Westone Audio MACH 40 Review

Westone Audio MACH 40 Review

This is a review of the Westone Audio MACH 40 which is a quad-balanced armature driver universal in-ear monitor from their new MACH series. The current price is £599.

Disclaimer: This is a sample sent in exchange for our honest opinion. Headfonics is an independent website that does not have any affiliate links. We thank both HiFi Headphones UK and Westone Audio for their support. 

You can click here to learn more about Westone Audio IEMs we have previously covered on Headfonics.

Note, that this article follows our latest scoring guidance which you can read here.

Westone Audio MACH 40 Review
Westone Audio MACH 40 Review
The Westone Audio MACH 40 has a rich, cohesive tuning that articulately blends the vocalist and instruments in the music together instead of pulling them apart for clarity. You can hear different backing instruments through the music, blending with the vocal but not over it, and the vocal performance sounds authoritative.
Slide here to add your score on the gear!16 Votes
Sweetened vocal
Slim profile
Consistent tone on different gears
Shy treble
Slightly power demanding
Reader's Score

We are back with Westone Audio’s latest MACH series MACH 40 earphones, the American company’s latest iteration of quad-balanced armatures designs featuring its proprietary 3-way, 4-driver configuration.

The MACH 40 inherits the aesthetics of the flagship model MACH 80, which means you can listen day-long without physical fatigue as it almost feels weightless in the ears.

The previous 4 BA releases from the company such as the Westone 4R were very popular models but how’s this sleeker successor going to perform this time around? We are all ears!

Tech Highlights

The MACH 40 under Westone Audio’s Premium Reference line houses 4 balanced armatures in a proprietary 3-way configuration featuring 1 tweeter, 1 driver for the mids, and 2 for the bass.

This is quite different from the MACH 50 which features dual tweeters, dual mids, and just 1 driver for the lows.

The MACH 40 is rated 100dB in sensitivity and 30Ω in impedance, which suggests that it is quite a bit less sensitive than the MACH 50 which has a 110dB SPL and a similar impedance rating. Despite this fact, it can be driven to sound dynamic fairly easily, even by my laptop.

Same as the other models in the line, the design features the T2 connector system that allows the design to be much slimmer than common MMCX/2pin connectors, and comes with the Linum SuperBax as stock cable.

This cable from Denmark measured just 0.6Ω in impedance and is extremely tough and light in profile.

Westone Audio MACH 40 Review


All MACH series products from Westone Audio come in the same housing design that is extremely sleek and compact. The layered, greyish theme looks futuristic and the finish on top is resistant to scratches. On the metallic front cover of the left side, the model number is labeled

Employing polycarbonate as housing material the MACH 40 is sturdy yet very light in weight, and the design allows it to spread the unit’s weight evenly on the ear without causing any stress. With the thin Linum cable, the overall design feels very professional and is ready for abuse.

Comfort & Isolation

We have been testing the new MACH series with a top-down approach and all members demonstrate excellent comfort with the rounded aesthetics, slightly tilted extrusion angle, and mega light profile that fits instantly on my ears without any needs to adjust throughout the whole listening session.

The almost weightless cable further enhances comfort especially when you put the cable behind the neck, the same way some artists wire their earphones to keep them away from view.

Microphonics is negligible on this set especially when you tie the cable behind the neck, and passive noise isolation is excellent no matter if you are using foams or the ear tips provided.

Westone Audio MACH 40 Review


The fitting and seal may contribute to the overall experience as well as the sonic qualities delivered. Westone is doing great in this department by including a lavish set of tips that are very well manufactured.

The tips are more elongated than common tips which helps enhance passive noise isolation and seal for firmer bass delivery. It also allows the weight of the IEM to spread more evenly on the ear. 

There are 5 pairs of silicone flanges and 5 pairs of Westone Audio’s True-fit foams such that everyone can easily find the best fit. Foam tips yield the best isolation and when being used it feels almost as quiet as using custom monitors, while the bass kicks slightly deeper and more prominent.

Westone Audio MACH 40 Review

Stock Cable

We have mentioned the stock cable Linum Estron SuperBaX a few times and this is one of the coolest stock cables on the market. Not only does it look professional and stealthy, but the low resistance rating also measured at just 0.75Ω allows coloration to the output.

