HE-35X (Drop)

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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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The HIFIMAN HE-35X is a dynamic over-ear headphone intended to be driven directly from portable equipment. Drop sells this for around $90.- but the second drop may be a little bit more expensive.
Because it has a low impedance (19Ω) this headphone is designed to be driven directly from portable equipment. It isn’t really suited for commuting etc. as the headphone is open and lets in ambient sound only slightly attenuated.
The ‘portable’ part here is for people who want to enjoy music when at home or in a hotel or such directly from a phone. The headphone doesn’t fold flat so it will take up quite some space in the luggage.

The earpads are much improved over the previous version (HE350) and are ‘hybrids’ with pleather outside, velours against the skin and a fenestrated pleather inside. Very comfortable. These pads also are slightly angled.
The yokes are sturdier than those of the HE350.
Also the headphone plugs have changed. Where the HE350 had 2.5mm TS jack plugs the HE35X has 3.5mm TRS jack plugs which are a bit sturdier as well.

The headphone is not super lightweight but still feels quite light on the head. This is a very comfortable headphone due to the wide headband and comfortable pads.

The cable is clearly intended for portable usage being just 1.35m long and has a 3.5mm angled TRS jack. The cable itself is supple. I see no reason to replace it unless you want a longer cable or straight plug. It is a bit microphonic so you can hear (mechanically conducted) sounds when touching the cable.

Everyone around you can hear what you are playing and you can hear all ambient noises unattenuated. It is an open headphone.


Type: Over ear, open
Usage: Home
Driver type: dynamic
Pads: replaceable, slanted hybrid pleather/polyester cloth
Internal pad dimensions: diameter 55mm  depth: 20mm front, 25mm back
Collapsible: No.
Headphone connector: 3.5mm TRS (marked L and R)
Cable entry: double sided
Cable: replaceable, 1.35m with gold plated angled 3.5 mm TRS plug
Driver size: 50mm Ø
Nom. power rating: (estimated 200mW)
Max. voltage: (estimated 2V)
Max. current: (estimated 100mA)
Max. S.P.L.: (estimated 116dB)
Impedance: 19Ω
Efficiency: 93dB/1mW (110dB/1V)
Weight: 303 gr. (without cable), 346 gr. with cable
Colour: black
Clamping force: low/medium
Accesories: 6.3mm converter

Sound description:

The overall sound is warm in the mids with a present bass. The mids lack a bit of clarity/presence but the treble is present at the correct level.
The HE350 was more ‘neutral’ and had a lot more clarity and ‘feisty’ treble up top but also was a bit ‘boring’ in the bass area and is rolled-off in sub-bass.
The HE35X is tuned more ‘modern’ and the tonal balance is much better for listening to popular music as bass is accentuated and ‘brightness’ in the recording is reduced. Audiophiles looking for a realistic sound do not need to bother but would also not be looking at this price point.
The sound is coloured and bass oriented with suppressed upper mids and then some treble up top of decent quality. It is somewhat lacking in ‘air’ and ‘brilliance’ but is not completely devoid of it. It does not sound rolled-off or subdued.
The overall sound will definitely be more ‘agree-able’ for most folks that like the looks. Lush mids and full, but not overblown bass, with enough treble up top.


Below the frequency response of the HE35X (Left, Right)FR HE35X
These plots were taken at around 95dB around 200Hz and appear to roll-off from 100Hz.
They don’t sound rolled off though but the reason for this becomes clearer further down this article. The downward slope from 300Hz to 2kHz is what makes this headphone sound ‘lush’ and lacking in clarity/presence in voices. From 2kHz upwards there is more output again making the instruments sound clearer than male voices.
The treble starts to drop off from 13kHz but still has some energy up to 20kHz.
Slightly subdued in ‘air’ and ‘brilliance’ of cymbals and violins etc.

Below the difference between the HE350 and HE35X.HE350 vs HE35X
The difference in the bass and lower mids is quite obvious. A bit more extension and more level around 200Hz. Both headphones have a slight dip in the upper mids.
The treble peak of the HE350 is clearly higher than that of the HE35X.

This is because the HE35X has a filter built-in that I designed for the HE350. Massdrop asked me if they could use this filter in the HE35X and am fine with that as it improves this headphone substantially in the treble.
Below the effect the (band) filter has on the driver, response of the HE35X (filter removed) and with filter (stock)filter action HE35X mk2
The effect is clearly seen. The filter action is reduced when this headphone is used from gear that has a higher output resistance. Everything below 10Ω output R is O.K.
Most portable equipment is. Only some desktop equipment and tube gear could have a higher output resistance. Below the filter mounted on the small green Printed Circuit Board.


As the seal of headphones is of importance some experiments below are showing the effect of a seal breach on the tonal balance.
(lots of) hair between the headphone and ear or an ear shape that does not allow a proper seal can/will affect the tonal balance.
Below: Perfect seal, a small seal breach by thin armed (reading) glasses just above the skin, thick armed glasses and a big seal breach.seal
The good news is that a seal breach doesn’t affect the tonal balance very much. So no problems when wearing glasses or when not having a proper seal.
The effect of a seal breach on the HE350 was bigger.

Below the distortion measurements of the HE-35X (left channel)dist

Below the distortion plot but displayed in percentages.dist percentThe distortion levels are quite high for the lower frequencies. The very high 3rd harmonic distortion points towards ‘compression’ of larger excursions (lower frequencies need/have larger excursions). Below 100Hz the 3rd harmonic distortion reaches an audible 8%. This drops to around 5% at 80dB SPL. This lowers the sound quality of the bass somewhat. Quite similar to the HE350. Jude’s measurements show a lower THD of 3% (@ 90dB) but even this can be considered high.
For the mids and treble the 2nd harmonic distortion is much lower but still on the high side of things around 2.5kHz. There is a technical reason for this.

Below the CSD of the HE35X. (Left and Right are superimposed)CSD HE35XThe driver is well damped and above 2kHz there really is little to complain about. No deal breaking resonances are seen.

Below the spectrum plot of the HE-35X. spectr HE35X
This too looks quite good. Lower frequencies are damped quite well. At 1.5khz there is some very short lived lingering at very low amplitudes and most likely not even audible.

The step response (Left, Right) below shows the sub-bass is slightly rolled-off. This is evident by the horizontal trace dropping quickly after 2ms. The resonances are fairly short lived (< 1ms) and not high in amplitude. The impulse response is 4dB lower than the mids and shows an emphasis in the lower-mids/ upper-bass. It thus sounds warm and bassy. step HE35X
The dip is the 7kHz ‘notch’ and is a bit deeper in the HE35X than in the HE350. That notch may well be responsible for the treble quality which is just decent.


The HE35X is an improved HE350 on several points. The price has not changed so this is still a cheap HIFIMAN headphone with a pleasant sound which is easily driven by portable equipment and directly from phones, tablets etc.
It has a warm and laid-back sound. Don’t expect this to be a cheap alternative to the orthodynamic offerings from HIFIMAN.
At this the pricepoint there some alternatives but may not be as comftortable nor have similar looks.

NOTE: The HE35X measured above is a prototype which has a small issue that may possibly be addressed by the manufacturer before the final (August 2019) drop. Drop is trying to get this modification implemented which improves technical performance of this particular model. They, however, never sent me the actual product to test so have no idea how the actual product ended up.

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