Who is running a aftermarket rear that is quiet?

[Sieg]

I've been intrigued with acoustical damping ever since watching a show featuring an Aston Martin assembly facility on Velocity TV where an "engineer" was strategically applying a material similar to Dynamat Extreme in lightening bolt and wave shapes on interior cabin panels. I've always wondered how much science was behind their application considering the sophistication of their engineering.

I finally found a picture (and a great tour of the facility) tonight.

On these Vantage chassis I was interested to see these reinforcing strips added to the interior, applied as a result of noise, vibration and harshness studies to improve the characteristics of the chassis.

http://www.speedhunters.com/2013/08/...dream-factory/

[Twoblackmarks...]

Personaly I dont mind some whine, it makes the car feel more "racier" As long it is not too much.

I would think leaf spring transfer more sound than 4-link, soft mushy bushings MUCH less or zero sound vs. urethane and such. Frame car vs non frame etc..

I dont think my 87`Olds 442 8.5" 3.73 was very "developed" by GM to be honest. But it has a very "quiet chassis" that is forgiving for everything in sounds. -Super sweet car by the way

78 Camaro With 2.42 -No sound. Put in a used 3.73. Some mild sound when hanging on gear if i remember correct -could be the pinion bearing, or faulty setup, (also had been used...) even when set up by professionally. But to be honest I just think the aftermarket has a little less quality in it, or sound is not their ultimate deciding factor for the parts, but it still is somewhat weird I think, but the parts for US cars are really cheap to buy, so that explains atleast a portion of it. -For many types of parts..

If you ultimately want a quiet ride, install mushy bushings in everything, so they absorb everything you dont want to hear and feel, and lots`o sound deadening. I think that Cures most sounds..

I work With New cars, and they are very sensitive to tire noise, out of round, sounds from drivetrain. If you take the Wheels of an old impala that glide like an boat at 100mph, they could be "oval" without feeling it, put them on a New car and it would feel horrible at 40-50mph and may make a LOT of tire noise.

Because every year they get harder bushing, more Direct mounting in body, lighter spindles, shocks and springs etc.

Now it is really good for driving to get less unsprung weight, but at the same time that unsprung weight act as an vibration/torsional damper, and usually the lighter/less mass an vibration damper have, the worse it "Works"

Since it ability to absorb vibrations, and even sounds lessens, and the more sound and vibrations then go through the modern hard bushings into the body and to the driver in one way or another.

Now I wrote much more than I was going to, I still think rear gears should be somewhat quiet, Stock or not, Depends somewhat though, what type and such. My Moser makes some sound, but not more than my exhaust, so dont know at the moment, and I am ok With it too, so it does not really matter, it is a Hot Rod, not a Rolls Royce

4mul8ion Has great Points.

Here we have a lot of modified cars like Voyager type cars With removed rear seat and changed carpets and different stuff, (because of TAXES!) Many of those complain about noises from everything, since the rear compartment now acts as a huge speaker.

This may be a messy post without much answer, but I still post it, and se what happens

[chr2002ca]

I've purchased 2 new complete 12-bolt rear setups from Moser for my '69 Camaro. The first was a 30-spline unit with Eaton posi and 3.42 gears. It made a little bit of noise after about 3000 miles but it wasn't too bad and I didn't really notice it much. The 2nd unit I purchased which is currently in the car is a 33-spline TruTrac with 3:42 gears again. It's perfectly quiet right now, but it only has about 550 miles on it. Time will tell. If it develops a whine, oh well, it doesn't really bother me. I have sound deadener laid down all the way to the back of the trunk, so maybe that helps.

[Boostable]

My Moser is pretty quite!! But then again Im still pushing the car around

In all seriousness, I hope there is not an issue as with some of you other guys I have had mine awhile, and will be more then a year before she see's the road from time of purchase.

[cluxford]

Strange locker in mine
35 spline
355 gears

can't hear anything over the roar of the 632 cube BBC running through twin 3" pipes and single magnaflows

[4mul8ion]

Originally Posted by Twoblackmarks...

...
Here we have a lot of modified cars like Voyager type cars With removed rear seat and changed carpets and different stuff, (because of TAXES!) Many of those complain about noises from everything, since the rear compartment now acts as a huge speaker.
...

That's a great point. I'll be running 3.55s from us gear and I don't remember what was put down for lining my trunk.

[4mul8ion]

Originally Posted by Sieg

I've been intrigued with acoustical damping ever since watching a show featuring an Aston Martin assembly facility on Velocity TV where an "engineer" was strategically applying a material similar to Dynamat Extreme in lightening bolt and wave shapes on interior cabin panels. I've always wondered how much science was behind their application considering the sophistication of their engineering.

I finally found a picture (and a great tour of the facility) tonight.





http://www.speedhunters.com/2013/08/...dream-factory/

Very cool.

There's probably quite a bit of science behind those shapes. Check out this video that shows a flat plate going into motion at various frequencies.

[Sieg]

If my post was cool........your's ranks as Ubercool!

It would be interesting to apply sections of Dynamat to the underside of the test sheet to see how it impacts the patterns.

Flat plate in set gauges is one thing, plate formed by stamping has to be an entirely different animal.

Are there sensors that can be applied to plate to measure frequencies?

Thanks for the education!

[4mul8ion]

Thanks. This has been a fun discussion but apologies to 69x22 for pulling the topic of this post not just into the weeds but now through the weeds, through the guard rail and halfway into the corn field.

You're absolutely right. Formed steel is completely different. With different boundary constraints, bends and dimples, you can change the performance of the panel. They test it by having something apply a known force and measure the response using an array of accelerometers to measure the response.



Dynamat has done something to determine the effects of their acoustic material to the patterns. Look at what they say for their XTreme product.
http://www.dynamat.com/technical_spe...at_xtreme.html

I'm not sure what the effective absorbing range it can cover but for gear noise it needs to be most effective in the 300 - 600 Hz range to absorb gear mesh frequencies. That product may only be effective at absorbing lower road noise related frequencies.

Not sure on that.