[WJH]

My car has a little more road noise than I would like on the highway. Has anyone attempted to mitigate the road noise with their car? I'm curious as to what can be done or if I just need to live with it.

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[mbardeen]

Yes, quite a few people have done it.





See this thread for some:

http://www.968forums.com/topic/9969-dyna...-the-doors



Or search for "Dynamat". I'm sure there's plenty more threads out there.

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[flash]

leave the kids at home?



seriously - dynamat extreme on every surface you can find your way to get to.



while you have the rear panels off, you can also do the "rear speaker enclosure mod" and really improve the sound of the stereo.

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[Cloud9...68]

I used Dynamat on the doors of my 968 (which I should rip out now that I'm turning it into a track car, but taking the door panels on and off this car ranks second only to rebuilding the steering rack as far as pegging the anti-fun meter), but on the recommendation of www.sonicelectronix.com, I used a much cheaper alternative that they sell (they also sell Dynamat, but the rep told me their substitute stuff - can't remember the name - is actually thicker) on my daughter's car when I did her stereo upgrade. The sound deadening achieved through the installation of a product like Dynamat to the insides of the door skins is attained strictly through the weight of the material - you could achieve the same result, though far less conveniently, by gluing fishing lures or small barbell weights to the insides of your doors. Dynamat was the first on the market with this material, but there are far less expensive alternatives available now. They'll work just as well as long as the weight per unit area is the same or greater.

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[flash]

that's actually not quite right.



mass is an important component of sound deadening, and lead sheets work very well for one type, but there are a number of factors involved in sound transmission.



first off, there are 2 basic sources of sound with which to be dealt:



1. external sound

2. internal reflection



both types can generate resonance. the frequency at which they resonate depends on the energy being generated, and the frequency at which it is generated, and the materials the sound is hitting



for external sound, mass will have the largest effect. however, an elastic compound will also act like a shock absorber, which will attenuate the energy hitting the sheet metal, and thereby reduce the amount that permeates it. basically it converts the hard surface of the sheet metal to one that is pliable. this function absorbs energy.



for internal resonance, the elastic properties also work very well in attenuating resonance, but soft uneven surface materials do even more for reducing reflection. unfortunately there is no easy way to do that in a car, beyond what they have already done in upholstery and headliners and such.



the differentiation in materials out there is all about the elastic properties. a heavy gooey compound will work better than one that is lighter and stiffer.



i've seen the charts, and the dynamat extreme outperformed b-quiet. it wasn't by a lot, but it was there. i haven't seen charts yet on acumat

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[DaveN]

I used the B-Quiet as it was so close to Dynamat in specs and way cheaper (weighs less too). I only chimed in here because I think someone here was selling a roll as it was not going to be used so maybe a good deal if you decide to try this.

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[flash]

it really depends on the frequency. the b-quiet info floating around out there is at a frequency that lends itself well to marketing. looking at the entire spectrum though, and then looking at the foil thickness, as well as the adhesive used, it's pretty easy to see that DE does better. even the competitors say DE is better, as do the audio pros who have used them all.



that does not mean that BQ is not a good product. it is. if cost is a factor, then it's close enough that you'll see most of the benefits, at a lot lower cost. if cost is no object, then DE is the better choice.

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[WJH]

Thanks guys, good information. From the reading it would seem the greatest benefit is from doing the rear areas. I think I'll try those first before the doors. I hate messing with the doors.

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[flash]

lol - if you're like the rest of us, you can plan on doing the doors. i am pretty positive that once you do one area, you'll want to do the rest. it isn't that hard anyway

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[WJH]

[quote name='flash' timestamp='1348879794' post='133152']

lol - if you're like the rest of us, you can plan on doing the doors. i am pretty positive that once you do one area, you'll want to do the rest. it isn't that hard anyway

[/quote]

You're probably right, car work always leads to more car work!

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[rxter]

We did the doors with DE. Other than a fair amount of bleeding the install was simple. We then attacked the trunk. It worked so well that it eliminated the low frequency drone that we get around 1200 - 1400 rpm, which strangely we like- so we ripped it out.

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[flash]

hmmm - that's the vocal range.

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[Cloud9...68]

Messing around with just the doors, wheel wells, and rear hatch is for amateurs - why not go all the way, like "Robby the Cable Guy" of Higher Connections fame did in his 951:



   



   



   



Now that's what I call some serious sound deadening!

