HD250 Linear II

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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.

sound descriptions mine

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Sennheiser HD250 Linear II

HD250 Linear II

The Sennheiser HD250 Linear II is a closed over-ear dynamic headphone. It is a quite old headphone (from around 2001) already but when you can find one second hand for not too much you will own a closed ‘fun’ headphone that sounds surprisingly ‘open’ with DEEP bass and feisty treble. Isolation is quite good.
The headphone is comfortable and lightweight with a low clamping force. The pleather pads may become somewhat ‘sweaty’ on longer listening sessions.
The cable can be changed. The cable is quite long and somewhat microphonic.

specifications:

Type: Over ear, closed
Usage: Home
Driver type: dynamic
Pads: replaceable pleather
Foldable: No
Headphone cup connector: 2 pin Sennheiser connector
Cable entry: dual sided
Cable: 3m 3.5mm TRS to 2x Sennheiser plug
Driver size: 38mm
Max power rating: 0.2W
Max. S.P.L.: 120dB
Impedance: 300 Ω
Efficiency: 96dB/1mW
Weight: 215g. cable ads 60 gr.
Clamping force: low
Accessories: 6.3mm TRS adapter

Sound description:

Big bass… Not necessarily the type of bass that bassheads are looking for though. It goes deep but is not ‘detailed’ as far as bass can be that. The bass is somewhat dis-attached from the mids. I prefer that over bloated bass myself. The mids are realistic and clear. Even though the bass and treble are considerably boosted the mids don’t sound recessed at all.
Open, forward with good clarity/presence.
Then there is the treble. When you are coming from Grado or Beyerdynamic headphones the you may not find the treble objectionable. When you are used to more neutral headphones the treble can be harsh and grating with a lot of recordings. It does give the impression of being extremely detailed because of it. But … it’s just boosted upper treble.
Not really suited for portable usage unless you have an amplifier or only want to play music softly.

Measurements:

Below the frequency response of the HD250-II (Left, Right)

FR HD250-II

This tells the story indeed and shows perfectly what is heard. Big bass (+10dB). The small dip around 200Hz ‘disconnects’ the bass from the mids. Those mids are very realistic and as ‘neutral’ as can be. From 300Hz to 2kHz it is impressively flat. The treble area is about +10dB opposite the mids. This is quite a lot and very audible. At around 11kHz +15dB is reached !

 

output resistance / damping-factor

As this is a dynamic headphone the frequency response might be amplifier output resistance dependent when certain higher output resistance amplifiers are used.
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.
FR HD250-II R 120

The tonal balance changes just slightly when connected to a higher output resistance amplifier. You get about 0.5dB more bass. This will not be audible so it is no problem to drive this headphone from amplifiers with a higher output resistance.

Below the distortion plots of the HD250-II.
The distortion products are shown in dB. Below the left channel is shown.Dist HD250-II L

 

The distortion profile is quite typical for a dynamic driver. Higher 2nd harmonic distortion in the bass. Below the right channel.

Dist HD250-II R

When one looks closer the Right channel has a lot less distortion around 200Hz.
To show this a little more clearly below the same distortion plots but in percentages instead of dB distance. Left channel below.
Dist HD250-II L percent
Those levels are VERY high. 7% at around 200Hz is quite severe and is possibly the reason why the bass isn’t exactly ‘detailed’ and only ‘booming loudly’. Below the right channel.

Dist HD250-II R percent
Bass distortion is MUCH lower here and are normal levels. 2% 3rd harmonic for the lowest frequencies is not so bad.  1% for the 2nd harmonics is ‘normal. The mids  are quite good with levels between 0.1% and 0.2%. Clean mids …
It looks as though the left driver may have some issues. I would expect most HD250-II’s to perform close to the Right channel of this one.

Below the CSD of the HD250-II (Left and Right channel are superimposed)
CSD HD250-II

Some ringing is visible at 8kHz and 11kHz as well as 17kHz. Even at around 27kHz it rings.
I would not be concerned about that one though… The slight wiggle at 3kHz is not audible. Mids appear to be reasonably well damped.

Below the spectrum plot of the HD250-II (Left channel)spect HD250-II L

Some small lingering around 2kHz and 3kHz but these are not sound threatening. Otherwise this looks pretty decent. Bass does linger on a bit longer than desirable and may also be responsible for the somewhat ‘fatty’ bass.

Below a step response plot of the HD250-II (Right channel)
step HD250-II R

The step response clearly shows the ringing. This ringing is poorly damped and simply is too high in amplitude and rings on way too long. The bassy character is shown by the somewhat lower initial rise of the signal and the +5dB hump afterwards. Below the left channel.
step HD250-II L

The left channel seems slightly better damped.

