Pros: Extreme neutrality except for the added low frequency boost, amazing detail, build quality
Cons: Price for an optioned out 6.A comes very close to the 8.A because the 8 includes free woody/carbon options
I don’t think I need to say much about Heir Audio at this point – in a very short amount of time they went from being an unknown startup to being one of the most highly respected and sought after companies in the business. Their 8.A flagship is one of the best customs available at any price. Their entry level 3.A is well liked, and is actually one of the cheapest 3-way triple driver designs around. And the 4.A, probably their most popular model, seems to hit a sweet spot between performance and value. Yet there is one more offering in their lineup, one that doesn’t get as much attention as the others. I’m talking about the 6.A.
The reasoning behind this obscurity is probably fairly simple: even with the current promo price of $899 (regular price $1099), it is still within a few hundred dollars of the flagship 8.A which goes for $1099 promo (regular price $1299). As an added incentive, the 8.A comes with a free upgrade to carbon fiber or wood faceplates. When added to the 6.A, those options cost $80 (CF) or $150 (wood), bringing the price of a woody 6.A extremely close to that of a woody 8.A. I imagine most people spending around $1k on custom IEMs are willing to spend a little more to get the top of the line model. On the other end, people looking for a value offering are likely choosing the significantly cheaper 4.A model and saving over $400 in the process. So is the 6.A even worth bothering with?
As the name implies, the 6.A is a 6 driver design. In that way it is similar to flagship models from various other companies such as the JH13, UE18, and UM Miracle. Like those, the 6.A utilizes a 3-way crossover. But the similarities stop there. Rather than using what has become the “typical” configuration of dual low, dual mid, and dual high frequency drivers, the 6.A goes in a different direction. It uses 4 drivers for the lows, and a single driver each for mids and highs. Like its 8.A sibling the 6.A features a triple-bore configuration for the sound tubes exiting the canal. And like the 8.A, the tube which carries low frequencies is the smallest at less than 1mm thick. This is said to be a key factor in getting the best control and articulation possible. The 6.A keeps the same concave tip in order to prevent clogging this tiny outlet.
In terms of drivers, the 6.A uses a pair of DTEC variants to handle the lows for each side. The “D” in DTEC stands for Dual, so a total of 4 drivers. Mids and highs are handled by a TWFK variant.
In anticipation of an obvious question being asked, I played devil’s advocate – I asked Dr. Moulton what made the 6.A stand out from the 4.A. After all, the 6.A could be seen as just a 4.A with an extra DTEC unit, for a significantly higher price. In his usual clear and simple fashion Dr. Moulton explained it to me like this, and I’m paraphrasing here:
The 6.A design is a 3 bore. There are several reasons for this, but a major one would be that each bore allows for the application of an individual damper. As you know dampers are used to tune sound. Beyond that, the impedance for these specific drivers helps control the amount of power being sent to the TWFK. In other words, impedance balancing is being done via the use of drivers rather than a complex system of resistors etc.
That makes sense to me. Consider the difference between a Nissan Altima 2-door with the V6, and a Nissan GT-R. On the surface both seem to have a lot of similarities, with one addition (the turbocharger) being the most obvious change. But the difference between them with regards to performance is rather large. Or in headphone terms, consider a stock Denon D2000 compared to the Lawton modified LA2000. Add some damping and wood cups, and a good mid-fi performer turns in a fairly high end headphone. Same story with the Fostex T50RP compared to the Smeggy Thunderpants TP1. I’m not saying the 4.A is a poor design by any means, but rather that there is still room for the 6.A to be enhanced further even if it has many similarities. I do appreciate that The Wizard is willing to do unconventional designs like this because they fit his vision of sound, even though he knows that the general public expects an even distribution of 2-2-2 drivers. It speaks to his integrity and unique abilities as a designer.
