ACOUSTICS IN FLOOR CONSTRUCTIONS
GENERAL INFORMATION

Acoustics

Table 1

INTRODUCTION

This document provides practical guidelines regarding acoustics in Junckers hardwood floor constructions.

Actual values regarding step-sound reduction can be found the Specifier's and installation instructions for the individual floor system, see chapter C for commercial and residential buildings and Chapter D for sports floors.

Certain terms are used to describe acoustics, e.g. airborne sound and step sound. The most common terms can be found in the glossary at the last page of this document.

Fig. 1

Clip floors

Flatness of the sub floor
Subfloors for clip systems must be level and meet the required specifications. It is important to consider avoiding rebates or casting joints, as they may result in very unfavourable sound transmission. An uneven subfloor can thus reduce the step sound reduction figure in relation to the recommended step sound reduction for a given floor system.

Ensure that the subfloors corners and edges along walls are clean and appear sharp, and that they are free from concrete and plaster residue, so that the Junckers floor can expand freely without contact between abutment and subfloor or walls, see fig. 1.

Fig. 2

Distance to walls
Junckers expansion strips, which are fitted closely between board ends and walls on the clip system, ensure that the board ends do not touch the walls. Without this the flank transmission would increase, see fig. 2.

Fig. 3

Batten Systems

Soft packings are used for packing/levelling of traditional batten systems, see Fig. 3.

The packings commonly consist of soft wooden fibre boards, and are placed at the lowest point of the elevation. Soft packings are made from 12-13 mm thick soft wooden fibre boards of 100 cm² e.g. 125 x 80 mm, and have a density of 225-300 kg/m³.

A plywood board, at least 12 mm thick, is glued on top. Packers are fixed to the battens with lost-head wire nails, which must never go into the soft material or touch the concrete. This would result in significant deterioration of the floors step-sound reduction properties. Alternatively, plastic wedges or foam backed cradles with similar properties may be used.

Fig. 4

Packings/wedges must be close to cuts in the battens on both sides, see Fig. 4. There must be a minimum clearance of 10 mm between the lower surface of the board and batten and the pipe insulation to avoid sound bridges.

Fig. 5

Distance to walls and fixed installations
The recommended expansion gaps between battens and walls, and Junckers floor boards to walls and fixed installations must be followed to avoid contact between the floor construction and other structural parts, see Specifier's and installation instructions for each individual floor system. see fig. 5.

Fig. 6

GLOSSARY

Airborne sound
Sound that travels in the air, e.g. from a loudspeaker, is called airborne sound.

The airborne sound can pass through structures via openings or transmission through or radiation from structures, see Fig. 6.

Airborne-sound insulation, ^∆Lw [dB]
A figure indicating the ability of a partition, e.g. a wall or a dividing floor, to prevent transmission of airborne sound, e.g. sound from a loudspeaker, see Fig. 6.

Fig. 7

Step sound
Step sound is the result of mechanical impact, e.g. when walking on floor or deck constructions, and the sound is transmitted to and radiated in adjacent rooms, see Fig. 7.

Step-sound level, L´n,w [dB]
A single-figure measure of sound transmission to a room, when the floor of another room (usually the room above) is affected by a standard beater, see Fig. 7.

Step-sound reduction, ^∆L_w [dB]
The step-sound reduction of the flooring, Δ Lw, indicates its capability to reduce and thus improve step sound. It is defined as the reduction of the step-sound level in an adjoining room separated by a dividing floor by laying flooring in relation to the step-sound level of the deck structure, see Fig. 7. The weighted step-sound reduction is indicated by a single figure.

Fig. 8

Drum sound
Drum sound indicates the special type of step sound radiated in the same room from which the sound originates. Drum sound is for example common in long corridors where much noise can occur, see Fig. 8.

Reverberation time, T [sec]
Reverberation time indicates how quickly the sound pressure level falls when the noise source in a room is switched off. The reverberation time depends on the room absorption. In most rooms, a brief reverberation time is recommended, see Fig. 8.

Fig. 9

Absorption
When sound waves hit the surface of a building, some of the sound energy is absorbed.
This results in a reduction of the sound pressure/sound. The absorption can be used to reduce the noise level in rooms, see Fig. 9.