Fixing the flanking phenomenon

Matthew Cand

Matthew Cand, Associate Director, Acoustics

Developing our new software tool to tackle a major acoustic challenge.

Flanking is a common undesirable phenomenon in which the performance of your very good (and expensive!) ‘acoustic’ partition is completely degraded as the sound bypasses it and goes through a side path…

In our time as acousticians, we’ve seen how impactful these effects are, and are experienced with regularly advising clients on how best to minimise them to control unwanted noise transfer between different building spaces.

However, flanking is something that is particularly difficult to predict and, in some cases, requires expensive mock-up tests to be undertaken.

In response, we developed an internal software tool to evaluate the performance of different flanking scenarios. The result, Flank-SEA, allows us to predict the effect of different scenarios on potential flanking performance for the sound insulation from ceilings, floors, and side walls. The software is based on Statistical Energy Analysis techniques or SEA.

Real-world testing

The images below show a classic example where the cavity above a mineral fibre suspended ceiling can degrade the performance of a double-skin plasterboard partition by more than 10 dB, a significant loss of performance. Blocking off the ceiling cavity with a plasterboard panel gets you half-way, but the best performance is obtained by taking the partition all the way up the soffit. In this case, Flank-SEA predicts the performance of each scenario within 2 dB of the expected performance based on reference information, an impressive performance.

Time spent developing a tool like this is a valuable way of deploying our statistical modelling skills so that they can be more easily and quickly deployed in any situation – a sound solution indeed!