Non-recessed sockets are standard
Partial view of the DTEC drivers
As usual, Heir Audio hits it out of the park with exceptional build. With custom IEMs it’s all about the personalization. I feel like the Wizard has outdone himself once again with this masterpiece – my 6.A is done in a custom bluish color with fine gold dust coating the shell, and a faceplate made of amboyna burl with gold carbon fiber inlay. I took numerous pictures to try to capture the beauty of the design, but as usual Heir Audio products look even better in person. The gold dust is especially hard to show - these pics look like they might just be a regular custom with a somewhat blurry shell, or a lack of polish and shine. I can assure you that is not the case. Unfortunately the gold dust combined with the darker choice of shell colors makes it a little difficult to get a good view of the internal components. The glare doesn't help either.... I'm not the best photographer and it was a beautiful day outside so I couldn't resit.
Interestingly, my 6.A fits a little different than my 8.A and reshelled LiveWires. All were done from the same impressions but somehow the 6.A is a tad looser fitting. At first I was considering having to send them in for a fix, but now I’ve figured them out – upon first insertion, they don’t quite seal perfectly, especially on the left side. But after maybe 30 seconds or so my ears seem to almost “bond” with the shell and the seal is great. I can actually hear the background noise fading away as the 6.A settles into place. It’s a strange sensation but once in use they are extremely comfortable. My 8.A and LiveWires have a nice tight fit and really fill up the ears. They would work better for active use at the gym or something. The 6.A fit is so light that I can hardly notice them at all. Not as suitable for active use but perfect for my listening area at home.
Fit is slightly more loose than the 8.A (seen here in red)
The 6.A comes with the same Heir Audio branded storage case as the 8.A, and I believe all the other models too. Cable is a black Westone style braided affair. The 6.A gets a 2-year warranty, which is double that of the lesser models. It also comes free with the Heir exclusive "ownership transfer service", an optional extra for lower models. On the off chance that the owner wishes to sell the 6.A, the purchaser is entitled to a remold from Heir for just $70. You can't even do a cheap reshell with another company for that price much less a top-tier remold service like Heir. They also check out all the internals and make sure the custom is essentially good as new. I believe this feature adds value to the product - someone on HeadFi recently sold his 8.A and it went in a matter of hours. It's hard to know for sure but I suspect the ownership transfer feature played a big role in that.
I’ve told this story before but it bears repeating here. As Dr. Moulton explains it, he had been working with this particular variant of the DTEC driver for several years. He made the designs for the 3.A, 4.A, 6.A, and 8.A, and eventually launched Heir Audio as a company to sell those products. Out of nowhere, Knowles Acoustics contacts him to advise that this particular DTEC variant is actually a proprietary model, and Dr. Moulton was never even supposed to have it. Obviously there would be no further orders taken. The stock that Heir had on hand was all they would ever get.
For those unaware, it sounds like a simple problem with an easy solution – just grab another DTEC variant and throw it in the 6.A. They sell them at Mouser and Digikey so how hard can it be? The thing is, each variant has very specific set of parameters. In a highly complex design like the 6.A, even a minor change would ruin the end result. Dr. Moulton advised me that he has enough drivers in stock to produce about 6 more sets of 6.As and then they will be gone forever. For that reason we have been unofficially calling this the 6.A LE, for Limited Edition. Once he catches his breath from all the orders coming in, I’m sure Dr. Moulton will eventually come up with a new 6 driver design as a replacement. Will it be as good as the 6.A LE? Better? Worse? Cheaper? More expensive? There’s no way to know at this point. It could use a similar configuration or it may be wildly different, so there’s no point in speculating at the moment. All I know is that someone interested in the 6.A LE should act sooner than later.
Dr. Moulton initially asked me not to do a review on my 6.A, because he didn’t want to create demand that he couldn’t meet. But I convinced him that a write-up like this, maybe not as long as my usual, would be a good idea and hopefully not lead to problems.
The following equipment was used in my evaluation of the 6.A:
Source: JF Digital HDM-03S music server, Squeezebox Touch with Enhanced Digital Output, Marantz SA-1, Hisound RoCoo D power edition, Sansa Fuze, iPad 2
DAC: Yulong Sabre D18, Violectric V800, Anedio D2, Matrix Quattro DAC, Grant Fidelity TubeDAC-11, KAO Audio UD2C-HP, Yulong D100 MKII
AMP: Matrix Quattro Amp, Yulong Sabre A18, Violectric V200, Analog Design Labs Svetlana 2, Audinst AMP-HP
Power is handled by a CablePro Revelation conditioner with CablePro Reverie AC cables. Interconnects are Signal Cable Analog Two and Digital Link, Pailics Silver Net XLR, and Monoprice Premier XLR. I used the stock Heir Audio cable as well as the Beat Audio Cronus. The 6.A was burned in for well over 100 hours prior to any critical listening.
