Design
When trying to minimise the noise produced from an exhaust, it is essential to consider
the system as a whole. This includes pipes, silencers, and emission control devices,
all of which have their own impact on noise as well as interactions with each other.
Designing a quiet exhaust system involves lots of complex mathematics but experience
still has a role to play too. These days the calculations tend to be performed using
specialist software, but even so not many designers would claim to be able to optimise
the design with their first prototype. This is especially the case with noise which
emanates through the walls of the exhaust system rather than the tailpipe. Often
known as 'resonance', 'skin' or 'drive-by' noise, this is less amenable to calculation
than tailpipe noise, yet in an application where the exhaust is mounted high up
on a vehicle rather than underneath it can be a very significant component of overall
noise.
(Photo: Colourmap analysis of exhaust noise, used to identify
acoustic trends and resonances)