Ollo S4R (v1.1, 2022) Review
Opening
As of 2022,
Ollo audio doesn’t seem to gain much awareness from audio hobbyists or enthusiasts. This is not surprising, this small company located in Slovenia has been focusing on those on the production side, not audio/music consumers. Their two products are claimed to be tuned for mixing, tracking, and mastering duties.
This may arouse the first question. Why should we, audiophiles, care about this company? It’s because I do believe there are numerous common virtues required to be good headphones for both worlds: neutral frequency balance, separation, layering, detail retrievals, etc. But let me make it clear that I do not agree with so-called “hear musician’s intention” thoughts.
On top of that, Ollo has two very unique characters that captured my attention. First, their products are fully serviceable on the customer end.
Their webpage sells literally every component of headphones. It’s even possible to buy cheaper used products then upgrade to the newest versions by ourselves. Buying a closed-back version then changing to an open-back on our end is also possible (
confirmed by Ollo!). It voids warranty therefore never recommendable to new purchasers though. Their finished products are sold for reasonably low prices, thus practically there’s no reason we should do those, but this level of serviceability is impressive enough for me.
Furthermore, Rok, the founder of Ollo audio, runs
a youtube channel disclosing development processes, thoughts, and even music impressions done with his headphones. There are a lot of informative and/or educational pieces to help customers better understand their headphones. For example, how their headphones measure, why they are tuned in specific ways, what were improvements over the previous versions and why, etc etc. Any interested party should check out his videos.
For these reasons combined with curiosity, I ended up buying the latest version of S4R (called v1.1), their closed-back model, early last month. With frequent usages of air conditioner or tower fan in the house, I spent most of my listening time with them as they isolate me from environmental noise very well. And now I think it’s a good time to drop collective thoughts.
Overall, I found them a very competitive product even from an audiophile’s perspective. Why? Let’s find out.
Setup / Associated Gears
I did most of the in-depth evaluations with Gustard X18 and SMSL HO200 as primary dac and amp respectively. But occasionally used Motu M4 and iFi Zen Signature as a secondary upstream.
The S4R connected to HO200 via XLR balanced outs. I was using a custom-built PC-OCC balanced cable (2.5mm trs on the headphones end and 4 pin XLR on the amp end) but the stock cable terminated with quarter-inch TRS seemed very decent -- I just prefer balanced outs. I didn’t use any digital processing/equalizer in evaluation except for 8x upsampling software on the digital domain.
Comfort, Build Quality, and Aesthetics
The specific S4R pair I bought weighed 390g and felt neither heavy nor lightweight. This is probably due to the very sturdy stainless-steel frame. The clamping force is known as 5.5N and my experience can confirm it although it got slightly lowered as time went. Probably to make a better seal and isolation.
In one of the youtube video, Rok emphasized he took great care of sound leakage in upgrading S4R because it’s one of major feedback from the original version
There is a self-adjusting leather band which reminds me of Audioquest Nighthawk. I’m personally a big fan of this mechanism and it could fit very well with my big skull, too. The headphones sit relatively comfortably on my head.
The stock ear pads are hybrid containing two different materials on the surface. Inner and outer sides are pleather while the contact side is velour (also probably with memory foam inside). The dimension (50mm inner diameter and 20mm depth) look small and my big ears slightly touch inside. But I didn’t find much annoyance to date. I can easily list up a number of much shallower and more annoying ear pads I might dislike.
The wood cups are made out of walnut wood, but they don’t look particularly beautiful to me. I’d also note the cups have almost zero swivel although they can fully rotate. This per se is not much of a problem in my head but I saw a little loose seal with my measurement fixture on the bottom of the pads.
Another minor complaint is the steel headband isn’t decoupled with cups/drivers enough. This means if the steel headband is lightly touched by something, you can immediately hear the microphonic sound.
Sound Impression
Let me begin with S4R’s perceived lower frequency response. Based on what I heard with the ⅓-octave warble tones (center frequency being ranged between 20hz and 1khz), I could not hear any hint of humps in lower registers. At my normal listening level, I could hear down to 20hz very linearly, which is very impressive for small headphones. But I want to note the lower range response was rather lean and thin to me. They didn’t come with enough quantity.
Listening to actual music recordings, I could confirm that S4R very accurately tracks all the details of gradation in bass frequency. Everything sounded tight and well-pitched. Good articulation, too. But they lacked macrodynamics and punch, which damaged engagement a bit. When there are busy passages filled with various groups of percussion instruments, S4R never fails to articulate and delineate. I really liked how things were analytically disentangled and separated in neutral ways.
