Review: Metal Magic Research GáeBolg – Of Brilliance and Bloodlust

The dark arts. Ooh.
The dark arts. Ooh.

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A design for life and a quest for perfection, Metal Magic Research’s GáeBolg screams “one-of-a-kind” in every facet and fiber of its being.

Times are tough. You can pretty much get by on a single paycheque, but to appreciate the finer things in life (like caviar, champagne, and taking selfies with luxury cars you’ll never own) you need a main job, a side hustle, and a side hustle to your original side hustle. All of this can be circumvented by having a solid investment plan, and as I type this amid tears, you know I don’t have one.

Mr. Joseph Mou knows all about side hustles, oh yes. Not content with being the founder of well-regarded high-end IEM brand Jomo Audio, he’s gone on to the extensive research of metallurgy, alchemy, and the dark arts (I kid, I kid) that led to the foundation of Metal Magic Research, or MMR.

MMR was established to break free from the shackles of being a 100% Singapore-based venture. Led by an international team of specialists in industrial design, manufacturing, marketing, and research – like the United Nations of IEM companies – MMR pursues the cost-no-object route to create breathtaking works of art. Their first two IEMs, Thummim and Homunculus, are statement pieces of their philosophy.
Bottom Line

Metal Magic Research's GáeBolg must be the Bohemian Rhapsody of IEMs, armed with an assortment of hooks. The intricate design and construction are one, as is the captivating, take-no-prisoners sound signature. It won’t be a stretch to say that GáeBolg are a pleasurable multi-sensory experience, a feast of vision, sound, and touch that reflects your good taste.

What We Like 😍
  • Avant-garde design
  • Exemplary build quality
  • Good fit and comfort
  • Superb isolation
  • Overall tone and timbre
  • Epic-scale, engaging tuning
  • Full-bodied, dynamic bass
  • Lifelike, captivating mids portrayal
  • Masterclass vocal performance
  • Extra deep soundstage with meticulous layering
What We Don't Like 🤢
  • Large earpieces
  • Full-on signature might overwhelm
  • Bass decay affects resolution and speed
  • Rolled-off treble
  • Narrow soundstage

Britney Spears

Today we look at the boldly-named GáeBolg, the gateway IEMs for MMR’s cause. The name draws inspiration from Gáe Bulg, or “spear of mortal pain,” a weapon from Irish mythology wielded by demigod Cú Chulainn. GáeBolg are made of 5 custom-tuned BAs and a 4-Way passive electro-frequency division system, delivering sound via a patented and customized GáeBolg Acoustic Chamber (GBAC).

Of course, it would be remiss if I did not mention the pièce de résistance, the full aluminum housing featuring a jaw-dropping faceplate design. The faceplates are painstakingly CNC-machined, sandblasted, and colored a striking scarlet, resulting in an absolute aesthetic delight sure to turn heads.

Where To Buy

The GáeBolg are available from MMR’s official website in Lite or Complete packages. The Lite, priced at USD 1199, are the GáeBolg IEMs paired with a stock cable, whereas the Complete at $1399 includes the Eletech Prudence cable “to enjoy GáeBolg’s tuning in full.”

I’d like to give my sincere thanks to Joseph for the review sample and for allowing me to be a part of the virtual launch event.

Equipment Used:


  1. FiiO M15


  1. Metal Magic Research GáeBolg
  2. Stealth Sonics U9 JDM
  3. Unique Melody MEST


  1. Amber Rubarth – Sessions from the 17th Ward
  2. Daft Punk – Random Access Memories
  3. Dua Lipa – Future Nostalgia
  4. Fleetwood Mac – Rumours
  5. Kendrick Lamar – To Pimp a Butterfly
  6. Lana Del Rey – Born To Die
  7. Taylor Swift – folklore
  8. The Eagles – Hell Freezes Over
  9. The Weeknd – After Hours
  10. Tool – Lateralus

