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Listening at home⏱️ Estimated reading time: 13 min
On this page: Overview
Key Takeaways
An in-ear monitor takes an electrical signal from a phone, player or stage pack, splits it with a crossover if it has more than one driver, and turns it into sound with tiny drivers. Sound tubes and the nozzle carry that sound into your ear canal, and the ear tip seals it in.
The seal turns your ear canal into a small closed space that the drivers can pressurise, which is where an IEM’s bass comes from. If air leaks out around the tip, the low frequencies leak with it.
The engineer sends a monitor mix from an aux output on the mixing desk, or each musician sets their own on a personal monitor mixer. It reaches a wired belt pack or a wireless bodypack receiver, and the IEM plugs into the pack.
Yes, passively. The sealed tip and closed shell block much of the sound around you, usually more in the mids and treble than in the bass, depending on the fit. A good seal lets you listen at a lower volume, but IEMs are not hearing protection.
Press play and the music is in your ears almost instantly, yet the signal passes through several parts first. So how do in-ear monitors work? An in-ear monitor (IEM) is a sealed earphone that turns an electrical signal into sound inside your ear canal, and every part, from the plug to the ear tip, has its own job.
Many explanations stop at “tiny speakers in your ears”. We go further, through the crossover, sound tubes and nozzle, and show why the seal decides more of what you hear than the driver count. For the basic definition, see our explainer on what are in-ear monitors.
At Bollsen, we are a family-owned earplug company and the official UK & EU partner of Unique Melody. Our examples come from Unique Melody’s published product pages, and figures they do not state are left out.
How do in-ear monitors work?
In-ear monitors work by taking an electrical audio signal from a source, splitting it into frequency bands with a crossover when there is more than one driver, converting each band into sound with tiny drivers, and guiding that sound through sound tubes and a nozzle into an ear canal sealed by the ear tip. From the plug onwards, a musician’s IEM and a listener’s IEM work in exactly the same way. The only real difference is where the signal comes from.
What happens to the signal on its way to your ear?
The signal passes through nine stages between the source and your eardrum, from the plug and cable through the 2-pin connector, crossover, drivers, sound tubes and nozzle to the sealed ear canal. Each stage changes either where the signal goes or how it sounds.
- Source: a phone, dongle DAC, player or stage pack sends an analogue left and right signal.
- Plug: a 3.5 mm, 4.4 mm balanced or 2.5 mm balanced plug connects the cable to the source.
- Cable: copper conductors carry the signal up to each earpiece.
- Connector: a detachable 2-pin connector joins cable and shell.
- Crossover: in a multi-driver IEM, it splits the signal into bass, mid and treble bands.
- Drivers: each driver converts its band into sound.
- Sound tubes: small bores carry the sound forward, often through acoustic dampers.
- Nozzle: the bores meet in the nozzle, which sits in your ear canal under the tip.
- Sealed ear canal: the tip closes the canal so the sound, bass included, reaches your eardrum.
Not every IEM uses every stage. A single-driver model such as Unique Melody’s From The Start needs no crossover, and a bone-conduction driver skips the sound tube altogether.
Where does the signal come from: a music player or a stage feed?
For everyday listening the signal comes from a phone, laptop, dongle DAC or music player, while on stage it is a monitor mix sent from the mixing desk or a personal monitor mixer to a wired belt pack or wireless bodypack receiver. At home this is simple. Unique Melody’s 2HT and 3DT have a 3.5 mm cable for a phone with a headphone jack, a phone without one needs a USB-C or Lightning adapter (which has its own DAC inside), and 4.4 mm balanced models need a 4.4 mm dongle or player. Our guide do you need a DAC for IEMs explains when a separate source helps.
On stage, the engineer builds a separate mix for each performer from the desk’s aux sends. Yamaha’s guide to getting the most out of in-ear monitors points out that a console with six aux busses gives you six mono mixes or three stereo mixes.
The mix then goes to a wired belt pack, a small headphone amplifier clipped to the performer, or to a wireless transmitter and bodypack receiver. The IEM plugs into the pack’s headphone socket, and our comparison of wired vs wireless in-ear monitors covers the trade-offs.
What do the plug, cable and 2-pin connector do?
The plug, cable and 2-pin connector carry the left and right signals to each earpiece without shaping the sound, so their real jobs are compatibility and durability. You need a plug that matches your source and a detachable cable you can replace when it wears out.
A 3.5 mm plug is the common unbalanced type, while 4.4 mm and 2.5 mm balanced plugs give each channel its own return wire and need a matching balanced output. On the MEXT and MEST Jet Black you choose one of the three plugs when you order.
The 3DT, MEXT and MEST Jet Black all state a 0.78 mm 2-pin connector, as do the 2HT and MEST MKII. Other models list a 2-pin connector without a pin size or do not state the connector, so check the product page before buying a spare cable. In our view, a cable changes fit and handling noise far more than it changes the sound.
What does the crossover do inside the shell?
A crossover splits the incoming signal into frequency bands so that each driver in a multi-driver IEM plays only the range it handles best, for example bass to a dynamic driver and treble to a balanced armature. It does this with electrical parts, acoustic parts or a mix of both.
An electrical crossover filters the signal before it reaches each driver, and an acoustic crossover shapes the sound after the driver with tube lengths and dampers. Sonion’s earphone design guide, published by a maker of balanced armature drivers, says crossovers of 6 and 12 dB per octave are common in earphones.
