Sundara (2021)
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published: Sept-01-2022, updated Feb-03-2023
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 severity 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.
HIFIMAN Sundara (2021)
The HIFIMAN Sundara is an orthodynamic over-ear headphone intended to be driven directly from desktop gear and the better portable DAPs as well. You can connect these directly to a phone and it will play nicely, but just not very loud. The sensitivity is about similar to that of the Sennheiser HD650.
It retails for around € 349.- which is not really cheap but competitive with other planar magnetic headphones. It has been around since end 2017 and was € 500,- when launched. Around 2020 the Sundara got different pads and the 2022 version even comes with a ‘headphone stand’ (the foam piece inside the box can double as a stand).
It is positioned between the HE400SE and Ananda, both in price and sound quality.
The headband works well and can be adjusted over a decent range in height and width.
The sideways motion (swivel) is almost non existent though. Fortunately they sit just fine on my head to get a good seal.
The headrest is easy to adjust and has a wide contact area on top of the head.
The pads are comfortable. The outside is pleather but the part that touches the skin is made of fabric. In fact the whole headphone feels comfortable to me. These pads are angled so it is important to look at the L and R markings on the inside of the headband.
The supplied cable is a bit stiff and ‘springy’ but the good news is that it is not annoyingly microphonic. The 1.5mm cable have L and R marked 3.5mm TRS plugs on the headphone side. Only the Tip and Sleeve of the straight TRS jack plugs are connected which makes it important to plug these connectors in the correct cups. The connector sockets are positioned so the cable points a bit in front of you and not to the shoulders.
The versions from 2022 onward have better quality cables (no difference in sound, just mechanically better)
The sensitivity is not very high and about on par with the HD650. It does draw 8x more current at the same SPL level though. This means if you want to play impressively loud or EQ the bass up you will need a decent desktop amp capable of delivering 1W in 40Ω. You can of course listen to it directly from a phone/tablet/dongle/laptop but you cannot reach loud levels without distortion.
It is an open headphone so while it can be connected to portable gear and plays very nice, but not loud, from it there is absolutely no isolation from outside noises. Everyone around you can hear what you are playing and you can hear all ambient noises not attenuated.
specifications:
Type: Over ear, open
Usage: Home usage
Driver type: orthodynamic
Pads: replaceable, 12 degrees angled hybrid pleather/polyester cloth
Inner pad dimensions: depth: 28mm rear, 21mm front side, Diameter: 55mm
Collapsible: No.
Headphone connector: 3.5mm TRS (marked L and R)
Cable entry: double sided
Cable: replaceable, 1.5m with an angled goldplated 3.5mm TRS plug with 6.3mm adapter
Driver size: 60mm
Nom. power rating: not specified (assumed 2W)
Max. voltage: 9Vrms (assumed 2W)
Max. current: 230mA (assumed 2W)
Max. S.P.L. 126dB (assumed 2W)
Impedance: 38Ω (measured)
Efficiency: 93dB @ 1mW
Sensitivity: 107dB @ 1V
Weight: 385g.
Clamping force: low/medium 4N.
Accessories: 1.6m. cable with 3.5mm TRS jack and 6.3mm adapter, booklet.
Sound description:
The Sundara is a bit ‘lean’ in the bass area. The bass does sound fairly good and is well extended but not on a desired level.
The mids sound good and sound dynamic and realistic. There is a somewhat of a sharpness heard with some recordings on voices and instruments
The treble sounds a bit elevated but is of good quality. A passive in-line filter is available that addresses the 9kHz peak and makes the treble sound smoother and not ‘sharpish’. Parametric EQ also works and one can EQ in some more bass. This headphone reacts very well to EQ.
measurements:
Below the frequency response of the Sundara (Left, Right, dotted = perceived)
Channel matching is decent. Subbass response is excellent and goes down well below 20Hz.
The dip between 1kHz and 5kHz is smaller in reality than it measures because the so-called concha-gain. This is because the drivers are angled and thus make use of the concha which ‘boosts’ frequencies under an angle.
A small dip in this part of the frequency range is more desirable than a peak.
Treble extension is good, above 20kHz there still is some life just not at the same level. Ignore the sharp dips above 10kHz which are measurement artefacts and are only visible (not audible) because no smoothing is applied to this plot.
Around 9kHz there is a peak which is audible as ‘sharpness’ (not brightness) to instruments and voices. When you want to get rid of this you can use a passive inline filter or use parametric EQ.
Seal
Loss of seal with closed headphones usually means a substantial loss of bass. With open headphones this is less of an issue. The pads are shaped to conform to the head and ensures a decent seal in most cases. Below the effect when used with perfect seal, with thin arm glasses, thick arm glasses and with thick arm glasses that do not rest against the skin, pads lifted slightly versus pads lifted 2 mm. 
What is interesting is that a seal breach does reduce the subbass extension but bass levels actually increase slightly. No real need to worry about needing a perfect seal.
pad compression
When pads become older they get softer and compress a bit more so the driver comes closer to the head. To mimic this effect the headphone is measured with its normal clamping force and with the pads compressed. (Right channel)
The tonal balance does not change much and the treble peak is not lower but shifts a bit higher. So aging pads will not have a dramatic impact on the sound with this particular headphone.
comparisons
The Sundara got new pads around the start of 2020. This improved the frequency response a bit between 1kHz and 7kHz resulting in better upper mids sound quality and room for the ears. Below a 2018 and 2021 Sundara (smoothed 1/12 oct).
