The Science Behind The VoxGuard

  • Sound Of The Room
  • Eliminating The Sound Of The Space
  • The VoxGuard Design

The VoxGuard is a simple device that employs well known acoustic principles to minimize room ambiance from entering the microphone. This allows a greater percentage of the source to be captured without the echo, reverb and resonance from the room. Once the 'dry recording' is on tape, artificial ambiance in the form of digital reverb, echo and EQ is then added.

The science behind the VoxGuard is simple. It combines absorption by way of high density open-cell foam with an acoustic shield to prevent ambient sound from entering the mic. This page explains the science behind the design.

Eliminating The Sound Of The Space

Put up a microphone in a room and hit 'record'. The sound of the voice will compete with the sound echoing off the walls. These are known as primary reflections, flutter echo and standing waves. These will invariably arrive at the microphone after the original sound and depending on how loud they are, will cause varying degrees of phase cancellation known as comb-filtering.

Although in some cases one may want to record using the natural room's effect, today it is common practice to record a dry vocal track and only add artificial ambiance during the mixing phase. Most engineers prefer to work this way, as committing to room ambiance early-on usually conflicts with the instruments and limits options.

The VoxGuard Design

With acoustics, one can either absorb sound or reflect it. The VoxGuard performs both functions at the same time. First, when singing into the microphone, sound is captured by the mic while a good percentage of sound breezes by. In space, this 'extra' sound would go forever without echo as there are no boundaries. In an anechoic test chamber, sound is completely absorbed as there are no hard reflective surfaces. In this case, the VoxGuard's high density open-cell acoustic panel absorbs much of the energy in the critical voice range.

Without VoxGuard


An open microphone picks up a mix of direct sound (blue arrows) and reflected sound (red arrows).

With VoxGuard


The VoxGuard baffel blocks reflected sound from entering the mic and the absorber layer minimizes reflections within the baffel allowing the dry vocal to be recorded.

What spills over is then spread into the room. This echoes around in the form powerful primary reflections and flutter echo that create the room's reverberant field. The VoxGuard's curved outer shield is designed to reflect unwanted energy away while the larger size—upwards to twice as big as others —reduces flanking. This effectively creates a boundary that stops sound from coming back into the mic, reducing the ambient effect.

The result is predictable: With more of the original source and less of the reverberant field, the recording engineer is better able to control the sound of the voice or instrument to best fit the recording.

Primacoustic is a division of Radial Engineering Ltd. Copyright 2013. All rights reserved.