Ollo Audio S4R and S4X: Doppelgangers offering impressive performance


Mis à jour le 27 September 2021.

Today we are reviewing two hi-fi headphones made by the young Slovenian brand Ollo Audio: the Ollo Audio Recording S4R closed-back hi-fi headphones and Ollo Audio Reference S4X open-back hi-fi headphones. These non-identical twins have a very similar design and benefit from an exemplary build quality.

The Ollo Audio Recording S4R and Ollo Audio Reference S4X headphones have a very appealing vintage design.

These over-ear headphones have a low impedance of 32 ohms combined with a high sensitivity of 108 dB for the S4X and 111 dB for the S4R. Presented as professional models, the Ollo Audio S4R and Ollo Audio S4X headphones have a very linear frequency response from 20Hz to 20kHz. Likely to please purists, will this “pro” sound signature also appeal to casual users?

Ollo Audio S4R & S4X: the brand

Ollo Audio is a Slovenian brand that produces hi-fi headphones with a very transparent sound, intended for both personal and professional use. The company was founded in 2017 in Slovenia. For its founder, Rok Gulič, the idea came about while mixing the new CD of his band, Sabalmoza. Mixing on speakers at night was impossible, and above all intolerable for his wife and children. After a lot of research, he created the prototype of his first pair of headphones and founded Ollo Audio in collaboration with his friend Mitja Sajovic.

Ollo Audio S4R & S4X: packaging and accessories

Concerned about its impact on the environment, Ollo Audio has opted for eco-responsible packaging with no plastic. Consequently, we received two small boxes (one containing the Ollo Audio S4R headphones and the other the S4X). Both were decorated with the name of the brand, the reference of the headphones and some information about its origin.

The Ollo Audio S4R and Ollo Audio S4X headphones come in eco-friendly packaging: no environmentally harmful materials are used.

Inside each box is a cardboard sleeve containing a dated certificate of authenticity, the frequency response curve printed on an A4 sheet of paper, a card with a QR code leading to the latest updates regarding the warranty and a multilingual user manual. We then took out the headphones, perfectly secured by two thin paper pouches containing pages of old newspapers. Under the headband of the headphones is a small cardboard box containing a leatherette carrying pouch. Finally, wrapped in a similar cardboard sleeve, a removable two-meter long Y-cable (2×2.5mm to 3.5mm) and a 6.35mm adapter complete the accessories.

The Ollo Audio S4R and Ollo Audio S4X headphones both come with a detachable two-meter long 2×2.5mm to 3.5mm cable, a 6.35mm adapter and a leatherette carrying pouch.

Ollo Audio Recording S4R & Reference S4X: presentation

For the development of the S4R and S4X hi-fi headphones, Ollo Audio chose to collaborate with professional mixers and sound engineers, which is the assurance of a rigorous and scrupulously observed set of specifications. The result is two very promising sets of headphones, each featuring two 50mm neodymium magnet dynamic drivers and offering a particularly linear frequency response between 20Hz and 20kHz. Lastly, in order to be more versatile, their low impedance of 32 ohms is coupled with a sensitivity of 108 dB for the S4X and 111 dB for the S4R. These characteristics, combined with the use of a 3.5mm mini-jack cable and a 6.35mm adapter, broaden the possibilities in terms of associable sources. While these headphones can be connected to a smartphone, tablet or computer, they sound best when powered by an audiophile DAP, DAC or headphone amp.

Two models, two designs

Ollo Audio Recording S4R: closed-back headphones

Originally designed to be used for recording, production and podcasting, the Ollo Audio S4R headphones have a closed-back over-ear design. Combined with the presence of thick ear pads, this design ensures good passive isolation.

The Ollo Audio S4R are closed-back headphones. The isolation offered by this design makes it possible to enjoy listening sessions both on the go and at home.

The main characteristic of closed-back headphones is that they only transmit sound towards the listener’s ear, which gives the user a cocoon-like feeling and limits, if not eliminates, the risk of sound leaks. It is therefore possible to enjoy the Ollo Audio S4R headphones in a relatively noisy place without disturbing anyone or being disturbed.

Ollo Audio Recording S4X: open-back headphones

Primarily intended for mixing and mastering, the Ollo Audio S4X headphones adopt an open-back design with circumaural coupling. With open headphones, the sound is diffused both towards the listener’s ears and towards the outside of the shells, which are perforated with small holes.

The Ollo Audio S4X are open-back headphones. This design allows them to offer a very pleasant listening experience with a wider soundstage than the S4R.

