Page 17 (Updated 23-Oct-2008)
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Cabin / Chassis Tuneup:
- Noise Insulation <-- vs. --> Soundproofing
- Rust Protection
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NOISE INSULATION:
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Once upon a time Rolls Royce ran an ad: "our car is so quiet, that while speeding, the only thing you hear is the clock ticking..." After the CEO read that advertisement, the R&D department received a strict order: "replace the clock immediately!"
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Mapping the Environment ; What is happening there?
Energy waves induced by bumpy road, engine etc, do travel in metal in all directions. Some of it raches the cabin area and induces air to carry its energy all around. This is picked by our ears as noise...
Wave paths:
To depict those noise waves entering the cabin, I take one example of the cacophonic 'stormy sea' impacting the speeding vehicle. Next picture shows how road noise propagates one route (metallic struts) to the chassis. There are other routes also: connecting rods, direct travel via air, indirect via reflections etc.
Other noise sources (engine, wind etc.) behave similarly, propagating in the chassis via metal, air, pavement reflections and so forth.
Strut assembly ends attached to the chassis 'make' four noisy points.
Wave Transmission 'stations':
These four points act now as transmitting stations, sending multiple wavelengths of noise traveling and echoing in the metal. The metal conducts noise differently, and as it is emitted into air, its wave bend forming a total cacophony. From this cacophony might rise at some frequencies so called standing waves: interacting points where these waves boost each other.
(This is of course very simplified view: multiple rods, exhaust, engine, reflections via road from engine bay... constantly conduct myriad sound frequencies from every direction.)
Strut assembly ends emit noise around. Hypothetical standing wave point at A pillar.
The noise travels the A, B, and C pillars on top of our musical instrument.
Mechanical Amplifiers:
As soound/energy waves reach the roof, they cause all materiel they travel through, to vibrate. The pillar innards also form organ pipe structure: the air efficiently echoes all vibrations, without any dampening, from their metal structure. In the end of their journey' they reach our chassis top = speaker diaphragm. The roof element works very well in repeating the road surface, translating it to noise...That is why it is most often (like in maxima) well insulated.
Our vehicle is a moving instrument: recorder, amplifier and transmitter with bass speakers. Tires record every pebble on the road, transmits warped reflections into chassis, acoustical chambers amplify and play back the 'tunes'.
To cut this noise, Nissan experts tried to insulate the rear strut end. They built a rubber boot around the struts end and nuts. This well intended system ended in fiasco: now the back strut noise is amplified with this mechanical amplifier. Your first task is to take this off, and fill the cavity with some dampening foam or cloth.
Rubber boot nut "shield" (1.), rigid sound
guiding walls (2.), speaker membrane (3.)
Noise propagation from the road to the "Nissan -amplifier"
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What do You Want?
- Sound Soundproofing -OR- No Noise -
First we have to define those two:
Noise is nonwanted air pressure fluctuations entering a defined space.
Sound is self induced pressure waves in a defined space.
Note: Your Sound - My Noise!
Hillarious Concepts:
Typically car manufacturers mix noise dampening concept with killing all sounds. The sound environment is 'spoiled' by softening all surface inside the cabin. As all sounds (with noises) are drowned, discussion becomes impossible. That is the wrong and easy way to go.
The right way is to insulate the cabin from outside noise, and use hard and soft paneling to create a 'normally' sound reflecting environment for discussion, music listening...
Nowadays some car manufacturers are producing sandwich chassis structures: two metal sheets , between dampening material. This effectively kills the sound & vibration conductance.
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On the 'other end', with all leather, the cabin can become eerie glass house: all sneezes and 'ear scrubbing' become noticed if all outside noises are totally insulated off without suitable soundproofing, also attending cabin echo's. Inside cabin there has to be a balance between sound insulating and sound reflecting surfaces.
I do not have all leather inside, but plush -fabric with plastic panels which create a nice discussion environment. But to reach there, all outside noises needed noise-proofing...
On the noise producing environments opposite is true: The more varying angles a surface has, the less possibility is to crate an mechanical amplifier. Ideally the surfaces should be absolut non reflecting, but anything degrading noise reflection properties helps. The noise sources should be tightly insulated, the surfaces around them arranged to kill or disperse the oncoming waves.
