Fit and Comfort

Seen above is the Altiat CAL.1H placed on a mannequin head, to help show how these headphones would look on the human head. Note that the head is slightly under average sized, so account for the discrepancies accordingly. As with all headphones, getting a good fit and seal is crucial, so do your best with the vertical sizing and earcup rotation on offer here, knowing by now that the CAL.1H does not offer earcup swivel. You may want to play around with positioning of the headband slightly forward or backward than you usually do too, since the earcups are slightly angled and the pads themselves are not contoured. I see lots of room for improvement if Altiat were to make a new product, but thankfully what they do provide does make for a comfortable fit and seal around my ears without much problem. Also note that the solid ash wood ear cups will weigh significantly less than the aluminium ones, with an estimate of the entire headphones ranging from 250 to 400 g based on the material chosen. This particular unit weighed in at 391 g, which is not surprising given the substantial metal chassis and further paint finishes applied. It's nothing for me compared to the heavier planar magnetic headphones I tend to use, but is a step up for those who are used to plastic headphones. Do keep in mind that the CAL.1H is an open-back set and thus will be best used in a quiet environment without others in the vicinity.

Audio Performance

Audio Hardware

I mentioned before how Altiat does not shy away from saying the dynamic drivers used in the CAL.1H are simply sourced from someone else, as opposed to making it yourself. This is almost always the norm, since manufacturing dynamic drivers yourself is harder than many people assume. Going for a competent driver from a factory/OEM capable of providing the units at a price that works for your headphones bill of materials is the smart thing to do. Usually the drivers also tend to be tuned quite well, although the customer—Altiat in this case—can also influence the final tuning significantly with the choice of ear pads, damping materials, and also the chassis the driver is placed in. Even things such as the grille on the back can matter, as evident with our review of the HIFIMAN Susvara Unveiled. So keep that in mind and let's give credit to Altiat where it is due. The CAL.1H uses 50 mm dynamic drivers with an infilled PET (polyethylene terephthalate) diaphragm, and Altiat says these drivers were chosen for precise, linear low-frequency production while minimizing undesired side effects. We do not know much else here, be it about the surround or the magnets, let alone the damping materials used. Regardless, the end result is an easy-to-drive set with a rated average impedance of 28 Ω and sensitivity of 104 dB/mW (at 1 kHz), and here too Altiat makes it a point to mention the higher sensitivity enables end users to more easily use EQ to fine tune the frequency response. When you add in an EQ preamp, it usually gets more demanding on the amplifier and thus the CAL.1H being already easy going helps in this regard. In fact, you can easily get away with using a competent portable DAC/amp, many of which have EQ functionality these days, let alone a desktop source. I can see a shorter cable being handy here such, with the default longer one more useful for desktop use.

Frequency Response Measurement and Listening

I will mention that I have a general preference for a warm-neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Our current headphones test setup uses a set of two custom in-ear microphones for the two channels. These microphones closely adhere to the IEC711 class, but have been tweaked to be more reliable in the >10 kHz frequency range, the precise issue with my previous setup, that is otherwise still very good and will continue to be used for IEMs and earphones. Two soft silicone pinnae are installed on the sides, separated by a distance matching my head, and multiple "height" adapters have been 3D-printed for further customization, based on fit, head size and shape. Each set of microphones has an XLR output I separately adapted to 3.5 mm. I used a transparent source—the FiiO K19—for measurements, although I also used a DAP, as seen above, to confirm it was no different for this purpose. This artificial head simulator feeds the microphone lines into a reference USB sound card, which in turn goes to a laptop that has ARTA and REW running. I begin with an impulse measurement to test for signal fidelity, FFT to test for headphone seal, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/12th setting, netting a good balance of detail and signal-to-noise ratio. The default tuning was used for testing, and no app or program-based EQ settings were chosen, unless specifically mentioned. Each sample of interest is measured at least thrice with separate mounts to account for any fit issues, and an average is taken of the individual measurements for statistical accuracy.


