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Discussion Starter · #1 · (Edited)
Re: I just took a unique perspective picture from *inside* of the left rear compartment where the fuses are.

It stands to reason that the most noise that enters our Volt is via tire noise. The hatchback layout and thus opening in the back lends to rear tire noise. I have the accessory that goes between the rear two seats and I think that helps with some noise. I've tested other things based on threads here but did not think they made much difference at all.

There is no doubt they have done extensive work in controlling the sound ... no doubt with recording mics in different locations. Taking apart the back area peaking around you can see sound deadening material *everywhere*.

Anyway this thread was really not to rehash those. I just wanted to show the unique perspective pictures from *inside* of the left rear compartment where the fuses are. See pictures below. You cannot put your head in that area but I could put my camera in there.






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Other threads:
Adding-insulation-in-back-to-muffle-road-wheel-noise
http://gm-volt.com/forum/showthread.php?9263-Adding-insulation-in-back-to-muffle-road-wheel-noise

Rear-seat-blocker-and-cargo-mat
http://gm-volt.com/forum/showthread.php?9375-Rear-seat-blocker-and-cargo-mat
 

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So I've read in the past that one the main things that the Volt and Cruze share is sound dampening technology and material and design. Check out this article and videos.

Redefining Compact: 2011 Chevrolet Cruze Sound of Silence - 2010-09-14

DETROIT – Compact cars are rarely associated with very quiet, refined interiors. Chevrolet's engineers developing the 2011 Chevrolet Cruze took that as a challenge: deliver the quietness of a larger, upscale vehicle while maintaining the value and efficiency of a compact.

“Reducing noise is fairly easy if you have the flexibility to add cost or increase weight,” said Cruze Performance Manager, Brandon Vivian. “For Cruze, every change had to meet two criteria: It could not increase the Cruze starting price of $16,995, and it could not add weight that would jeopardize Cruze's outstanding fuel economy.”

To meet their objectives for the U.S. market, engineers developed more than 30 acoustic treatments that mute unwanted engine, road, and wind noise. Here are 10 of the most significant features:

  • 500 inches of structural adhesive reduce structural noise and increase body strength
  • Seven pints of liquid sound deadener on the cabin floor mute road and friction noise, and weigh 30 percent less than conventional sound-deadening materials
  • A five-millimeter, acoustic-laminated windshield quiets wind noise
  • Triple seals for all four doors block wind and road noise
  • 30 “Snickers bars” of expandable, sound-blocking baffles in the roofline and window frames quiet noise transmitted around the door openings
  • The 26- x 50-inch hood liner features acoustic materials that mute engine noise
  • Two sound-absorbing mats on both sides of the front-of-dash panel isolate engine noise, and save three kilograms of weight by using lightweight materials
  • A 15-millimeter-thick mat in the spare-tire well absorbs road noise
  • Four wheel-well liners, backed with textile material, block tire noise
  • A five-layer headliner muffles cabin noise

The quietness of the Cruze illustrates how addressing one sound often brings less-noticeable noises to the surface.

“Every noise masks other, quieter sounds,” Vivian said. “For example, reducing a wind whistle on the highway can uncover a tire rumble on coarse roads. With Cruze, we recently added a dampener to the fuel line, because the interior is so quiet that we could hear fuel flowing through the line.”

It seems that the engineering team may have hit their mark. After driving the Cruze, MotorWeek’s John Davis wrote, “the ride was not only free of vibration, it was big-car quiet.”

DriverSide.com’s Alison Lakin concurred, writing “Chevy engineers worked hard to improve sound damping in the car, and it has clearly paid off. The Cruze cabin reaches levels of luxury car quietness. Seriously.”



Check out the 1st video here: http://media.gm.com/content/media/u...n/2010/Sept/0914_cruze_sound?id=1318140119978
 

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Discussion Starter · #3 · (Edited)
From all my studying on home theater forums sound is a funny thing. You need specific material to handle specific types of sounds and frequencies common to the situation.

From this MS Word doc:

http://media.gm.com/content/dam/Med...unch/10_Chevrolet_Volt_Structure_&_Safety.doc

Refinements give Volt a quiet cabin

On top of the Volt’s already-quiet electric drive system, designers and engineers incorporated numerous initiatives throughout the car to isolate road and drive system noise away from the cabin.