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Engine Bay Soundproofing
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Noise reflection dispersion mat at bottom, behind radiator (not Maxima)
Noise sources:
Engine is the most noisy system in the car. This is so, because manufacturers so far have not been able to cost effectively to dampen the myriad vibrations from rotating masses, explosions directed into exhaust. This is all possible, the cost is the key issue.
Pinpointing the noise sources in this system may result in a plan to insulate those: exhaust pipe is typically insulated for heat related problems, but works well on soundproofing also. Intake piping 'leaks' out sounds and may be insulated.
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Noise reflectors:
Next step is to focus on the echoing surfaces: One typical place where air enters in around after market open filters etc. should be designed/dampened not to allow unrestricted wave reflection. Dampening material in the engine bay corners cut standing wave reflections.
Most important is hood downside: the original hard flat "soundproofing" acts as an mirror playing together in concert with the road surface. Adding any material dispersing the flat wave -mirror helps. If this material is not flat, and can also reflect sideways all incoming sound energy, the hood will not be tuned with road surface as a giant bass drum... which may be heard miles away (problem mostly with large diesels). Any add-ons here have to be Absolutely! secured not to fall down (fire hazard).
Note: In the engine bay, one has to make sure that any add-ons, be it insulation or some gadget, will not get loose, drop on exhaust and start fire. Foam is not a the best solution due to somewhat increased fire hazard, however, engine bay already contains rubber, plastics, gasoline and myriad other flammable materiel...
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Reflection dispersion surface; trunk & hood underside, engine bay wall
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The noises propagating to the cabin.
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The cabin contains noise emitters (although second hand), reflectors and mechanical amplifiers. Each aspect has to be identified and tackled accordingly.
Note!: Airbag system owners, do take battery negative terminal off ½ hours before removing seats, working under dash. (this also resets ECU tables.)
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Emitters:
Worst noise source in a cabin is a pinhole to engine bay. Former 'projects' where holes to engine bay are left ajar, produce 95% of all engine noise in the cabin. Close.
All bare metallic surfaces, screw ends emit some of the wavelengths 'floating around' in the chassis. The engine bay wall has to be 'combed' through, and insulation added on all places where sound insulation is not adequate.
Note: Do NOT! mess around pedals with loose insulation, that is a real hazard. All insulation has to be tightly glued, not to drop between pedals.
One of the worst emitters inside of the dashboard is the 2" metal pipe inside dash going from one side to other. It is also round, acting as nice six foot, 360 degree organ pipe emitter right under u nose... This has to be wrapped as much as feasibly reached. If the pipe can be stuffed, the better.
The Dashboard support pipe emitting chassis noises, hypothetical noninsulated plastic device box "X" resonating and amplifying some of its frequencies.
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Amplifiers and Reflectors:
The dashboard contains 'zillion plastic amplifiers'. I took long insulation strips, inserted with 'third hand steel wire' on hard to reach parts. Best way is to open all dashboard and meticulously glue all insulation in, but lazy me did not this time go so far... These strips cut the air wave reflections inside the hard plastics.
No room for reflections inside filled dashboard
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The floor needs insulation also. Original insulation is patchy, and 'pipe organ tunnels' under front seat, rear seat need some echo cutting insulation stripes. The heater plastic tunnels from front to rear, are also bare needing some.
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Pillars:
Pillars 'work' both as reflectors and emitters.
Best way to insulate noise propagation on steel, is to glue something on it. If it was possible to tell all the variables in this living, constantly changing (wavelength, echoes) environment, it would be enough to glue small damper into the one exact point. Best way is to test, and try to block all waves. Gluing cloth on the pillar, and on its finishing plastics shield cuts wave propagation upwards toward the roof, and stop noise reflections via the hard plastic cover by dampening it. The arrow in the pic shows the snapper hole, route to fill the whole pillar inside with noise dampener. I did not fill all, just inserted long pieces of cloth all along the pillar.
