INOX (Technical Analysis and Release Report)
We are very happy to finally announce our new Headphone – INOX. For the very first time in Headphone history, a Consumer/Production Closed-Back Electrostatic Headphone.
There is a lot to uncover and I will try my best to give a brief introduction about the technical aspects and details of our latest development -
Background :
We launched the RR1 Conquest in 2019 as our foray into Headphones and making my life-long passion of building something of my own into reality. The RR1 has been in continuous production for 5 years now, which is something we are truly grateful for. We are constantly amazed by the demand and interest the RR1 still gets and the motivation it provides us to keep going. Against all odds, the RR1 has managed to cement its place in the industry and we plan to keep Manufacturing the RR1 for as long as we feel it is needed.
During COVID, we made the Electrodynamic CAL.1H under our sister company, Altiat. The CAL.1H was conceived completely at home while we all were stuck doing nothing. With the success of the CAL.1H we had the funding to make something that we really wanted to do for a long time, and…..it wasn’t the INOX.
We did not set-out to make a Closed-Back E-Stat. We wanted to make a Flagship open-back E-Stat and had spent a year developing something quite special and came very close to finalizing it. Unfortunately, since we do not make Headphones for money, it was boring. It was so boring and unchallenging for us that we just could not proceed with it. It felt almost embarrassing to give a go-ahead on yet another Open-Back Headphone. So, we scrapped it and began from scratch to build the very first “Consumer” market closed-back E-Stat for the first time in Headphone history.
Design/Manufacturing :
As with our previous two Headphones, the INOX is a completely Bespoke design with no part takeover from our previous Headphones. The entire design is a fully ground-up effort. This is something we are very proud of. The work needed to come-up with a full re-design is not an easy task and even the most experienced of Manufacturers do not do this often at all. The use of parts-bin in Headphones is as prevalent as it is in the Automotive industry. Nothing wrong with it but, it is not challenging enough when you are trying to create a special product.
With INOX, we have employed the use of our most skilled Manufacturing techniques thanks to our Vertical Integration set-up allowing us to use Multi-Axis CNC machines in conjunction with various Electrical-Discharge-Machining processes to come up with conjoined solutions to Manufacture parts which otherwise would have been impossible to do without the use of additive Manufacturing in Metal. Anyone with a Manufacturing background will be impressed with the details and skill put into the production of the INOX’s componentry.
It is in no small part when we say it is World-Class and extremely difficult to produce the componentry used in the INOX in a production capacity using the techniques we have used to build a product at a cost that is feasible. It is only possible due to the Vertical Integration and the skilled machinists/technicians at work and our primary business as a Contract Manufacturer that has made it possible for us to create the INOX. With that said, we can focus more on the material details further below -
Build/Materials :
It all starts with a 2.5mm Torx bolt. During the development we jokingly challenged ourselves to try to have only type of bolt for the entire construction of the Headphone. Although it proved difficult, the INOX just needs one screw-driver for a full assembly/disassembly. Might seem like a small thing to some but for the geeky among the enthusiasts, I think it is a nifty achievement!
Materials are an important topic as the name INOX is derived from one material that makes up the bulk of the Headphones – Stainless Steel. More specifically, 316L Stainless Steel.
Being a mechanical watch enthusiast, I’ve always loved Stainless Steel. The material makes a lot of sense for a watch case but, can be an issue in a Headphone as the weight concerns far outweigh the potential benefits over traditional Thermoplastics or even Aluminium. Both excellent in their own right if integrated properly. Luckily the inherent design of the INOX complements the use Stainless Steel. Taking advantage of the tensile strength, we were able to turn the dial on our wall-thicknesses way down, which otherwise would have been impossible if Aluminium was used. Not only does this provide much relief in our weight targets, it also adds to the visual beauty thanks to the thin profiles and walls.
The Headband is a Manufacturing work of art consisting Multi-Stage usage of CNC turning, milling and EDM. We machine out a solid-block of Delrin to create our unit-construction harp that integrates the lovely clicks and dulcet tones of our adjustable on the fly spring-steel harp which is precision cut on our EDM machines. It is haptic joy to use the headband on the INOX, a major improvement from the RR1 and CAL.1H designs which both featured a strap-mechanism which is an inherently different design and significantly easier to Manufacture. The use of unibody Delrin is a first and is much more premium feeling than using injection PC-ABS. Again, this is usually not done because it is pretty damn expensive to make. The Delrin unibody harp is incredibly robust, soft to the touch, has the absolute perfect clamping force and an extremely high-quality surface finish to boot.
High-End unit construction headbands have become a thing of the past as it was only usually done well by Legacy Manufacturers who have slowly opted for less-complicated options.
Things aren’t built to last nowadays and we want the INOX to last decades without intervention but, if need be, the Headphones are completely serviceable.
