i worked quite a bit on a sound deadeing project for the engine compartment of a coach design
sound will come as a whole from a certain source when you consider it (i.e. the engine of a car), but in origin there are high and low frequencies
when you try to solve the problem, you have to separate the solution to handle those high and low frequencies
it is a common case that high frequencies will excite the sheet metal in their eigen-frequencies (that depend of the material, geometry, and structure (reinforcements, welded parts, ...))
meanwhile low frequencies will travel mainly by air finding all the holes, and openings to make their way out from the hood, or onto the interior of the car
to make a long story short, if your intention is to run a more comfortable car for you and for the people walking in the street, .....you should buy a new car !!:twisted:, no, seriously, you have to perform two different solutions, first of all, if you identify vibrations in the hood sheet metal, you will have to add an autoadhesive load pad (it is commonly used in the thin sheet metal walls of washing machines ), this will make the eigen-frequencies go higher and subsequently your mechanical components will not excite it
for the low frequencies an open cell foam will be the best, this will expose a multiple surface (consider all the surface of the hollow cavities that the cells are presenting) to the upcoming sound wave, the foam will transform the energy of the sound wave into vibration and finally heat (negligible for the engine fucntion)
the problem of that open cell foam design is that it will be soon blocked by dust and dirt, so in many cases the finishing of this insulators will include a plastic film or aluminium film, those two will improve the later but will reduce sound deadening performance
modern cars use a design of a special material that combines heat and pressure together with a epoxi to join vegetal fibres together, but you need a press to produce those parts, so it is out of reach for us
hope this helps
regards
sound will come as a whole from a certain source when you consider it (i.e. the engine of a car), but in origin there are high and low frequencies
when you try to solve the problem, you have to separate the solution to handle those high and low frequencies
it is a common case that high frequencies will excite the sheet metal in their eigen-frequencies (that depend of the material, geometry, and structure (reinforcements, welded parts, ...))
meanwhile low frequencies will travel mainly by air finding all the holes, and openings to make their way out from the hood, or onto the interior of the car
to make a long story short, if your intention is to run a more comfortable car for you and for the people walking in the street, .....you should buy a new car !!:twisted:, no, seriously, you have to perform two different solutions, first of all, if you identify vibrations in the hood sheet metal, you will have to add an autoadhesive load pad (it is commonly used in the thin sheet metal walls of washing machines ), this will make the eigen-frequencies go higher and subsequently your mechanical components will not excite it
for the low frequencies an open cell foam will be the best, this will expose a multiple surface (consider all the surface of the hollow cavities that the cells are presenting) to the upcoming sound wave, the foam will transform the energy of the sound wave into vibration and finally heat (negligible for the engine fucntion)
the problem of that open cell foam design is that it will be soon blocked by dust and dirt, so in many cases the finishing of this insulators will include a plastic film or aluminium film, those two will improve the later but will reduce sound deadening performance
modern cars use a design of a special material that combines heat and pressure together with a epoxi to join vegetal fibres together, but you need a press to produce those parts, so it is out of reach for us
hope this helps
regards
