There are two types of transducers used for IEMs: dynamic drivers and balanced armature (BA) drivers. Dynamic drivers (moving coil) are like little speakers and are typically less expensive. They require a vent in the shell because there is a diaphragm that has to move some air, which tends to result in a more powerful bass. This type is slower to respond and generally not as accurate as the balanced armature design.
Balanced armature drivers are tiny and don’t require outside air to produce sound, so no vent is required and they have a tighter response. This design offers greater accuracy and speed, therefore more detail, but it lacks the bigger low end of air-moving dynamic drivers. Multiple drivers improve this because crossovers can split the audio into two or three frequency bands, taking the pressure off one driver to represent all the frequencies. This increases efficiency and results in a more natural sound. Some companies feature multiple BA drivers for each frequency range for their higher-end models and several companies offer a hybrid model with a dynamic driver for the bass and BA drivers for midrange and highs.
(Left) Fig. 2. Example of a simple wired IEM setup employing a small personal mixer.
Once you have your earpieces set, the next step is figuring out what sort of system is best for your situation. The simplest and lowest cost option is going for the wired approach by getting a little mixer to set beside your kit, sending a stereo monitor mix of the band from the house system into two of the channels, and plugging your IEMs into the headphone jack. This is the method Richardson employs with her duo, Mental 99, where she takes a simple stereo feed from Gore’s laptop into her Mackie 1202 to hear and cue off the loops he creates while sending it to their PA through the main outputs. You could also send other sound sources such as a click track, your vocal, or perhaps an ambient mike into the other channels to set up your own personal mix while adjusting your overall volume with the “control room/phones level” potentiometer (Fig. 2).
To use the headphone jack of a standard mixer rather than one specifically designed for IEM use, you’ll likely have to adapt. Typically IEMs have a cable terminated with a mini plug which you can use for receiver belt packs and personal listening devices, so you’ll have to use an 1/8"—1/4" adapter, or do what Richardson did with some help from her tech geek bandmate: They delicately modified her cable to give it extra length and terminated it with a 1/4" connector. This MacGyver maneuver requires a bit of finesse and even more bravery (because you’re hacking into the cable of your relatively pricey IEMs).
(Left) Fig. 3. Shure P2TRE2 PSM200 Personal Monitor System is a basic wireless setup with IEM bodypack receiver and transmitter.
If you don’t wish to be hardwired to a mixer, wireless is another way to go. It means spending more money, but it can tie you into the rest of the band if everyone is using in-ear monitors too. You’ll be sporting a receiver body pack into which you’ll plug your IEMs, and there will be a transmitter to which the soundperson is sending an auxiliary monitor mix dialed up to your specs (Fig. 3). You can have either a stereo mix of the band or a mono mix of the band plus your vocal, your click, or whatever you wish that has a mike on it through one of the transmitters.
There are fixed-frequency wireless options, which cost less but offer only one frequency, and then there are frequency-agile systems that feature multiple operating frequencies – though not all frequencies are necessarily available at the same time. The price increases with more flexibility. More fully featured options offer automatic-scan mode and selection of the best available frequencies. True diversity systems employ two radio receivers and two antennas to help prevent dropouts and increase signal stability. Diversity systems have one radio receiver and two antennas.
Each transmitter can get a separate mix, and multiple packs can be used per transmitter by simply setting the packs to the respective transmitter’s frequency. Transmission of wireless signals has a limited bandwidth, so a compander is incorporated into the system. Compression is employed at the transmitter to limit the bandwidth for wireless transmission and expansion at the receiving end. This can affect the sound somewhat, but not necessarily in a bad way. Another thing to keep in mind when going wireless is that FCC regulations currently do not allow wireless in-ear monitors or microphones to operate in the 700mHz band (698—806mHz) because bandwidth here is at a premium.