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[MB968]

I'm looking forward to at some point applying one of the above mentioned materials to help abate the interior noise levels in my car.



That being said, there are a few things in the above posts that aren't technically correct. It's not a big deal, but if someone really wants to geek out on this subject and possibly end up with a better result . . . then you'd want to understand how these materials work. To do this look up info on non-constrained layer damping and constrained layer damping (the foil backed variety probably falls into this category, although usually the constraining layer would be a little thicker sheet of metal).



The key to an effective material cannot be told by how it feels. There are very specific tests that have to be performed over a wide temperature range to obtain the loss factor (sometimes called loss modulus) characteristics of the material. Viscoelastic materials with usable (high) loss factors always have them in the transition range between the material's glassy region and it's rubbery region. These do not describe how the material feels, but are material characteristic specific terms. Thus the testing for loss modulus is done over the temp range of interest. For instance certain enamels, not the paint variety, have been used on turbine blades to add non-constrained layer damping to them. They have to be in the trasition region of the material at the operating temp that they see inside the turbine.



I don't know if any of the above listed companies publish the lost modulus values of their materials over the range they would see on our cars, but if they do, it would be a way to choose between suppliers or between applications. Since the door in some areas will see very hot and very cold temps, you'd like to have a material with a wider range of good loss modulus. If the material is used to make the sandwiched sheet metal plate that covers the front of the flywheel area on our car, it would need to have a good loss modulus at a much higher temp due to being attached very close to the engine block. I doubt that the above suppliers offer any variety in their materials, but if you are using the product by the exhaust, you'd ideally have one whose transition range was much higher temp than material used in the door.

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[tamathumper]

I wonder what the loss modulus is on my volume knob? That's what I use to reduce road noise...

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[Rap]

Do you still have the same sense and feel of the car when you eliminate all this noise? Me I love the sound of my exhaust and wouldn't want to eliminate that. In fact I've never replaced the broken sound system because of that point. I'm thinking of doing or not doing the same thing on the second one!

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[flash]

mb - yeah - it was hard to talk about the stuff without getting too technical. i also didn't want to get into the temperature issues, since it would be very hard to say which one would be best without a lot of climate data for each individual. being an audio engineer, i can go on forever about this stuff, but i see people's eyes glaze over as soon as i start talking about harmonics.



rap - yes. it actually tends to put you more in touch with the car, since the extraneous noise is reduced, and what you hear is what you are supposed to hear. i find myself much more relaxed and able to pay attention to the subtleties.



if the sound system is broken, and you therefore don't use it, remove it in the track car. it's just dead weight at that point

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[Rap]

Having only driven the new car from point a to b the day I bought it and not seen nor heard it since I'm looking forward to hearing it! Both radios are not working. Doesn't adding damping increase overall weight? So I assume we are just talking about none track cars. I don't have your technical background, and years of listening to loud music plays some influence, but for the average joe like me, do you really discern that much of a difference?

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[flash]

the difference in what the car sounds like, as well as the stereo is night and day. the constant drone of road noise just goes away. that sort of noise wears on you and tires you (at least it does me). of course you have to have a working stereo to get the stereo part of it.



yes, it adds weight. not a lot though, and it's evenly distributed. if you do the whole rear of the car, the rear speaker enclosures, and the doors, you only add about 20lbs.

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[Cloud9...68]

Yes, it's not so much the volume of the sound, it's the quality - the droning these cars make gets real tiring. If I ever bought another 968 to use as a pure street car, I would go nuts with the sound deadening, but then install a nice-sounding exhaust, like an RS Barn cat back.



I think the shape of the hatch area in the coupes has a lot to do with the level of droning. A few years ago, I rode in a first generation BMW M coupe, which as a similarly shaped rear hatch area, and it had exactly the same level of droning. I've never ridden in a cab, but if my theory is correct, I would imagine they have an entirely different level and type of interior sound.



There's an impressive level of knowledge of acoustics on this site (the extent of my knowledge on the subject is limited to a half semester of undergraduate physics). For the experts, what percentage of the noise (particularly the annoying low-frequency droning) would you estimate is coming from the external sound, vs. the internal reflection components? My guess would be that a sizable majority of it is external sound, which is why I would think the weight of the sound deadening material is the biggest factor in its ability to reduce interior noise. If it can't get into the car in the first place, there's nothing left to reverberate and reflect off the hatch glass, in other words.

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