How to quiet down a portable generator?

hi, box idea below fine except that, unless timber of box thick indeed un reduce noise , vibration much. sound waves have damped down in order work box lined insulation boards trick.
these boards can seen @ following link http://www.screwfix.com/p/cavity-boards-45mm-12-boards/76418?kpid=kinasekpid&cm_mmc=affiliatewindow-_-datafeed-_-building%20and%20joinery-_-cavity%20boards%2045mm%2012%20boards-61071&source=aw can buy them more cheaply @ builders merchants. used insulationg cavity in house wall , have dense build reflective coatng on 1 side.
can see how used in house wall @ link. http://www.diydoctor.org.uk/projects/cavity_wall_insulation.htm

reflective coating (when used building house) reflect heat building have no use in job doing. when build box , line these boards should put reflective coating facing box rather generator. box should large enough ensure there 150mm gap round generator , should add 50mm hole in top allow exhaust fumes ourt. hope helps.

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