Technical Specifications

  • Driver: 5 Custom-Tuned Balanced Armatures
  • Configuration: 1 Tweeter, 1 Vented Mid-High, 1 Mids, 2 Vented Lows
  • Crossover: 4-Way Passive Electro Frequency Division
  • TriBore Waveguide
  • GáeBolg Acoustic Chamber™
  • Frequency Response: 20Hz-40kHz
  • Impedance: 25ohm
  • Noise Isolation: -18db

Packaging and Accessories

Being an early adopter ain’t easy. I received the reviewers’ care package, which has the GáeBolg, large Acoustune AET07 ear tips, stock cable, and a metal carry case. Rest assured what you’re getting, dear reader, is much fancier. Days before GáeBolg’s official release, I was treated to photos of their official retail package.

Photo courtesy of MMR.
Photo courtesy of MMR.

The full Irish breakfast, if you’ll pardon me, has a gorgeous, grandiose presentation box with Celtic symbols and artwork, in a black/scarlet theme. You will get the full gamut of AET07 ear tips in various sizes, a cable of your choice, an exquisitely-designed leather carry case, and what looks to be a metal membership card. Extravagant, yes, but befitting GáeBolg’s storied stature.


GáeBolg Complete comes paired with Eletech Prudence, a silver-plated copper cable. You can read more about the cable’s physical attributes in my review while I dive into the sound characteristics here. The Prudence, in my words, is a “caffeine shot for IEMs, injecting youth and vigor into otherwise lifeless sound signatures, awakening them from stuporous slumber.”

These words hold true still, and I can safely say that the synergy between GáeBolg and Prudence is beautiful and impactful.

On their own, the GáeBolg sound full-bodied and eminently majestic. Prudence improves on GáeBolg’s technical attributes by tightening up the bass, revealing more note definition, and providing a dark background for it to shine its brightest (or stab its deepest, you choose). The end result is a vibrant, immersive listening experience that, to me, justifies the asking price.

People don't say MFEO anymore, shame.
People don’t say MFEO anymore, shame.

Design and Build Quality

Within these aluminum shells are feats of technical wizardry. The BA drivers aren’t lifted off shelves nor ordered en masse, but rather precision-built and custom-tuned to MMR’s requirements. Each driver serves a specific range of the audio spectrum, and are integrated using MMR’s own crossover design, dubbed the 4-way electro-frequency division (EFD) system.

And further off the beaten path, rather than use traditional sound tubes to direct audio to the listener, MMR deploys a patented, exclusively-made acoustic chamber for the task. Appropriately named the GáeBolg Acoustic Chamber (GBAC), the chamber is in charge of phase correction and dampening before delivering optimized sound from the drivers to the TriBore Waveguide, a triple-bore structure at the nozzle.

Tin Can

You won’t see the above engineering marvels, though, as they are safely contained within the aluminum shell halves that form the earpieces. In front, the faceplate design features the Gáe Bulg spear with fierce, ruby-red tribal accents set against a matte black background. At the back, a Celtic symbol atop a raised backplate calls your attention, as does a thick, robust sound nozzle that tapers towards the end.

GáeBolg possesses one of the most elaborate and desirable designs I’ve ever laid eyes on.

If looks could kill, please, slay me now. The level of detail poured into the earpieces impresses from the inside out, particularly the faceplates’ hyper-precise CNC machining. The construction is also noteworthy, boasting a solid, resilient build contrasted with smooth finishing throughout the inner surface, and always with an eye on ergonomics. This is a transcendent build that represents the pinnacle of quality.

They'd make great stocking stuffers.
They’d make great stocking stuffers.

Fit, Comfort, and Isolation

Bearing the name of a legendary spear and the appearance of a tattooed warrior à la the Rock, you can bet GáeBolg are as conspicuous as they come. Ever eager to show off their ink, the shells are unapologetically large. This might pose a problem for users with smaller ears, but thankfully the earpieces are lightweight despite the all-metal build, and the angle of the nozzle helps greatly with the fit.

