Boundary microphones are many a sound tech's secret weapon. Unlike standard condenser microphones, boundary microphones can be lain out flat or secured to a wall or ceiling for the acoustic benefits.
How Do Boundary Condenser Microphones Work?
Technically speaking, boundary microphones - also called pressure-zone microphones (PZM) - work just like any other condenser microphone. The difference has to do with the housing, which is flat in the case of boundary microphones so they can be placed on desks, tables and floors - no microphone stand needed. Besides a practical upside, there's an acoustic advantage as well: by placing the microphone on a table, any sound and echoes in the room reach the microphone at virtually the same time. As a result, unwanted reverb as well as 'comb-filtered' sound is countered. The comb-filter effect occurs when any direct sound is mixed with reflected sound arriving at the microphone a moment later. This leads to certain frequencies getting boosted while others are toned down, resulting in a hollow sound.
Miking Up a Piano or Grand Piano With a Boundary Microphone
Due to their humble dimensions and flat-bottomed design, boundary microphones are perfect for recording or amplifying a grand piano. You can even close the top after placing the microphone on the soundboard, but if you'd prefer to leave the lid open, you could also place one or two boundary microphones inside it. This way, you won't have to worry about the lid creating any unwanted echoes. Just so you know, boundary microphones also work like a treat when you want to capture the sound of kick drums and cajons.
Boundary Microphones for Online Meetings
Boundary microphones are also frequently used in conference rooms, since four people sitting around a small table need only one boundary microphone (and a computer and/or audio interface) to guarantee crystal-clear recordings or online communications. In the case of multiple speakers sitting around a large boardroom table, you can either set up multiple boundary microphones or give each person at the table their own microphone. Most boundary microphones feature XLR plugs, but there are also various plug-and-play USB boundary microphones out there.
Studio Boundary Microphones
While boundary microphones aren't often used in recording studios, they can make for a valuable addition to any microphone collection since they're great at capturing bass drums. Simply place the microphone on a pillow placed inside your kick drum and you'll get both a defined 'tick' and deep lows. In addition, boundary microphones are also superb room microphones. Room miking is a technique used to capture the ambient sound of a room, which can then be mixed in with the sound of a close-miked instrument for a super-realistic live-take. With a boundary microphone, you can also make a small room sound much larger than it actually is.
Boundary Microphones for Live Sound
So, boundary microphones are excellent at capturing the sound of a grand piano, but did you know that they were originally designed for theatre shows? Regular microphones are hard to keep out of sight and tend to register the reflections that bounce off the stage, which muddies the sound. Set up three or so boundary microphones and you'll be able to capture the actors' voices without destroying the immersion or losing out on highly natural sound.
Frequently Asked Questions About Boundary Microphones
How does a boundary microphone work?
A boundary microphone is basically a condenser microphone in a flat housing. They're easy to set up on a flat surface or mount to a wall; require no microphone stand; and keep unwanted reverb and sonic colouration at bay.
