One of the problems of building budget studios is that sound isolation and studio acoustics often have to take second place to equipment when money is tight. After you've wired all your equipment up and started making recordings several problems may suddenly become very apparent. The propagation of sound and the working principles of microphones are well understood, however, when building a home studio many people don't apply any of this scientific information to any aspect remotely connected to the construction of their studio. One reason for this may be that they can't lay their hands on the right information and therefore rely on methods related to them across the bar table over the odd pint or two.

Within this series of Acoustics articles we hope to cover most aspects of studio construction and hopefully answer many people's problems.

Reasoning

A case for the floating floor. When you are recording loud instruments such as drum kits and bass guitars the low frequency elements of the sound travel through the walls and floor of the room. These sounds present two main problems:

One, they can cause objects in both the studio and control room to rattle and therefore interfere with your assessment of the instruments' sound over the studio monitors. Secondly, the sounds travel through the building's structure and cause annoyance to other people. By constructing a floating floor both problems can be reduced to an acceptable level.

The most important point when constructing a floor is to ensure that none of the new floating structure touches the original floor. Any contact between the two will seriously reduce its performance as a sound isolator. If properly constructed, the floor should provide some 30 to 40 dB attenuation of sound.

Construction

The basic principle is to build a wooden raft structure covered with sheets of floor boarding which then lie on top of a glass fibre matting.

Start by accurately measuring the floor dimensions and draw up a plan. Calculate the number of joists required, these should be spaced no more than 18" apart. Additional cross-bracing should be included at random points to add rigidity to the raft structure. Lay out the rolls of glass fibre onto the floor, don't overlap the edges, instead butt them together. Carefully lower the raft structure down over the matting. Fold the glass fibre up around the edges of the joist ends so that they don't come into contact with the walls. See diagrams.

When you have completed laying the raft you can lay the final covering. Plywood or chipboard is ideal, it comes in 8' x 4' sheets so it makes the job a lot quicker than using tongue and groove floor boards. The thickness of the wood depends on the total floor area but should not be less than ¾". The covering can then be screwed down onto the joists.

A further improvement would be to apply another layer of glass fibre matting on top of the joists and then put the floor covering down.

Where the joists lie on top of the glass fibre the matting will compress to approximately 3/8" and provide the cushioning necessary to float the floor. A wooden finishing trim may be fitted as a skirting board. The trim can be nailed to the wall but must not touch the floor. By careful positioning you can pin the edges of the glass fibre matting securely against the wall.

Finally a carpet or carpet tiles should be laid. If you are working on a floor which is already on joists the principles are the same, by referring to the diagram you can see that it's necessary to remove the existing floor boards, lay the matting and then replace the boards. Their method may sometimes require additional bracing.

Having constructed the new floor you may encounter several problems. If the glass fibre matting has moved during construction then part of the joist will touch the floor and result in a rocking motion. Similarly, carefully check the edges to ensure a tight fit with a good overlap of glass fibre; too loose a fit will allow the floor to move.

Materials: Joists: 2" x 3" minimum, soft wood. Covering: ¾" min. plywood, chipboard or T&G floor boards. Matting: Glass fibre 2" min, loft insulation.