Just the nozzle angle itself is not sufficient, though, as they need to have good length too. I cannot stress enough how nozzle length affects fit, and GáeBolg delivers. Paired with just about any ear tips of reasonable length, once they’re on, they stay on, rarely breaking seal. While the GáeBolg’s weight doesn’t really disappear, they won’t weigh your ears down and are actually comfortable enough to be worn for hours.

Fortress of Amplitude

Being an all-BA IEM means there aren’t any vents in the aluminum enclosures, so GáeBolg’s isolation quality is excellent. They can drown out indistinct hums and idle chatter, and with the music loud enough, you’re in your own world. It’s good enough for commuting, but the amazing isolation means you might miss out on casual compliments by passers-by, denying you a chance to show off.

Long and thicc. Shiny too.
Long and thicc. Shiny too.

Sound Quality

Look, I’m stoked, and maybe you are too. IEMs that look and feel this good should sound up to par, at least? Before you can say Gaylord Focker, let’s analyze the sound characteristics.

Overall Sound Signature

The GáeBolg possess a gargantuan sound that is big, bold, ballsy, and boisterous, like a Death Star marching through space.

Their most distinguishing features are condensed to three D’s – darkness, depth, and dynamics. Darkness in the sound signature and the pristine, pitch-black background. Depth referring to the deep, abyssal soundstage, and dynamics as in excitement and fervor.

Before we get carried away, the heart of GáeBolg’s signature is L-shaped, which depicts enhanced bass and lower mids regions, a mostly neutral mids response, followed by a slight rise in the treble. Notes are full and weighted, resembling board strokes of a brush rather than precise markings of a needle. Unique to GáeBolg is the fanatical layering from front to back, owing to the soundstage’s tremendous depth.

L is for Lavish

The GáeBolg are a colored IEM that prioritizes musical enjoyment and a rollicking good time above all, reveling in engagement factor and an agreeable tone. The tuning is anti-reference, so the obvious shortcomings come in detail retrieval and resolution. Still, by then, you’d probably be having too much fun to care, willingly succumbing to the manhandling that GáeBolg dishes out for free.

Listening Conditions

Critical listening was done after 100 hours of burn-in, because you never know if extra metal or magic might happen. The main review setup is FiiO’s M15 player, Eletech’s Prudence cable, and the provided AET07 ear tips.

Like Phil Collins would say, we need to hear both sides of the story.
Like Phil Collins would say, we need to hear both sides of the story.


A good day is when you have pie; a great day is when the pie has more meat than crust. I present GáeBolg’s bass section, the meaty monster. Characterized by fully-formed notes and a bloomy, lingering decay, the bass is as lush as it is organic, with excellent timbre to match. Like a lounge chair to sink into, the bass is a smooth and easy listen, albeit in large doses.

Sub-bass reach is decent, with some rumble felt in the throat, but the focus is mainly at the midbass. The size of the notes cannot be ignored, in both magnitude and length. Notes attack and decay with such roundness and smoothness I don’t think “attack” is an appropriate word. It’s more “smother with fluffy pillows” with its rich and decadent texture.

Hippo in a Tutu

Don’t be fooled by the lovey-doveyness, though, for GáeBolg’s bass packs physicality and dynamism, pounding waves of solid authority thanks to its expert layering and depth. More than once I thought, “notes this size shouldn’t sound so clean,” but yet, they do, with the midbass and upper bass staying clear of the mids.

The plus-sized bass yields one problem; that is, the hefty notes will inevitably lead to congestion in complex passages. No matter how effective the layering is, physics always wins. The rounded texture lacks bite and definition, too, preferring to lull you with teddy bear fists. Resolution, clarity, and speed are not um, up to speed for GáeBolg either, due to the lengthy note decay. With a bit of tightness, the bass would have been flawless.

Want a good time? Many strings attached.
Want a good time? Many strings attached.