A-pillar metal surface dampened, cloth insertion
inside this "organ-tube".
Panels:
- Inserting the panel back onto the pillar.
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I used leftover plush for my project: this fabric contains short perpendicularly attached tight hair to base fabric & thin foam. These multiple physical properties work quite well in sound insulation.
Noise insulated A-pillar panel end with on glued plush.
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Lower chassis
The first thing in a Maxima, should be filling this powerful "piano" box created near the front tire: open metal box covered with hard plastic = mechanically amplifying loudspeaker... Immediate huge difference in road noise.
Driver side left panel taken off: metal chamber waiting to be dampened.
Trunk monkey ears can relax here: the original hard gray wheel well covers need some soft dampener behind it, glued on the metal if possible. The rear window shelf has to be glued, one major sound route to cabin from the trunk.
Insulated wheel well cover (3.), Shelf (2.), ABS computer harness gnd (going inside cabin(1.).
Doors:
Doors form also big mechanical road noise "box" amplifiers. The panels itself are quite hard and do echo noises back to the "boxes". Gluing one ply of plush cuts the echo from one side of the box, cutting the edge off from mechanical amplifier. I think it is not wise to glue inside the door, or any other place suspect to direct moisture: it will boost rust in the chassis.
All metal connected parts and bare metal emit the wavelengths traveling in the chassis, and have to be shielded.
Noise insulated door panels, front seat chassis attachment screws.
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The insulation cost? 10$ for the glue, endless hours...
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CHASSIS RUST PROTECTION:
Tools:
Typical pneumatic sprayer
DIY rust protection with compressed air tools employs long special hoses that penetrating the smallest corners. Do NOT use the special rustproof products: these form non breathing sticky 'plastic' coat that keeps any water under... Drying the chassis beforehand doesn't help: used compressed air always contains and also spreads water... Now when this 'rustproof' water sits under the coating, the rust countdown may be started... At shops, their treatment contains also high pressure wash, and vehicles are often too hastily sprayed before chassis has really dried.
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How Oil Works:
Oil is 'breathing'. Oily metal will never rust. Oil spread last summer, will continue to live next summer: hot day will get oil expanding and running and spreading further (see the pic above). All cracks that have appeared will 'heal' and not start to rust as non oily things will. The rust that has started, will stop. The oil will even seep through layers of mud, although washing before spray is recommended.
Last time I had power washed a chassis and added oil from a small dropper and watched oil trickling down to a double metal sheet seam, a nice phenomena resulted. As Oil trickled in, the water still sitting there between the seat was pushed out - big water droplets strted rolling down the chassis... Try this!
The Living Chassis:
The chassis is a ever bending, living, box-system. All weld points are under constant bend stress forces, hair cracks in paint (also metal) continue to increase as long as car is driven. Condensed water will enter any place inside chassis cambers, its furthermost corners - if no oil, salt in air plus water will fulfill its ugly deed...
Shielding rear wheel wells from chipping stones, gravel:
Rear wheel well rust protection: add on mudguard sheets
Two sheets are cut to fit the well. Two rivets connect these sheets together, two rivets, each in both ends attach these to sheets chassis (red arrows). The gas tank filler hose shield has now a cut (green arrow) to allow rear sheet insertion. Yellow arrows indicate where the sheet is bent for rigidity.
This attachment allows bending, yearly cleaning from sand and dirt. Insert shows the wheel well form (cyan) and arrow points how the add on shield (black) works protecting upper part from wear of direct stone hits.
The tank filler pipe costs maybe 250$ from ? dealership, price for a 'new' maxima. One was successfully repaired using glassfiber and bits of gas suitable hose fitting around. Leaking pipe is a fire hazard...
Brake Lines:
Also Brake lines may rot. They may look adequate until scraped clean. If no fluid changes have been ever done, they might be rotten inside as outside, bursting on next full panic emergency brake. My Opel lines came down like serpentine when I touched them, after brake pedal started to hit bottom...
Rust protect oil-spraying:
All chassis corners under the new shield is sprayed liberally with oil. The four new small attachment rivet holes into chassis are also sprayed with oil under the sheets.
