Sound Impressions


Tonality with the BD4.2 is largely going to depend on the bass setting. You can get neutral to almost non-existent rumble with the bass adjustment set to zero and overpowering warm ‘thunderbass’ when set to the max.

There are a lot of variables in-between, in fact, there is a 24dB variable between min and max bass settings. That is a heck of a lot of potential and you could well be playing with the bass port all day for whatever genre you desire.

The most sensible balance seems to be around the halfway mark (12 o’clock) which Lear has defined as the extreme end of Studio monitoring and just before things go a bit more musical and coloration takes control.

Bass Adjusted

With the bass adjusted to around halfway you get a very mild u-shaped frequency response with a neutral midrange, a full sounding warm to neutral bass response with all the characteristics of a dynamic driver (longish decay), a slightly forward lower treble response around 5-7k then a fairly quick drop off with a tiny peak at 10k again.

I wouldn’t classify the treble as rolled off, it just the interplay between it and the bass levels is largely depending on your bass setting and it will sound more forward the less bass you inject into the BD4.2 and subsequently less so when you pump it to the max.

Definitely the micro-dynamic drivers do work to the advantage of the BD4.2 creating a spacious presentation but the skew is little more to excellent height and depth and a little less on absolute width. I would certainly rate the staging bigger than the V8 from 64Audio, the Harmony 8 or the AAW W300AR (also a dynamic hybrid) but it doesn’t convey the same width or 3-D depth as top tier units from Visions Ears or 64Audio.

Overall at 50% bass adjustment the tonal balance on the BD4.2 is very natural sounding with just a slight low end emphasis giving it a nice warm sheen to an otherwise neutral signature and keeping everything smooth, flowing and nicely detailed.



The BD4.2 dual dynamic driver design offers a very natural sounding bass signature but with a longish decay compared to BA equivalent. It is not the fastest, leave that to BA designs, but in return though it just sounds far more realistic and offering better staging.

Texture and detail are excellent and at 50% bass adjusted it stays very coherent with the rest of the frequency range but just a bit more planted than in the studio monitoring range. That additional weight and authority works particularly well on some EDM (read Moby) and hard rock that maybe requires a bit of depth rather than out and out slam.


Adjust the bass right down to zero and you get a very flat and neutral bass response that is a little tighter sounding than at 50% but doesn’t extend as well and lacks a bit of authority compared to the 50% setting.

Mids and treble do come into the fore a bit more and the treble sounds a little more present and forward. A zero setting though does not mean this is a lean bass signature by the way. It doesn’t suddenly become thin, cold or edgy, rather it simply gets dialed down.

I can see quite a few people who like their dynamic driver to run a bit more linear or flat enjoying this bass response so I can see why Lear had this tuning and why they labelled it as a Monitoring type setting.


Resetting the bass to 100% and it is a massive change to the signature. There is a huge rise in the mid-bass elevation from 80-100hz upwards and the decay gets decidedly longer. Naturally, it can’t retain that tight level of control or definition you can get at much lower bass level settings; it does sound looser and there is a bit of bleed in the lower mids.

The tonality with a full bass setting does get decidedly warmer than either the 50% and lower levels. This is an out and out colored bass head experience. There are very few CIEMs (if any!) that can touch the level of bass presence that the BD4.2 can achieve when full-on.

Tracks such as LMFAO’s Party Rock Anthem sounded like a 15″ sub long-throw stuck in the back of a Fiat 500c with about a ton of deadening just to make sure your sides don’t fall it off even if your ears do, it is that intense.

But here is the cool bit. Yes, it does bleed at 100% but it doesn’t suffocate. Treble response is still present and vocals are not lost, they just play second fiddle to the elevated mid-bass response. The BD4.2 does not turn into one of those awful dark attenuated no-name headphones you find in a Tiangge mall, it still has some sense of coherence even with all that slam.


The Lear BD4.2 has an inherently neutral midrange that is not as forward sounding as say the AAW W300AR or the Harmony 8. Whilst there is plenty of clarity and detail with a nice pacey BA snap you don’t get a huge vocal presence. As such the BD4.2 does not present an intimate stage, being placed a few rows back at least.

Instrumental timbre is reasonably accurate, particularly in the lower mids. Guitars had plenty of crunch and definition, particularly with hard rock numbers. There was a tiny bit of thinness creeping into the upper mid-range that kept the tone from sounding totally natural but overall it remained clear and accurate.