You have the mental metal and the radical research, but what lies in the middle? Magic. Beautiful, blissful mids magic. The overall tone leans toward a mellow warmth, while instrument timbre is natural and accurate with a sweet, golden hue. Notes are rich with grain-free fluidity and luxurious texture, like a well-made Magnum ice cream ad.

Vocals, especially, are given a spot in the limelight with their stunning portrayal. The enhanced lower mids gives a gruff, chesty character to the male voice, while a slight taming of the upper mids gives a velvety allure to female singers. Positioned just slightly in front, vocals entrap the listener with its sweet, sweet poison.

Mids Medication

Instruments, too, are given preferential treatment. Hear as strings and pianos swell with pride and emotion, as they sweep you off your feet with haunting realism. And unlike the bass, the size of the notes are just right, weighty and wispy in equal measure, and brimming with detail. Like a trip to nostalgia, you’ll want to experience this again and again. Once more, with feeling.

GáeBolg’s mids are as charming and captivating as they come, with lifelike renditions that send chills down my spine.

I'm growing into you.
“I’m growing into you.”


GáeBolg’s treble might have to participate in a weight-gain program to match the bass and mids’ size and girth, but thankfully it has other ideas. Striking out on its own to pastures new, the treble deviates from the rest of the signature by showcasing nimbleness and grace while maintaining GáeBolg’s trademark impeccable tone.

The Hummingbird

The lower treble is raised to bring some much-needed energy and sharpness to GáeBolg’s heavy-handed signature. Notes flit past and sparkle with purpose and refinement yet sound coherent with the rest of the spectrum. The middle treble is neutral and ever-present, giving the signature an airy boost to help with the painstaking instrument layering.

Unfortunately, the treble drops off after the mid-treble, losing out on the last vestiges of micro-detail and resolution. You can view this indiscretion through an optimist’s lens, though, that the treble is consequently rendered merciful and forgiving. I wish I were an optimist.

Parting the red sea, are we?
Parting the red sea, are we?

Soundstage and Imaging

Ever watched an episode of Twilight Zone and wondered what would happen if you slipped into the vortex? Would you spiral into the great beyond, or emerge at the other side, if there was one? An audio review is not where to look for answers or meaning in existence, sorry. However, two of GáeBolg’s strongest attributes, the depth and darkness, surface in this section, fittingly.

Simply put, the GáeBolg possess one of the deepest soundstages I’ve ever heard. The listening experience is akin to staring down a tunnel or witnessing Wile E Coyote fall off a cliff with a puff of smoke in the end. Audio imagery projects in front of you, with a strong, prevalent center image, and intricate, manifold layering taking hold.

Dark City

The intense depth, coupled with the immensely dark background, are chief reasons why the GáeBolg manage to sound organized and uncongested even with full-bodied, broad-brushed notes. Layering and imagery are precise as they are detailed, containing libraries of musical information at their fingertips. The only trade-off is the narrow soundstage.

There’s a learning curve involved in getting used to its unique presentation, but once you’re adapted, the GáeBolg hit like an avalanche.

Shootout at the Okayyy Corral.
Shootout at the Okayyy Corral.


Stealth Sonics U9 JDM

The U9 JDM are my gatekeeper for $1000-and-over IEMs, bringing a fun and detailed all-rounder sound with nary a misstep. Like the company’s namesake though, it has flown under the radar but remains one of my go-to recommendations for people with deep pockets. Against the GáeBolg, this is the battle of Singaporean manufacturers. What’s at stake? The hearts, minds, and ears of enthusiasts everywhere.

The GáeBolg issue a mission statement almost immediately, with their bold and boisterous signature overshadowing even U9’s exciting U-shaped sound. The Metal Magician have more wholesome and rounded notes coupled with a forward and dynamic presentation, resulting in a better engagement factor for the listener. You can’t help but be sucked into GáeBolg’s brand of musical immersion.

