Xiaomi (or Mi for short) have been on a roll, showing time and time again that you don’t need to pay much for quality, style and functionality. Their portfolio of electronics continues to grow, as does their brand presence, spreading out radially from China.
As a (primarily) mobile device manufacturer, their diversification into selling mobile phone accessories was very fitting, and their efforts have not gone unnoticed. Their most popular In-ear Headphones, produced by 1More Design, achieved a 2015 Red Dot Design award and has been a highly recommended budget option around the internet. Just recently, on the 11th of November, Xiaomi launched their new In-ear Headphones Pro (English|Chinese) to the Chinese market, a follow-up product produced by 1More Design. This promises to be even better by bringing a hybrid dynamic and balanced armature driver configuration while still sporting an extremely affordable 99 RMB / SGD 27.99 price tag (roughly AU$21 to 28 by conversion).
Thanks to the generosity of the PR staff at Xiaomi Singapore, I was sent a set of these directly for review under the review challenge terms. As usual, the standard disclaimer around Xiaomi products apply – namely that there are possibly counterfeit items floating around, so please purchase from only known authentic sources to avoid disappointment.
As I received this product direct from Xiaomi, there is no doubt as to the authenticity of the product. High resolution images of the unboxing are provided to illustrate the inclusions, and may serve as a point of reference if in doubt as to the authenticity of your product.
The product comes inside a milky white plastic bag with an adhesive edge seal. There is a barcode label on the outside of the bag, which allows the product to be scanned without removing it. There is a bit of yellow on the adhesive in my photo, as it had stuck to the cardboard box in shipment.
As with other Mi products, the box sports a very simple, clean look, featuring a clear window on the front that allows you to admire the fine details of the milling processes used to create the earphone chambers and remote control body. The rear of the box features Chinese text, and gives an overview on specifications – namely 32 ohm impedance, 14 gram weight, 1.25m cable, 101dB/mW sensitivity, 5mW power rating and 20-20,000Hz frequency response. That being said, most people would know by now to take these specifications with a grain of salt as they rarely describe much about how good a set of earphones is to listen to. The box is opened via a tear-off strip, and the bottom is sealed with a circular transparent plastic label, which ensures hygiene by ensuring the package is tamper evident.
While the product is called the Mi In-ear Headphones Pro in English, realistically, it is considered an earphone or canalphone or even vaguely, an in-ear monitor (IEM). I will use these terms interchangeably.
The top of the box features a break-away section as a hanger, for use when displaying in shopfronts, and the bottom has logo-text which shows that the product is the work of 1More Design, who were responsible for previous award-winning efforts in the Xiaomi range.
Opening the box up is a joy, thanks to some intelligent packaging design. The rear card which has a tab at the top makes it easy to slide everything out without any fuss.
Included are the earphones, which come pre-fit with the medium-size silicone tips. The first thing you notice when you handle them is the build quality, which is second to none. The metallic chambers are all milled and engraved, with fine details showing up in the polished finish. Each of the chambers appears to be vented for better frequency response. These are mated to the plastic front and stiff plastic lead-in for the wire. The plastic front has a moulded area to show which side is the left and right, although the remote control also serves as an indication as it is always on the right. The stem is standard in size, allowing you to use other tips if necessary. The end of the stem has a metal mesh filter.
From an aesthetic point of view, they are very pleasing, and the lack of obvious branding aside from the “HD Audio” text is a big bonus for those who don’t want to be too conspicuous with their choice of earphone.
When fitted to the ear, I had no big irritations, although the stem of the plastic did get close to my face, it did not cause any irritation or indentation. The medium-tips that came pre-fitted was sufficient but slightly loose for my larger ears, whereas the large tips were a little too large and caused slight irritation due to the pressure.
The remote control features three buttons, with the three buttons functioning on some Android handsets, whereas on others they all seem to perform the same action (probably handset dependent too). On iPhone, the center button works, but the outer two appear to be ignored. These actuate with a nice click, and the two outer buttons have a raised edge to allow them to be identified by feel.
