Sound Reduction with Minimal Wt. Penalty
 

I've been thinking about how to attenuate some sounds without incurring too great weight penalty for a while. Somebody sent me a PM on this, so I guess I'll jump the gun on it. This will be a thread of ideas and thoughts, rather than results.

Now, what we want to do is to have "good" sounds come thru to us in the passenger cabin, and to attenuate "bad" sounds as much as possible.

What we call Good sounds can vary -- with age, with the presence of a companion of the female persuasion, or with the type of trip we take (a 'fun' muffler might not be so interesting after droning on the hwy at 70 mph for hours on end - then when we get to our destination, it might again become 'fun' - say the next day on curvey roads.

For such changes we need some sort of muffler cutout, either a simple cap, or a solenoid controlled re-routing (which adds more wt.).

Other sounds we think of as good are:
- air fan noise
- timing chain noise (?)

Noises that are always BAD include:
- wind whistles, etc.
- tire drumming, etc.
- gravel strikes
- CV joint and transmission whine

The best situation would be if we could attenuate certain frequencies and not others. This is commonly done (or attempted) in many fields. We have other constraints:
- a sports car must be as light as feasible
- we don't want to screen out the "Good noise"

Generally, we can assume that any noise coming from the front or side should be reduced to zero (or as close to that as feasible). Sound from the rear needs to be filtered - and filtering by frequency is easiest.

For the front - a close inspection of every hole in the panels is useful.
- elec. wire feeds
- fuel, fuel vapor, cable, and hydraulic hose feeds
- heater hose feeds
- radio speaker (early cars have one in the dash)
- fresh air vent system
- radio cables, wires
- mechanical cable feeds
ALL of these need to be carefully sealed to prevent air and sound intrusion.

We also want to work hard on the side, front vent and rear vent windows, plus sunroof to eliminate sounds.

The door seals are another issue - I know some have put or plan to put the double SC seals onto their early cars.

Here are some more (really undigested thoughts) from a MS Word outline file I started:

Filling Crevices

The problem with all mat materials is that they do not get down into crevices. NOW -- think about what a crevice looks like... it looks something like a funnel or horn shape, right?? Or maybe a long, thin slot.
- A viscous liquid is surely the best thing to fill such spaces.

What do we use horns for folks?? To magnify sounds, right?
Think of Miles's horn - or a tuba, or an old horn type record player before the electric ones came along, or a Klipsch horn speaker... or a sound reinforcement system at a concert...

So not filling crevices is more of a problem than you might think.

Places to be Concerned About
- holes for seat belt bolts
- approximately 8 stamped oval-shaped holes in the rear deck
- all corners & crevices in rear

“Holes” to Outside and Engine Area
Transmission Tunnel & Its Opening to the Rear
Sprayed Quiet Coat under trans. hump (and covered with clear coat for durability)
also sprayed Quiet Coat into interior of trans. tunnel above that area - coupler area; RonIn LB's idea
I covered it with a spray clear paint for protection

Transmission Tunnel Openings
The area just to the rear of the tunnel exit is very noisy. Noise from the transmission, the front part of the engine, the rear wheels and CV joints, as well as road noise is easily propagated into the tunnel through openings or by reverberation of the tunnel sheet metal.

Noise that gets into the transmission tunnel can travel out of it through the 3 large access panel openings or through any seatbelt holes that are unfilled.

Rear Triangular Cover for Shift Coupler
“Also, the coverplate for the shift coupler is another noise source. Did you know there's a 1/4" x 6" air gap near the coverplate? It is normally filled with carpet, but it's a gap nevertheless.”

Middle (Handbrake Cover)
Hole is filled by handbrake Sheet metal so may be fairly quiet. Leather and Rubber covers will further quiet noise from this area.

Front Opening to Tunnel
farthest opening from transmission, etc. but completely open except for carpet; make a small cover with foam on bottom to fill this area


Ventilation Slots Above Rear Window
The Factory apparently used an open cell foam blocking noise from outside there. This is something to be attended to when replacing the headliner, or possibly when R&R ing the rear window.

Air Leaks from Front Trunk
- air leaks can come through the glove compartment light housing & the speaker – see UpFixing III, p. 132


Wt. of Stock Sound Deadener
Yes -- my 11 pounds was front and rear floor only.