As before, you can find my headphone frequency response measurements on VSG.squig.link along with all the earphone measurements. Scroll to the bottom and choose different targets there, including some from Harman Kardon developed after years of R&D. The Harman 2018 over-ear target in particular, is a reference curve many headphone makers aim for now, but I find it too bass-boosted—especially for open-back sets. As such, I am opting for the Harman 2018 curve with the bass target from the Harman 2013 curve, which is what is referred to as the "Harman Combined" target. Before we get talking about the sound signature of the Altiat CAL.1H, I want to briefly talk about the measurements themselves and the channel balance achieved here. I think a single look at the measurements above can confirm the excellent driver matching on my set, and this is all the more impressive when you realize this is a randomly chosen show demo sample. Altiat, as with Kaldas Research, sports some impressive testing equipment on hand including a G.R.A.S 45BB-14 KEMAR™ w/ KB5000/50001 anthropometric pinnae, a G.R.A.S. 12AX power module, and an Audio Precision APx515 audio analyzer, so it would be fair to say their measurements are more accurate than mine and also that each finished unit is likely to get a similar treatment when it comes to channel matching. This is excellent to see from a small brand and is far beyond any expectations I had, and I have no concerns about quality assurance or control thus.

As for the sound itself, keep in mind that I do not have the velour pads here. From my limited time with the CAL.1H at CanJam London, I thought the velour pads sounded better in the mids but the alcantara pads were easily more comfortable and also less prone to getting dirty. The latter costs $50 more, and some of the more expensive/limited editions of the CAL.1H come with both sets so you can try what works better for you. All my testing was done with the alcantara pads only, and measured with them as labeled in the graphs. Also, I'll say right away that I tried this at the show, knew almost immediately this was not for me, and yet acknowledged its strengths enough to immediately purchase it as a gift to someone I know will absolutely adore it—spoiler alert, I was right. The CAL.1H is a bassy open-back set, and that is already quite rare. It does so with a few quirks in its tonality you need to be aware of though. There's sub-bass dip, as expected from a standard open-back dynamic driver set, although the front damping and the rest of the analog tuning done makes it less obvious than many other such sets. Helping further is the part where the dip is only noticeable until ~70-80 Hz to my ears, below which there isn't usually much information in music recordings. Mid-bass is clearly what you are going to get the CAL.1H for, with its thick and hard hitting notes working quite well for the likes of heavy metal and rock music. I ended up turning the lower mids down a touch to clean up the bass and male vocals for me, but I suspect most people will prefer how it sounds already—or simply use the velour pads which seem to handle this better while also filling up the upper mids to an extent.

The warmer, thicker mids combined with the generally relaxed treble (past 7 kHz anyway) can make for a smoother sound for many. I absolutely see this as a winning solution for people who want a casual listen of many music genres too, which is good because the CAL.1H isn't the most resolving set on the planet by any means. It is easy to drive but the drivers themselves can distort in the mids if you push them up—ideally use EQ to cut down regions you feel sound hot, and be generous with the preamp. The tuning doesn't help either, since a lot of detail is in the highs that we don't get much of by default. Then there's the cavern in the upper mids which, while it can make for a larger sense of space, also affects imaging and makes some vocals feel slightly hollow. The same can be said about brass instruments too, with piano keys and strings generally faring much better. Timbre is thus hit-or-miss depending on your music library, and yet I personally know many people who could not care less about this and just love how the CAL.1H puts out its bass for guitars and drums in addition to having a more "analog sounding" male vocal range.


There aren't a lot of such bassy, warm open-back sets I have here, especially in the price range the CAL.1H goes for. I thought about the Philips Fidelio X2HR, although this feels more like a weird mix of taking the lows from the X2HR and the highs from the Fidelio X3. But one is not easily found for purchase anymore and the latter was a fail in more ways than one. We do have some very competent headphones to consider though. With the recent price cuts by HIFIMAN, the Edition XS now costs even less than the CAL.1H in its starting configuration. In return, you get one of the best sounding headphones on the market and certainly a better all-rounder than the CAL.1H. But you also get one of the weakest build qualities and headbands too, even if it does have earcup swivel. It does feel like a case of choosing what is more important to you, and whether your music library tends to be more specialized or diverse. Then there is the Sennheiser HD 6XX, which even in the more expensive HD 650 version is in the same ballpark as the CAL.1H. Those in the US can find the HD 6XX for significantly less, and I would absolutely recommend it for someone who wants just a single set of headphones. The CAL.1H is more specialized here too, but I will say going back and forth made me appreciate the hard-hitting and dynamic bass here too. The issue is Sivga makes similar bassy sets, and has wooden ear cup offerings too, so things get harder for Altiat if you are open to purchasing from Aliexpress, provided your country does not have it on Amazon in the first place. The SV023, for example, is one of my favorite headphones in this price range and is closer to how I heard the CAL.1H with the velour pads, so keep that in mind. If you absolutely want a cool aluminium finished set of ear cups then the CAL.1H is still the way to go, but it would be fair to say that a lot of people are going to probably find other options more fitting from purely a sound perspective.