Every single component of the INOX is meticulously crafted in metal with weight concerns kept in check. There will be also use of certain exotic alloys and precious metals in the build.
Some of this we cannot reveal at this time as we are still are unclear with the final specifications. As with the RR1, the INOX will be offered in two variants. More information on this will follow once we get closer to the official launch at CanJam London 2024.
Measurements :
List of the Measurement Equipment :
- G.R.A.S 45BB-14 KEMAR™ w/ KB5000/50001 Anthropometric pinnae
- G.R.A.S. 12AX Power Module
- Audio Precision APx515 Audio Analyzer
Amplification :
- STAX SRM-252S for All Measurements
- Mjölnir-Audio KGSSHV for 112dB Measurements
1) Frequency Response : A Closed E-Stat has never been done before for the Audiophile market. The SR-4070 was built for broadcasting, Koss made the closed ESP-900 for MRI and other medical applications. None built for the purpose of listening to music. So, the natural conclusion is that a Closed E-Stat must suck or else more people would have attempted to build one. At least that is the thought we went into when we decided to begin the INOX development.
Luckily, that isn’t the case. An E-Stat can perform at a World-Class level in a closed coupling - Dynamic, fast, precise, musical with exceptional bass response and excursion capabilities. The INOX has all these attributes meanwhile having great compliance to the Harman Target Response. I will let the graphs to do the talking but, before that:
The INOX will come with two earpads in the box: one Hybrid 21mm and one Microsuede 21mm. On top of that, there will be 3 tuning options that mostly control the LF response. The Microsuede has essentially perfect compliance in the Mid-Range to the target compared to the Hybrid which is slightly lower than the target. The point of this exercise is to not force the customer into what we or anyone else thinks is the “correct” response. The INOX has exceptional compliance but, it comes down to personal preference and we have given the choice.
A: 21mm Microsuede “Target Tuning”
B: 21mm Hybrid “Factory Tuning”
C: 21mm Hybrid w/ Port Open “Fun Tuning”
2) %THD
Another important metric that is usually much more challenging for an E-Stat driver compared to an Isodynamic driver, especially in the Low Frequencies. The INOX driver at 30Hz (94dB SPL) manages to touch 0.024%, the lowest recorded points are between 1.5Khz to 3Hz, coming in at under ~0.008%. The broadband average seems to be around 0.03-0.04% at 94dB SPL. All very respectable figures considering we are noise limited by our chamber.
For 112dB SPL we had to bust out the Mjölnir-Audio KGSSHV. The baseline and barebones STAX 252S just does not have enough juice to drive the Headphones without corrupting the results with clipping. Even with the KGSSHV, we had to boost the signal internally through the APx software in-order to achieve 112dB and I’m sure that the result has some clipping artifacts in it as well. These high SPL measurements are ridiculous in the real world but, very useful nonetheless. The results are frankly incredible for a driver with a theoretical displacement limitation of 500 microns. E-Stat’s don’t have the luxury of free excursion and hence it’s a very delicate dance between the right gap and sensitivity targets. Increase the gap and you are further limited by the lack of power swing capabilities to boast your technical prowess in high SPL %THD results due to clipping. If you’re an E-Stat Manufacturer, you know exactly what I’m talking about.
We are currently at our interim facility as we are awaiting the construction of our newly purchased office where we will be making an isolation chamber that is a significant step-up from our previous design, which was not particularly great with the outside noise levels and challenges we face during %THD measurements here in the very noisy part of Bombay, India.
3) Impulse Response
The Impulse Response of the INOX is World-Class, settling in under 1ms. Now as excellent as the Impulse Response is, this is one place where it’s $500 open-back brother - the RR1 beats the INOX. The RR1 settles in around 500-600μs. Proper quick!
4) Group Delay
As good as it gets? From the Measurements I have seen; nothing currently quite matches the results of the INOX, especially for a Closed-Back E-Stat.
Driver :
The knowledge gained from the RR1’s driver development gave us a clear picture of where there was room for improvement. The INOX culminates a lot of those ideas into a new driver specifically designed and tuned to be used in the INOX chassis.
Starting off with the:
1) Stator: A further improvement was made in the overall refinement of our PCM Manufacturing process of our in-house Stators to further increase the profile smoothness at a microscopic level. Moreover, our Stators are now Electroplated in pure Rhodium. Not cheap but, a small price to pay for significant improvement in corrosion protection. Does it make a difference to the sound? Probably not but, that’s not the only improvement we have made in driver sophistication.
2) We have decreased the tolerances of our PMMA driver body and increased the use of DTI inspections to improve the overall tolerances from around 200-260 Microns (Which was the acceptable average we had for the RR1’s driver) all the way down to 10-20 Microns. A substantial improvement that requires a lot of machining expertise as well significant investment of time in verification of the said tolerances at the QC stage before assembly.