To fully enjoy the Ollo Audio S4X headphones, it is therefore necessary to be in a noise-free environment, because if those around you can hear your music, even at low volume, you can also hear surrounding noise. Thanks to this open design, these hi-fi headphones offer a spatialization and airiness similar to that of a traditional hi-fi system consisting of an amplifier and a pair of speakers, but without the clutter.

Build quality

The Ollo Audio S4R and Ollo Audio S4X headphones are handmade in Europe from sturdy materials selected for their high quality.

In addition to their very appealing vintage look, these two headphones inspire confidence: the real wood shells connected to the stainless steel arch and self-adjusting headband with a large screw give a real impression of quality.

The Ollo Audio S4R and Ollo Audio S4X hi-fi headphones benefit from a very impressive build quality, which indicates that they should last a long time.

This screw also ensures that the shells can be rotated 360°, which is very practical when storing the headphones flat. Finally, both headphones have thick acoustic foam ear pads covered with soft leatherette and velvet, which further enhances the impression of quality.

Removable cable

The Ollo Audio S4R and Ollo Audio S4X headphones come with a detachable 2 meter-long Y-cable with a 2.5mm mini-jack connector on one end and a 3.5mm mini-jack plug on the other. In addition to this well-made cable, there is also a mini-jack to 6.35mm jack adapter to connect them to a wide range of sources. To accommodate this cable (identical for both references), the headphones are each equipped with 2.5mm format inputs on their shells. It should be noted that contrary to the connectors of the detachable cable, the letters “L” (left) and “R” (right) do not appear on the shells. Consequently, there is no particular way to connect the cable in order for these two Ollo Audio headphones to work properly.

The stereo sounds right as long as the “L” connector is to your left and the “R” to your right when wearing the headphones.

Nevertheless, there is a solution to improve comfort in case the source is placed in front or on the side. As the connectors are not located exactly in the center of the shells, it is possible to position the headphones so that the connectors are oriented towards the front. This will stop the cable from rubbing on your clothes.

Comfort, high linearity and transparency

“What is the connection between comfort, linearity and transparency?” you ask? Well, although the materials and adjustments of the drivers carried out by engineers play an important role in the linearity of the frequency response in order to obtain the most neutral reproduction possible, the design of the ear pads is also important.

The Ollo Audio S4R and Ollo Audio S4X headphones both have highly linear frequency responses.

In addition to comfort, the ear pads also contribute to the sound signature. The challenge is to combine comfort and optimal sound reproduction.

The thick ear pads of the Ollo Audio S4R and Ollo Audio S4X hi-fi headphones have been designed to offer great comfort and excellent sound reproduction.

Ollo Audio worked extensively on the choice of materials and the size of the ear pads. Consequently, after numerous tests the brand chose to associate acoustic foam, velvet and synthetic leather with increased elasticity for its detachable pads, which are 2cm thick and have an inner diameter of 55mm and an outer diameter of 99mm. The guarantee of great comfort and a high-quality reproduction.

The Ollo Audio S4R and Ollo Audio S4X headphones both feature an adjustable headband designed to be comfortable to wear.

Made of stainless steel and leatherette, the self-adjusting headband was carefully crafted to provide a balanced weight distribution for optimum comfort.

Ollo Audio Recording S4R & Reference S4X: key specifications

Ollo Audio Recording S4R

  • Type: closed-back
  • Coupling: over-ear
  • Transducer: 50mm, dynamic
  • Frequency response: 20Hz – 22kHz
  • Impedance: 32 ohms
  • Sensitivity: 111dB
  • Weight: 382g

Ollo Audio Reference S4X

  • Type: open-back
  • Coupling: over-ear
  • Transducer: 50mm, dynamic
  • Frequency response: 20Hz – 22kHz
  • Impedance: 32 ohms
  • Sensitivity: 108dB
  • Weight: 350g

Ollo Audio Recording S4R & Reference S4X: listening conditions

For our review, we paired the Ollo Audio S4R and Ollo Audio S4X headphones with the Naim Uniti Atom Headphone Edition headphone amplifier to enjoy our Qobuz playlists (24-bit/192kHz) as well as FLAC files stored on a USB stick.

Ollo Audio Recording S4R & Reference S4X: listening impressions

Ollo Audio Recording S4R

Led Zeppelin – Babe I’m Gonna Leave You

We had the impression of rediscovering this song that we have heard many times. Although the Ollo Audio Recording S4R headphones have a closed-back design, they provided wonderful reverb, notably with Robert Plant’s voice and more subtly during the instrumental interlude. Despite their closed-back design, these headphones offered a feeling of openness, which is rare enough to be mentioned! The S4Rs were also very strong in terms of stereophony: our left ear enjoyed the lead acoustic guitar, while the right one savored the singer’s tortured voice. A consistent quality supported by perfectly detailed instrumental parts.