Below the square-wave and impulse response plots. On the left the Left channel, on the right the Right channel.
SQR
The difference in the bass (40Hz square-wave) is quite visible here. The left and right plot don’t look quite the same.
The 400Hz square-wave shows the considerable ringing. This is also visible in the impulse response plots. There is overshoot and the impulse has lost it’s shape and has turned into lots of ringing instead.

I encountered a second HD250-lin II. This one seems older and needed some T.L.C. to say the least. The one above has gray plastic rings around the pads, this one has aluminium rings. This is how it looks like after a revision. Haven’t found a headband yet.
HD250 lin II

The original pads are pleather. This is a thin layer of vinyl on some cloth. The vinyl tends to flake off after many years. The more it is used the quicker it decays.
Below a picture of the original pads it came with.
HD250 padsAs the original pads are no longer available I looked around in my pad collection.
You can still find Chinese made replacement pads on e-bay but have no idea how they change the sound. Also you can still buy original Sennheiser pads for the HD520/HD530 which are slightly bigger but can be fitted.
You can re-use the plastic rings that hold the pads to fit other pads on.
The pads I had lying around were from a HD681-EVO and these were closest in tonal balance to the original pads.
Also I wanted to address the rather substantial amount of piercing treble.
I ended up with a sandwich of 2 plies of toilet-paper covered with 3mm thick woolfelt (not synthetic felt !) which replaces the foam discs that are normally there.
These foam discs also decay and turn into a sticky black stuff and this one came without these discs anyway.

Measurements of the modified version:

Below the frequency response of the HD250-II (modified and with Superlux pads)
(Left, Right)HD250 modified
Below the differences between an original HD250-II and the modified one with Superlux pads.HD250-II stock vs modified
The same ig bass (+7dB). The  dip around 250Hz ‘disconnects’ the bass from the mids. Those mids are very realistic and ‘clear’. The treble around 7kHz is about +7dB opposite the mids. This is audible. The narrow dip at 6kHz and the narrow peak at 7.5kHz are part of the biggest problem area of this driver. The bands are very narrow so less audible as they look. The treble above 9kHz is of higher quality and exactly on the right level. In the not modified version the amount of treble is about 10dB higher !

 

The tonal balance changes just slightly when connected to a higher output resistance amplifier. You get about 0.5dB more bass. This will not be audible so it is no problem to drive this headphone from amplifiers with a higher output resistance.

Below the distortion plots of the modified HD250-II.
The distortion products are shown in dB. Below the left channel is shown.
Dist L

The distortion profile is quite typical for a dynamic driver. Higher 2nd harmonic distortion in the bass. Below the right channel of the original HD250.
Dist HD250-II R

 

Below the distortion plot (left channel) of the modified HD-250 but in a percentage scale instead of dB distance.
Dist L percent
For comparison the distortion plot of the original HD250 also in percentage.

Dist HD250-II R percent

The distortion levels of the modified version is somewhat better above 10kHz. Most likely because of the damping materials in front of the driver (toilet-paper + felt).

Below the CSD of the HD250-II (Left and Right channel are superimposed)

CSD HD250-II modif

Some short-lived ringing is visible at 7.5kHz. I am not very concerned about that one though, the amplitude might be worse than the ringing. Mids appear to be reasonably well damped.

Below the spectrum plot of the modified HD250-II (Left channel)
spectr L

This looks pretty decent. Bass does linger on a bit longer than desirable but is slightly better damped than in the original one. Perhaps the felt in front of the driver and or pads make the difference.

Below a step response plot of the modified HD250-II (Right channel)
Step HD250 mod R
As a comparison the original HD250 below (also right channel)
step HD250-II R

The step response clearly shows the ringing at 7.5kHz. This ringing is slightly better damped than in the original version. The original version also shows more (higher in amplitude and frequency) ringing. The bassy character is shown by the somewhat lower initial rise of the signal and the +5dB hump afterwards.

summary

This headphone is great for those that like impressive (thunderous) bass and like heavily over-accentuated cymbals and isn’t afraid of feisty treble. The mids and overall sound is excellent. So is the comfort. When you can find one of these 2nd hand and don’t have to pay absurd prices. Between € 50.- and €125.- is probably a fair price depending on the condition of the pads.
Fortunately the feisty treble can be reduced to a higher quality treble by replacing the foam discs in front of the driver with 2 plies of toilet-paper and 3mm thick wool-felt discs of the same diameter as the foam discs. Removing the pads is not even needed.
The headphone is quite comfortable as it is lightweight.
Quite suited for home usage and when driven from an amplifier that can supply a reasonable voltage.

post separation

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