The craftsmanship continues with the remote body, where a sharp cut-out is made in the rear for the microphone, and the shallow ribbing is seen in the metal. It is very surprising to see this kind of build quality at a price where most competitors are putting out flimsy plastic headsets with visible seams.
The wire to the headphones feels like a standard insulated PVC wire of the average sort of thickness for such headsets. However, that changes as soon as we meet the join where the left earphone cable meets the right. Here, there is a transistor shaped moulded joint with the Mi branding where the cable joins a thin braided wire to the plug.
At first, the braided wire felt almost too thin, but after some use, its merits became apparent. While it is thin, it seems sufficiently strong to stand up to everyday use, and the braiding adds strength to the cable. The side effect is that the cable seems to have less shape memory and loses any kinks or folds more readily than it otherwise would. The braiding also provides a textured slippery surface which helps prevent the cable from binding to itself, which reduces tangling almost completely and makes untangling and straightening the cable exceptionally trouble free.
The plug itself also has a milled metal body and strain relief and feels incredibly solid. The plug is a 3.5mm TRRS plug with CTIA wiring layout, making it compatible with iPhones and Android handsets, except some China domestic and older Nokia handsets which use the OMTP wiring layout. Due to this plug, it may not operate properly with basic music players which expect a 3.5mm TRS stereo connector. A tag is attached to the braided cable with the branding and a QR code for more information on the rear.
In all, four pairs of silicone tips (including the ones pre-installed) are supplied, ranging from XS, S, M, L. The tips fit very snugly, and seem to hold well. Also included is a Chinese instruction manual.
It would be nice if a TRRS to TRS adapter was included for compatibility with conventional music players and computers, and a portable carrying pouch as well, but I suppose that might be unreasonable given the price.
I spent a good week using the Mi In-ear Headphones Pro as my primary audio device both at home and during my commutes on public transport. In order to do this, a third-party (not included) TRRS to TRS adapter was used to allow the earphones to be connected to high-quality sources such as the Asus Xonar Essence STX sound card in my computer. Other sources were also tested, such as my LG D686 phone, iPad (3rd generation) and FiiO X1. These were used directly as they supported the TRRS connector.
Numerous listening sessions were held with FLAC rips of music which I am well familiar with to compare with my reference headphones, namely my AudioTechnica ATH-M50x. Other points of reference include my Ultimate Ears 200vi headset, AudioTechnica ANC23 in-ears and ANC9 headphones, and memories of my formerly owned Sennheiser CX300-II and Vsonic R02 Pros which both have been the victim of long-term use.
As a rule, opinions about how headphones sound are quite subjective and depend on a person’s “headphone resume”, as well as the condition of their ears and how they expect to hear a particular sound. What some reviewers may describe as analytical and harsh is the sound signature which I generally prefer, as is evident by my choice of reference headphone. It may be considered by some that comparing in-ears with over-the-head headphones at about ten times the price to be an unfair comparison, but this is exactly the sort of comparison you need to make if you want to know whether you are getting a good deal, and to know what you might be missing out on. Needless to say, I am the sort that can tell a FLAC from an MP3 with ease, especially at 128-192kbit/s, and I generally find the “bundled” headsets with phones to be quite unsatisfactory, so I’m not exactly making things up.
As is common with most IEMs, especially recently, they often have a punchy bassy character, and the Mi is no exception. It appears that the Mi has a pronounced sharp boost to the boomy bass in the 50-100Hz range, which makes a strong showing in songs such as Sir Mix A Lot – Baby Got Back, Lady Gaga – Starstruck, Black Eyed Peas – Imma Be and 3OH!3 ft. Katy Perry – Starstrukk. Despite this, the bass was relatively tight and clear, rather than a “one note” boom.
Since the bass hump is limited, songs like Back-Eyed Peas -Boom Boom Pow seem to move in and out of the sweet spot, resulting in a slightly lopsided presentation. It is hearty to see that the bass response does still audible to below 23Hz, in the low notes of Sam Smith – La La La.
