Also online at: www.dijonline.co.uk Acoustic engineers will measure the time it takes for sound pressure to drop by 60dB and this is called reverberation. The quicker the pressure drops, the ‘deader’ a room will sound. So for instance, if the pressure reduces by 60dB in less than 0.3 seconds the room will sound ‘dead’ but if this takes more than five seconds there will be an echo. Optimum reverberation time depends on use of space: one second might be ideal for clear speech in a lecture hall, but 3.5 seconds would provide fuller and richer music sounds. In general, acoustic engineers will try and tune a space to reverb between 1.5 – 2.5 seconds. The other issue of concern to acoustic engineers is the influence of sound created outside of the measured space and the ability of a building to minimise the transfer of external sound through a structure. This is referred to as sound attenuation and it is the measure that generally applies to structures between spaces such as walls, windows and doors. This is why acoustic doors are, in reality, sound attenuating doorsets. Sound attenuation is measured using a logarithmic scale. Within the range applicable to most doorsets, an Rw.3dB variation in performance may be taken to be a doubling or halving of performance. For example, an Rw.36dB doorset provides for double the performance of an Rw.33dB doorset. While the structure of sound attenuating doors is clearly vital, many are let down by the seals selected. Sound, unlike air passage can - and will - escape from the tiniest gaps: a door open 1% will let 50% sound through it. In our experience at Norseal, most soundproofing issues or noise leakage problems are down to either a lack of the correct acoustic seal, or badly-fitted or damaged door seals which have gone unnoticed. Also it is common to find acoustic door seals fitted to just the head and jamb but the threshold - which presents the largest gap - often has no acoustic seal fitted at all. Norsound is an acoustic seals brand by Norseal Ltd - stockist of the largest range of acoustic and intumescent products in the UK. Committed to the design, development and distribution of acoustic door seals, Norsound products are manufactured using the highest-grade materials and pass the most stringent of tests; ensuring the best quality every time. www.norseal.co.uk THE door industry journal summer 2019 111 Timber & Metal Doorsets Have you liked our facebook page yet? We post news everyday! www.facebook.com/DoorIndustryJournal Part E of the Building Regulations includes acoustic requirements for certain door types: • Rw.29dB for Entrance doors to residential units • Rw.30dB for Classroom and lecture areas • Rw.35dB for Music Rooms Acoustic door seals need to be tested, like our Norsound range, in accordance with: • BS EN ISO 10140-2 & BS EN ISO 717-1, the harmonised European standards for measuring the sound insulation of building elements. Acoustic seals can provide multiple functions on a door and therefore should comply with the requirements of: • BS 476-31.1:1983 - Methods for measuring smoke penetration through door sets and shutter assemblies. • BS 476-22 - Methods for determination of the fire resistance of nonloadbearing elements of construction. Third party schemes also give scope for the use of acoustic seals. • BM TRADA Q-Mark and Certifire schemes can provide additional reassurance that your products are fit for purpose through on-going compliance to the original product specification. Building Regulations • Approved Document M Compliant - Building regulation in England to ensure that people are able to access and use buildings and their facilities.