Proof of active shield:
The nuisance: for example door outside panel will next summer have about one inch stretch of oily film dust. This is because I one year ago sprayed all doors with oil, and the seams will start to leak on hot weather (those seams that seem to be absolutely water resistant, absolut non rust). To me that tells about the oil film's creepy POWER. If it can come down those 'hair' cracks, and climb one inch up, it surely will fill all potential rust starting points in inner chassis structures. And where is oil, rust will be killed as oxygen cannot pass through and react with steel.
The Inconvenient Truth:
Sprayed oil leaks through fitment cracks outside, oiling all microscopic 'channels' between body parts. Capillary forces are in play... In-pushing oil also forces water off from metallic cracks & surfaces forming an layer against oxygen reaction =rust.
Here seen at gas filler opening. Its oil not gas created dust.
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Ugly Rust:
At Left: Enhanced pic from net to show how my Bluebird came to be; view from trunk side to the
wheel well. Alas, no NTHSA rust recalls here; maybe taxes do recompense that?
Pic above, right: No money DIY: Buy pitch and then buy sheet metal from scrapyard. It is good if the metal is galvanized or at least well painted. Whack, scrape all loose rust off. Next cut pieces of the sheet metal so that they will block the holes. Take pitch pieces and spread around your art, place metal patches on top. Take heater blower and start heating until the pitch boils and flows all directions inside/outside: all water will be boiled out, seamless patch forms. Paint over. Do all this in well ventilated place... The sheet metal patch here was actually welded first; but on some occasions welding is not necessary if chassis is structurally sound.
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Spraying oil inside drivers door with compressed air tools.
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Process of Rusting:
Rust comes from metal reacting with oxygen (air) plus water; salt from roads or salty sea air works as a catalyst. Oil film does not allow oxygen to pass to the metal, but water can travel freely OUT. Also oil pushes itself into tinier cracks as water, and pushes water out. Water cannot rot metal if no air is present even is some may exists between oil/metal. Oil can also creep 'five inches' in any direction, continues to creep and fill any old/new cracks years after application.
Where the all water comes in?:
Any structural 'pocket' is 'breathin' continuously in or out, depending on ambient temp related to structure temp. Incoming air always carries moisture that will condensate on colder surfaces: there is no corner safe from this water coming in. Only oil film can shield the metal from corrosion, even with the moisture. Oil is better than sticking plastic like substances which keep the water (that came during application with compressed air/water). With glue like plastic substances ever present water cannot escape. With oil, when the car sits in the sun, any water left in structures, evaporates through the oil - an never can return with air - on the oily metal surface.
This is just one poor laymans view. Rust issue is focus of lots scientific research projects all over the world, google it.
Conclusions:
The shops typically laugh at oil spread community, as there i$ a threat to the indu$try. U bet the 'real' rustproofing will cost anything from 10x to whatever, compared to DIY oil spray.
Those who say against, I tell to test first - and speak later. Seen how a new door with expensive rustproofing is rotten through in two years. This happens in winter conditions as car is driven continuously in/out from extremely cold to warm (normal) garage. The snow melts in garage floor, evaporates, and is condensed again with salt on any cold surface. Read: water seeps into remotest chassis, cracked weld point areas...
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P.S. Look at page 26, bottom page 26 , for rust recalls (US only) and see if your car is eligible for free Nissan repair around filler tube rust.
Check out also:
- http://www.cardomain.com/ride/1146109
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When rust is NOT tolerated - oil flies in...
Eh. Also this ultralight tube-frame airplane site has now been discontinued. Basically they fill the ultra-light welded frame tubing with oil, then drain all oil out. This kills all hidden rust that cannot be tolerated in an aircraft. Oil leaves behind a living, oxidation inhibiting film coat inside. If such flush doesn't reach every point, capillary action will do it.
Maybe you want to try if this clic works:
http://members.eaa.org/home/homebuilders/building/basics/Rust%20Protection.html
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"He layeth up sound wisdom for the righteous: He is a buckler to them that walk uprightly" ; Solomon. (...Happen to know that Solomon also had wisdom to handle the 'sound'...)
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