3) Another significant improvement made to the driver from the RR1 is the sensitivity. The RR1’s DS gap was set higher than we personally would have preferred at 0.8mm. The INOX is back to the traditionally correct DS gap of 0.5mm, ideal for the PRO Bias supply. Many Electrostatic Manufacturers including us with the RR1 preferred the higher DS gap as a more forgiving gap. Only STAX had the mastery to do it at a consistent level. With our experience of Manufacturing drivers for 6 years now, we have gained the knowledge about the nuances that only comes with experience and time. Thanks to that, we are now able to go down to 0.5mm with ultra-high reliability and performance.
4) Due to the increased efficiency, the drivers will naturally be subjected to high SPLs. We faced non-linearity issues in controlling the pressures on the Stator. With limited air volumes due to a closed coupling and the damping profiles required, any major changes to the chassis orientation to solve this led to catastrophic deviation from our Frequency Response targets. This complicated loop’s solution was “baffling” and was embedded deep inside classical Acoustics. This integration into our PMMA driver body gave us the extension needed in the low frequency response as well as increased axial reinforcement gave the driver’s an extra edge in the %THD response.
Quality Control/Reliability:
The RR1 will complete its 5 years of production this year. The RR1 had a rough start and it was an early learnt lesson for us to set our targets of QC and reliability at the very top. As the RR1’s production progressed, we put in place multi-point checks during from assembly to the final delivery. As far as we know, the RR1 till this day is the only Headphone to come with an Individual Measurement Certificate and an attested APx copy showing the Channel Matching as well. We go through vigorous hours of tests on our HATS as well as subjective/ human testing. I can confidently say that only a very few Headphones go through the stringent testing procedures that we have put in place for the RR1’s production. Our efforts have not gone in vain as we have noticed incredible success results of our units since the past 3 years. We are extremely proud of going the extra mile in our QC procedures and will continue to do so. With that said, it was a no brainer that the INOX had to match the same stringent tests. Despite the price disparity between the RR1 and the INOX, our mentality is exactly the same. The cheaper Headphone does not get a free pass.
The Channel Matching thresholds written in fine-print of our RR1’s Measurement Certificates are mentioned between 0.1dB-0.4dB @1Khz. 98% of the time, we do not pass headphones that don’t have at least 0.1dB matching. If a Headphone is passed with a higher tolerance at 1KHz, it might be due to the subjective tests and broadband matching accuracy carrying more weight than at a particular point i.e., 1KHz. All this is to say that we do not mess around with Channel Matching of the RR1. Below are some examples of the RR1 units, these examples are all random customer units:
1) 0.079dB
2) 0.061dB
3) 0.053dB
4) 0.071dB
We haven’t been complacent with the RR1 and it’s hard to improve upon something that is already being done with meticulous attention. The only thing we can improve is the said fine-print. So, we will certify the matching accuracy of INOX at 0.05-0.15dB @1KHz, a first in the industry. We hope our efforts lead to more cohesively accurate Headphones for all of us.
Comfort :
Major emphasis was given to the comfort and ergonomics of the INOX. The INOX gets full Micro-Suede treatment, from the Earpads to the Headband padding. The attachment of the Earpads is the same as the RR1s setup with the 3M Double-Sided Tissue Tape. This Earpad attachment is simple but is very important to achieve the low-frequency targets we wanted which otherwise would have proved very difficult in a Magnetic set-up which we tried and failed at. But our system is great and replacing Earpads is extremely simple! The same can also be said about the Headband padding, which are again fully crafted in Microsuede using CNC Hot-Wire to achieve the profiles we wanted exactly as per our design.
The only components not made by us in-house are the Earpads and the Headband padding. The Earpads are made by our supplier in China with whom we have been working with for the last 6 years. They are the sole OEM for majority of the Headphone Manufacturers out there. The quality they provide is second to none and we are very happy to have their support for the INOX. The INOX upholstery is proudly Made In China with exceptional quality!
The entire purpose behind the INOX is getting to enjoy the inherent advantages of an E-Stat driver with privacy in an uncompromised form. If fit and comfort was poor to begin with, why bother with a closed-back Headphone at all. We think the INOX scales very favourably in the overall wearability and comfort but, the jury is still out on that until customers can share their thoughts.
Launch/Pricing/Ordering :
We officially will be showcasing the INOX at CanJam London this year in July and will follow-up with another CanJam in North America as well.
The expected pricing will be $1799. There will be two variants. More on this later as the details about that are extensive and not quite finalized yet.
There will be no “pre-orders”. We aren’t interested in holding people’s money. We will start accepting orders as soon as we are prepared to do so which mostly will be after CanJam London 2024. Some of our close private customer friends have known about the INOX since last year and some of the early Serial Numbers have already been spoken for.
