[scottf200]

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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[scottf200]

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/us/en/chevrolet/vehicles/cruze/2011.detail.html/content/Pages/news/us/en/2010/Sept/0914_cruze_sound?id=1318140119978

 

[scottf200]

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/Media/documents/US/Word/101010_volt_launch/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.