Here are some more weights for the dense panels that were glued to the tub in the areas indicated:

Rear seat buckets -- 2 @ 8.5 lbs each -- 19 .0 lbs
Rear wheel arch -- 2 @ 11 oz each ------ 1.3 lbs
Rear flat side panel -- 2@ 1.25 lbs each ---2.5 lbs
Rear shelf & upper fire wall --------- 1 @ 10.3 lbs
Floor (front & rear) -----------------------11.0 lbs

Total ------------------------------------ 44.1 lbs

I also seem to remember (I did this work 7 years ago) that there were the same type of panels glued to the front side foot wells behind the carpet pockets, but I don't have any weights recorded for them. Can anyone verify that there are sound mats in that area or was the carpet just glued to the tub?

How to Remove Stock Sound Deadener
to remove the thick hard factory floor insulation/sound deadening stuff on the floor before repainting try using a Fein Multimaster with the scraping blade.

misc

“Quick update: I have roughly 10 lbs. of Quietcoat on the rear seat, rear deck, and interior wheel wells. I was originally very disappointed in the noise. Well, the interior is bare (no interior, rear seats, or seat belts). The noise was coming through the inner seat belt mounts (through holes directly to transmission area). After covering the holes with masking tape (temporary measure), the noise levels decreased immensely.”

Also, there's significant noise coming from the transmission hump area, and the panel directly behind the rear seat backs. It would be smart to add more material in these areas, and use less Quietcoat near the inner wheelwells.

Yet another noise source is at the joint of the rear deck and the headliner. I haven't figured out how to attack this noise source.

I honestly believe attacking the noise sources will reduce noise immensely, even in a stock 911. Until all air gaps are eliminated, I cannot fully evaluate the performance of Quiet Coat. However, I have high expectations.


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I put in a layer of Thermotechs Thermo Guard FR on most of rear interior.
http://www.thermotec.com/products/full/14120/14120.html

The sound level with the thermo guard would be liveable but I'd like it quieter if possible without adding too much weight. The G50 is very noisy. The thermoguard 48x72 was 5.26lbs and I used pretty much the entire roll. I think two coats of quiet coat plus the thermo guard will do a better job and not add too much in weight. I removed 50lbs from the back and would like to put back 10 or less. With quiet coat, it might be more like 15lbs back in.

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Thank you for the inquiry. We have a floor barrier that will block road noise from entering the vehicle. However, the barrier is designed for interior use. I recommend using one sheet of VB-3.5 to mold over the transmission tunnel, and 3-4 sheets of VB-4.5 for the flat areas of the vehicle. I do not recommend exterior use of the barriers. Primarily due to the damage that can be sustained by exterior influences. If you need to put a coating underneath the vehicle, use our VB-1X spray vibration
damper, and cover it with a rubberized undercoating. (But remember, barriers are designed to block low frequencies, and dampers make things vibrate less. Use barriers on the floor, and dampers in the door.)
There are many other things to discuss, feel free to contact me if you have further questions.
Also, you can buy direct from us if you are unable to find a Cascade dealer near you.

Best Regards,
Linken Olsen
Customer Service Manager
Cascade Audio Engineering
PH: 541.389.6821
FX: 541.389.5273

IN general, there are (now) two types of noise attenuation materials:
1. sound dampeners
2. sound attenuators

re #1 - these are heavy asphaltic or even lead based materials that act to lower the resonance frequency of panels in the car. These panels act like drum heads and vibrate at certain "resonant frequencies." The freq. is based on their size, thickness and configuration - just like a drum head. The original version of Dynamat is in this category, as is Brown Bread, etc.

materials in class #2 are designed to prevent sound energy from moving thru the material. For example, some are made of micro-beads and convert the sound into (tiny amounts of) heat energy.

One such is made by Cascade Audio.

The nice thing about a liquid is that it will tend to fill those tiny horns referred to above.

So, I would do that before putting big heavy pads on my car.

Subscribed Randy. I am reading your findings with great interest as my LW is basically an empty oil can... that I will be driving to Treffen from IL with a sport muffler.:eek: I may not be able to hear you when I get there.

Active noise cancellation fed into the stereo and then the speakers?

