Speakers for studio monitoring are almost always made with magnets and voice coils – the moving-coil mic in reverse. Electrostatic speakers, like a condenser mic in reverse, can offer much more accurate response than the magnetic type, but they can’t do very much at low frequencies. This is because to move air with the same amplitude at all frequencies throughout the audio range, the speaker driving element’s travel must be inversely proportional to frequency. In other words, if a speaker cone producing a 5kHz tone travels back and forth 1/100-inch, to give the same sound level at 50Hz the cone must travel one inch. A magnetic driving system produces this effect automatically, due to various laws of physics too messy to explain here, but an electrostatic system’s diaphragm travel is equal for all frequencies, and rather limited besides (no electrostatic speaker has anything near an inch of free motion). So unless the electrostatic speaker is huge, it’s only good at higher frequencies, and must be combined with a cone woofer. Electrostatic speakers also operate at high polarizing voltages, which tend to arc and short out, and which can be hazardous as well. So these speakers have a reputation for being nice when they work, but troublesome.