The midrange presentation is somewhat mixed, as the character of the lower-midrange between 200-600Hz seems to be slightly muffled or veiled in comparison to the upper midrange which is sharp and clear. This is especially notable with some vocals, for example, Jason Derulo – Breathing, Celine Dion – My Heart Will Go On, The Weeknd – Hills and Taylor Swift – Shake it Off. However, when compared with dynamic driver IEMs, especially at lower price-points, it still offers more clarity.
Other songs don’t seem to provoke this as much, and instead benefit from the added clarity of the upper mid-range allowing for a much sharper vocal presentation, for example Britney Spears – Overprotected, Mariah Carey – Always Be My Baby and Lady Gaga – G.U.Y.
It seems from my listening that K-pop and J-pop with cleaner mixes don’t seem to provoke this deficiency as much, and listening to many of the songs from SNSD, T-ARA, HyunA proved rather satisfactory in the mid-range. Electronic/Dance music and Rock music also seem to work rather well with the Mi, as the distortion is not as apparent in due to the very complex wall-of-sound (e.g. Linkin Park – One Step Closer) or more focused mix (e.g. Madeon – Icarus, Serebro – Mi Mi Mi).
Where the Mi excels is at the treble, where it completely blows all of the dynamic driver competition out of the water. The treble is very much present and sharp, even making MP3 encoding artifacts audible at times. However, it doesn’t have an overly sharp character, and like the mid-range, there seems to be some frequency ranges where it is not as clean and feels somewhat veiled. This added treble adds a bit of brightness and sparkle to instruments and sibilant sounds in vocals, for example, in Celine Dion – Falling Into You and Daft Punk – Digital Love. It definitely balances out the presentation and makes the Mi sound much sharper.
On the whole, the supplied silicone ear tips provided a good seal with minimal irritation provided the correct size is chosen. Aftermarket tips can be fitted to these, should you prefer them. Isolation was generally good as expected of IEMs, and sufficient to exclude most noise in commuting on trains and buses, although not quite as good as the active noise cancelling units I regularly use.
Overall Listener’s Verdict
On the whole, the Mi offers a much clearer presentation than pure dynamic driver in-ears. It is much sharper in all ranges than the CX300-II and UE 200vi and the treble adds much needed sparkle to instruments and the upper-midrange clarity brings out more from the vocals. Best of all, the bass is not sacrificed in any way, and retains a tight and punchy character similar to the dynamic in-ears mentioned before, which may be a little strong in a quiet room, but is useful when commuting with competing background noise.
Compared with the reference, the slightly bassy character does cause the Mi to possess a slightly darker presentation by comparison. It is clear that there were compromises necessary, namely some veiling in the lower mid-range which may be due to resonance, and an inconsistent and nervous treble. However, in terms of casual listening, this is hardly objectionable and does take the edge off of the more analytical presentation I generally prefer, resulting in a more laid-back signature. That being said, male vocals do sound noticeably less clear, and certain genres of music needing the lower-midrange clarity can be seen to suffer slightly.
Some people might be put off by the small 5mW figure on the packet, but needless to say, they do absolutely play loudly enough for most people with decent hearing. I did not have to push them at all to achieve respectably loud volumes, and during testing of headphone impedance (later), they were so loud at the rated power that they were audible across the room.
Regardless, I did very much enjoy the Mi In-ear Headphones Pro, and much more-so than some of the other IEMs I have owned purely because the sound is quite agreeable even for an audiophile like myself, especially when the price is considered. I found myself more engaged with the music, and happily singing along, whereas other products often left me distracted with their more muddy presentation. It would be highly recommendable as an inexpensive upgrade to a regular OEM headset for someone who cares about their music as it easily outperforms even AU$70 options on the market today.
The adapter was used to connect the Mi In-ear Headphones Pro to a Zoom H2n handy recorder to test the microphone, as it had the best quality recording input of my family of devices. For comparison, an LG OEM headset, Samsung OEM headset and UE 200vi headset were also tested.
The recorded audio samples can be heard here.