You can buy mini ones for airplanes that have an output and in input (for an ipod). If your stereo in your car has an 'aux' input you could simply plug it in. You could even listen to your ipod.

Actually my dad has one of those, I am going to see if I can borrow it the next time I see him, would be interesting to know my silly idea even comes close to working.

RWEBB: you're not messing around here, are you?

Being an audio engineer, I must say that your endeavor is quite large, as the holes (anywhere) will provide pathing of many frequencies..

Guess I should pack up the spectrum analyzer or TD spectro pieces and send it to you so that you can "quantify" your tasks? Are you, in fact, measuring this stuff?

I've designed and tuned MANY a room but NEVER a frikin car (and certainly had NO weight limitations along the way!!). An interesting proposition, to say the least. Sounds like you need attenuation approaches, and you seem to be on your way as to that regard.

I've a few rides that provide great listening environments with reasonably high $$ pieces. My studios are MANY levels above this... My '89 911 (environment) is absolutely (without question) the poorest of anything I've ever experienced as to audio,..and I've considered working on it to be much better.....HOWEVER,..(and I'm quite sure others will ring out),..that 3.2 is a band in itself,..but can supply fatigue just as much as anything else can...For now, she stays just as I bought her..I just have to crank RUSH a bit higher when need be....and I've plenty power for that, if necc. One thing this 911 WON'T outrun is the power reserve in the audio section.....

Interesting endeavor, you have there. I'll be watching this one.

BTW: mine's bone stock.


Best,

Doyle

I'm thinking of getting some baseline spectrum plots (both pink/white, Steely Dan) on what the 911 renders within the cockpit...I've the proper mics for this,..should prove interesting once the engine fires up.... ...

Best,

Doyle

Thx Doyle. You could make a great contribution to this....

Altho I'd love to have your spectrum analyzer - we almost bought one to analyze bird song vs. ambient in noisy env.s but our research went a different direction.

re: messin' around -- I'm not saying how many pennies I would spend on this or how much of my labor... but it's good to take a pretty broad stance on paper or "in mind" before resources are committed.

I think active noise cancellation (or isolation - see some of Jack O's posts re his car) is not a good direction for me.

Two Queries for those out there:

1. Anybody know much about noise reduction materials in general aviation arena?

2. Anybody remember the issue of Road & Track where they presented color waterfall plots of noise from different sports cars? IIRC, they had Corvette & 911 (993). The latter had a much broader band of output from the motor...

Very interesting topic, Randy. I look forward to more suggestions and trials of the different materials. My car is LOUD (and I still have the factory sound deadening in the rear) to the point where I must wear foam ear plugs for long drives, especially during and after track days.

heat transfer is an issue for the rear firewall - I thought it needed a separate thread.


for starters, fill in this chart:http://forums.pelicanparts.com/uploa...1214259507.gif

BTW - if was going to do something right now w/no more add'l research or thought, I'd:
- use factory foam pad
- strip stock gunk off interior of firewall & adj. panels
- get some of the Cascades Designs liquid and roll it all over everything with drippings going down into all crevices
- use foam to pad off the openings in the center tunnel & make sure the rubber seals there are all in good shape
- test drive & see what sort of panel resonances I got - maybe add strips of ashphaltic matting rather than entire sheets

do the front sealing stuff noted above.

I couldn't resists, but here's the best noise attenuating device with the least weight penalty. :)

http://www.earplugstore.com/images/f...er/earsoft.jpg

Really though, my BMW has great noise level inside the car, but it's at a high weight penalty. I just don't think I'd be able to find a compromise between the sporting purpose results of my sporting purpose car and the luxo cruiser level of noise and physical comfort of my daily driver.

My 911 project will have a cutout for when I want low exhaust noise, otherwise everything will be nice and tight to eliminate the rattles....that's sporting and comfortable enough.

My biggest beef in any car is rattles and creaks....without that, everything else is tolerable.

Randy, noise reduction in GA aircraft consists of quilted pads under the headliner and in the upholstery panels.

This is why we wear David Clark or Bose ANR headsets- just a few minutes in the combination of low-frequency exhaust rumble and the propeller spinning along with high-frequency air leaks will drive you crazy and make you want to land.

