has anyone tried to reduce road noise in the car?

[cwiert]

I hear a lot of road noise in the car. normally i don't care, just turn the radio up, but where there's a passenger in the car, the road noise annoys me because it's too loud. I'm assuming 20+ years of insulation deterioration is the culprit. But what can be done?
I've been thinking about spraying in foam insulation behind the rear wheel wells. I'm just curious if anyone else has tackled this issue.

[AaronM]

It's hard for insulation that was never there in the first place to deteriorate. These are sportscars, not Grand Touring machines and there's going to be a lot of road noise; especially with aggressive tires.

If you're serious about reducing noise, try switching to grad touring all-season tires. You'll give up a good amount of handling and grip, but it will be quieter. The other option would be dynamat, but that can be both expensive and heavy.

[pontifex4]

Theory says that the two ways you can kill road noise in a car are by:

1.) blocking transmission of sound between the source and you
2.) reducing structure-born vibration

Most people who do this kind of work to make a living (and while I agree, I am not one) will tell you that you need to do both in the case of a car, since it is both a diaphragm which makes noise and an ineffective barrier for other noises.

There are variations on the theory of noise barriers, but, fundamentally, to block sound, you need to add mass. Popular mass loading materials include thick sheets of vinyl and even lead. Not foam.

Expanding foam (while it is really messy) will help you with the second class of noise: structure-born vibrations.

Believe it or not, another popular material for reducing structure-born vibration, as well as (to a lesser degree) for blocking sound, is non-hardening modeling clay. Seriously. Choose any colour you like. You'll find that jammed into crevices all over award-winning SQ cars at stereo competitions, especially in dash and door trim, and on the backs of thin plastic interior panels.

I should note that I haven't tried anything on my own car, yet, though I certainly intend to soon. Perhaps it's time for a detailed "noise killing in 944s" thread?

As AaronM notes, above, tire noise is the real culprit on these cars (you share the passenger compartment with the entirety of the rear wheel wells, so the largely undamped resonance from performance tires is transmitted to your ears quite effectively).

[flash968]

actually, they are GT cars and not sportscars - the back seat and hatchback give them away, let along the sheer size, weight, and roof

that aside, dynamat extreme does an excellent job at quieting things down - i have it in both the 968s, the M3 and the denali - it has done a phenomenal job at knocking down road noise in all of them

[AaronM]

Originally Posted by flash968

actually, they are GT cars and not sportscars - the back seat and hatchback give them away, let along the sheer size, weight, and roof

2,700 pounds and a 94.5 inch wheelbase don't exactly qualify as "sheer size and weight."

The 928 is a GT, the 944 is definitely not. Anyone who has taken an extended cross-country trip in a 944 can tell you that it's not a GT car. The suspension is too harsh and the level of luxury too low.

If you want to hang onto the contention that a sportscar cannot have more than two seats and must have a leaky convertible top and resultant limp-spaghetti chassis, that's fine. But that definition hasn't been current since Kennedy was president.

[cwiert]

Thanks for the responses. Yeah, the 928 definitely is a GT, the 944 I wouldn't put in that category. But that aside, I looked at the Dynamat and it seems like a good solution. Unfortunately, as mentioned earlier, it's pretty expensive. I guess, for the time being, I'll stick with my time-tested solution for solving road noise. A slight twist of the radio knob.

[flash968]

way off topic, but a moment for clarification:

comparisons to a 928, while in the same GT class, are not relevant - you might think the 944 suspension is stiff, but i happen to feel that the stock 944 suspension is mushy - i feel the 928 is VERY mushy - but then i spent 25 years driving sportscars, so my perspective is different - take a long ride in an elva, an old triumph or even an mgb and then, after you get back from the chiropractor, come back and talk to me about how stiff your stock 944 is

you can wish and dream all day long, but the reality is that the car is what it is, and while a smaller version, it's a GT - that isn't a bad thing either - i'm not slagging the 944 at all - in fact i happen to think very highly of the car - it was one of the transitional cars that set us up for many of the cars of today

somewhere in the 70s, when the gas crisis hit, we were on odd and even days, and car sizes changed, as did the overall availability and construction of performance cars, we started calling coupes and hatchbacks sportscars - car manufacturers wanted to appeal to the buyer who still wanted a fun car, in spite of how politically wrong it was to own one - the marketing strategy was amazingly effective, and opened the door for a lot of crossover cars we have today

again, not a bad thing

but, they are not sportscars - they can be sports exotics (ferraris, lamborghinis, etc), sports coupes (bmws, nissan 350s, etc), or sports tourers (jaguar xk, aston martin, etc), or they can be GT cars like the 911, 928 and 944

perhaps not by today's standards, but 2700lbs is incredibly heavy to those of us who grew up in much lighter cars - even my 77 toyota corolla 4 door was only 2200 lbs - the turbo version had 145hp - was that a sportscar? a sportscar, by definition is much smaller and lighter, and has no intrinsic purpose beyond pure sport driving - a sportscar is basically a race car with passenger accouterments - typically a sportscar will not weigh much more than 2300lbs in full trim

clearly the car does not fall into the sports exotic category

by definition, having a back seat precludes it from being a sportscar, and would put it in either sports coupe or GT

by definition being a hatchback precludes it from being a coupe, since there is no trunk, and all coupes have trunks

by definition having a roof precludes it from being a true sportscar

that leaves GT

by the way, take a spin in either one of my cabs and you will have a very different opinion of the chassis and the top - very stiff, and in fact now stiffer than a standard 944 - i have a pic of a single floor jack lifting 3 wheels well off the ground, and still able to open and close the doors without any binding - no leaks on the tops either

however, neither of those cars qualify as a sportscar either, as they are both too heavy, and not sporty enough (though the blue one is getting pretty fun) - that's ok - i'm old and cranky now, and really don't think i want to drive a sportscar anymore (though i am looking forward to playing with the TR-4A later this year)

back on topic, as to the cost of the dynamat, i think i spent about $300 on the entire car - almost free, especially considering the results