Dial-up the bass and it does color the midrange a bit more with a bit of bleed into the lowers giving it a bit more warmth but at the loss of a bit of clarity and presence. Dial the bass down to monitoring levels and the midrange becomes a lot more present in the mix along with the treble presentation. I would suggest somewhere around 30-50% bass adjustment is ideal to maximize the midrange performance and clarity on the BD4.2


Again, depending on the level of bass injected into the BD4.2 presentation, its treble response can vary. At 50% I find the treble to be even-paced, natural-sounding, and with a very nice balance.

It has a decent extension, not huge but decent, a hint of 10k sparkle and good air. There is a tiny peak at 7k but with the 50% bass mix it doesn’t really translate into a peaky tonal experience. Percussion work is controlled nicely without any splashiness.

Sibilance, though present at times, is very minimal with this setting. Lear has managed to tune a detailed and articulate treble experience without it ever sounding too brash or forward.

Dialing the bass down to completely flat does give an additional dimension to the treble response making it sound a little bit brighter and more forward than at 50%. Once you push the bass up again to way above 50% onwards to max treble presence doesn’t get swallowed up but it lacks the speed and sparkle to stay anywhere higher than a second fiddle to the low end.



Despite its relatively modest 30 ohms at 1k and 110dB sensitivity ratings, the Lear BD4.2 is one of the less efficient CIEMs I have reviewed in a while.

This is actually good news for me personally but it does mean you should think about your source a bit before pairing. It won’t sound great in other words with a weak-sounding source/amp and will scale to greater heights with a good portable amp or source with similar technical amping prowess.

The BD4.2’s lower level of efficiency also has a very nice plus point for being rather hiss free with most sources I threw at it.



DAPs such as the FiiO X7, the Opus#1 and the Cayin N5 did need to move to either high gain or a relatively high volume step count on low gain to drive the BD4.2.

For example, on low gain, the FiiO X7 combined with the mid-power AM2 module required a frightening amount of additional power (around 70 steps compared to 40-45) over and above say the Campfire Audio Jupiter, Se846, and even similar 30-ohm units such as the Noble 4C.

On the Cayin N5, the BD4.2 required around 35 steps on low-gain which is a good 17 steps higher than the Campfire Orion and 15 steps more than the Jupiter. The Opus#1 even hit triple figures using the single-ended jack out (100 steps, compared to the Orion at around 60 on low gain) and only about 10 steps lower in balanced mode.


Tonally all 3 DAPs matched the BD4.2 quite well but if I had to pick one I would go with the X7 (AM5 anyone?) and the AM2 module. The clarity and resolution on the Opus#1 were excellent but lacked the low-end oomph of the X7/AM2 combination sounding a little polite.

Switching the Opus#1 into balanced mode made it a little more competitive especially on sub-bass rumble which was excellent but again that additional clarity and fuller sound sat best with the X7.

The Cayin N5’s musical signature was a lot of fun with the BD4.2, and it is a pairing I would recommend if you intend to really jack up the bass performance on the BD4.2 or add a touch more edge to the BD4.2’s treble attack.


IEM Amps

The BD4.2 scaled rather well with plenty of good portable amps. My preference tended to veer to anything which would enhance the dynamics or tease out a bit more midrange performance.

IEM amps such as the RX from ALO did ok, there was enough gain to drive them pretty well actually and staging/dynamics sounded pretty good but it didn’t quite have the expansiveness in the midrange I was hoping for.

Aurender Flow

The Aurender Flow is an excellent high-end transportable amp with a very clean sound with tons of clarity but the match with the BD4.2 wasn’t right even though the detail flowed.

The Flows restrained midrange is not the best pairing with the BD4.2 neutral mids. Both combined to make the midrange performance a little blunted and lacking in air. It is, however, an amp that performed better with the BD4.2 bass set to zero.

Mass Kobo

Amps such the Mass Kobo 394 on low or high gain (slight introduction of hiss but minor) opened up the midrange on the BD4.2 nicely sounding far more spacious than the RX or Flow and requiring just a little less juice than the RX for optimal performance.

Chord Hugo

The Hugo was also an excellent performer with the BD4.2 with a fantastic level of clarity right across the board and an additional level of sparkle and air in the treble performance.

The staging was far superior to the IEM amps such as the RX and the Kobo 394. Certainly, the BD4.2/Hugo pairing was the best for micro detail out of all the amps I tested and the best also for poppy female vocals such as Delta Goodrem.

Bakoon HPA-01M

The Bakoon HP-01M was a better pairing than I thought possible also particularly for hard rock and metal. Maybe due to the lower efficiency but hiss was absent though the noise floor was a bit higher than ideal. However, once it got going in voltage mode it sounded wide, very wide indeed.

