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How Loud Is Your Car At 70Mph?

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So I'm curious to know how loud or quiet your '02's can get when going down the road at 70mph.  I'm installing some sound deadening on my doors and realized I should actually try to measure the cabin as I do this install to know how much of a difference it makes.

I downloaded an App called "Decibel 10th" on my iPhone 5 to get at least a reasonable idea of how noisy it gets in the car.  The result, though not flattering is quite funny:




I think the Average Blender at 90dB is about the feeling I get from my car. 

It's a '72 tii with:

-4 speed tranny

-stahl headers,

-RAAMmat and Ensolite on the passenger door only (albeit installed in the wrong order as you can see here http://www.bmw2002faq.com/topic/139831-sound-deadening-on-door-panel-not-door/),

-nothing covering the driver's side door,

-Not much insulation but carpet and floor mats on the floor

-195/50R15's on the ground.


Anyone want to take me up on this? 

(I mentioned the phone I have and the App to try to get a good comparison.  Apparently that app is optimized for the mic on the iPhone 5 so it should be close to accurate)


I'll post an update when I get the other door done. 

By the way, I did this on relatively new asphalt.


** Update **

After putting in the insulation and reassembling the driver's side door the noise was in my mind noticeably decreased, but really only went down by 3dB.  Well at least this little App says it sounds like the Avg Automobile now...


Edited by diathermic
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I've got the rear seats out of mine, and its all kind of noisy. The stock headliner is in good shape and the stock door panels and carpets are all original. Like the poster above, I've got to turn the radio up pretty loud. Its about as loud as my Fiat convertable, but it has a better sound system! I'd help out with some more scientific results, but I don't do the "iPhone" thing. I don't do "i" anything.

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My 76, with 2 coats of paint on the floor and firewall for sound dampening, a 2.2 liter stroker, Ireland headers and exhaust, and dual DCOEs, runs at 98dB at 70 in 4th when pulling up a hill, and about 95-96 on the flats. It quiets down a bit if I shift to 5th on the flats. The noise level might also have something to do with all poly bushings, racing camber plates, and stiff springs.

Our Lemons Tii, with a 2.2 liter stroker, side exhaust, metal rear bushings, poly front bushings, and skinned everything, runs well over 100 dB at 70 in 4th. Earplugs and a helmet are absolutely necessary.

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As far as sound deadening both my '75, and my wife's '76, both automatics, have everything pretty much stock.  Both cars have always lived in Southern Arizona and have no rust.  I don't know if that's a factor, or not. Both cars have realitively new BMW door seals in good shape. 


My '75 is fairly quiet on the road (usually drive between 75 and 85 on our lightly-populated Interstate) and conversation at normal levels is adequate, even with my 75 year-old ears.  The radio needs only be turned to a low-level to be heard comfortably.


On the other hand, my wife's '76 is noticably louder inside.  For one thing, her '76 came from the factory with a 3.90 (or 3.91) rear-end vs: the stock 3.64 in my car.  This results in her car turning about 400 rpm more than mine at the same speed.  Hers also sat fallow for nearly 15 years down here in our hot, low-humidity weather, so some things on hers are a little more deteriorated than on mine.


Both cars have fairly new underhood rubber, so that's not a factor.  We run with cheap poly-foam pillows under the rear seat, as well as esty trunk carpets, but both cars do have parcel shelf speakers - a potential source of outside noise.  The firewall insulation on both cars appears to be in very shape.


Bob Napier


I forgot to mention that I have front and rear spoilers on my '75, and, when we first installed the rear spoiler we all expressed surprise at how much quiter the car had become. I think the two of them do make a difference on interior noise levels.


Edited by Napes
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Both cars have fairly new underhood rubber, so that's not a factor.  We run with cheap poly-foam pillows under the rear seat, as well as esty trunk carpets, but both cars do have parcel shelf speakers - a potential source of outside noise.  The firewall insulation on both cars appears to be in very shape.

Putting some cheap pillows under the rear seat is a pretty good idea. Must cut a decent amount of noise that way.

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Seriously though, it's not all that terrible. I have a gaping hole in my muffler that drones at speed which is annoying, but since I replaced door seals and put some sound deadener on the door panels, rear quarters, and under the rear seat it is totally bearable. definitely better around 75-80mph then at 70, though at 60 it feels right at home. A 5 speed would make things a ton better, as would actually having a floor on the passenger side of the car, instead of the piece of foam stuck to a sheet of copper that pretends to be a floor (lift it up and you can see daylight)  :P . Car is a 76, stock aside from a weber 32/36 and a ported head with oversized valves. stock header (for now). once I re-do the exhaust system it should be surprisingly quite. I don't notice any noise aside from road noise through my passenger floor (gaping hole haha) and my crap exhaust. Just a wee bit of transmission whine since my trans is fairly worn. Aerodynamic mods should also quite down things. Very little tire noise (none perceivable over the other noises) thanks to the old school high profile tires :)


If I wanted a quite car I would have bought a lexus. The extra noise just urges me on faster... I'll often do between 80 and 90 while on the turnpike so long as the rest of traffic is moving at those speeds. Between 75 and 100 I don't notice much difference in sound, probably due to the wind noise overcoming everything else. 

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I just installed "Sound Meter" on my Droid (it's free).  I'll get a reading on my way home.

that is what i have used.


my car is in the low 90's for db's at 65mph.  ear plugs required for anything resembling a long drive.  stereo is unuseable without contributing to deafness.  i am trailering it to vintage....


s14, 5spd, 4.10 diff, loud exhaust, cf airbox, raammatt and ensolite in interior.

Edited by mlytle
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One of the best ways that I have cut down engine/road noise is through decoupling the interior. I worked as a Car Audio fabricator for quite some time and for many of our competition cars it was imperative to lower the noise floor for sound quality.the same principle applies for road and engine noise.

For the most part, most builders tend to dampen the body of the car using products like dynamat or tar paper which only slows down vibrations on the sheet metal but barely slows down any sound that does not emanate from the body of the car. It is a great first step but to really cut down the noise, it is important to trap the sound once it enters the cabin. This can be done in a few ways but the most effective way that i have found is a mass-loading product like Cascade Audio's barrier VB-3 (http://cascadeaudio.com/car_noise_control/vb_3.htm). The basic concept is a sandwich of closed cell foam with a thin lead or dense material in the middle. This material would be layered on top of a dampening material on the floor, firewall (cabin side), back panel and doors. Then lay a thin jute padding under the carpet for comfort. For the roof, deaden and lay a 1/4" neoprene foam on top. Use a quality hood line to help reduce any engine noise radiating Out of the engine bay. This combination of layers deadens, isolates and reduces the overall noise floor in the cabin.

Jute padding: http://www.stockinteriors.com/jute.asp?ItemId=4794&kw=%7Bkeyword%7D&gclid=CPfl8Y-6hbcCFWRyQgodTRoA0w

Edited by mattbenimble
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