Wow I am really to lazy to read the whole thing so if this was covered sorry. You can really reduce the fan noise by polishing the fan. I am surprized at how lousy a job they did on cleaning up the casting. I sanded down all those nasty seams and now I can hardly hear the fan. The fan won't hold a high shine so unless you want to paint it or clear coat it don't even bother doing a complete polish in three months it will look like good old magnesium again. I am sure the fan is also more efficient now.

Also remove muffler and install bypass. You have now reduced all sounds to One.

Randy,
As you can tell from my screen name, I fly a very loud airplane. The only sound deadening is the aluminum skin.:eek: Most of us wear noise cancelling headsets these days. All aircraft are loud - even the corporate stuff. I am sure the manufacturers use something, I just don't know what it is. I am debating on bringing noise cancelling headsets and and intercom system for the long ride west in September. Should be interesting... Carry on.

To call that R1340 very loud is to call an SR-71 fast.

This is a product designed for noise attenuation in vehicles. This company makes audio abatement products for buildings vehicles and whatever might need it.

It is applied as a liquid via spray or brushing. I have not personally used it as my project is currently on hold, so can not speak for its effectiveness.

http://quietsolution.com/html/quietcar.html

Randy,

While this is purely anecdotal, I had good results with a similar project last year. I removed all of the factory sound insulation on my SC Targa, including the asphalt mats from the floor and the kick panels, removed the thick rubber covering over the rear seats and firewall, the inside of the doors, and the for lack of a better word carpet pad type material behind sides of the rear seat area and the plastic kick panel covers. I mainly used a heat gun and paint scraper to get it all out.

I added two layers of quiet coat to the floor, firewall, doors and kick panel. A layer of HeatWave was added to the rear firewall. I also used a closed cell foam from Second Skin to replace the carpet type material on the sides of the rear seat area and the backs of the plastic kick panel covers. I also taped over the various holes in the rear seat and firewall area. I did not want to go crazy with the mats because of their weight, but in this small area it I think it was well worth it.

The steel kick panels, at least on a Targa, produce a lot of noise. Without the asphalt mats they are like a drum. The Quiet Coat noticably reduced the noise coming through them. I added a layer of Second Skin sheets to these areas to reduce their noise even further. With the Quiet Coat and the mats, there is a substantial reduction in front suspension noise coming through this area. This may be an area on which to focus your efforts.

Although I did not weigh the materials going in or coming out, the stock sound attenuation material was very heavy. The materials going back in were much lighter.

Again, I did not weigh the materials or use any instrumentation as to the noise inside the care either before or after. However, I am happy with the results. The car has less noticable noise from the suspension, creaks from the body and high frequency noise. Being a widebody Targa, the car used to have a noticable amount of chassis noise over rough roads. That is pretty much gone now. There is no noticable reduction of the sound of the engine over stock. But that is what I was looking for- just a reduction in some of the "bad" noise with the side benefit of losing some weight.

Good luck with your project, and thanks for a great thread.

Mike

...moved.

Better?

Randy,

Thank you for doing the research.

use factory foam pad
- strip stock gunk off interior of firewall & adj. panels
- get some of the Cascades Designs liquid and roll it all over everything with drippings going down into all crevices
- use foam to pad off the openings in the center tunnel & make sure the rubber seals there are all in good shape
- test drive & see what sort of panel resonances I got - maybe add strips of ashphaltic matting rather than entire sheets

Have you tried any of the noise reducing liquids? I have used Dynamat with minimal results. I really don't like the added weight and it seems very crude. Your details about noise coming into the interior from holes in the body is very important. I can say that just improving the insulation and plastic barrier in the doors and replacing the weather stripping can make a big difference. I was considering Quiet Coat but are they all the same?

I've used the Cascades Designs liquid (Quiet coat) in a few small areas - near the transmission tunnel opening on the floor and the other side of the sheet metal, the curved area of the tunnel surround (think that was Ron's idea). The ext. coating wa then sprayed with a clear paint.

The sound attenuation materials often use micro-spheres encapsulated in a liquid matrix.
QUiet coat seems to better know what they are doing compared to others. Do a search & you'll see that in prev. threads I've written a number of these places (a "Dr. Webb" letter re vehicular protoyping) and most did not make much of a response, or just shoved a sample pack out the door.

here is a material to look at:
http://www.polytechinc.com/products/barrier.php

Great thread, subscribed!