The guide warns that phase and delay issues from the crossover “can make the earphone sound muddy”, while good designs “keep the kick drum out of the vocals”. A driver count on its own tells you little about the sound.
Unique Melody states the crossover for only some models. The MEST Jet Black uses a 4-way crossover for its air-conducting drivers and a separate 2-way crossover for its bone-conduction drivers, while Stardust is listed as 4-way and The Multiverse Mentor and Mason FS as 5-way.
How do the drivers turn the signal into sound?
A driver turns the electrical signal into movement and the movement into sound, and IEMs use four families of them. Dynamic drivers move a diaphragm with a voice coil, balanced armature drivers move a tiny reed, electrostatic drivers move a charged membrane, and bone-conduction drivers vibrate the shell itself.
A dynamic driver is a miniature loudspeaker: a coil in a magnetic field pushes a diaphragm back and forth. The 3DT is all-dynamic, with two 7 mm composite-diaphragm drivers and one 10 mm CNT dynamic driver per side.
A balanced armature, the type of driver Knowles builds for hearing aids, balances a small armature between magnets in a sealed case, and the signal makes it rock while a tiny drive pin passes that motion to a stiff diaphragm. They are small enough that several fit in one shell.
Electrostatic drivers move a very thin membrane with an electric field and usually handle the top of the treble. Bone-conduction drivers vibrate the shell rather than sending sound down a tube. The MEXT pairs one dynamic driver and four balanced armatures with one bone-conduction driver, for which Unique Melody states a range of 200 Hz–7 kHz. Our guide IEM driver types explained compares the four families in more depth.
How do sound tubes and the nozzle shape the sound?
Sound tubes carry the sound from each driver to the nozzle, the short stem that sits in your ear canal under the tip, and their length, bore and acoustic dampers shape the frequency response before the sound reaches your eardrum. Sonion’s guide says nozzle and tube lengths of 6 to 20 mm and diameters of 1.5 to 2.0 mm are common, and that small-diameter tubes reduce high-frequency output. Dampers, small acoustic resistors that smooth out peaks, sit best at 50% to 75% of the distance from the driver. These are general design values; Unique Melody does not publish tube or bore sizes.
The bores meet in the nozzle, and a mesh over its opening keeps earwax out. The 2HT, for example, has a metal nozzle with a mesh.
Why does the seal matter more than the driver count?
The acoustic seal matters more than the driver count because a sealed ear canal is a small closed space that the drivers can pressurise, and that pressure is how an IEM produces bass. If air escapes around the tip, the low frequencies go with it, whatever drivers sit inside the shell.
Sonion’s guide says balanced armature drivers “are not ‘leak tolerant'” and must seal tightly “to ensure good low frequency/bass performance”. Yamaha’s guide agrees: “If the earphones are not sealed properly, bass response will be very poor.”
We think this explains many complaints that a new pair sounds thin. A tip can feel comfortable and still leak, so try every tip size in the box before you blame the tuning. A ten-driver IEM that leaks can sound thinner than a single-driver IEM that seals.
Sonion notes that single-flange tips are comfortable “but at the cost of seal and passive noise reduction”, while foam tips seal well. Our guide to choosing IEM ear tips covers sizes and how to test the fit.
Do IEMs block outside noise?
Yes, IEMs block outside noise passively, because the ear tip seals the canal and the closed shell stops much of the surrounding sound before it reaches your eardrum. They usually block more in the mids and treble than in the deep bass, and how much depends almost entirely on the fit.
That passive isolation makes a clear stage mix possible, and it takes getting used to. Yamaha’s guide says it “quite literally sounds and feels like sticking your fingers in your ears”, and an ambient microphone fed into the mix brings the room back.
A good seal lets you listen at a lower volume. In a 2008 study by Federman and Ricketts, musicians’ minimum acceptable listening level was about 6 dB lower with in-ear monitors than with floor monitors, yet the level they preferred was only about 0.6 dB lower. The seal gives you room to turn down; you still have to do it.
IEMs are not hearing protection; for gigs and festivals take Music SoundPRO, our reusable earplugs with a passive SNR of 24 dB. For the full answer, read our article do in-ear monitors protect your hearing?
What does this mean when you choose a pair?
Start with the fit when you choose IEMs, because the seal decides how much of the drivers’ work reaches your ear. Then match the plug to your source, or to your belt pack or bodypack if you play live. Drivers and crossovers come last.
To compare driver layouts and plug options model by model, see our page for Unique Melody in-ear monitors (UK). Get the seal right first, and the rest of the chain can do its job.
His connection to hearing protection stems from personal experience with sound sensitivity during live events and work in noisy environments, an issue that made him more aware of the long-term risks of unmanaged noise exposure. Today, as both a communicator and a user of BOLLSEN products, he is passionate about raising awareness around the importance of proactive hearing care.
At BOLLSEN, he develops data-driven marketing campaigns, writes SEO-focused articles, and manages communication channels that connect customers with practical knowledge about hearing protection. His work ensures that BOLLSEN’s message—prioritizing health, performance, and sustainability reaches a global audience in an engaging and trustworthy way.
Passionate about writing since childhood, Timotej combines creativity with a strong analytical approach, continuously testing new ideas in digital marketing, performance advertising, and social media. He believes in learning through innovation and collaboration, balancing leadership with openness to new perspectives.
Beyond his professional role, Timotej is committed to a healthy lifestyle and finds inspiration in fitness, sports, and quality time with friends. His personal passion for well-being aligns with BOLLSEN’s core values, making his work not only a career but also a cause he deeply believes in.