If I had to describe the 6.A sound in a quick sentence, I would call it a neutral, highly transparent sound with a bit of a mild low frequency boost. It’s a very different sound compared to the big, lush, engaging 8.A signature. Dr. Moulton says the 4.A is his most strictly neutral design while the 6.A is even more transparent but also has some extra kick in the lows to keep things interesting. I find his description fairly accurate although I haven’t heard the 4.A to compare.
Bass surprised me at first. I tried a few random recordings, nothing “audiophile” quality, and the bass didn’t sound overwhelmingly great. Sure, it was incredibly tight, and had nice impact and definition. I also thought it had just about the perfect amount of presence without drawing too much attention to itself. But it just didn’t always sound as nice as something like my triple driver LiveWires or 1964 Ears customs. I investigated further by playing some of my high quality tracks that I specifically use for low frequency tests. These include: Khmer by Nils Petter Molvaer, an eclectic mix between jazz and “techno” where some parts sound like good old fashioned Miami bass music. Cantos De Agua Dulce by Marta Gomez, with sublime percussion that can really test the speed and resolution of a playback system in the low frequencies. Super Double Bass: The Artistry of Gary Karr which features the unique virtuoso Karr playing his famous “Karr-Koussevitzky” double bass, formerly called “the Amati bass” until it turned out not to be a real Amati. Between these three albums I’m able to get a view of the full capabilities of a headphone in terms of bass performance – to earn high marks, it not only has to boom and thump, but have texture, depth, refinement, speed, control… there are plenty of decent headphones that can sound great with one of these albums but not the other two. I expect a higher end headphone to at least handle two of the three. But it’s rare to find an example of all three sounding brilliant. The 6.A actually manages to pull this off.
It turns out that the somewhat less than spectacular initial results had been caused by the recordings themselves rather than the 6.A. It does bass in a way that is so revealing and so detailed that it exposes flaws in the recording and mastering process which most headphones just glaze over. Even the mighty 8.A doesn’t quite pick up on some of these little things in the same way the 6.A does. Does that make the 6.A a better headphone for bass reproduction? Possibly. It depends on whether you want brutal accuracy or enjoyable musicality. But it’s important to note that there is a bit more bass presence here than with some of the other “neutral reference” type headphones such as the Sennheiser HD800.
Mids and highs on the 6.A strike me as very clean, very accurate, and very linear. Another way of saying that is to call them flat and boring. It really depends on your outlook. No single frequency seems boosted over any other, but everything is neutral and transparent. Transients are handled with extreme accuracy and quickness. Mids come across as more forward than the 8.A although less forward than the typical UM house sound as heard in the Miracle or Merlin. Some would mistake the excellent high frequency extension as brightness, but I don’t hear it that way. The 6.A just captures everything there in the recording, be it a well recorded cymbal strike or a splashy, nasty one. It’s all laid bare right there in front of you, for better or worse. Frankly I’m really surprised that this level of extension and clarity is even possible with just a pair of drivers, since most competitors use double that. But then again the UE Reference Monitor is “merely” a three driver model and it is very highly regarded.
The mids and highs echo the bass when it comes to unraveling poor recordings. Modern pop music is all but unlistenable (which tends to line up with my subjective taste on the genre anyway), but a good amount of reasonably modern music still holds up well enough. I enjoy such non-audiophile groups as Further Seems Forever, Daft Punk, Meshuggah, Marc Houle, Pendulum, Eric B & Rakim, The Weepies, Sister Sparrow & The Dirty Birds, Soundgarden ... most of those are quite presentable with the 6.A, even if they do have some shortcomings exposed. The important thing is that the 6.A is not creating any new issues like sibilance – a common problem with “reference” type headphones.
