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The Prius is a very nice car out of the box. Its really quiet. Im going to try to make it REALLY Quiet. Ok, So Im obsessive compulsive. So are you or you wouldnt be reading this!

Using one-inch thick professional soundproofing heavy foam. Its rated for aircraft use and is very fire resistant and designed for use in engine compartments. The foam does not hold water and is not affected by oil.

The plan is to fit a blanket to the inside of the hood to mask engine noise coming through the windscreen. Also, removal of the plastic wheel well liners and using adhesive, make a noise barrier around the tires and into the quarter panel. Then reinstall the liners. Lots of road and tire noise is channeled through the quarter panel into the interior. Lastly, cover the floor under the rear seat and in-between the cheap barrier in the trunk including the speakers. This should remove any road rumble from the rear.

I will let the group know how it works out.

Have fun.
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Sure would be nice to beg, borrow or steal a sound level meter, and run some tests under various conditions. That way you could tell us which mod made the most difference...


First, Yes, you are correct about our obsessive compulsive natures. Now with that out of the way; I will be quite interested in your sound deadening adventure. Please, if it works, let us know what you feel was the single best area to insulate against sounds.

Best of Luck,
I'm interested in your method of quieting the wheel wells- I tried spray-on rubberized undercoating/soundproofing (one can per wheel well) and found it didn't make much difference, except perhaps for the high frequencies.
Progress report

I am also putting different speakers in the rear deck, so I started soundproofing here. Under the rear shelf, I replaced the felt with closed cell sound material 1 inch thick. The shelf is easily removed, its held on with push plugs. In the trunk, 2-inch barrier against the rear seat. Also, filled the wheel wells by the sides of the rear seat with as much as I could jam in. Then replaced the thin plastic and felt factory barrier. This is a tight fit so you need to bend it some.

The road noise from the rear is reduced, most noticeable when going over a rough or wet road. I am going to cover the rear wheel wells, floor and trunk hatch next. A section to cover the speakers will be fitted as well. After this is done I will move forward to the doors.
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