Thanks for your reply and i do understand your reasoning.
In the Automotive world (based upon ~20+ years in hands-on NVH development
there),
the other issues were 1) moving the resonating cavity/intake openings as far
away as possible from the operators ear - usually to the front of the engine
bay, as, like reductions from mass damping, distance makes about the same
difference
in attenuation (double the distance, halve the sound power), and 2) working
to try and tune the intake pipework so that it does not resonate at the
typical cruise engine RPM. Most cars have intake resonators that take this
problem
away - some of them are even closed-loop, measuring the tone and then adjusting
the effectiveness of the anti-resonator to minimise it.
I wish we had the freedom to tinker here in the UK that you have - changing a
nut
and bolt can invoke cries for the mandatory need for a scrutinised MOD required,
here.
And I dearly wish i still had access to the rather expensive test equipment i
could
get my hands on back then, a Campbells diagram [Sound level or Vibration
amplitude vs both RPM and frequency scales - for both engine Vibration and
emitted
noise vs RPM for e.g. a Rotax engine installation in a Europa], could tell
us all so much - why exhaust springs break so easily, why the noise in the cabin
is what it is, and what the optimum engine RPMs would be to minimise those
etc.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510465#510465
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