.
Bass is boosted and it is just slightly ‘dis-attached’ from the mids.
When you prefer to listen at low volumes only the U-shaped sound signature may well work. At higher listening levels the bass is overblown (yet not in a nasty bloated way) but the treble becomes too much after some time.


Below the frequency response of the AH-D600 (Left, Right)

FR AH-D600

The first thing that stands out the is left-right difference below 300Hz. It is a good 3-4 dB but isn’t very audible. This is because for  these low frequencies the brain doesn’t do its localization thing yet.
The bass boost is similar-ish in shape to Olive-Welti but overdone by a few dB. When one considers O-W bass ‘boost’ is already a bit more than ‘neutral’ you can easily conclude the bass is raised. The small dip at 300Hz makes the bass slightly dis-attached but also ensures the bass doesn’t sound ‘bloated’ or ‘fat’ !
The frequency response for the mids (300Hz to 4kHz) is pleasantly ‘neutral’ as in ‘realistic’. Instruments have a pleasant real-ness to it. The peaky and elevated treble (+10dB !) is not ‘harsh’ sounding but can certainly be piercing at higher levels and with some pop/rock music. The boosted bass won’t mask this.

output resistance / damping-factor

As this is a low impedance (25Ω) dynamic headphone the frequency response of some of this type of headphones, changes when used with a higher output resistance (desktop) amplifier.
To test this the headphone is measured via a low impedance amplifier (0.2Ω) and a high impedance amplifier (120Ω). On a higher output resistance amplifier the output level will be considerably lower. To compensate for this the amplifier is cranked up to the same level (at 1kHz) as the low impedance amplifier. This way the plots are overlay-ed and it is easy to see how the tonal balance changes.

Right channel only, driven from 0.2Ω and 120Ω amplifier.FR AH-D600 R 120
As can be seen the difference is negligible over the entire frequency range. So the sound signature won’t change at all when a higher output resistance source is used.
It also means that the used drivers are mechanically damped and do not rely on electrical ‘damping’.

Below the distortion plots of the AH-D600: (only Right channel shown)
The distortion products are shown in dB.

Dist AH-D600 R

As can be seen in the plots the high amount of distortion in the bass is typical for dynamic drivers. Fortunately high amounts of 2nd harmonic distortion aren’t perceived as such but rather as a ‘warming’ of the bass. The 3rd harmonic ‘component’ is more perceived as a ‘clipping’/’limited’ sound and less benign. Below the same plot but in percentage.

Dist AH-D600 R percent

It shows the bass distortion is quite high. Above 300Hz the distortion should be low as distortion starts to sound as actual distortion from there. The AH-D600 is (and sounds) quite ‘clean’ in the mids. The distortion is down to low levels and 3e and higher harmonics are very low.

Below the CSD of the AH-D600 (Left and Right channel are superimposed)

The ringing for the mids is a bit higher than some of the other headphones. The treble area (>5kHz) consists of several short lived resonances. This isn’t that problematic.
When driven from a higher output resistance amplifier nothing changes that much.

CSD AH-D600 R 120

Above the CSD of the AH-D600 (right channel) via a 0.2Ω output resistance amplifier and also when connected to a 120Ω amplifier. It looks like around 2kHz the driver performs slightly better from a low output resistance source. The difference is extremely small and don’t expect this to be audible. Electrical damping does help a tiny bit here.

Below the spectrum plot of the AH-D600.

spect AH-D600 R

This plot shows bass is a bit resonating and the 2kHz problem area is seen. At 3kHz and 6kHz there are also some short lived small resonances. They are reasonably well damped though so not that problematic.

Step response plot of the AH-D600. (Left channel)
step sine L
On the left you can see that there is some overshoot and (short lived) ringing at a few frequencies. There is a bass boost visible but not as much as the frequency response shows.

This is a quite decent step response.  Below the Right channel.
Step AH-D600 R
The differences between L and R driver are quite visible in this plot. Less amplitude but longer lived ringing and the bass boost is at a lower frequency and a lot more.

The square-wave and impulse response plots below tell the same story.
On the left the Left channel, on the right the Right channel.


The overshoot in the bass on the left channel (upper 40Hz plot) is a lot more pronounced than the right driver. Even though that driver too has elevated bass response.
The left driver seems to be better damped for higher frequencies than the right driver which basically can’t seem to stop ringing. This too is indicative of splashy treble.
On the 100μs pulse it is obvious that the right driver rings on longer than the left one.
Driver matching or quality control seems to be lacking here.
The Fostex TH-X00 headphone I measured has better L-R matching and damping.


summary (stock version)

The Denon AH-D600 is aimed at the portable market. Boosted bass helps here. Boosted treble may not be an issue when listening to Youtube quality recordings.
The bass is quite boosted, for pop music it has a somewhat healthy boost. For better recordings, however, the bass level is way too much and after an hour or so became nauseating for me. Too much and too fat and somewhat disconnected lows.
Treble level is too high to be called neutral and will cause listening fatigue after some time.
The mids sound good though, the slightly dis-attached bass makes the listening experience pleasant… that is if you can stand the elevated treble.

