Janine Elliot checks out the multi-driver Optoma HEM4 In Ear Monitors costing a penny short of £250.

Normally when I am confronted with multi-driver IEMs I am rather worried that the sound will be disjointed or confusing. In an ideal world a single driver is the best option, and generally the bigger the driver the better the bass, though there are some 5mm drivers that get pretty low as well as a speedy extended top end. So, to be confronted with a new series of four IEMs with 1, 2, 3 or 4 of the successful high-resolution Knowels™ balanced armature drivers for each ear was going to be interesting for me. The HEM4 as the second model in the range is equipped with two drivers, part of the range designed to please the budding on-the-go listener right through to the professional musician and audiophile.  American company Optoma really have pulled out all the stops to create a complete range of IEMs to please everybody. I have reviewed a number of Optoma IEMs in the past and this product was for me the pinnacle of my acoustic travels with the company.

The use of Knowels™ drivers is paramount to the success of this series of monitors. Their history goes back to 1946, set up by Hugh Knowles in the USA and originally making microphones, speakers for TVs, and hearing aids. Balanced armature drivers have actually been around since the 1920s primarily in headphones used with crystal radios, though they were then much bigger with the diaphragm round-shaped, like the soundbox on a wind-up phonograph. In the simplest of terms these modern rectangular shaped balanced armature receivers have a coil inside which due to inducing a magnetic field when playing audio through it moves one end of a “U” shaped metal unit which has a magnet attached. As the end of the u-bend moves about it vibrates a diaphragm above it via a minute “pin” that joins the two. The change of air pressure inside is forced out of a little hole which then forms the music you hear. Having several of these diaphragms inside, for specific frequencies is like having a 2 – 3 ½ way loud-speaker in your lugholes. A clever idea, but what is really clever is making sure the sounds mix well together. The larger the balanced armature receiver, the larger the diaphragm is and therefore it can displace more air making it potentially louder than a smaller one.


For this review I chose the HEM4, at mid-price of £249.99 as this is the sort of price an audiophile should start serious listening at. Designed for professionals and audio enthusiasts this model has two Knowels™ drivers; a larger and smaller diaphragm for low and high frequencies, respectively. In blue this was my favourite colour; the others are in red for the HEM2 and black for both the HEM6 and HEM8.  What always pleases me with Optoma products is the high level of accessories and standard of presentation, and this model was no exception. Not only is there a solid carrying case for you to put the headphones in (common to all in the range), but it also has a waterproof display case, just in case you take it into the shower with you. Whilst looking superb, like the waterproof cases for sports cameras, this case isn’t much use unless you remove the foam insert inside it which is to place the IEMS in when detached from the cables. Yes, you have a choice of two cables to insert, both of which are superb quality, but slightly tricky to do correctly, largely finding which is the left and which is the right lead, as only the earphones themselves have L/R, and the instruction manual isn’t that helpful with colour-coding of the cables. But, once you have mastered this (yellow line is right, white is left) makes future dismantling easy. Firstly there is a basic cable with microphone and inline remote, and a better looking braided high-end cable for the best possible performance. The high-end cable is made of OFC and silver, while the 2-pin cable connectors are a proprietary mix of silver and copper with separate ground return for each channel. Both cables have ‘L shaped’ 3.5mm jacks, a must for the serious audiophile. Not only does it look better and less likely to be whacked but it also reduces the chances of the socket being disconnected from the PCB on your portable player if knocked. The list of accessories is equally well thought out, with a 3.5mm – 6.3mm gold plated adapter, 5 pairs of soft silicone ear tips, 2 pairs of Comply™ memory foam ear tips, a cleaning tool with brush and a very important lapel clip.  I found that very useful; most manufacturers miss these out so I end up making something out of paper clips to save cables jangling about as I walk to the shops.

Putting on these IEMs can be harder than you think first time, as the cable needs to go around your ear-lobes and which then holds the earphones firmly in your ears,  but as a veteran of IEM testing I have now got it sorted. As a wearer of glasses I am not in favour of this method, but that is only my personal opinion. The Optoma instructions show you how to fit them around your ears in case you do need help, so you will also need a mirror. Once secured you hardly notice you are wearing them at all; doing swift walking and bending down didn’t budge them, largely explaining why this type of design is favoured by musicians and broadcasters. They are also very comfortable, especially using the Comply™ memory foam ear tips, which gave the better bass and sound isolation.

On first listening my thoughts were just how musical and exciting the sound was; they are very efficient players with 110dB sensitivity and a frequency response of 18-40,000Hz. The sound was very ‘forward’ showing a surprisingly excellent 3D soundstage for IEMs.   Listening to Sibelius Symphony No 2 (Simon Rattle, Berliner Philharmoniker 24bit/192kHz) showed an excellent warmth and clarity, with exceptionally fast transients, something also very noticeable with the acoustic guitar in David Gilmour Rattle that Lock ‘5 A.M’. It might be early in the morning but the instruments were wide awake and crystalline clear. I could even detect a squeaking gate at one and a half minutes in, perhaps David leaving for his mobile recording studio on the Astoria houseboat on the Thames, something I hadn’t heard before. The earpieces themselves are manufactured using an acoustically calculated, vibration-free Lexan™ polycarbonate resin which is an amorphous engineering thermoplastic, considered to have outstanding mechanical, optical, electrical and thermal properties. They are also very lightweight at 5 grams.

Whilst the mid’s and treble were exceptionally detailed and with a warmth that made you want to keep on listening, the bass was equally powerful. For those liking extreme bass clout you will not be disappointed; Pink Floyd Pulse track “Astronomy Domine” has an aggressive percussive bite particularly with kick and toms that the Optoma played with pout. If this track hadn’t woken me up listening on my choice IEMs, the HEM4 certainly did now. Not that it was OTT. It was just so clear and speedy.  Boy, was this so much better than the Primo 8 four-driver goliath that I reviewed last year, and that one was a thoroughly good player at £150 more.  Playing Britten’s Sinfonia da Requiem (24/96kHz, Kansas Symphony Orchestra, Michael Stern) on that bicycle helmet looking IEM gave a transparency of sound that more than met its price point. Now on the HEM4 this music was even clearer. Where the Primo 8’s top-end left me wanting, the new HEM 4 was superb,  producing  better coherence between instruments with a much tighter and clearer portrayal of the music.  Dadawa ‘Sister Drum’ track “Crossing the Ridge” separated the drums, flute, voices and synthesiser instrument parts with ease and authority. This album is not the easiest to hear well in a crowded road, but this IEM could have been studio monitors as it kept me informed with detail even as I wandered the high street.


At a penny under £250, these IEMs are a highly recommended choice for the serious music listener and professional alike. With musicality pouring out of everything I played with both warmth and clarity, it played classical music with affection and heavy rock with grunt. Once you get used to inserting in your ears you will wonder why you didn’t wear earphones this way before.


BUILD QUALITY:  Very comfortable and lightweight. Excellent build with lots of accessories. Detachable leads.

SOUND QUALITY:  Accurate, full frequency sound with excellent bass and articulation of sound
VALUE FOR MONEY:  Excellent value for money package. More than £249.99 worth of quality sound.


Excellent full frequency response.
excellent warmth and clarity, with exceptionally fast transients.
Effortless musicality.
Lots of accessories, and excellent cable.


Nothing at this price. Perhaps bass could perhaps be over enthusiastic at times.

Price: £249.99

Janine Elliot

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