The 6.A, and to a lesser extent my Earproof Atom custom IEMs, have caused me to re-examine what I had previously thought a neutral sounding IEM really sounded like. There was a time where I would swear up and down that my UE10 was neutral. Then came the ES3X and the UE10 just became “flat” and “boring”. Now the ES3X was the definition of neutral. Then along came the JH13, which showed me the romantic midrange and lower bass boost of the Westone unit. From then on the JH13 was the most neutral thing in the world. Later I would retract that and say it was actually somewhat aggressive in the upper mids, to create a false sense of excitement that became a bit fatiguing in the long term. The UM Miracle is what caused me to feel that way about the JH13. Fast forward now to the 6.A (and the Atom), and I’m starting to think that even the Miracle (and its sibling the Merlin) are a little bit north of neutral in the upper mids/highs area. They aren’t as far off as the JH13 but still seem to have a little but more “zing” up there than might be natural. This is strange because I imagine that my hearing in the upper registers is only getting worse as I get older; yet my standards of what might be considered “aggressive” or even “bright” is going the opposite way. In any case, the 6.A is not that far off from the UM sound, but it does fit closest with the descriptions I’ve heard about the UE Reference Monitor.
Soundstage presentation is quite good. Accuracy seems to be emphasized more than size, though I do find them on the spacious side as well. On better recordings, one can clearly make out the special cues indicating where the performers are in relation to one another. Unfortunately we also get to hear the lack of this information in many recordings – the 6.A won’t create an artificial ambience like some other headphones or IEMs do. I can see how opting for the accurate approach might be less desirable for some listeners, but I think it is in keeping with the spirit of the overall presentation here so I wouldn’t want it any other way.
Another thing the 6.A inherits from the 8.A is the superb coherency between drivers. This is something that can be difficult to measure until you spend a considerable amount of time with an IEM, unless of course they do a very poor job which makes it obvious. After getting to know the 6.A really well I have to say it is one of the most well-integrated designs I’ve ever heard. Frankly it makes something like the ES3X sound sloppy with respect to driver blending.
Heir audio 8.A – The 8.A is very different from the 6.A – so much so that it’s almost hard to believe they came from the same designer. The 8.A has massive bass, rich creamy mids that suck you right in, and extended yet ultra smooth highs that are almost never offensive. It really tends to make the music sound better than it might actually be. In contrast, the 6.A is truthful to a fault.
It’s hard to adjust when switching from the 8 to the 6, since everything initially seems so flat and boring. But give it 30 seconds and you’ll find yourself delving deep into the mix, appreciating all the subtleties of each instrument and voice. The bass presentation, while smaller overall, is still generous, and conveys high amounts of realism. Soundstage is a bit smaller but with more accurate imaging. Mids are more forward and don’t have that “full size headphone” type presentation like the 8.A has. Keep in mind though that the mids are still very smooth and not overly aggressive. Highs seem to be more linear, resulting in more perceived detail with some tracks and more perceived grain with others. The 8.A is ultra-smooth up top and extends seemingly forever thanks to an array of dual high and dual super-high frequency drivers. The 6.A can’t quite match it but does an extremely capable job nonetheless, which is astounding considering it does all this with just two drivers. I speculate that the crossover point for the quad low frequency drivers might be higher than most designs, thereby giving the mid and high drivers less ground to cover. But this is just a guess and I don’t pretend to have even a fraction of the knowledge that Dr. Moulton has on the topic, or even some of my fellow HeadFi members for that matter.
UM Merlin – The Merlin is also a very different animal than the 6.A. Keep in mind that my Merlin is a prototype unit with less of a boost in the low frequency area compared to the production model. It turns out that the 6.A and my proto Merlin actually have very similar levels of bass impact. Both are boosted beyond what we would call neutral, and both stop a bit short of what might potentially satisfy a basshead. The 6.A handles bass in a more technical manner. It reminds me of a fast electrostatic type impact where everything sounds just right. In contrast, the Merlin and its dynamic driver are more like a planar headphone, where technicality is also high but there is an almost indescribable sense of ease that just can’t be matched. It’s hard to explain the difference and both sound great on their own, but I have to give the slight nod to Merlin in overall realism, due to the sense that some more air is actually being displaced. It is a very close contest though and I wouldn't argue with someone who concluded the opposite way. Please note that I don’t feel that the production model Merlin has the same advantage over the 6.A – it’s a different animal and goes for a different sound. At one point I had the proto and production models in house, both full custom molds, and I chose the proto for this exact reason.
