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published: Oct-29-2017, updated: Jan-06-2022

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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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Grado SR125i

The Grado SR125i is one of the many Grados in a line up. All of them are highly related to each other and appear to have similar drivers.
They have built quite a cult around them. These are a love it-or-hate it headphones though.
The biggest differences between the cheaper versions, SR60, SR80, SR125, SR225, SR325 seems to be in the pads and perhaps in better driver matching. The SR125 has been replaced by the SR125i (measured here) and later by the SR125e (different pads) and SR125x versions. Differences between the various suffixes seem small, certainly not as big as some reviewers would like you to believe.
The e-versions have a slightly higher efficiency.

These are low impedance headphones (32 Ω) and are suited to be driven directly from portable gear.
The 6.3mm plug on this SR125i won’t fit and you would need a 3.5 mm to 6.3 adapter cord. I wouldn’t use a 3.5mm to 6.3mm adapter because the weight of the cable and plug will ruin the 3.5mm socket.
The newer versions do have a 3.5mm plug and a 6.3mm adapter and have less thick and stiff cables.

That cable is very thick, heavy and stiff. Fortunately it isn’t very microphonic and dual entry. Comfort and modern looks aren’t great… I would even say poor compared to most other headphones. Clamping force is low.
These headphones can only swivel in one axis and may be a poor fit to some because of it.

The replaceable on-ear foam pads are not the most comfortable ones. Changing the pads for those on more expensive models or after-market pads can change comfort and sound.


Type: Over ear, open
Usage: Home, travel
Driver type: dynamic
Pads: sturdy foam
Foldable: No but the cups can swivel flat.
Headphone connector: non replaceable
Cable entry: dual
Cable: 1.8m with 6.3mm TRS plug
Driver size: 44mm (diaphragm diameter) housing = 50mm Ø
Max. power rating: unknown, assumed 200mW
Max. voltage: 2.5Vrms (7.5Vpp)
Max. current: 80mA
Max. S.P.L. 118dB (assuming 200mW)
Impedance: 32Ω
Efficiency: 95dB @ 1mW
Sensitivity: 110dB @ 1V
Weight: 150 g.
Clamping force: Medium/low

sound description

Bass is roll-off and sub-bass is completely lacking. Bass itself doesn’t appear to be really ‘lacking’ but it sounds ‘thin’ and without ‘body’.
These headphones do sound very ‘forward/open’ and appear to sound highly detailed and have good ‘clarity’.
The SR125i treble sounds a bit ‘coarse’ and ‘sharp’. Sibilant on some music and ‘piercing’. Together with the lack of ‘body’ and the flat upper-bass to mids it sounds anaemic and thin.  Not particularly bad sounding as it also has some decent qualities to it but it lacks in certain areas.


Frequency response is shown below (Left, Right)FR

The driver matching isn’t that great but it isn’t audible to me. Low bass is lacking. Bass does sound tight but a bit ‘thin’. Mids are very good. The peak around 2kHz makes the sound very ‘open’ and ‘dynamic’.
The treble is a bit elevated and can be sibilant and sharp.

compared to:

Below the SR125i compared to the much more expensive GS2000eGS2000 vs SR125i

output resistance / damping-factor

The Grado can also be connected to a high output R amplifier (120Ω in this case) but this will ‘cost’ about 11dB in SPL. You gain a little lift in the bass area by max 2dB, and the upper treble by +1dB. A slightly bassier sound is the result.
Below the plots of the SR125i when driven from a 0.2Ω amplifier and a 120Ω amplifier (right channel only).SR125 120 ohm

Below the phase response of the SR125i (Left, Right)phaseSlow phase shifts are not very audible. Sharp changes in a narrow frequency bands may well be audible.
Some sharp but not severe phase shifts at 2kHz and between 3kHz and 10kHz.

Below the distortion plot of the right channel.
distThe plot above shows the level differences between the signal (upper trace) and the harmonics.
Most people prefer to see percentages instead of level differences so below the exact same plot except ‘normalised’ to the actual signal and level differences given in percentages.
dist percent
Distortion below 200Hz is rather high. Also 3rd harmonic distortion below 150Hz is on the high side and indicates some light ‘compression’ above 90dB SPL. Also between 3kHz and 6kHz the distortion is higher than desirable and may be responsible for the treble not sounding a bit coarse.
The actual 2nd harmonic distortion may well be lower than 0.2% . A shortcoming of my measurement rig.

Below the CSD a.k.a. waterfall plot (Left and Right are overlaid)CSDBetween 1kHz and 6kHz the headphone resonates like crazy at various frequencies. Also the peak at 10kHz is clearly a resonance. The ear canal itself also shows resonance in the same frequency range so these resonances may not be as audible as they appear.

A different plot is the spectrum plot. This basically is a CSD (Waterfall) plot but viewed from above where the level differences are colour 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 SR125i (Left channel)spectr

Bass frequencies up to the mids decay fast. Above 2kHz the resonances are quite visible and linger on for quite some time.

Below the step response of the SR125i (Left, Right)
stepThe sharp signature is clearly visible. The initial rise is very steep (fast) and overshoots and rings the mids by 5dB. The continuous drop in level after 500μs shows the ‘thin’ character.


The Grado headphones are an acquired taste. You either love the light bass, forward mids and accentuated treble or you don’t.
The Grado SR125i is not much different than the rest of the Grado line-up.
It also does not differ much from the SR125 and SR125e that much.
Comfort is not the greatest, looks and build quality are utilitarian at best.
One can change the comfort and sound a bit by changing the pads for larger ones. These can be from Grado or after-market pads. It won’t turn these headphones into great performing and sounding headphones but they will sound different/better.

These headphones are quite sensitive and work well directly out of a phone. Driving these from higher output resistance sources increases bass a little.

Audition these headphones before buying !

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