  1. The front-of-dash panel is sandwiched between two damping mats to help block noise transfer from under the hood. The passenger compartment side is covered with a 25-mm-thick rubber mat tuned to specific acoustic dynamics of the car and “buttoned” to the panel close-out caps at the attachments to ensure a tight fit.
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  2. The engine/drive system compartment side of the dash panel has a tight-fitting, 10-mm formed fiberglass mat. All holes in the panel for wiring harnesses or cables are as small as possible and closed off with composite grommets for more noise reduction.
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  3. On the underside of the hood, a formed fiberglass blanket provides an effective noise barrier, and rubber seals along the hood lines and between the rear edge of the hood and air induction panel ensure a snug, well-crafted appearance and also reduce noise.
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  4. To block transfer of airborne noise through the hollow structures in the vehicle’s architecture, composite nylon baffles in the structural intrusions reduce noise by 40 decibels. The Volt’s CFM (cubic feet per minute) airflow measurement is only 20, among the lowest of any Chevrolet vehicle ever built. The baffles are molded to fit in the strategic areas where they are applied and close out the sections through the use of an adhesive foal that expands when the body passes through the paint oven.
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  5. The Volt’s five-layer acoustic headliner is made of a thermal fiber acoustic design found on premium vehicles. Three layers are a polyethylene/felt substrate for sound insulation; and a two-layer polyurethane skin, called Taffeta, provides a premium-looking woven fabric appearance.
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  6. Even the Volt carpeting does double-duty as a sound-reduction tool. The carpet module is precisely formed to the floor pan and incorporates a composite backing with a thick, 14-ounce carpet. Its precise fit eliminates gaps between the floor panel and the carpet to reduce or eliminate noise transfer from the floor panel to the cabin.
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  7. Liquid-applied sound deadeners, which are lighter and easier to use than conventional sound-deadening applications, are the first acoustic treatment applied to the body structure, including the floor pan and footwell areas. Robotic equipment is used to ensure the deadeners are sprayed uniformly and into hard-to-reach locations. The liquid-applied material is tuned to meet the needs of the Volt’s metallurgical resonance.
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  8. The door areas, a common source of wind and road noise, include several noise reduction measures including a flexible acoustic water deflector – similar to those used on Cadillacs – that covers the entire center portion of the interior door. All holes within the door’s interior structure are closed out with composite grommets. All doors feature a triple-layer sealing system that includes body mounted seals on all door openings and trailing edge seals on rear doors.
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  9. Composite wheel house liners at all four corners help block rain and other travel noise (such as on a gravel road). Lower-profile, structure-less windshield wipers reduce wind noise about one decibel compared to conventional wipers.
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  10. Another common source of noise occurs in chassis-to-body structure interfaces. The Volt incorporates an isolated front cradle, with hydraulic mounts between the cradle and the structural members coming off the front motor rails and the dash, to which the cradle is mounted. This minimizes road and drive system noise and vibration from transferring to the cabin.
 

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Thank you for a great thread Scott :) I learned several things about what GM had done to suppress sound.
 

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Where are all these charming graphics coming from, Scott? I've seen a few threads recently from you with production exploded illustrations. What book or software did you get access to, if you don't mind my asking?
 

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Impressive! You won't see me driving along with my windows open, with or without the modified mirror covers, with wind buffeting causing temporary hearing loss (as reported in a post) by the time I get to my destination. I am enjoying the quiet, good music without all the background noise, and automatic air conditioning comfort. I feel I've already done enough on my part conserving energy, and I still get 40 miles range in this weather.
 

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The Volt is quiet, so quiet that noises that are usually masked in a "normal" car become apparent. Unfortunately while the overall sound level is lower, these previously masked sound become more apparent.
 

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For all GM's alledged sound deadening applications, if you traded a Lexus for a Volt as I did, the noise level in the Volt is appreciable. I did not just stick my head in the back panel, I ripped the entire back interior of the car out and covered it entirely with dynamat. GM failed miserably insulating the rear portion of this car. That being said....I still love the economy, ride, and after my personal modification of the rear insulation, the QUIET!
 

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Could you describe your experience with the dynamat installation in the Volt? This is an interesting topic.
 

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Discussion Starter · #10 · (Edited)
Anything can be taken to the Nth degree. 80/20 or 90/10 rules often apply, however. As do co$t and complications on the assembly line.

Could you describe your experience with the dynamat installation in the Volt? This is an interesting topic.
For all GM's alledged sound deadening applications, if you traded a Lexus for a Volt as I did, the noise level in the Volt is appreciable. I did not just stick my head in the back panel, I ripped the entire back interior of the car out and covered it entirely with dynamat. GM failed miserably insulating the rear portion of this car. That being said....I still love the economy, ride, and after my personal modification of the rear insulation, the QUIET!
Here is farmboy's previous post on the subject:
Added-Bose-subwoofer-amp-Dynamat-to-my-Volt&p=143393
http://gm-volt.com/forum/showthread.php?11615-Added-Bose-subwoofer-amp-Dynamat-to-my-Volt&p=143393
 

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I did a lot of stuff on my '05 GTO with just average results. Here are my learnings:

1. Sounds travels through openings so close 'em up - turn on the tv in one room and walk into an adjacent room / bathroom etc. with a door on it and start slowly shutting the door. Notice how you can hear the sound from the other room at almost the same level until the door is almost entirely closed. Covering openings at 90% may net little reduction, but that last 10% is a winner.

