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Old 11-24-2012, 02:12 PM   #11 (permalink)
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Where to begin...

Some of the things I say may be controversial, but I have verified them with decibel meters and RTA analysis. I have gutted my entire car twice in the pursuit of sound reduction for audio purposes and spent probably 80-120 hours on my car alone. I have also gutted someone else's car for the same purpose.

First of all, sound deadeners like Dynamat, Second Skin, and the knockoffs are not meant to reduce outside noise. This is good because they don't. What they do is stop metal from resonating and causing noise that way. If you have large drivers in your doors or a sub in your trunk, deadening mats will keep the metal from vibrating. They don't do squat to stop tire noise or outside noise from entering the car.

Closed cell foam: by itself it does next to nothing to stop outside noise or road noise. Road noise usually runs in the 80 Hz - 250 Hz range. Closed cell foam is completely ineffective in this range. Closed cell foam only starts to be effective about 3k Hz.

Acoustic insulation: this stuff is the real deal! It's what car manufacturers use under your carpets anyway. Bonded Logic makes great cotton insulation out of recycled blue jeans. It's cheap, light, and easy to work with. You stuff the 4" batting in any empty crevices that don't get wet so fill up the entire gap between the outer panels and the inner trim. They also make a 1/2" foil backed sheet that goes under carpets or headliners. This is great stuff! Use it liberally.

If you really want to stop all outside noise you need mass. That's the only thing which will be effective against low wavelengths. The two most common materials are lead and mass-loaded vinyl. Dynamat Extremeliner is the only commercial product I know that has lead sheeting sandwiched in it, but it is ridiculously expensive. It's much cheaper and arguably more effective to make your own mass-loaded vinyl sandwich.

This is how I did it: You use a deadener like Dynamat, Second Skin, etc., on your outer panels. This will stop any resonating (don't bother with structural metal, it's so thick it won't resonate anyway). Second, you glue a robust closed cell foam layer on top of that. I use Ensolite, but there are dozens of foams out there. The foam doesn't do anything by itself, but it makes a great substrate for step three which is a mass loaded vinyl layer. You glue the mass loaded vinyl on top of the foam. The theory is that the sound waves pass through the foam but are reflected by the vinyl until they dissipate in the sounding rejecting sandwich that you've created. Finally, you add the Bonded Logic on top of that. Voila! You will now see a huge reduction in sound!

Naturally most people won't go to the lengths I did. If you only do one step, get the Bonded Logic acoustic insulation. It's the cheapest, and easiest to install and also the most effective at noise reduction for the money.
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Old 11-24-2012, 02:35 PM   #12 (permalink)
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This is a Honda Prelude not an OB, but the procedures are the same...

Step one: coat the outer panel with a deadener. I used a paintable elastomeric compound. This is a door by the way.



Step two: use a good adhesive to glue your 1/2" Ensolite or other closed cell foam on top of the deadened layer (here's a hint: buy scrap remnants of foam it's really cheap that way)



Step three: Use a good adhesive to glue your mass-loaded vinyl on top of the closed cell foam. I used a product called Audimute. This is a finished door:



This is a finished floorboard after the same procedure:


Once you have done that, stuff the insulation anywhere you can:


All over the trunk:


Behind trim panels (this not only blocks noise but stops trim panels from squeaking and rattling)





And finally, yes, it all does go back together again, but it will be a tight fit
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Old 11-24-2012, 02:57 PM   #13 (permalink)
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^^^ Nice job albeit a lot of work!! I used Dynamat and found it to be very useful in quieting down the car. It didn't stop all the noise but helped a lot in reducing the odd vibration in the panels and made the doors close with more authority. If I wanted a dead quiet car I would get a Rolls Royce... As my finances aren't such I can afford one, I'll take what I can.
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Old 11-24-2012, 03:04 PM   #14 (permalink)
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Yes, mats like Dynamat are great for rattles, but they don't block sound from entering the car. They do help, however, because sometimes the body panels can resonate, depending on the type of surface you're driving on. Mats will stop the resonating, but they don't block the sound of the tires on the road which is actually quite high judging by my Outback. Those Contis are LOUD! To stop that noise, you need to go hardcore.

