FiiO has been making affordable quality audio gear for many years, but the FT3 is their first full-size headphone. Launched in 2023, it has a 60 mm dynamic driver with a rated impedance of 350 Ohms and a sensitivity of 105 dB. FiiO has also introduced a 32 Ohms version, which is more suited for portable setups.
The HD660S2 was also launched in 2023, succeeding the now-discontinued HD660S. It inherits a proud lineage, building upon the legacy of the HD600 and HD650, both still in production. The HD660S2 has a 38 mm dynamic driver which is rated at a nominal 300 Ohms and is relatively efficient at 104 dB.
BUILD AND COMFORT
The FT3’s housing is made of an aluminium alloy and it feels premium. It is fairly light and I find it very comfortable. Some might find the cups and pads a bit on the smaller side, but I do not.
The headband has a well-functioning self-adjustment mechanism with a hidden elastic material inside the headband itself. Time will show how durable this is. Elastics tend to become loose over time.
The FT3 is shipped with two pairs of pads with different sonic characters. One pair is made out of a synthetic suede-type material, the other one is a hybrid with a suede-type material on the inside, protein leather on the face and fenestrated protein leather on the outside. I don’t know if they used the same foam or not. The difference in sound is quite big and they have their respective strengths and weaknesses.
I personally tend to prefer the suede pads because they tend to make the sound warmer and lusher. In this comparison, I have only used the suede pads on the FT3
The HD660S2 is built like its predecessors. Plastic cups and plastic yolks, metal grills and steel headband sliders. These metal sliders are bendable and for many people with larger heads, it is necessary to adjust them to avoid the clamping force.
Both headphones have detachable cables. The FT3 uses 3.5 mm connectors, the HD660S2 uses the proprietary plugs used in the rest of the HD600 series.
All in all, I think both are well-built and I find them equally comfortable.
SENNHEISER HD660S2 SPECIFICATIONS
- Wired Circumaural Open design
- 38mm Dynamic Driver
- Impedance: 300 Ohm
- Sensitivity: 104 dB (1V) SPL
- Frequency range: 8 – 41,500 Hz
- Distortion factor: <0.04% (1 kHz, 100 dB)
- Velour ear pads
- Two-sided detachable cable routing using HD600/650 type connectors
- Weight: 260 g
- Included: 1.8 m cable (6.3 mm stereo jack), 1.8 m cable (4.4 mm balanced), 6.3 mm to 3.5 mm stereo adapter and carrying pouch
- Made in Ireland
Check price on Amazon: Sennheiser HD660S2
FIIO FT3 SPECIFICATIONS
- Headphone type: Open circum-aural.
- Driver type: 60mm dynamic driver
- Diaphragm material: Berylium-plated gasket + DLC diaphragm
- Impedance: 350 Ohms
- Sensitivity: 105dB (1Vrms)@1 kHz
- Frequency response: 7Hz-40kHz
- Weight: About 391g (excluding cable)
- Earpad pressure: 4.0N±0.3N
- Cable length: About 3m
- Cable material: Furukawa monocrystalline copper wire
- Detachable cable with dual 3.5 mm connectors on headphones.
- Exchangeable plugs and adapters are supplied for amplifier connection.
- 2 types of pads with distinct sound signatures: Suede and hybrid pads
Check price on Amazon: FiiO FT3
COMPARISONS
When listening to the two headphones I soon found out that the Sennheiser especially was a bit dependent on a good match and I tried them out with several amps.
ROUND 1: Topping A90
It Could Be Sweet by Portishead
Starting with the FT3, the bass is nicely thumpy but not overpowering the very clear vocals. The percussion is also very clean, and the soundstage is pretty large.
With the HD660S2, there’s less deep bass and less definition in the lower regions. The vocals are a bit warmer but not as clean sounding. Compared to the FT3, the treble lacks a bit of clarity and the soundstage is smaller.
Jambi by Tool
They’re quite different here. The FT3 goes deeper in the bass and has a more crisp treble. It’s more detailed and spacious. The bass is a lot more massive.
The HD660S2 brings the midrange to the front in a very nice way but lacks the bass depth, detail and treble clarity of the FT3.
Smile by Pearl Jam
Again, the FT3 is more spacious, the bass is deeper and more detailed, and the highs are cleaner. The midrange is less pronounced, but not withdrawn. Eddie Vedder’s “S”-es are a bit sibilant with the HD660S2 but not with the FT3.
Black Crow by Cassandra Wilson
Again, the FT3 has more space, deeper bass and cleaner treble. There’s generally more detail and better imaging.
Albeit technically inferior sounding, the HD660S2 sounds good. It has that delicious timbre and really brings the vocals nicely to the front.
Young Vivaldi Violin Concerto RV813 III by Ensemble Modo Antiquo
Starting with the HD660S2, the strings sound very natural. They are rendered with a beautiful timbre and a nice amount of texture and detail. Separation is adequate. It’s a very enjoyable presentation.
The FT3 is a bit differently tuned. It’s not quite as dense in the midrange, there is more air and details. The soundstage is larger, but it’s not a huge difference.