2. No need for the lunar lander look - the primary purpose of the traditional aluminum foil backed rubber sound deadening material you see everywhere is to quell VIBRATIONS (which have noise all their own). It is NOT to block airborne sound sound...say that with me once again...it is NOT TO BLOCK AIRBORNE SOUND! You only need enough material on any given panel to deaden it. Thump the panel. If it rings put a square of material on it. My guess is one square will quell most of the vibrations on the average panel. More is not necessarily better. You might plaster a door and make it shut with more or a thunk, but it won't be significantly quieter

3. Heavy Vinyl on Closed Cell Foam is Your Friend - This is what I found to be most effective at deadening road noise, exhaust noise, noise from other cars, etc., and SURPRISE when you start pulling interior pieces out of a late model BMW or Mercedes, heavy vinyl deadening is what you typically find. Stuff like luxury liner pro from http://www.secondskinaudio.com/index.php/products/mlv-noise-barriers/luxury-liner-pro-detail is an example of this. It is more of a pain to install, but that's the price you pay.

Hatchback cars are worse, simply because they don't have that extra barrier (and ANY barrier blocks some sound) that sedans do between the trunk/wheel wells/exhaust (the latter less of an issue in the Volt obviously).

Anyway, that's my '02.
 

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I'll have to dig out my data, but yes, the Volt is 6-10 db louder than my Honda Ridgeline truck. Most of it is tire noise, yes. Some of that might be whacked by more stuff you could apply. But most of the tire noise is conducted through the various suspension bushings, which makes the whole car chassis a radiator of it, and it's mostly low frequency, which is the hardest type to stop/absorb.

It seems like 1/F type noise with a corner around 200hz. The higher frequency stuff that comes through the air, yes, you might do some further treatment for that, but I've not dug into things enough to do it yet and report results. That "goop" they put on things doesn't affect that much (it's too hard), and some sort of felt absorbent might help there, but most of it is just conducted to every part of the car through the chassis. Quieter tires might be a better solution if some can be found that are good in all the other ways.

I strongly suspect that's also the main difference between the Volt and the truck here - the truck has big ol soft Michelin M+S tires on it with high sidewalls.

I have a stretch here where I go through lengths of old asphalt and brand new stuff. The difference in the noise level between smooth old asphalt and brand new shiny stuff is incredible (might be as large as 20 db) - it's really all tire noise...the car is dead silent on the super smooth stuff. FWIW, I tried running the tires with low air pressure to see if that'd help. Not much...hard rubber is just hard. It hurt the range of course, as well.
 

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Interesting stuff DC. So what you're thinking is that the flooring is a giant subwoofer that's excited by the tires, transmitted through the suspension. That would be might tough to kill, short of lining the floor with lead?

I've noticed the asphalt makes a LOT of difference as well.

My X3 had terrible tire noise, and different tires made a world of difference.

I do seem to get some wind noise thru the hatch. Oddly, some days more than others.
 

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There is a section of 2 lane highway I travel on often that is pretty coarse asphalt and at my normal speed of 65 mph in the Volt is annoyingly loud. However, yesterday I was playing around with another driver in a BMW (I think it was a 135i), he was making aggressive passes and traveling 10-25 over the speed limit. So I thought I would stay on his rear bumper to see how the Volt would do making the same types of moves as he was. What I discovered was that on the same section of coarse asphalt the noise levels seemed dramatically lower at the higher speeds. So maybe by driving faster, the frequency of the input is higher and therefore less objectionable. So maybe the solution is to go faster. :)

BTW I did pass him at triple digits just to show him I could. He backed off and didn't want to play any more. ;)

VIN # B0985
 

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It seems like 1/F type noise with a corner around 200hz. The higher frequency stuff that comes through the air, yes, you might do some further treatment for that, but I've not dug into things enough to do it yet and report results. That "goop" they put on things doesn't affect that much (it's too hard), and some sort of felt absorbent might help there, but most of it is just conducted to every part of the car through the chassis. Quieter tires might be a better solution if some can be found that are good in all the other ways.
I've been tempted to try the ComforTred or something similar - tires specifically designed for low noise and bump absorption. There'd likely be a penalty in range/mpg, but it might be worth it, if it makes the tires quiet enough...
 

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I've been tempted to try the ComforTred or something similar - tires specifically designed for low noise and bump absorption. There'd likely be a penalty in range/mpg, but it might be worth it, if it makes the tires quiet enough...
I think the ComforTred or Michelin MXM4 might both be an improvement. I know with my GTO experiment while it all made a difference (75 sq ft of damplifier and another 40 sq ft of luxury liner), I think different tires would have made a much bigger difference...blocking the noise will never be as effective as removing (or reducing) the source.
 
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