I can make almost any car as quiet as a Roller. The two problem areas are door seals and glass. That's where you get the most outside noise anyway. Luxury cars use dual pane glass. That's the one area where I can't make any improvement on an ordinary car. They also use triple door seals. While I can do something just as effective, it won't look stock (and actually kinda ugly).
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Old 11-24-2012, 05:08 PM   #15 (permalink)
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Not to be disrespectful of everybody's hard work, but these cars at least my marshmallow riding 10 is as quiet as your going to get for a $20xxx car/SUV. If you want total isolation I guess you should of reached deeper in the pocket for a Lexus. Drive the current Forester or the new Impreza and you will no what noise is. I have found with my previous Honda's that tires and some undercoating will make a small difference but it is what it is. Although I have not tried put the effort in some of other people have with extensive soundproofing methods
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Old 11-24-2012, 05:52 PM   #16 (permalink)
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Those Conti tires are on the way out anyway and a set of Michelins are in the future. That will improve handling sound levels and vibration too. I just put new brake pads on my car and found out that just one wheel has 7 oz of weights on one side and 4 on the other.. WTF is up about that?? Those tires suck the wind out of life IMHO..
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Old 11-24-2012, 06:27 PM   #17 (permalink)
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I for one am very appreciative of the effort others have put in to document their work. Like some of the folk here, I find the OB a bit too noisy for my tastes, and I'll likely undertake a project like this.

I don't consider it a waste of time at all, and applaud anybody who tries to intelligently tailor their personal vehicle (regardless of how expensive - or cheap - it is) to their own tastes.
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Old 11-24-2012, 08:53 PM   #18 (permalink)
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Quote:
Originally Posted by pgh View Post
Not to be disrespectful of everybody's hard work, but these cars at least my marshmallow riding 10 is as quiet as your going to get for a $20xxx car/SUV. If you want total isolation I guess you should of reached deeper in the pocket for a Lexus. Drive the current Forester or the new Impreza and you will no what noise is. I have found with my previous Honda's that tires and some undercoating will make a small difference but it is what it is. Although I have not tried put the effort in some of other people have with extensive soundproofing methods
A Lexus doesn't have nearly the utility of an Outback. As long as you do the work yourself, it doesn't cost much to get Lexus quality noise isolation from an Outback. Actually, you can get a lot quieter than a Lexus. An Outback + $1,000 in materials is an excellent alternative to a luxury vehicle. You could get excellent results just by adding lots of Bonded Logic Ultratouch.
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Old 11-24-2012, 09:10 PM   #19 (permalink)
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Having owned Lexus and many BMWs which I still own I can say that the 3.6L 13 Outback is extremely quiet. I have been surprised how quiet this car is. Very impressed. Also the dual door seals help a good bit.
I see no point in doing any sound deadening efforts but then again my perspective is different from what yours might be...
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Old 11-24-2012, 10:27 PM   #20 (permalink)
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Originally Posted by fun2drive View Post
Having owned Lexus and many BMWs which I still own I can say that the 3.6L 13 Outback is extremely quiet. I have been surprised how quiet this car is. Very impressed. Also the dual door seals help a good bit.
I see no point in doing any sound deadening efforts but then again my perspective is different from what yours might be...
I agree that the OB is a respectably quiet car. The one problem are those Contis. They HOWL on concrete above 65 MPH. I've had horribly cupped tires that weren't as loud as the Contis. They aren't as bad on asphalt, but **** they make a racket on concrete! The easiest solution is just to buy quieter tires, but it would be cheaper to stuff some insulation inside the cabin above the wheels wells.
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