The cable is very soft so there is no need to worry about memory effects and it doesn’t get tangled easily despite the gauge.

The slider with locking mechanism is also a handy feature that allows an instant, secure lock on the neck, this is much better than traditional slider designs that rely on friction and when used it could help suppress microphonics, securing the earphones in place even when running on a treadmill.

Westone Audio MACH 40 Review
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Packaging & Accessories

The compact packaging design is clean and futuristic like MACH 40’s other siblings. Inside there are 10 sets of tips, also an Impact Resistant Pelican carrying case that is practically designed for everyday carry.

Aside from that there are a set of cleaner tools and a cable binder plus an additional cloth bag for storage.

Sound Impressions

The MACH 40 has some of the pedigree of the MACH 80 and MACH 60 of the Premium Reference line. That means it inherits the smooth articulation over the midrange frequencies, also the distortion control power in the bass at a higher volume.

With four drivers it won’t be as resolving and extended especially in the upper register, so it is tuned towards being more rounded, sweetened, rolling off earlier in the upper register to form an M-shaped, retro-styled tuning but with agile response speed.

To my ears, the MACH 40 favors vocal works, pops, and EDM. It sounds pretty dynamic even when playing out of my MacBook. The higher impedance allows it to sound more consistent across different sources, where it remains smooth in articulation with an engaging, slightly mid-forwarded signature.


Having two drivers in the lows doesn’t stress its bass power, but focuses on the quality and air. Testing with big drums, you can feel ample bass power on the left side of the spectrum which colors it slightly to the warm.

Testing on the Hiby R6 2020 the bass sounds effortless and punchy with an elaborated decay. By feeding it with more power on the FiiO K9 Pro ESS, the bass gets firmer and faster but remains quite shy on the very low end.

The tuning matches well with pop and rock with its big and bold bass image and elaborative harmonics, which sounds very engaging with live music especially ones with a lot of drumming and acoustic elements. The bass line is also rhythmic, and the upper strings of the bass guitar are clearly defined.

On the other hand, the bass transients on the MACH 40 are quite dependent on the source. Faster and more powerful amplifiers will strengthen the resolution, but even when powered with smaller DAPs and dongles such as the HiBy RS2 R2R player, it doesn’t sound veiled or blurred.

The bass response seems to mimic dynamic drivers and is airy and relaxing, instead of extracting every bit of the details in the track and pushing some frequencies for clarity, compromising naturalness.

Westone Audio MACH 40 Review


The mid-bass on the MACH 40 is full-bodied but not fat, favoring low-pitched and powerful voices. You can hear the vocal line on top of the bass instruments, presented very naturally with just a hint of warmth adding to the vocal authority.

The separation power is satisfactory and when paired with a cooler-sounding or powerful source the vocal will cut through the mix more prominently. The MACH 40 works well with streamed content which often tunes up the bass and upper mids for clarity and stronger dynamics.

When testing with the RME ADI-2 Pro it sounds more controlled and tightened, bringing more power to the upper mids. Resonating vocal harmonics are well captured too as such older blues and pops with stronger vocal effects from the 80s-90s are a joy to listen to on this pair. 


The treble on the MACH 40 isn’t exactly shy but well-polished to take away harshness, it doesn’t get hot even when listening to sharp violins or sopranos at high volume, though it is not that exciting if you want sharp cymbals and very forwarded treble frequencies.

The MACH 40 sounds fairly expansive but you may find it not grabbing as much detail in the treble as some other IEMs that boosts the very high frequencies to sound clearer and wider.

The MACH 40 doesn’t take this approach and chooses to be more loyal to the recording opting to be more precise and unaltered which aligns with its reference monitor positioning.


As the vocal penetrates through the mix and stays on top, the MACH 40 brings the listener closer to the performer and has its bass slightly elevated such that vocal works sound intimate and immersive.

The vocal image is elaborative, as are acoustic guitars which are well-weighted and it works best with songs that don’t have too many instruments backing the track.

You can clearly feel the presence and picture where the acoustic guitar radiates from as if the performer is pointing the wood cabinet to you a few feet in front.

The cozy, unintrusive tuning does not overly stretch the headroom and it sounds natural with air and harmonics delicately captured. The treble has decent control and even at high volume instruments are still well-defined without blurring all over.

Click on page 2 below for pairings and our select comparisons.

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