Fortunately this headphone is relatively easy to modify.

  1. The pads need to be removed. This is easy … just pull them off.
  2. Remove the 4 screws. The ones with the red arrows are easy to find.
    The ones near the green arrows are hidden under 2 round stickers.
    These are easy to remove and can be put back again later on.DSCN0161
  3. The complete baffle incl. connector comes out. No need to worry about wiring.
    In the version I had here there was some slight difference in the way the wire
    coming from the driver was ‘fixed’ between L and R driver (red oval).
    I am pretty sure this explains the imbalance I found as I could not get L & R
    matching correct. I had to make both ‘wire fixings’ similar.DSCN0165
  4. The modification is simple. Just tape the hole in the cup shut (magenta arrow).
    You can do this with tape. I recommend to use something more ‘permanent’ than
    for instance cello-tape as that tends to dry up over the years and come loose.
    Below the cup with tape over the hole (green oval). As the air pressure in the cups can’t easily escape from the cup any more because there is foam on the baffle sealing the cups the small cable run through in the cup becomes a ‘port’.
    When this cable feed-through (brown arrow) is ‘sealed’ with the foam cable retaining strip the bass completely disappears. The cable feed-through thus must NOT become sealed with that small piece of foam. The cable must be held in place in the way shown in the red circle 2 pictures above.
  5. Put the baffle back on the cup. Make sure the baffle sits perfectly on the cup and tighten the screws lightly. Don’t put a lot of torgue on those screws as you will rip out the thread in those screw posts.
  6. To tame the treble 1 sheet of 2-ply toilet paper (or 2 pulled-apart plies from 3-ply or 4 ply luxury toilet paper) must be cut to fit the inside of the baffle and placed on top of the driver as shown below.
    Put the pads back on and it’s ready.

What do we get in return of this modification ?
Well… see the frequency response below (Left, Right)

FR modified AH-D600

A ‘flat’ response all the way from <10Hz to 20kHz. There is still a slight ‘bump’ of 4dB in the bass area which gives it a nice ‘full bodied’ sound with an excellent sounding bass.
No dis-attached bass any more and no overblown bass.
Really nice mids. realistic, leaning to a slight laid-back signature.
The treble is not piercing any more but still is slightly ‘off’ in that it is not ‘highly detailed’ with the nicest finest details. But have found this to be the case with most bio-dynamic drivers anyway. Still … a LOT better than it was before.

Below the difference between the stock version and the modified version. (left channel)
Stock vs modified

I wanted to see how low the bass extension goes as it is still ‘flat’ at 10Hz so made a plot ranging from 2Hz to 30kHz. (Left channel only).
2Hz to 30kHz FR
One should realize that the drop-off below 10Hz is also partly because of the amplifier, microphone and ADC as well as I only calibrated from 10Hz upwards.
6Hz is still on the same level as 500Hz. 5Hz is about -3dB.

Below the distortion plots of the left channel.
Dist L modified percent
The plot above is in percentage and from the modified version.

Below the CSD of the modified version (Left and Right superimposed)

CSD modified D600

This shows a quite well-damped driver and shows no worrying ringing or lingering.

Below the step response plot (in dB scale) from the right channel.
Step modified R

A vast improvement over the stock response. The left channel measured closely the same so is not shown. Excellent response.

Below the square-wave and impulse response plots of the stock AH-D600 on the left side and the modified version on the right side.
Note that the amplitude scale of the stock the 40Hz and 100us impulse plots have a different scale.


The changes in the 400Hz are obvious. The stock version has way too much bass and the measured response is much bigger than the actual stimulus signal.
The modified version still has slightly more bass response than neutral but is much improved.
The 440Hz square-wave shows much less ringing (because of the toilet paper) and looks much closer to the applied signal.
The ringing in the impulse response plot is also much improved. The initial rise is not overshooting  any more and is much better damped.
Note that you need to look at the differences in each plot as the scale on the stock version is different.

summary (modified version)

The bass is very slightly boosted. Not enough for bassheads though. Still slightly higher than ‘audibly neutral’ which in itself is already bassier than ‘measured neutral’.
The integration of bass into the mids is excellent. It has a warm and full bodied tone with clear mids.
The treble part is much improved and no longer piercing. This headphone doesn’t have the same excellent qualities as the bass and mids. It is nice and on the proper level but the finest nuances are lacking slightly. This can be experienced with a lot of headphones using the Foster bio-dynamic drivers. The treble does sound nice and detailed and has no obvious peaks or dips. It just isn’t able to produce the finest details as nicely as the bass and mids.
The only downside it still has is the cable. Too long, too thick, too stiff, cloth covered and very microphonic. Fortunately this cable can easily be replaced by an after market cable.

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