• Typical Vocal Booth Design
  • The Problem With Vocal Booths
  • Controling Room Acoustics

If you think about it, common sense tells us that placing a single absorptive panel on the wall of a gymnasium will have zero effect on the acoustics in the room. At the other extreme, covering the walls and ceiling will render a room completely dead. Simply stated, the greater the absorptive surfaces one applies to a room, the more energy you will take out. If you remove the ambience from the room and make it acoustically ‘dead’, you can then ‘electronically’ add the ambiance later in post production. This, in fact, is the basis behind what is commonly known as a voice-over booth.

Today, voice-over booths are used in all kinds of audio production. A common application is in the studio for recording a voice such as a lead singer of a band. Another is voice over for film and TV post production. This extends into ring tones, computer animation sound tracks, and on-line pod-casting. In the majority of these situations, the intent of a vocal booth is to take away the rooms ‘personality’ so that you can add the ‘desired character’ electronically to fit the scene. In other words, you start by recording a voice without any ambiance and add echo to make it sound like you are in the Grand Canyon, excessive hall reverb to sound like you are in a gymnasium, or maybe just a touch of echo and a smattering of reverb with a dark EQ to sound as if you are in a dark back alley.

The Typical Vocal Booth Design
Traditional vocal booths are usually small isolation rooms that are completely covered with acoustic panels. The intent is to completely surround the vocal talent with absorptive panels while isolating the vocal microphone from other instruments or street noise. Better isolation rooms are made using heavy walls with high quality absorbers and are usually very expensive.

Although most vocal booths do a good job at controlling noise and eliminating ambiance, they are not without problems. Most employ a thin layer of acoustic foam that is only effective at absorbing upper frequencies and therefore tend to make the voice sound boomy. This is due to the combined effect of the room geometry, subsequent room modes and the lack of low frequency absorption. The good news is that this problem can easily be addressed by adding a couple of bass traps like the Cumulus in the tri-corners.

The FlexiBooth
For those that do not have the space or budget for a full size voice-over booth, the FlexiBooth presents a viable alternative. The design begins using the same concept as a voice-over booth whereby three full size acoustic panels surround the talent with an acoustical barrier to create a dry acoustic zone. This contains the voice within the absorptive zone and reduces the spill from exciting the room. And since the doors are made from heavy MDF board, these block much of the room ambiance from re-entering the microphone which would otherwise affect the dry recording.

What sets the FlexiBooth apart is the quality of the acoustic absorbers. Unlike open cell acoustic foam that is practically useless at absorbing low frequencies, the FlexiBooth employs high performance 6lb per cubit foot glass wool panels. The main absorptive panel is made from 2” material while the side door panels employ 1” material. These combine to provide even absorption right down into the lower voice range.


Sound reflected off the nearby wall is blocked by the doors. The glass wool panels absorb the rooms ambience.

The Problem With Vocal Booths
The Flexibooth’s hidden advantage is the lack of closed boundaries. As previously described, the problem with most vocal booths is that they are small and generate unwanted resonance in the lower mid range. Because the FlexiBooth is generally placed within a larger room, the resonant frequencies are at a much lower frequency which makes them much less prominent and easily equalized out of the audio track by simply using a high pass filter. Not only does the FlexiBooth do a better job at absorbing the voice energy, but also avoids the chest hump problem that plagues most voice-over booths. Very cool!

To demonstraight this lets compare the axial room modes for two rooms. We can calculate the lowest (and most powerfull) room mode by dividing the speed of sound at 1130 ft/per second by each room dimension. The first room is a small vocal booth measuring 4′ x 5′ x 8′. This small room will naturaly resonate at 141Hz, 226Hz and 282Hz. The axial modes for this small vocal booth are not only packed closely together they cover the complete low range of the human voice.

The second room is an average sized residental type room with 10′ x 12′ x 8′ dimensions. Using the same math this larger room shows modes at 141Hz, 94Hz, and 113Hz. These modes are spread out over a wider range and two out of three are below the male vocal range making them much easier to deal with using acoustic treatment and electronic filtering. At the same time the FlexiBooth give you the same dry sound as the smaller vocal booth.

Vocal Booth With “Chest Hump”


FlexiBooth In An Average Room


Variable Acoustic Control
Another cool benefit is using several FlexiBooths together to vary the room’s acoustical character. By simply opening or closing the cupboard doors, you can brighten or darken the room depending on the sound you are after. For instance when recording acoustic instruments, you could close the FlexiBooth doors to create a more ‘live’ environment. When recording drums, you could deaden the room by having all of the doors open. This of course is where we got the prefix Flexi from… it is just so wonderfully flexible!