I really think both headphones do a great job and it is hard to pick a favourite. However, the HD660S2 has something about the tonality that I like very much.
Follow by BMX
Both are very nice, but they are different. The FT3 is more spacious and has a sharper, clearer high end. It’s not too bright, just clearer sounding.
The HD660S2 is more midrange-oriented and less open sounding. The guitar, trumpet and saxophone all sound warmer and thicker. The highs are not as clean as with the FT3 but the general timbre is very nice.
Conclusion
With the Topping A90 amp, I tend to prefer the FT3. It sounds more detailed across the board and it’s more spacious. The HD660S2 has more midrange presence but lacks the deepest bass and treble is a bit coarse.
ROUND 2: EAR HP4
The Ear HP4 is a fantastic sounding and very expensive tube headphone amplifier, which always makes my headphones sound fabolous. Here’s how the HD660S2 and the FT3 compare with that amp:
It Could Be Sweet by Portishead
The HD660S2 sounds wonderful. It’s warm and delicious and details are presented delicately. The bass is nice and rendered with good definition. The vocals are wonderful, warm and lush with great timbre.
The FT3 sounds quite different. The vocals are drawn back in the mix, but very delicate and nuanced. Everything is a lot more spacious than with the HD660S2. The bass is strong but isn’t too dominant.
Jambi by Tool
Starting with the HD660S2, the bass is nice, the vocals are very upfront with great tonality. Details are nicely and effortlessly rendered.
With the FT3, the electric guitars are more massive, the bass is better separated and has more definition. The vocals are less present and the soundstage is bigger and the imaging is better.
Smile by Pearl Jam
They are not very different here. The HD660S2 sounds good and almost on the same level as the FT3 concerning soundstage. The more pronounced midrange suits this track very well. There’s no issue with sibilance with either headphone.
Some Day My Prince Will Come by Coryell-Coryell-Vitous
Starting with the FT3, this piece of jazz sounds wonderful. The bass is quite strong. The guitar is polite and gently presented. With the HD660S2 the guitar takes centre stage. The bass is still very present, but not dominant. The soundstage is smaller than with the FT3.
Black Crow by Cassandra Wilson
The FT3 has stronger bass and it can become a bit much. The presentation is very open and the imaging and separation are very good. With the HD660S2, the vocals are stronger and fuller, the bass isn’t as dominant, the soundstage is smaller but the imaging is good. Both deliver nice levels of detail.
Young Vivaldi Violin Concerto RV813 III by Ensemble Modo Antiquo
Starting with the HD660S2, the strings sound warm and with lots of body and texture. Timbre is very natural. The FT3 is less warm sounding in the midrange, but there is more air and the soundstage is a lot larger.
Follow by BMX
The FT3 is more spacious, with more treble presence. The HD660S2 is more midrange-oriented and less open sounding. The midrange is warm and the highs are delicate. The timbre is very nice.
Conclusion
With the Ear HP4 amp, the HD660S2 really shows what it is capable of. The detail level is a lot higher than with the Topping A90 and everything just sounds more right. The effect on the FT3 is not by any means as big, it sounds more similar than not to what it did with the Topping A90.
ROUND 3: SPARKOS LABS GEMINI
The Ear HP4 amp is a ridiculously expensive piece of equipment. It’s a complete overkill for these headphones, but I wanted to make sure to get the best possible performance. The Sparkos Labs Gemini hybrid tube amp is not exactly cheap but it is a lot more reasonably priced. I find it to be a great all-round performer, and especially capable with higher impedance amps.
It Could Be Sweet by Portishead
The HD660S2 sounds wonderful. It’s warm and delicious and details are presented delicately. The bass is nice and presented with good definition. The vocals are wonderful, warm and lush with great timbre.
The FT3 sounds quite different. The vocals are drawn back in the mix, but are still very delicate and nuanced. Everything is a lot more spacious.
Jambi by Tool
The FT3 has more deep bass and a bigger soundstage, the HD660S2 has more present mids. The detail level is similar. I tend to prefer the HD660S2.
Smile by Pearl Jam
They are not very different here. The soundstage is slightly bigger with the FT3. The vocals are more natural and present sounding with the HD660S2. There’s no issue with sibilance with either headphone.
Some Day My Prince Will Come by Coryell-Coryell-Vitous
Again the FT3 sounds a bit more spacious with stronger bass, the HD660S2 has a warmer sounding and more present midrange. The electric guitar has a very nice glow to it with the HD660S2. The FT3 sounds more distant. The detail level is about the same and imaging is similar on both.
Black Crow by Cassandra Wilson
Similar to the above. The vocals are more present with the HD660S2. Both headphones have good separation of instruments and good imaging.
Young Vivaldi Violin Concerto RV813 III by Ensemble Modo Antiquo
Although the FT3 sounds good, the HD660S2 sounds more entertaining and energetic. The strings are warmer sounding and more pronounced.
Follow by BMX
The FT3 is slightly more spacious. The HD660S2’s warmer mids bring more glow to the electric guitar and more energy to the trumpet and the saxophone.