Now my stock description of the staging qualities of the BD4.2 was one of height and depth more than width but imaging and width take a big leap up with amps like the Hugo and the Bakoon so the BD4.2 does seem to perform better with the more powerful portable amps out there.


Select Comparisons

The BD4.2 price point is a bit of a sweet spot for a lot of customs monitors both BA only and hybrid. The stand out pitch of the BD4.2 is its tuning flexibility and dual dynamic driver plus BA design so I thought it would be interesting to pitch it against hybrid drivers at a similar price point as well as those with tuning tweaking features.

Custom Arts Harmony 8


The silicone design of the Harmony 8 is off the charts in terms of color combination, secure fit and excellent seal. I would rate the Harmony 8 as king of comfort above all other customs I have had to date including the Minerva Mi-Pro silicone edition.

Mind you that is no shame for the BD4.2, and with their new semi-hard shell edition it should be a lot closer. However, the size and depth of the BD4.2 shells to accommodate the dual dynamic drivers will always add some external heft no matter what the material is.

In terms of seal though both are excellent with the BD4.2 suffering little or no loss from the bass ports compared to say the Merlin. Just to note that the Harmony 8 is vastly more efficient than the BD4.2 rewiring 15-18 steps volume on the FiiO X7/AM2 setup on low gain. This is a continuing theme for 3 out of 4 of these comparisons,


The Harmony 8 has a full sounding bass performance that is slightly elevated in comparison to the rest of the range but otherwise remains tight and snappy as a good BA design should.

It doesn’t have the sheer power or slam of the BD4.2 dual dynamic configuration, nor does it quite have that natural-sounding decay but it does have speed in its corner. I would never term the Harmony 8 as having a bass head low end but it has authority. The BD4.2 on the other hand is positively dating your bass low end and loving all 24db of that adjustable range.

The midrange is where the Harmony 8 excels with a slightly forward and thicker note compared to the more stand off and thinner sounding BD4.2. The additional drivers of the Harmony 8 also convey a bit more resolution and detail in the mid-range.

Tonally the BD4.2 has a far more neutral u-shape to it than the N shape of the Harmony 8, vocals do sound more fleshed out and convincing on the Harmony 8 than the BD4.2.

Yet the Harmony 8 lacks in air and space compared to the BD4.2, particularly in the treble response. It is overly smooth and lacking in detail and whilst the BD4.2 is not a treble monster it certainly has the chops to out sparkle the Harmony 8 (non-Pro edition folks).


This is a classic acrylic design with 3 drivers, one dynamic, and a single BA for mids and another for highs. It’s a relatively smallish unit due to the small number of drivers with a relaxed fitting and good but not great isolation. It also sits a bit flusher in the ear than the bigger BD4.2 but the seal and isolation on the BD4.2 are superior.

That may be due in part to the impressions I gave and I did have to get a minor adjustment on the original fit which had gaps so YMMV. Both have excellent cables by the way with the quality choice being the Null Audio Vitesse on the W300Ar but tonally it’s too warm for the W300AR, unlike the BD4.2 C2 cable which is a better match.

Tonally the W300Ar is more neutral-sounding than the Harmony 8 with slightly less bass weight and a stronger emphasis on vocal performance. Bring a dynamic hybrid though the bass is more natural sounding much like the BD4.2 it just doesn’t have the same level of presence, flexibility, and slam. If you dial the BD4.2 down to around 0- 20 on the bass it starts sounding a bit closer to the W300AR but there is still a bit more authority and weight in the BD4.2 bass response overall.

The midrange of the W300AR is thicker sounding than the BD4.2 but not as thick as the Harmony 8 with a bit more space and a more accurate instrumental timbre. The W300AR has a beautifully natural midrange with a wonderful vocal performance and sad to say the BD4.2 thinner-sounding midrange can’t compete with or connect on the same level.

The BD4.2 though does have an edge in detail and resolution with a touch more speed and articulation in its treble performance. The soundstage on the BD4.2 has better depth and height and sounds more spacious than the more intimate W300AR.

UM Merlin

Very smooth and well-made single dynamic and 4 BA design CIEM which still holds it’s own 5 years later. The bass port on the Merlin though provides less isolation than the equivalent on the BD4.2 making it inferior for an overall seal and isolation but it is smaller and fits a bit flusher in the ear.

The Merlin is far more efficient than the BD4.2 though requiring 20 steps less using the FiiO X7/AM2 module on low gain.

Tonally the Merlin is a touch warmer sounding than the BD4.2 with decent clarity and detail whilst the BD4.2 sounds a little brighter and cleaner of the two, particularly in the mids. Both have a relatively forgiving sound signature with the BD4.2 having the more neutral and articulate treble response to the more laid back Merlin treble performance.

