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published: Jul-02-2013, edited Feb-19-2023

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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.
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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Sennheiser HD25-1


This is a professional headphone that is used very often by sound engineers and sometime by DJ’s . It has good isolation due to it’s clamping force but after one or more ears your ears might start to hurt because of the high pressure on the ears. It is a plastic headphone and looks a bit flimsy but in reality is VERY sturdy and can take some beating. Only the headphone cord is a bit questionable. Just like the HD215 one earpiece can be rotated so it can still be firmly on the head with one ear ‘free’. I know it is held in high regard by some circles in the hi-fi circles but honestly don’t get this at all. The comment I often hear it is good for Rock is true though but don’t see it as valuable for other genres. It sounds a bit ‘dirty’ and very ‘forward’ which is good for rock and vocals. It is very suited for monitoring though due to it’s excellent isolation and speech is very ‘real’ so great for interviews e.t.c. The cable is bit mircophonic.


Type: On-ear, closed
Usage: Portable, studio
Isolation: high
Driver type: dynamic
Pads: replaceable, pleather
Outer pad dimensions: ∅ 73mm
Collapsible: no
Headphone connector: fixed, left side.
Cable: 1.5m straight with gold plated 3.5mm TRS plug + 6.3 mm screw-on adapter
Driver size: ø 38mm
Max. power rating: 0.2W
Max. voltage: 4V
Max. current: 50mA
Max. S.P.L.: 128dB
Impedance: 80Ω (measured)
Sensitivity: 116dB @ 1V @ 1kHz
Efficiency: 105dB @ 1mW @ 1kHz
Weight: 140g. (without cable)
Color: black
Clamping force: medium (2.5N)
Accessories: 6.3mm adapter. 1.5m  cable (+3m for plus version)

Sound description:

The overall sound is dominated by realistic mids and ‘present’ bass. If the area around 150 Hz is EQ’ed down by a good 5dB it sounds a bit better though. Bass is tight and goes quite deep. Above 4 kHz the highs get a bit ‘gritty’ and the peak around 9kHz isn’t helping here at all. The sharp drop-off above 13kHz is responsible for the lack of ‘air’ and details aren’t really there.


Below the frequency response of the HD25-1 (Left, Right)FR HD25
The channel matching is decent except around 250Hz. Bass is elevated a bit.
Mids are neutral and have good clarity.
The treble has a hint of sharpness with some recordings.

Phase response

Below the phase response of the HD25-1 (Left, Right)phase HD25
Slow phase shifts are not very audible. Sharp changes in a narrow frequency bands may well be audible. Around 6kHz and above 9kHz there are some steep phase shifts.

HD25-1 compared to the similar looking but much cheaper HD562
red = HD25-1, green = HD562

Below the distortion measurements of the HD25-1 (Right channel)Dist HD25 The plot above shows the level differences between the signal (upper trace) and the 2nd harmonic only.

Below the CSD (waterfall) plot of the HD25-1. (Left and Right are overlaid)CSD HD25

CSD shows good behaviour up to 2.5kHz above that part resonances (short lived ringing) starts to appear at 4kHz, 5kHz and between 7khz and 10kHz. This together with the drop off and peaky behaviour is responsible for the somewhat ‘coarse’ highs.

Below the Group Delay plot for the HD25-1 (Left, Right)
GD HD25There is is quite some ‘pad bounce’ from 80Hz to 200Hz. This is caused by the pads storing and releasing energy in that frequency range. This does not help the already emphasized bass response.

A different plot is the spectrum plot. This basically is a CSD (Waterfall) plot but viewed from above where the level differences are color coded instead of being in the vertical axis. Also the frequency range of the spectrum plot is wider (from 100Hz instead of 500Hz). The time span is also bigger in the spectrum plots and expired time is shown from below to top where in the CSD the time is shown from rear to front.

Below the spectrum plot of the HD25-1 (Left channel).spectr HD25A resonance at 3kHz is clearly visible. Also just above 4kHz and 6kHz there are small resonances visible.

Step response

Below the step response plot which, when the sound is balanced and well extended should show a fast rise to around 0dB, (indicating fast driver response) and then should be slightly sloping downwards indicating bass extension. (Left, Right)step HD25Bass extension is decent (with a good seal). The horizontal trace rises the first 1ms and then just slowly sags. This shows the elevated lows and ‘warmth’
The initial rise is reaching -3dB. The small peak (+2dB) around 200μs shows the sharpness that can occur.


The HD25-1 is highly recommended for monitoring and when you need good isolation or when you want the headphone to remain on your head while jogging perhaps. Wouldn’t use it to enjoy some classical music. A bit overblown but ‘good and tight’ sounding bass. A bit too little for bass-heads though. It’s only real downsides are the quality of the highs (not smooth/velvety) and the clamping force.

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