The Parts of an IEM System, Piece by Piece

An in-ear monitor system is five parts in a line: something makes the mix, something sends it, something carries it through the air, something receives it on your belt, and something puts it in your ear. Knowing which part does which job is how you figure out what you already own and what you still need.

The short answer

• Mix source: a console, a personal mixer or a playback interface. It makes the mix you hear.
• Transmitter: takes that mix in and sends it out as radio. Lives in the rack.
• Antenna: on the transmitter or, for several systems, a combiner and one shared antenna.
• Bodypack receiver: clips to your belt, picks up the radio, sets your volume.
• Earphones: plug into the bodypack. They decide how the mix sounds and how much stage noise gets in.

Skip the radio and you have the wired version: mix source, headphone amp, cable, earphones. For how signal moves through all of this in order, see how audio flows through an IEM rack.

The mix source

Every IEM system starts with a mix. On a small rig that is an aux or matrix send from a digital console. In a band where everyone wants their own balance it is a personal mixer per player, covered in personal monitor mixers compared. With tracks it may be an audio interface feeding the click and stems. Check: does it have a free output for every mix you need? A stereo mix uses two.

The transmitter

The transmitter is the box in the rack, usually half-rack width, so two share one rack space. Line-level audio goes in the back, radio goes out the antenna. One transmitter sends one mix, mono or stereo, and any number of bodypacks can tune to it. A Shure PSM300 transmitter is a common first one. The step-up families are compared in PSM300 vs PSM900 vs PSM1000. Check: the frequency band is legal where you play, and you have an outlet for its power supply.

The antenna

One transmitter can use the short antenna it ships with. Two or more in one rack interfere with each other unless their signals are combined and sent out a single antenna, which is what an antenna combiner does. The difference between combining (transmit) and distribution (receive) trips up a lot of first racks, so it has its own guide: antenna combiner vs antenna distribution. Picking frequencies that don’t clash is covered in wireless frequency coordination.

The bodypack receiver

The bodypack is the only part the performer touches. It receives one transmitter’s channel, has the volume knob, and has the headphone jack the earphones plug into. Most also offer a limiter, which is worth turning on; see IEM limiters and hearing protection. A PSM300 bodypack pairs with the PSM300 transmitter. Check: it must be from the same family and frequency band as the transmitter, and you need one per performer plus a spare.

The earphones

The earphones decide what all the gear before them sounds like and how much stage noise they block. Two examples show the range:

Shure SE535: three balanced armatures

Three drivers per side, two woofers and a tweeter. 36 ohms, 119 dB SPL per milliwatt, and Shure rates the isolation at up to 37 dB. The cable detaches at a locking MMCX connector and ends in a 3.5 mm plug, so a broken cable is a cheap swap rather than new earphones. SE535 gear page.

Sennheiser IE 400 PRO: one dynamic driver

One 7 mm dynamic driver per side, 16 ohms, 6 Hz to 19 kHz, on a 1.3 m detachable cable. Sennheiser has since marked it no longer available, so expect to find it used or as old stock. IE 400 PRO gear page.

Universal earphones like these fit with foam or silicone tips. Custom molds are made from impressions of your ears and seal better. Either way the seal is most of the isolation, and a loose fit loses bass first. If a tight seal leaves you feeling cut off from the room, look at ambient mics for IEMs.

The wired alternative

A drummer or keyboard player who doesn’t move can skip the transmitter, antenna and bodypack. A headphone amp such as the Behringer HA8000 takes the mix and drives earphones on a cable. No frequencies to coordinate, no batteries, and much cheaper per player. For plugging earphones straight into an interface, see plugging IEMs into an audio interface.

What a first system needs

• One mix output per mix (two for stereo).
• One transmitter per mix, or one headphone amp channel per wired player.
• An antenna combiner once there are two or more transmitters in the rack.
• One bodypack per performer on wireless, plus a spare.
• One pair of earphones per performer, with spare tips and a spare cable.
• Rack space, outlets and power for all of it; see rack power planning.

For what an IEM rig is and how it grows as the band does, start with IEM rig basics.

Preamps

None of the parts above has a mic preamp. The transmitter takes line level, the bodypack and headphone amp drive earphones, and the earphones are the end of the line. The preamps that feed an IEM mix sit upstream on the console or stage box, so if the band needs more inputs, that is where to count them; see how many preamps your rig needs.

Sources

• Shure SE535 spec sheet: drivers, impedance, sensitivity, isolation, MMCX, 3.5 mm plug
• Sennheiser IE 400 PRO product page: 7 mm dynamic driver, 16 ohms, 6 Hz to 19 kHz, 1.3 m cable, availability