The 6.A counters by having a smoother and more linear presentation in the mids and highs. Mids on the Merlin do have a more prominent role in the mix. While the Merlin is a tad laid back compared to the Miracle, it still comes across as slightly edgy compared to the 6.A. Female vocals are the main area where this plays out – the 6.A is like a razors edge, cutting deep to the full extension of each syllable, the full breath of each annunciation. But it remains so tight and under control that we only hear sibilance if it is present in the recording. The Merlin tends to slightly overstate consonant sounds, veering ever so slightly into the edgy category. This is the UM house sound and it is highly enjoyable, yet not strictly neutral. Just like with the bass comparison though, I don’t find either model lacking when played on their own. Only direct comparisons will bring this out, and both models are still very strong performers even in the categories where they land in second place.
This comparison is of course somewhat limited in usefulness simply because of the prototype status of my Merlin. The actual model that is available for ordering won’t have as much in common with the 6.A, since it will have a more significant bass boost. Although I believe the rest of the spectrum remains very similar to the proto, the added bass gives a different perspective as to the tonal balance, and shifts the focus of the listener. So in reality the Merlin and the 6.A are reaching for two different customers altogether.
I have to mention a bit about system synergy with this phenomenal IEM. While the 6.A is capable of scaling to great heights with better gear, surprisingly it doesn't sound too bad with more basic equipment. I like it just fine out of a Sansa Clip or iPad 2. Bad recordings become that much harder to listen to, but good ones are still enjoyable. This is a bit different than what I had been expecting but I'm glad to be wrong in this case.
On the other hand, the highly resolving nature of the 6.A is also perfect for exploring the differences between sources and amps. Using my Analog Design Labs single-ended triode amp, I was able to rotate from one excellent DAC to the next, and the 6.A gave me a clear view of the character of each one. Then I used my best DAC, the Anedio D2 and did the same swap with my amps, getting a clear window into their capabilities as well. The 6.A is a perfect tool for someone like me who frequently evaluates new gear - the only thing it won't do is test the grunt of an amp, since it obviously doesn't require much juice. But if I want to know about the transparency of the amp, or the blackness of the noise floor, or the resolution, or any other characteristic, the 6.A does the job better than any of my other customs, and better than most full sized models too. The only things I've heard that can possibly be its rival is the Sennheiser HD800 and some of the better Stax gear.
I could keep going on about the 6.A, but why? It’s clear that Heir Audio has another winner on their hands. Despite a rather unorthodox driver configuration, or perhaps because of it, the 6.A performs like a full on flagship model. Despite living in the shadow of its older brother the 8.A with its higher driver count and larger price tag, the 6.A is absolutely a top tier IEM.
I had been interested in trying the UE Reference Monitor, and one of these days I still might, but at the moment I’m absolutely satisfied with what the 6.A delivers. If you like neutral, transparent, detailed sound, but also struggle at times to enjoy that type of signature due to the usual leanness of tone, the 6.A should definitely be on your radar. There’s really nothing else out there quite like it. And when the last 6 sets are sold out, there may never be anything like it again.
BONUS EYE CANDY
6.A in front, followed by 8.A in red with red carbon fiber, followed by reshelled
LiveWires Trips with checkerboard bamboo inlay
Hard to see, but the dual bass drivers in the 8.A are larger than the quad bass drivers
in the 6.A
The bass driver in the LiveWires is nearly as big as all 4 in the 6.A - but it can't really
compete with the resulting sound. I do love the LiveWires though
This almost looks as if they are printed graphics rather than hand-carved real wood
or genuine carbon fiber. In real life it's obviously the real deal