On the whole, the Knowles microphone in the Mi can be heard to provide a more balanced sound with good bass and treble content, although it does have more background hiss compared to the other microphones probably because of the internal amplifier. The LG headset is more bass-oriented with limited treble response, whereas the Samsung has less hiss but also limited treble response and slightly less bass. Finally, the UE headset has almost no significant bass resulting in a thin tinny audio.
In the end, the Mi is not a bad performer at all when it comes to the microphone quality with a more natural balanced sound at the cost of increased background hiss. The on-call performance is less sensitive to the treble content due to the limited audio bandwidth of phone calls, so the differences are less obvious to callers.
Since the unit was built very well, I really didn’t want to try and tear it down, as that would very likely result in the destruction of the unit. Through the course of the review process, I’ve actually become rather fond of the earphones, so I really didn’t want to harm them. That being said, how can we be sure we are getting what they claim we are getting?
All of this ties in with one of my audiophile friends who asked me a while back about measuring headphone impedance over a range of frequencies. While I pondered on how that could be done, I didn’t actually go and do it back then.
Why is Impedance Important?
This is a rather deep topic, which North-West Audio and Video Guy have done a comprehensive article about, but it basically boils down to a few points:
- Audio sources, especially portable ones, have limited output voltage and current driving abilities. Having a lower impedance headphone allows for them to play louder for the same input voltage, at the cost of increased current. Some sources with high source impedance cannot drive high currents, and will cause distortion in frequency response with low impedance headphones.
- Headphones/Earphones are dynamic systems which present a changing impedance (real and imaginary) over the frequencies which they operate, meaning that a resistance measurement is not enough and distortion may present at certain frequencies and not others.
- Getting the right match between the amplifier’s output impedance and the headphone impedance ensures you don’t get distortion or unusual frequency response changes, and ensures appropriate electrical damping.
Generally, with portable equipment, most manufacturers have been targeting a 32 ohm impedance, and this is no different for the Mi In-ear Headphones Pro. However, some have gone as low as 16 ohm to maximise loudness, especially where output capability of the source is limited (e.g. EU). Checking the real impedance by measuring it will let us confirm the manufacturer’s specifications.
But that is not all, as there is a secondary reason for checking the impedance. It is known that the impedance of hybrid/balanced-armature driver systems varies tremendously as a function of frequency, and by measuring the impedance, we can confirm the presence/absence of this arrangement without taking the unit apart.
How do you measure it?
If you’re lucky enough to have access to a headphone analyzer, or something similar, then measuring this isn’t much of a difficulty. As I had access to an LCR meter, I thought I could use that to perform the measurements, however, it was soon apparent that it was not a good idea.
The earphones were specified for 5mW maximum power. Given the 32 ohm impedance, the maximum RMS input voltage was just 0.4V, which was below the testing voltage of the LCR meter which was 0.71V. If I had used the LCR meter, I would have been limited by the frequency selection and also would have likely destroyed the driver on the earphones.
Instead, I decided to hack a system together with a bit of vero board, three 13 ohm 5% metal film resistors (39 ohms) in series, a stereo plug, a mono socket and aircraft adapter (since I ran out of stereo sockets) and a few header pins to make impedance measurement possible.
The first thing you need is a source to drive the headphones and voltage divider. Ideally, for convenience and accuracy, a source with low output impedance is best. Initially, I had wanted to use a function generator, but it had an output impedance of 600-ohms (much too high). Using an op-amp voltage follower buffer was a possibility, but my best op-amps on hand had about 1-2 ohm output impedance. A simpler solution was to use a high quality audio player, namely my FiiO X1 which has a <1 ohm output impedance, and use a generated lossless audio file of a slow frequency sweep as the source.
The next thing you need is an oscilloscope to measure the AC True RMS voltage from the source, and across the headphone impedance. For this, I used my Picoscope 2205A 25Mhz USB-connected oscilloscope, and you can see the sweep in action here. The values were recorded manually every 200Hz from 200Hz to 24000Hz (and believe me, it was a time consuming process).
Of course, to be sure that the introduced resistance isn’t doing anything funny, I also tapped the bottom 1/3rd of the resistance stack and used it to determine the impedance of the resistor across the tested frequencies. Needless to say, that wasn’t particularly fruitful, as the result was within 0.1 ohms of the expected value, but it serves as a control check to make sure everything is working right.
