Box-in-box acoustics

[edit] Introduction

Box-in-box is a construction technique that allows a space within a space to be insulated against unwanted extraneous noise and vibration. Such extraneous noise may be airborne (travelling through the air) or they may be structure-borne – travelling through the ground and building structure. These noises can be generated by cars, trains, aircraft or even people or music in adjacent rooms.

Box-in-box is an acoustic isolation technique that has proved effective in keeping out distracting noise, hence its widespread use in theatres, cinemas, recording studios and other instances where it is imperative to have as-near silence as possible.

As the name suggests, the technique involves constructing a room within a room (which may be the building structure), so that the inner room is acoustically isolated from the outer. This will involve isolating the walls, floors and ceiling of the inner box and using resilient mountings to achieve this.

[edit] Three main elements

Vibration control and acoustic floor systems specialist Mason UK Ltd identifies three main elements to achieving an effective box-in-box construction:

[edit] Floating acoustic floors

Floors are regarded as one of the most important elements of a sound insulated construction and are generally floated to achieve the requisite acoustic isolation. Typically, new floors will be constructed using concrete and rest on either springs or elastomeric bearings. This means that crucially, an air gap of up to 200mm is created between the old floor and the new. Where a lighter weight system is required, timber floating floors can be specified.

[edit] Acoustically isolated walls

Isolated walls can either be supported on the new floor (and may have to be fixed to the external building structure with braces and acoustic wall ties) or they can be built upon specially designed wall support plates.

[edit] Acoustic hangars

An acoustic ceiling will be the final element to complete the box construction. The new ceiling plane will typically comprise acoustic tiles suspended on drop rods from hangars fixed to the existing ceiling (soffit) or to timber joists.

Even with a completed box-in-box, there may still be low levels of background noise emanating from a ventilation system. This can be minimised by mounting ventilation ducts and other building services on springs with flexible rubber connections.

[edit] Related articles on Designing Buildings Wiki

• Acoustics.
• Acoustic materials.
• Airborne sound.
• Approved document E.
• Building acoustics.
• Building regulations.
• Decibel.
• Flanking sound.
• Floating floors.
• Impact sound.
• Pre-completion sound testing.
• Reverberation.
• Reverberation time.
• Sound absorption.
• Sound insulation.
• Sound masking.
• Sound v noise.

• Structure-borne sound.

  [edit] External sources

• Mason UK Ltd Vibration Control Products and Acoustic Floor Systems