A PRACTICAL APPROACH TO IMPROVING SOUND INSULATION MEASUREMENTS AT LOW FREQUENCIES

摘要

Since the publication of Approved Document E 2003 (ADE) of the UK Building Regulations 2000, concerns have been raised regarding the repeatability of sound insulation test results due to the introduction of the C_(tr) term, which places a greater emphasis on D_(nT) results at low frequencies and on the overall single figure rating D_(nTw) + C_(tr). The airborne sound insulation test standard BS EN ISO140-4 (ISO140-4) as required by ADE, was formulated assuming diffuse sound field conditions in both source and receive rooms; however, many measurements are made at frequencies where the sound field is not diffuse. The frequency at which the room becomes diffuse is defined by the Schroeder frequency, f_(s), which is approximated using the following formula: f_(s)(Hz) velence 2000 (T/V)~(1/2) where T is the reverberation time in seconds and V is the volume of the room. The majority of domestic rooms tested in the UK have volumes ranging typically from 20m~(3) to 50m~(3). The Schroeder frequency will therefore range typically from around 200Hz (e.g. V(velence)50m~(3), T(velence)0.5s) to around 500Hz (e.g. V(velence)20m~(3), T(velence)1.25s). In typical UK domestic dwellings therefore it is measurements below 500Hz which are of particular importance in terms of repeatability and measurement uncertainties. Any employed method should therefore be practical and cost effective yet reduce the measurement uncertainties below the Schroeder frequency.