Most HIFIMAN headphones have a quite similar tonal balance but do differ in upper mids and treble quality.
Below, alternating every 5 seconds, the 2021 Sundara versus several other HIFIMAN models and some better known Sennheiser models.
This makes one wonder why one would even consider buying the $ 6000.- Susvara when one can have a Sundara for $ 350.-.
There are differences well over 2 dB at various frequency bands so even though the plots show the overall tonal balance is comparable there certainly are audible differences between these models so do not sound the same.
Upper treble extension of the Susvara is better, subbass extension is better, treble quality is better. Whether the Susvara is $ 5600.- better (not 17x better) is something I won’t burn my fingers on. Price performance ratios drop dramatically for higher priced headphones. One needs to pay a LOT more for small, but for some appreciable, differences.
The Susvara thus is still in a different class/league. You can’t drive the Susvara from portable devices either. In fact the Susvara needs a really good and powerful amplifier.
That said … the Sundara is quite a capable headphone and can be recommended in this price range.
output resistance / damping-factor
As this is an orthodynamic headphone its impedance is as good as ruler flat so a higher output resistance amplifier will have no consequences for the frequency response/tonal balance/damping. Driven with an amplifier with (0.2Ω) and (120Ω) output resistance.
Of course the levels are compensated, because a high output resistance reduces the overall leve; due to voltage division. For 120Ω this is –12.4dB .
The good news here is that the output impedance of the music source is completely irrelevant.
No tonal balance changes with different output resistances.
Below the phase response for the Sundara. (Left, Right)
Slow phase shifts over a small frequency band are not audible. Sharp substantial changes in a narrow frequency band may well be audible. The steep change around 10kHz is coinciding with a resonance and is audible. Well, at least the resonance peak is audible, the phase shift probably isn’t contributing to this.
The phase shifts above 15kHz (phase is ‘wrapped’ so looks strange) for the right channel can safely be ignored these are caused by the sharp nulls also seen in the frequency response measurements.
Below the distortion measurements of the Sundara (Left channel).
Below the same distortion plot but displayed in percentages.
The distortion levels are very low. Below 0.5% in the lows is really excellent. Note: the 2nd harmonic distortion is most likely lower than the 0.2% shown in the plots. This is due to the limit of the measurement rig which being reached.
The peak around 5.5kHz is caused by a resonance as can also be seen in the CSD plots below. The distortion peak is very narrow but reaches audible levels.
Below the CSD of the Sundara. (Left and Right are superimposed)
The CSD above is made in the same scale as the other plots on this website so below the same plot but with a 10ms scale instead of the usual 5ms.
The CSD looks quite ‘messy’ compared to dynamic headphones. Around 5kHz there are quite a lot of narrow band resonances visible. Also between 9kHz amd 20kHz there are many, rather long lived resonances visible. This headphone is not fresh from a box and is used headphone so has had quite a few hours on it already (for those claiming burn in smoothes the treble over many hours).
The membranes aren’t damped that well it seems but this is seen more often with large planar membranes.
Below the spectrum plot of the Sundara (Right channel).
The membrane seems quite well damped for frequencies below 1kHz. Lower frequencies do not ‘linger’ on in this headphone. The blue ‘islands’ here and there above 500Hz may well be caused by ambient sounds during the measurements. This behavior is seen often with open headphones and is most likely measurement error.
The step response of the 2021 Sundara is shown below (Left, Right) 
The ringing at 9kHz is clearly shown. The hump around the first 400μs indicates somewhat mids centric tonal character.
The slowly sloping horizontal part shows the Sundara has good treble extension although a bit low in level. The wiggles that last over 5ms are various (small) reonances also clearly seen in the CSD that are not well damped.
9kHz filter
To get rid of the treble peak (when it bothers you otherwise you need not bother) you can use the circuit below or buy one ready made.
Below the effect of the filter is shown (left channel only).
Only the sharpness is removed. The rest of the sound remains as it is. Note that this peak is not seen in measurements made with expensive HATS. The reason for this is that these measurement systems have a considerable dip there which results in the peak not being seen. That doesn’t mean it isn’t there.
summary
Fit and finish, comfort, weight (for an ortho) are quite good. It is easy to get a good fit on the head and can be worn for hours.
In the € 300 to € 400 price range there is a lot of competition but the Sundara definitely is a very good choice in this price class.
The sound signature is ‘neutral’ as in not ‘warm/full bodied’ but rather a bit ‘lean’ in the bass but not lacking in bass extension. Deep notes can be heard just not as loud as most people want. This headphone reacts great to EQ so it is easy to use tone control or EQ to add some bass.
The Sundara has a non-offensive sound. The treble can be a bit sharp with some less well recorded pop music or older rock recordings. EQ (or the filter) helps very well and the treble sounds smooth and extended.
Classical and well made recordings sound good on this headphone.
Perfect for home usage from a decent source. Not suited for portable situations where isolation is needed.
For those looking for a clear and detailed sound without boosted lows and want ‘planar’ sound this headphone can be an excellent choice.
The Sundara sounds somewhat ‘better’ than the HE400SE (which is half the price of the Sundara). The Ananda is positioned above the Sundara and has a different sensitivity, much larger (egg shaped) drivers and different comfort and most folks find the Ananda to sound slightly better than the Sundara.
When one is bothered by the 9kHz peak a passive filter or parametric EQ is an easy fix.
DIY-Audio-Heaven 