I've put off removing stock sound deadening because of this and I don't even have AC!

I used sound deadening inside my doors, dyna-mat. It probably added about 5 or 10 pounds but damn the inside cabin is like a new car now. I was picking up so much tire and road noise through my doors.
I like it.

Not having an airplane, I'm not really able to play "mine is louder".

The point was that noise does not always come from seemingly obvious places - as cited, prop noise vs. engine noise.

Perhaps you will prefer these:
http://www.aerogel.com/markets/transport.html
http://www.quietcoat.com/html/technology_overview.html
http://www.b-quiet.com/
http://www.soundcoat.com/barriers.htm

Good topic. A quieter car is well up on my do-list.
Jim

Here is something Jerry Hubs posted on another thread - read & heed.

from Jhubs (who did an extensive soundproofing of his Carrera, w/o too much wt. concern):
The insulation and padding was what I chose to do because I thought it would make a big difference in the road noise issue that these cars have. I found that it made a difference, but not a big difference. The majority of the cabin noise (wind) comes from the side mirrors and the drip rail and the road noise came from the tires. Better tires made a big difference.

- I am not sure what Jerry means by "better" tires. It could mean tires that are a less performance oriented, and designed for sports luxury sedans like BMW or certain Lexi. These are still high performance tires but a tad of performance is given up for NVH reduction. Also, old tires with hard rubber will increase NVH, as will cheapo tires.

Strongly agree wrt the drip rail. That thing not only causes a lot of turbulence (= noise), but also creates a low pressure area that will suck air out along the weatherstrip. Mine is very noticeable, unfortunately. I also suspect the air vents over the back window are significant noise generators. Again, an area of both turbulence and low pressure.

Agree also on tires - harder/cheaper and tires with high inflation pressures have to be noisier. There also has to be significant noise transmission through the suspension. I just replaced all my suspension bushings with Neatrix and find that the car is noticeably quieter (but not "quiet") now that the bushings are healthier. Not wanting to turn the suspension into that of a Lincoln, however, I'm hoping that once the noise is transmitted to the body shell some of the sound coatings will make a difference. I think they work by reducing the sheet metal's efficiency as a sound radiator??

Randy,

Regarding A/C insulation, weight is always a big factor in small airplanes, also since most General Aviation A/C are 50 years old there wasn't the technology or requirement for noise reduction. I have a friend of mine who was a jet mechanic during the Korean war, they didn't even use ear plugs while doing run ups on the jet engines. He's now half deaf...

I replaced the wind shield gasket which was dried up and letting massive amounts of air under the gasket. I still wonder how much air sneaks through? This thread has me thinking that I might run some masking tape or duct tape around the W/S gasket to see if that changes anything. I've been told that the side view mirrors are a big wind noise contributor.

I hope you knowledgeable guys keep going on this for us touring types... it's appreciated.

As technology advances, one becomes more and more able to get the sound attenuation desired - both selectively and for lower wts.

The micro-bead type sound treatments are an existing example of light wt. attenuation products that were completely unavailable when these cars were manufactured.

In the near future, we can look forward to aero-gels. In fact, some of us may be able to prototype some in the very near future.

Obviously, no one is going to cut a master of an orchestra in a 911.

I'm with Doyle on this subject. I think you can improve the sound deadening but you will never completely solve the problem because the noise floor is so great. To overcome low end frequencies you need inches of material along with air space. If you were able to fill the area behind the seats with fiberglass batts you would really silence the engine...not to practical. The other option is gobs of wattage which is using your program material to drown out the sounds 911's make. Although this might seem like a good idea you are now in a listening environment that is approaching the threshold of pain. Today's popular music [as Doyle's mastering engineer friend will testify] is seriously lacking in dynamic range and most musicians and engineers complain about this. Dynamic range is the sound level difference between the softest sounds or silence and the loudest. The upside [if there is one], of overly compressed music with minimal dynamic range is that even the 'soft, subtle' passages will sound loud...Shania's inhale will be right up there with the snare? At this point everything is on 'eleven'. Really not the most pleasing musical experience but thats the state of things these days.
I always enjoy reading these posts because I'm always being turned on to new materials to use. I'm sure most of the new products are a major improvement over the tar and horsehair blankets that the factory used but I don't think we can get a 911 cabin to sound like a lexus..thats good!
Question...what do the cabins of the Porsches sound like?

