Sound insulation versus sound absorption
Sound insulation is all about slowing or stopping sound waves by physically blocking their travel from one room to another. Success in achieving effective sound insulation – or attenuation – is largely reliant on the building structure, the type of ceilings and partitions, and attention to detail.
A partition wall built to a lab-tested (Rw) 50dB+ sound rating will often fail due to sound transfer via flanking paths such as ceiling voids, trunking and ductwork, structural elements such as glazing mullions and poorly finished abutments. Low frequency sounds in particular travel through building structures so introducing mass by using dense materials and acoustic breaks (for example, in ‘dot & dab’ plasterboard) is desirable.
Sound absorption works by converting sound energy by friction into minute amounts of heat energy. By introducing sound absorbent materials into a room, we can totally alter the acoustic characteristics. We measure this primarily in terms of reverberation time (RT).
In general terms, the greater the area of sound absorbent material, the less reverberant sound in the room. In an acoustically well-designed working environment, because unwanted sound energy is absorbed rather than bouncing around inside a room, the acoustic pressure is reduced which aids both audibility and acoustic comfort. This benefits both the users of the transmitting room and the users of adjacent receiving rooms because the users can hear better and therefore speak more quietly so there is less noise fighting to penetrate walls and ceilings. This effect is shown in the table below.
Important note - sound insulation addresses sound quantity whereas sound absorption addresses sound quality. Both are important but in the UK interiors industry there is a disproportionate focus on sound insulation at the expense of proper sound absorption.