In the bass, the U9 have a more physical, party-certified sub-bass thump, but for both IEMs, the midbass slams equally hard and punches just as clean, with GáeBolg having a longer decay. The GáeBolg triumph in the mids with a distinctly smoother and more realistic timbre than the U9. Vocals, both male and female, are filled-out, grain-free, and placed forward, captivating and siren-like.

Unite for U9

Up top, the transition from mids to treble is smoother on the GáeBolg, as opposed to the U9’s lively upper end. GáeBolg shimmies and shimmers while U9 shines and sparkles, exciting but more prone to peakiness. For staging, the U9 follow the traditional route with a wider soundstage and diffuse left to right imaging. The GáeBolg offer a different flavor altogether with a deep, deep stage with intricate layering.

Both are adept performers in their class, but what I feel clinches it for the GáeBolg is the better mids tuning and timbre, being the more immersive and natural-sounding one of the two. Still, both are bags of fun, and you won’t feel short-changed either way.

Flex marks the spot.
Flex marks the spot.

Unique Melody MEST

Like Scorsese or Wes Anderson films, Unique Melody’s MEST are one of the critics’ darlings of 2020 and will be among the frontrunners for best-loved IEMs this year. UM is more known for their mad-scientist tendencies (the quadruple-hybrid MEST are a testament to that), but with a rich history dating back to 2006, this grand-daddy knows how to tune!

Right away, the MEST shine like a light through the fog, with a healthy dose of clarity and air throughout the spectrum. Stepping back from the full-on sonic indulgence of GáeBolg, MEST are clearer, airier, and more articulate, altogether more neutral. The mids are leaner and more relaxed, but with an equally arresting tone and timbre. Vocals and instruments sound luscious and sweet with fantastic focus.

At both ends, we see better extension and detail levels for MEST. The sub-bass has more natural rumble and physical thump, throbbing, and gloating with ease. The midbass is lesser in quantity than GáeBolg, leading to a cleaner stage and leaner lower mids. MEST’s treble is aggressive with high levels of energy and sparkle, and while superbly clear, introduces some grain that might be unwelcome.


What’s welcome though, is MEST’s awesome impression of space. Aided by an extra-wide soundstage with ample breathing room, air flows freely and gives notes extra definition and bite. And while stage depth is just shy of GáeBolg’s gaping abyss, imaging accuracy and layering are just as well executed.

Taken together, the GáeBolg are overall more aggressive and unabashed, focused mainly in the center image, with intense, headbanging qualities. MEST meanwhile, have an all-rounder quality tuning with dollops of whimsy and fun, whose only real complaint is slight treble grain. The MEST are a technical and musical masterpiece not to be messed (sic) with, while GáeBolg are not far behind.

I have chips and snacks. Marry me?
“I have chips and snacks. Marry me?”

Final Words

I grew up in an era where the catchiest part of a tune was called the chorus. When the word was changed to “hook,” I have no idea, but it does make hella sense. The hook, be it in songs, fishing, or marketing, is designed to reel them suckers in (sorry) and to sell. To use another term, it’s a unique selling point to differentiate themselves from a vast sea of similar unmentionables.

In that sense, Metal Magic Research’s GáeBolg must be the Bohemian Rhapsody of IEMs, armed with an assortment of hooks. The intricate design and construction are one, as is the captivating, take-no-prisoners sound signature. It won’t be a stretch to say that GáeBolg are a pleasurable multi-sensory experience, a feast of vision, sound, and touch that reflects your good taste.

Is This the Real Life?

Fortune favors the bold, and in branching out from Jomo Audio, MMR tapped a rich vein of creativity, all in the name of furthering the mastery of portable audio. From the materials to the tuning, they provide a refreshing change in perspective, just when the hobby is growing stale with cookie-cutter tuning templates and uninspiring designs. I’m genuinely excited to see what MMR will come up with next, although my wallet won’t be too happy.

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