And because of their less prominent bass reproduction and mid-centric voicing, the presentation across the whole spectrum in the midrange frequency is where S4R shines for me. It’s very slightly upwarding up to 2khz (roughly +1db/octave). Neutralists might complain that S4R might be aggressive and colored in the upper midrange. But for someone like me who listens to vocal and solo tracks a lot, it doesn’t count toward disadvantages. Vocals are opened up with high lyric clarity, without being too honky or nasal. I also hear better and more present attacks from major instruments.
In contrast to forwarding midrange, S4R’s treble feels rather controlled and even slightly recessed. No matter how harsh tracks I threw in, I was never annoyed or derailed by sibilance or edginess. While, as a treble-sensitive person, I appreciate this approach a lot, it sometimes feels too much though. Some tracks suggest S4R might kill some of the sparkles the track is capable of delivering. Rok said he acknowledged high frequency cancellation issues coming from closed-back design and was going to work on it in the future revisions. The open-back version, S4X, seems to mitigate this issue. I’m quite curious how S4X stacks against S4R. FWIW X also seems to elevate lower to middle bass, which also makes me curious.
Soundstage is ok. I wasn’t wowed much with live music but they at least didn’t trigger my claustrophobia. I could feel the void space between musicians and their places in a three dimensional context. Considering all the structural challenges (closed-back, small cup, etc), I’d say S4R is good in depth but just decent at best in terms of soundstage width. I’m also wondering whether and how much the S4X and/or alternative pads can improve this.
After all my experiments to push these headphones to the limits with various challenging tracks, I have to admit Ollo/Rok put a very capable driver in this one and it was able to show small details and nuances and very convincing PRaT in my evaluation. I couldn’t spot muddiness or veil unless I over-demanded (e.g., to compare to 20x expensive totl reference). Sometimes I hear things are too clean or perhaps oversimplified. But that may be too much nitpicking and far beyond what I require to hear for sub-1k range.
Finally, I can verify that S4R isolates both incoming and outgoing sounds. Maybe not enough for isolation purposes under a very noisy environment where ANC or IEM should be used. But they could almost perfectly block my room's environmental noise around 40-50 dbA. And nearly zero leakage makes me comfortable to use them in a public or shared space.
Comparisons
Compared to HD650, apart from functional merits (such as isolation and lack of leakage), I found S4R is faster and cleaner sounding with better PRaT. S4R also extends better particularly in lower registers. The HD650 to me was a bit muddy below the upper bass (usual for small-driver open-back headphones) but the S4R remained articulate and linear. By comparison, HD650 is more laid back and veiled in midrange to treble. While I roughly think they resolve equivalently, S4R presents resolved components in more easily understandable ways IME. HD650’s soundstage is slightly larger than S4R.
Compared to SV023 (which I acquired recently for Mid-fi reference purpose; a dedicated review to come), to my taste, S4R falls behind significantly in several areas such as naturalness, resolution, full-bodiness, and soundstage. While they are drastically different in all the presentation elements, I’m under the impression that S4R keeps track of all the details more honestly while SV023 tries to maximize virtual realisms. Maybe that’s the essential contrast between monitoring and audiophile headphones.
Comparison to Susvara is largely similar to the paragraph above, but with every delta being even more amplified.
Measurements
I am also attaching the measurement of the pair I evaluated in this review. All the measurements were done with MiniDSP EARS and my own compensation curve (HPN in lows + HEQ in highs + some adjustments) which I calibrated to make the flat horizontal line be close to perceived neutral balance. Results were averaged through multiple repositions and smoothed in the 1/24 octaves.
I’d emphasize that associating deviation from the target to one-dimensional quality (good vs bad) might be hugely misleading. There are various traps and pitfalls caused by individual HRTF variation (huge), different assumptions on artificial ears, and/or acoustic interactions between headphones and measurement devices. Thus, please do not over-interpret my results.
Below are comparative plots against Sony ZX701, Sennheiser HD600, and HD650. Both HD6x0 were measured with fresh new pads.
Conclusion
All things considered, every aspect of S4R seems well tailored to their intended role as mixing and tracking monitor headphones. I also do think, because of this very reason, S4R should be considered by serious audiophiles who want to do many analytic listenings. Their tracking and monitoring ability is legit and that can benefit any listeners to closely follow all the musical details contained in the recording.
While they are still sonically not perfect, most of the shortcomings I found come from structural limitations of the closed back headphones. There are some closed-back products I think sound better than S4R in some aspects. But they’re all 1) more expensive and 2) more leaking (bents, loose seals, etc). That said, I’m honestly very impressed with Ollo’s accomplishments.
S4R will remain as one of my stables. For this price, this closedness, and this tonal and technical performance in details and transients, I really can’t think of any other proper alternatives that can beat S4R. Great job, Ollo audio and Rok!
After experiencing S4R, I’m pushing myself to find opportunities to try out S4X. And I will be keeping my eyes on this small company and whatever they will come up with in the future.