[cwiert]

wow. that's one heck of an argument! OK, I won't disagree with you, but Wikipedia does... http://en.wikipedia.org/wiki/Template:Porsche
...not that wikipedia is the end all be all on car definitions.

[flash968]

lol - i could go in there and change that if you'd like - that's how "reliable" or "official" wikipedia is - fun tool and useful, but since it's written by the average joe, not something to be counted on as gospel - i tend to think that they snagged info from the marketing stuff from porsche

regardless, the dynamat extreme is an inexpensive way to quiet it down, and i highly recommend it - there are some less expensive alternative brands too, though i have not personally heard them - as an audio engineer, i can tell you it did a great job of attenuating low mid to high mid frequencies when used in the doors, trunk area, and wheel wells

[cwiert]

Originally Posted by flash968

lol - i could go in there and change that if you'd like - that's how "reliable" or "official" wikipedia is - fun tool and useful, but since it's written by the average joe, not something to be counted on as gospel - i tend to think that they snagged info from the marketing stuff from porsche

regardless, the dynamat extreme is an inexpensive way to quiet it down, and i highly recommend it - there are some less expensive alternative brands too, though i have not personally heard them - as an audio engineer, i can tell you it did a great job of attenuating low mid to high mid frequencies when used in the doors, trunk area, and wheel wells

is it a pain to install, especially in the doors?

[flash968]

sort of - you have to be patient and keep the stuff from sticking to itself - you'll probably scratch yourself up a few times too - but, once you get the pieces in there, and roll the tool around, it stays put and does an amazing job

hidden added bonus - your speakers will sound a LOT better

[pontifex4]

cwiert, I use and really like a Canadian product (of course, since I'm based in Canada) called B-Quiet (http://www.b-quiet.com/?fqaflt=rdhgold1&). The price is lower, it's quite easy to apply (though, as flash mentioned, still has the same self-stick frustration of Dynamat) and it's roughly equivalent to the best Dynamat (Ultimate) which is one of the better sheet-based deadening materials.

This is one (as I'm sure you've seen) of dozens of different products available to do essentially the same job: damp vibrating panels. My opinion differs a bit from Flash, though: I find that they're most effective on mid- and high-frequency sounds (like the sound you get when you rap against the metal with your knuckle), while road noise encompases a fair amount of low-frequency sound.

In past installations, I've used a sound barrier material called v-comp (from the same company) with great success. It's VERY heavy, though, so you may not be interested in using it, here. I'm still debating this, as well.

Once again, I'm only providing the theory and experience from other cars, here: I haven't treated a 944, yet.

[flash968]

so we all know what is what, low mid is (150 - 400) versus mid (400 - 1.5k) versus high mid (2k - 5k) or highs (5k up)

road noise is generally low mid and mid, sometimes reaching up into the high mids, depending on the design of the car, with the odd exception of big road grooves and such, which can be down around 100

that rap of the knuckles generally is low mid to mid, depending on the thickness and curvature of the sheet metal, as well as any structures that might contact it

highs are affected by carpet and soft materials like that, but not really altered by the dynamat, as they lack the energy to vibrate the sheet metal anyway

b-quiet is one of the ones i've heard good reports on, and the spec sheets look good

[pontifex4]

Flash -- sorry, I misread your "low mid" as "low." I think we're pretty well on the same page, here, though I do disagree that tire block rumble is predominantly > 100Hz. This is where your car-specific experience comes in, since, obviously, every car is different: were you happy with a single sheet of Dynamat over the interior skin of the door, and over the fender wells, etc, or did you work it into every little corner you could?

Also, in your experience, was the 968 cab noisy before you treated it with damping material?

I wish this thread would draw in more individual experiences, but I realize that adding sound deadening to a fairly light car is fairly unpopular.

[flash968]

single sheet - yes - but i used the extreme and not the standard

968 noisy - yes - M3 convertible was worse - both now much improved

again, given that it's already 2700lbs, another 20-30 won't really hurt it much - you probably drag that much junk around in the car

[pontifex4]

Not once I actually install the turbo calipers and rotors I've kept in the back seat all this time!

[flash968]

lol - too funny - i am constantly amazed at how much stuff some of my buddies drag around - it adds up a lot faster than you think - one of them we poke fun at carries about 75lbs of stuff

[SuperXRAY]

Our 944 isn't that noisy. It's not as quiet as say...the Vette that i had, but it also isn't as new.

There are alternatives to Dynamat, though they aren't quite as good. I have had good luck with FatMat, it's so cheap you can coat the entire car.