If there was one area I felt the Merlin edged out the BD4.2 was on sub-bass presence which I felt it had a slight edge over the BD4.2 which slams a good deal harder but close to the mid-bass 80-100hz level.

Both have slow decays and plenty of bass texture where you need it but again that additional flexibility in the bass tuning of the BD4.2, taking it from flat to thunderbass makes the Merlin feel rather more one-dimensional.

M-Fidelity SA-43

A quad BA CIEM with adjustable ambiance and bass switches, the SA-43 is cheaper than the BD4.2 but the workmanship is not to the same level as well as the choices in plates and shells.

The SA-43 is also a bigger CIEM than most though smaller than the BD4.2. Both seal incredibly well despite the differing sizes, in fact, both have the best seals out of all of the CIEMs I currently have (17 I think). Interestingly both had similar efficiency levels with both pushing the X7 to around 65-70 steps using the AM2 module on low gain.

Tonally the SA-43 has a more typical BA sound with a smaller soundstage and a slightly more forward vocal presence than that of the BD4.2. It’s still an impressive soundstage for a quad BA but It is also the tighter and pacier of the two customs.

The Bd4.2, however, has those twin dual drivers giving it a lot more depth and power in its bass response over the SA-43, and as such, it projects a more spacious soundstage than the SA-43 is capable of. Both have slightly laid back or neutral treble responses though the SA-43 has a slightly splashier lower treble peak than the BD4.2 which sounds a bit smoothed out in comparison.

Tweaking on the SA-43 can bring in an additional bass weight or flatten the performance a little but it really is rather subtler than the massive 24dB control you have over the BD4.2 bass performance. No contest there, if you want a bass head CIEM or go very flat the BD4.2 is the one to pick, if you want something a bit more intimate with better vocals then try the SA-43.

Our Verdict

The BD4.2 from Lear is unique and quirky as far as custom monitors go. From being the only CIEM that I know off for combining dual dynamic drivers as well as BA to having a bass adjustable port you only see on the likes of JH Harvey units it certainly stands out with plenty to offer.

If you are a bass-head you can get a huge amount of slam yet at the same time monitoring fans will enjoy the ability to dial that bass right down to an almost flat neutral level. The pricing for me is the sweet spot and if they can make a few adjustments in the build QC and changing the cleaning pick then I would say it outpaces a few competing CIEMs quite easily.

The Achilles heel is the midrange performance. It does feel a bit thin and vocals never quite engage in what is a very neutral performance outweighed by the weighted bass. It does not have the fastest bass performance either with a very long decay and the treble could do with a bit more speed also but in fairness its neither peaky, forward or harsh which makes it ideal for those with treble sensitivities.

The lack of efficiency as an audiophile is a huge plus as it suffers from next to no hiss on all but the most inefficient amps and of late quite a few of those amps have been no-go areas due to that very reason. I really enjoyed rolling out the analog amps once again and stacking them just like the old days. The BD4.2 can scale a bit and it does sound more convincing with good portable amps.

This is not a niche custom monitor, there is plenty of real flexibility in its sound signature. If you are scratching your head on bass, no bass, monitor neutral, or colored warm then the BD4.2 actually has plenty of those bases covered. That makes the HK$7,998.00 selling price a pretty good value.

Technical Specifications

  • Frequency response: 10~20kHz
  • Impedance: 30ohm @1000 Hz
  • Sensitivity: 110dB @1mW
  • Driver: 4 Balanced armature (2mid,2high)2 LEAR 6mm Dynamic bass driver
  • Crossover: Passive 3 way+ acoustic low pass filter

4 Responses

  1. givemeyourshoes

    Nice write up! And what a crazy and unique design. It’s nice to see a company innovate, as there isn’t much left to try these days.

    One quick note, 64 Audio no longer sells the V series CIEMs, so stating it competes with the V8 would only apply to 2nd hand units purchased or those that already own it.

    • headfonics

      Yeah I noticed, though I have been inquiring if there is significant change from the V8 to to the A8 and the answer maybe none and just a name change.

      • givemeyourshoes

        The V series from 64 audio is a standard CIEM, where as the A series moves to their ADEL technology. From my understanding its way more than a name change, and the ADEL technology changes the sound, plus makes for a safer listening experience. It also allows for user customizable turnings depending on if you opt for the -18db, -10db, or adjustable ADEL module.

      • headfonics

        I don’t doubt there have been some changes but the premise or pitch is the same – a basshead experience. The marketing and charts are virtually the same pitch as the V8. How much better or different to the old V8 I would be interested to know though. The price has almost doubled which is a shame.

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