My opinion on the technical aspects:
I don’t make Headphones for the money; this is my passion first. I am an enthusiast like all the rest of us here and have been in this hobby for the last 12+ years. So yes, while it may be strange to talk about my own Headphone, I hope this adds to some further relevant and objective information.
I will begin with the things I dislike about the INOX :
1) Trimming the X-Axis fat further : While I do think the INOX is designed relatively well, there were certain design compromises I had to make in order to tune in a closed chassis. A design should be thin, streamlined, and beautiful. I think all 3 aspects would have been absolutely spot on if I could have shaved 2-3mm in the overall thickness of the design.
I like thin, low-profile, low-slung designs. An example is motorcycles, I love my classic British bikes over anything modern which just aren’t pretty. Classic British motorcycles always had that low-slung profile to them which was due to the inherent lack of front and rear suspension prior to the early 1950s. Even after the advent of swinging-arms and front telescopic set-ups, the low-slung character and rake continued, all while having the design challenges to accommodate it. Which modern designs just can’t ever replicate. The point of this boring tangent and rant is to emphasize my nit-pick of failing to shave that extra 2-3mm off. Overall, it was out of necessity and in the end like everything for the INOX - form follows function.
2) +5dB rise in LF : This is more of a visual annoyance rather than a sonic one for me. I think the bass response of the INOX is superbly creamy. But, not getting the +5dB rise bothers my OCD more than anything else. The “Fun” response we showed is actually very fun with a tight and well bodied bass presentation. But, the “correct” flat response isn’t bad either. I think it just comes down to a personal preference and we will let our customers chose and tune very easily. I personally would have liked to match the +5dB like of our Planar compatriots but, with our design targets and displacement/surface area limitations to make the Headphone look as normal as possible. I am quite happy with the bass response of the INOX.
Now to the things I like:
1) An Industry First: The INOX is the first commercial attempt at a consumer-friendly Closed E-Stat design and we are sure that it won’t be the last. I think INOX slashes all cliches and stereotypes about E-Stats and the perceptions many people have about them. The INOX sounds just like a well-tuned Headphone with all the inherent and esoteric qualities people enjoy about Electrostatic transmission. While I do believe that a well-tuned system is a well-tuned system and if the design is done right, there is very little sense in debating about the merits or demerits compared to other transmission types. But, with that said, you cannot hide from the inherent technicalities of the system and the it’s esoteric advantages which for the most part, currently are immeasurable. Hence E-Stats have their place, Planars have their place and Electrodynamic systems have their place as well.
2) Manufacturing: The INOX is not an easy product to make. The machining challenges with Stainless and the overall cost of Manufacturing is prohibitively expensive for any rational Manufacturer to sign off. Fortunately, we are crazy and do not really care.
The INOX components are intricate and require a lot of machining skill to pull off. We are very lucky to have extremely experienced machinists and specialised technicians at Kaldas with decades of experience in the field to make it possible. In my opinion, every single component of the INOX is a work of art and can only be appreciated if one has a Manufacturing background to recognize the skill behind the design and execution.
3) Normal: Attempts at E-Stat’s are usually funky, the RR1 is a great example of that. We wanted to make sure the INOX looked as normal as possible with a sound that worked for everyone, not just the E-Stat enthusiasts. The presentation of the INOX is remarkably full-bodied and linear and suits pretty much every genre you want to throw at it. It is an uncompromised sound in an uncompromised chassis.
4) Leakage/Isolation: The isolation measurements are still new to us and hence it is a little difficult to know the accuracy of them. Tyll used to do great Measurements but, unfortunately all of Tyll’s data is gone and is difficult to replicate accurately.
What I can say is that I have a Sony CD9000ST, the JDM Monitor Classic and the INOX isolation seems to be very similar to that. The impressive part and the key takeaway is leakage. The INOX has excellent sealing and there is virtually no leakage from the Headphones. That is THE point of an Audiophile closed-back design and it does it quite well! Most passive closed-back Headphones don’t really have great Isolation characteristics. Leakage is the key, at least in my opinion. I personally would never bother with any passive Headphone if Isolation was my priority, I would just stick to ANC headphones for that.
A few final words before I end this :
My words and opinions are irrelevant. The jury is still out on what you all think.
We will be methodical with our launch of the INOX. We are currently tooling up for series production and will be making a batch of Production Prototypes soon, followed up by the initial serial run for our very close friends and customers who have placed their orders since last year.
This is a complicated product to Manufacture and we want to ensure everything is built with precision from the start and hence we are in no rush to make money, we do not operate like that and are not pressured to launch a new Headphone every other year or so. Hence, we will be adhering to the strict Production and QC directives we have set out for the INOX’s addition to our line-up.
See you at the CanJam’s this year!
Thank you very much!
Best Regards,
Aumkar Chandan