The next step is to measure the actual resistance of your voltage divider. The more accurate you know the introduced resistance, the more accurate your derived resistance will be. For this, I used an Agilent Technologies U1733C LCR meter to measure the resistance.
Knowing the voltage from the source, the voltage across the unknown impedance, and the value of the introduced resistance, we can solve for the unknown impedance. The voltage divider is as follows:
Let: X = known resistance Y = unknown resistance Xv = voltage over known resistance Yv = voltage over unknown resistance Vin = voltage in (i.e. Xv + Yv) Then: Yv = ( Y/(X+Y)) * Vin Rearranging for Y, we get: Y = (Yv * X) / (Vin - Yv)
It’s not so hard after all, but it took me a while to work it out!
Because I had intended to do impedance measurements before as an experiment, I thought it would a good coincidence to compare the impedance of the Mi In-ear Headphones Pro with all of my other owned headphones and earphones at present. Unfortunately, this makes the results somewhat cluttered, as you can see.
The key point to take away from this graph is that dynamic driver based earphones have mostly stable impedances across the frequency range. Some will have small peaks which denote free-air resonance points. Another key point is that active noise-cancelling headphones have drastically different impedances when switched on (high impedance) and when switched off (low impedance) which may explain partly why there are significant frequency response differences between the two modes.
The next graph looks closer at the “regular” <48-ohm region in more detail.
We can see that my Ultimate Ears 200vi headset and the LG OEM headset both are 16 ohm units, which represent the lowest commonly found headphone impedance, optimized for loudness. In contrast, the Samsung OEM headset is 32 ohm impedance, as are the other over-the-head headphones tested. Generally, the better quality dynamic headphones had smaller resonance peaks, possibly as the manufacturer added mechanical damping to smooth them out.
The big stand-out is the Mi In-ear Headphones Pro which has an impedance curve that has a small peak about 2khz, a large peak at 4.2khz and a dip at about 18.5khz. This might imply a resonance at 2khz, a cross-over frequency of 4.2khz, but this type of curve is typical of a hybrid balanced-armature driver configuration. As a result, the impedance plot clearly shows that they are being true to their word and delivering a hybrid dynamic and balanced armature driver at a low price.
The result does, however, imply that higher impedance sources (>2 ohms) may see treble frequency response distortions, however, as more portable equipment is capable of driving 16 ohm headsets, this should not be a problem as the 16 ohm headsets are even more demanding than the Mi at its worst. This will mean that the Mi headset would not play as loudly at the same output as a result of its higher impedance.
Xiaomi have, in concert with 1More Design, bought us another product which is hard to fault especially at the price it retails for. For the first time, a hybrid dynamic and balanced armature driver configuration is seen in an IEM for under AU$30, which is impressive. For that, we get the best of both worlds – a strong well-defined bass, which is characteristic of dynamic drivers, as well as sharp treble from the balanced armature driver.
In reality, the product impresses with its strong well-defined bass, sharper mid-range and very prominent treble especially compared with the dynamic driver competition within this price range (UE 200vi). It also boasts a superior design and exquisite build quality which would not be normally expected at this price point. While the performance still falls short of that of high-end monitoring headphones, it is punching well above its weight and is easily preferable both in sound and build quality to the venerable Sennheiser CX300-IIs which normally retails above twice the price. Its performance is more than sufficient to fulfill the desires of the majority, especially when used in suboptimal conditions (e.g. commuting).
Because of its low price, and its very commendable performance, it makes a very good value choice for those conscious about sound quality and build quality and don’t want to spend at least four times more for something even better. In fact, even if you didn’t care about sound quality, you would still have to pay a very similar amount for inferior quality products, so why take that chance?
Readers interested in purchasing the Mi In-ear Headphones Pro should consult the Mi website for their region, or an authorized reseller. As the product has not launched in all markets as yet, it may not be available for purchase, however, I can definitely see this product being highly sought after.