Conclusion
Both headphones sound very nice with the Sparkos Labs Gemini amp. The HD660S2 sounds truly great and very close to how it sounded with the Ear HP4. The FT3 sounds pretty similar, but I tend to prefer it with the Topping A90.
ROUND 4: HD660S2 with GEMINI vs FT3 with A90
After trying out several amps, I conclude that the FT3 sounds great with the Topping A90, whilst the HD660S2 works fabulously with the Gemini. The two amplifiers seemingly have opposite effects on the two headphones. The Gemini makes the HD660S2 more spacious and detailed, while it makes the FT3 ever so slightly less so, albeit warmer and fuller sounding.
In the following, I compare the two setups: The FT3 with the A90 and the HD660S2 with the Gemini.
Maple Noise by Greene Serene
Both are very snappy, dynamic and highly detailed. The imaging is great on both. The FT3 has a bigger soundstage and feels slightly more detailed. The HD660S2 is, however, more fun and engaging.
Donde Está Tu Cariño by Tomatito
Again both are very dynamic and detailed with great musicality. The guitar is crisp and natural sounding, the vocals are great with both. The FT3 is bigger sounding than the HD660S2, while the imaging is basically on the same level. As always the midrange is more pronounced with the HD660S2.
Summer 3 – Vivaldi Recomposed by Max Richter
Here they are quite different. The FT3 paints a wider picture. It feels like there’s more happening in the music. The HD660S2 sounds great too, but more aggressive and upfront. The FT3 gives everything more space to unfold.
Identikit by Radiohead
The FT3 has more deep bass and is more spacious sounding, the HD660S2 has more upfront vocals and a warmer sound.
In conclusion, these two setups both sound very good. It becomes clear that the Gemini definitely improves the HD660S2 with regards to clarity, soundstage and imaging.
OTHER AMPLIFIERS
Aside from the EAR HP4, the Sparkos Labs Gemini would be my preferred choice for the HD660S2 and the Topping A90 is the best match for the FT3, although the FT3 sounds relatively similar across amps.
I tried out some more amplifiers in the process and just want to comment on them very briefly:
The Rebel Amp does a very good job with both headphones.
Schiit Magni Heretic does a better job with the FT3 than with the HD660S2
FiiO K5 does very well with both the FT3 and the HD660S2.
WRAPPING IT UP
Sound Signature
The FT3 has more bass and also a bit more highs, the HD660S2 has significantly more present mids. Both are however relatively balanced and nothing is overdone. I’d call the FT3 slightly bassy V-shaped and the HD660S2 balanced to warm.
Treble
In most setups, the FT3 has relatively speaking more treble energy and often it is perceived as significantly cleaner depending on the amplifier used. It has a more airy quality to it, the HD660S2 is more grounded. Not that the treble of the HD660S2 isn’t good, but even with the right amplifier it does not meet the same level of resolution. However, the treble of the FT3 can sometimes be a bit on the bright side.
Midrange
The HD660S2 truly excels in its rendering of the midrange. While the FT3 delivers a commendable midrange presentation with good detail and texture, it doesn’t have the excellent timbre of the HD660S2.
The HD660S2 has presence and warmth and consistently brings the midrange more prominently forward, enhancing the listening experience in a particularly pleasing manner.
Bass
The HD660S2 has good bass, but in the lowest regions it rolls off and it is definitely not competing with the best planar magnetics. The FT3, on the other hand, has a slightly boosted bass with good definition and texture. It also doesn’t roll off like the HD660S2.
Soundstage, Dynamics and Detail
The FT3 has the widest, tallest and deepest soundstage. It also generally has better imaging, but the HD660S2 gets close with the right amp.
In terms of dynamics, the FT3 definitely has the better macrodynamics in the bass region. The HD660S2 has better dynamics in the midrange and arguably also in the treble region.
When it comes to detail retrieval, the FT3 generally gets the upper hand.
Timbre
The Sennheiser HD6-series has always been about midrange timbre above all. The HD660S2, although it has a little more bass and treble focus than its predecessors, is still about getting the midrange right.
To me, the FT3 generally has better bass and treble timbre. It has a nice and sweet midrange, too. However, in direct comparison with the HD660S2, it lacks that extra warmth, body and presence. is special.
CONCLUSION
Undoubtedly, FiiO has made a formidable entry into the headphone market with the FT3. It stands out as one of the top performers in its price range, delivering impressive sound quality across various amplifiers despite its 350-ohm rated impedance.
The Sennheiser HD660S2 is also a great-sounding headphone. Unlike the FT3, its optimal performance is somewhat contingent on finding the right amplifier pairing.
Both headphones deliver well-balanced audio performance. The FiiO features a more accentuated bass and a larger soundstage, while the HD660S2 stands out for its excellence in midrange timbre and presence.
Buy on Amazon: Sennheiser HD660S2
Buy on Amazon.de: Sennheiser HD660S2
Buy on Amazon: FiiO FT3
Buy on Amazon.de: FiiO FT3
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