The Corrs – Breathless

We noticed a slight emphasis on the voices of the three sisters, while Caroline Corr’s drums offered clean and impactful hits. When the sisters ventured into the highest tones, the Ollo Audio S4Rs managed to provide an accurate reproduction. Finally, the bass line added a nice fullness in the lows, which was very pleasant!

Candy Dulfer & Dave Stewart – Lily Was Here

This breathtaking instrumental piece was brought to life with the Ollo Audio SR4/Naim Uniti Atom Headphone Edition. Each guitar and saxophone note was reproduced with precision and clarity, without ever becoming sibilant.

Ollo Audio Reference S4X

TeenKats – Oui mon cher

We thoroughly appreciated the drums from the very first seconds. Each impact was physical. Then came the double bass, supported by rhythmic claps. The Ollo Audio S4X headphones were responsive at every moment, including when the energetic electric and acoustic guitars arrived. Each register was perfectly layered and the soundstage was spacious. We could simply close our eyes and imagine the rockabilly band playing in front of us!

Pedro Abrunhosa – Se Eu Fosse Um Dia O Teu Olhar

From the very first notes of the well centered piano, the S4Xs offered us a gentle, soft sound. Followed by an equally frontal drum kit, the entire song was wrapped in a soft cloud of synthesizer notes that gradually evaporated towards the outside of the headphones. We can compare the notes of the synth to waves: the first forms slowly, arrives at its climax, then slowly departs, overtaken by a second. In other words, the Ollo Audio S4X headphones offered us a soundstage of great breadth and depth. From the 27th second, Pedro Abrunhosa’s smooth voice took center stage, casting a very slight but measured shadow over the instruments. At the 52nd second, we even heard the muffled notes of the electric guitar and the musician’s fingers sliding on the strings to play a new chord for the first time.

Florent Pagny – Caruso

The Ollo Audio S4X hi-fi headphones honored the cover of this classic Italian song. We enjoyed a beautifully wide, deep and detailed soundstage. When closing our eyes we were able to situate every instrument, with Florent Pagny in the center. With this track, high frequencies are dominant and the S4R headphones managed to efficiently reproduce them, without fatigue.

Ollo Audio Recording S4R: compared to…

Meze 99 Classics: available for €90 less, the Meze headphones have a slightly more refined design. Also equipped with an adjustable headband, they have the same characteristics as the Ollo Audio model in terms of comfort. Concerning the sound, the Meze 99 Classics are warmer, whereas the Ollo Audio S4Rs are truer to the original recordings. It all depends on what you’re looking for!

Ollo Audio Reference S4X: compared to…

Sennheiser HD 660S: available for €429, the Sennheiser headphones provide a slightly less linear but more extended frequency response: as a result, they beat the Ollo Audio model when it comes to details. The German headphones also come with an additional cable (balanced 4.4mm mini-jack Pentaconn cable) for superior stereo and power. However, the Ollo Audio S4Xs are more versatile regarding associated sources thanks to their 32 ohms and 108 dB, compared to 150 ohms and 104 dB for the Sennheiser.

Ollo Audio Recording S4R & Reference S4X: who are they for?

The Ollo Audio S4R and S4X headphones are designed for anyone who wants to enjoy their playlists with a perfectly neutral reproduction. In fact, whether you opt for the S4Rs (closed-back) or S4Xs (open-back), music is reproduced with extreme accuracy. Therefore, both models are suitable for particularly well-produced recordings, and mainly for classical, jazz, rock (note: hard rock songs might lack character) and acoustic tracks.

Ollo Audio Recording S4R & Reference S4X: conclusion

Intended primarily for professional use, the Ollo Audio S4R and Ollo Audio S4X headphones are convincing for hi-fi listening sessions, provided you are fond of transparency and neutrality. These two models are a choice solution for purists, as they are capable of faithfully reproducing music. They also have the advantage of being able to be connected to a wide range of sources thanks to their low impedance and high sensitivity. They also proved to be very comfortable over time. Finally, although they have a closed-back design, the Ollo Audio S4R hi-fi headphones offer a surprisingly wide and very pleasant soundstage. As for the Ollo Audio S4X headphones, they offer us everything we can expect from an open-back model: a beautiful soundstage and a plethora of details.

We liked

  • The build quality
  • The neutrality and transparency
  • The level of detail
  • The magnitude of the soundstage

We would have liked

  • A balanced cable

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