Westone MACH 40 Review

Westone MACH 40 review featured

In this IEM review, I’m looking at the Westone MACH 40. The MACH 40 features a proprietary four-driver system with dual lows, single mid, and single high and a 3-way passive crossover. The price is $599.

Disclaimer: This sample was provided by Westone for an honest review. All observations and opinions here are my own based on my experience with the product.

Westone MACH 40 Review
The Westone MACH 40 has a warm, fatigue free sound that maintains accurate timbre and tone.
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Rich, intimate vocal and acoustic performance
Natural and organic sound signature
Smooth, warm tonality
Non-fatiguing treble
Micro-detail retrieval could be better
Intimate soundstage
Treble lacks energy, affecting overall vibrancy.
Our Score

Westone MACH 40


Sensitivity: 100dB @ 1kHz
Freq. response: 10Hz-20kHz
Impedance: 30 Ohms @ 1kHz
Driver configuration: Dual Balanced-Armature Bass Drivers, Dual Balanced-Armature
Midrange/Treble Drivers

In the Box
  • Mach 40 Universal fit In-ear Monitors
  • CABLE: Linum SuperBaX™ T2 Cable
  • TIPS: 5 Pair Foam + 5 Pair Silicone
  • Impact Resistant Pelican™ Case
  • Westone Audio Cloth Bag
Westone MACH 40 design


When examining the Westone MACH 40 shells, a futuristic aesthetic emerges. The space grey polycarbonate composite exudes sleekness, complemented by a lightweight metal faceplate.

A prominent feature is Westone’s iconic super-narrow nozzle design, particularly accommodating for those with petite ear canals. However, it can present challenges for tip-rolling.

Venting becomes unnecessary, thanks to the all-BA driver configuration. Craftsmanship shines, evident in the flawless joins and uniform segments.

Comfort finds a home in the MACH 40. The largest (15.5mm) stock foams are my preference, ensuring a perfect seal. The lightweight shells nestle comfortably in the concha area, and the ventless design enhances passive noise isolation—an asset for live stages and studio monitors.

The included LINUM® ESTRON SUPERBaX™ cable boasts a mere 0.75 Ohms resistance, promoting uncoloured sound. The T2 connector system, my preferred choice over MMCX, offers superb connectivity, though swapping cables requires T2-compatible options.

MACH 40 skinny nozzles


Gear used for testing includes the Topping MX3s, xDuoo XP 2Bal and Moondrop Moonriver 2: TI. The MACH 40 isn’t all that hard to drive but I found it performed better with decent sources like the ones listed above. Giving it some good amplification brings out the best in this IEM and maximises its grasp on dynamics.

The overall sound signature of the MACH 40 is warm and silky smooth, incredibly organic and inoffensive. It won’t please listeners looking specifically for big bass or sparkling treble. However, those looking for an authentic tone and something you can listen to for hours on end without experiencing fatigue will fall in love with this IEM.

I found the MACH 40 to sound good with all music genres but it really shines with vocal and acoustic music. In addition, I found it perfectly suited to rock music and especially forgiving on poorly mastered or aggressive rock recordings.

Westone MACH 40 frequency response graph

Being an all-BA IEM, the MACH 40 doesn’t seek to astonish with thunderous bass impact. Rather, its brilliance lies in the precision and authenticity of its bass rendition. Mid-bass notes exhibit a satisfying punch, akin to dynamic drivers, but as anticipated from all-BA IEMs, the sub-bass won’t induce tooth-rattling vibrations.

This bass presence gracefully infuses warmth into the midrange, devoid of any undue bleeding or bloat. The MACH 40’s bass performance becomes a cornerstone of its sonic signature, seamlessly interweaving with the other frequencies to craft a cohesive sound.


If you love an organic midrange, the MACH 40 is tuned for you. The mids here are rich and articulate and extremely natural. There’s one caveat, though: If you’re looking for ultimate (unrealistic) clarity and brightness, you won’t find that here. What you will discover is accurate timbre, with vocals taking centre stage, resulting in an engaging yet non-fatiguing presentation.

MACH 40 faceplates

Those rock albums with gritty electric guitars that often induce cringing, especially on “high-fidelity” IEMs? Put your worries aside. The MACH 40 offers buttery mids that you can enjoy throughout the day. However, it’s worth noting that they may not be the cleanest or most articulate. But rest assured, you don’t often hear mids that sound this natural and effortless.


The treble of the MACH 40 IEM is likely to spark a range of opinions among listeners. It boasts a velvety smooth character that faithfully preserves the essence of the original recording. This attribute aligns well with the essence of a reference monitor, as it offers an authentic and non-fatiguing sound profile. However, this treble doesn’t carry the most riveting or intricate quality.

This laid-back treble quality plays a role in imparting a slightly darker and velvety demeanour to the midrange. While the treble’s timbre remains true to life and possesses an airy quality, it’s positioned toward the rear of the sound mix. Musicians, audio professionals, and those sensitive to treble nuances are likely to be drawn to the MACH 40’s gentle and ethereal treble presentation.

Soundstage and Technical Performance

The soundstage of the MACH 40 IEM can be described as moderately intimate, a direct consequence of its prominent vocal presence and warmer tonal characteristics. Furthermore, the reserved treble nature contributes to a narrower stage compared to the expansive effect often found in brighter sound profiles. However, there’s a silver lining—the MACH 40 maintains commendable resolution and adept instrument separation. Despite the intimate feel, the stage manages to avoid any sense of congestion or stuffiness.

On a slightly less positive note, the velvety smoothness of the treble has a notable impact on detail retrieval. While prioritizing the comfortable and organic sonic signature, the treble’s texture doesn’t effectively expose micro-details.

Westone MACH 60 review featured
Comparison with the Westone MACH 60

The Westone MACH 60 (review here) has an identical design on the exterior but has 6 BA drivers (dual lows, dual mids and dual highs) compared to 4 drivers in the MACH 40 (dual lows, 1 mids and 1 highs).

The MACH 60 IEM showcases a heightened equilibrium among bass, mids, and treble frequencies, whereas the MACH 40 leans towards a warmer tone with a stronger bass focus. This divergence leads to the MACH 60 boasting a more expansive soundstage, enhancing its ability to delineate individual instruments in complex compositions.

Delving deeper, the MACH 60’s sonic character enhances its capacity for detail retrieval, particularly when it comes to micro-details. As a result, the MACH 60 cultivates a more spacious auditory panorama, allowing for increased separation between each instrument and vocal element.

Westone MACH 40 with DAP


In summary, the Westone MACH 40 IEMs offer a warm and smooth sound that caters to authenticity and listening comfort. Positioned as a slightly more casual alternative in the MACH series, these IEMs excel in vocal, acoustic, and rock genres while accommodating less-than-perfect recordings.

The precision in the bass, natural midrange, and velvety smooth treble create a balanced sonic signature. Despite a narrower soundstage due to its warm tone, the MACH 40 maintains strong technical performance with commendable resolution. While micro-details could be more pronounced, the IEMs remain an excellent choice for live performers and audiophiles seeking accuracy and fatigue-free listening.

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