Rwebb,

I deleted my posts, as you requested. My apologies for having caused any "disturbances" within your thread. You guys press on with your projects,..I'm sure you'll make progress, although not substantially (in my opinion). Progress: yes!!!

Luckily, we engineers have no distractions in our efforts (certainly none from a lack of scientists on board [[[now THAT was hilarious,..especially from a bird scientist]]] ). We do it every day,..and do it quite well...using science and (moreso) our "dog ears".....!

I'll make a better attempt to keep professional audio/acoustical comments over on the pro audio boards/groups where they truly belong (in my opinion). And they're really gonna' get a kick out of this one.............

Thanks to all,..AGAIN,..I hope I didn't offend anyone here. I'll see you guys in another thread.
Good work, RWebb !!!


My best,

Doyle

You know, I'd like to make a suggestion here. I think the original intent of this thread, given Randy's interest in light weight 911s, was something along the lines of replacing the sound deadening materials that were originally put it the older cars (say, those of the 70's and 80's) with newer materials that might help save some weight, without a significant increase in the noise level. Or, at least a significant increase in noises we don't like. Perhaps also, the locations that the material might be placed would be of interest, in that maybe what the factory did could be improved upon. Maybe they missed some spots, or had material in places it didn't do as much good as in other places.

I don't think there are that many people wanting to create a significantly lower noise floor, so that they might install an audiophile stereo system, which seems to be where things got sideways here. I've been down that path before and concluded I'm much better off spending my money on a nicer home system, than spending zillions on a car stereo. Perhaps this could be another thread topic, if anyone is interested.

Anyway, I've looked into some of the materials that are out there and also studied a little bit of acoustic theory, in conjunction with a project I have in mind at home one of these days. I've come to the conclusion that the information available from the companies that sell products for sound control, particularly those directed at the auto audio enthusiasts, is devoid of much value. It's mostly hype, or incomplete. But, I am no expert, so I'd really like to hear from people that could discuss the basics of sound control.

I'd also like to encourage anybody with more free time than I have, to test some materials. It wouldn't be all that hard to set up a test rig and I'd really like to see how the factory stuff performs, so that we might have a baseline for comparisons to what is out there. I'd even like to see what sort of noise a car makes, or at least what noises are composed of what frequencies. Wind noise we can't do much about, apart from what the factory did over the years, so I'd be more interested in things like tire noise, which I would assume annoys everybody.

So, any experts out there? Anybody with sound test gear? Anybody without a honey-do list a mile long?

JR

Just for the record,..Rusnak and I have kissed and made up...all is well,..he's a fine gent, indeed,..a priceless contributor here at Pelican University. Yes,..we did cock the thread sideways,..but now on point with the bird scientist's original proposition.

I'm quite interested in this thread and will definately put some time in to assess (when I can find the time, that is...work and honey-do list are long). I've plenty of pro test gear (hardware and software),..and have friends who have even more (although it's hard to get them to give up their VERY expensive boxes..)

Looks like there's much to address in the way of attacking the origin of the noise sources (the ones on the car). Some of the articles I'm reading are interesting as to their discussion of noise reduction techniques relating to noise reduction/vibration dampening at the source. I found it impressive as to what's being used to reduce the structural sound transmissions. Hell, I even found a bit on valve covers:

The powertrain engine is a major source of vibration and noise in automotive vehicles. Among the powertrain components, the valve cover has been identified as one of the main noise contributors due to its large radiating surface and thin shell-like structure. There has been an increasing demand for rapid assessment of the valve cover noise level in the early product design stages. The present study analyzes the radiated sound pressure level (SPL) of a valve cover assembly using the finite element method (FEM). The analysis is first performed using a fully coupled structural-acoustic approach. In this case the solid structure is directly coupled to the enclosed and surrounding air in a single analysis, and the structural and acoustic fields are solved simultaneously. In the next approach, the analysis is performed in a sequential manner, using a submodeling technique. First, the structural vibration of the cover is analyzed in the absence of the surrounding air. In the next analysis, the structural motion of the cover is used to drive the acoustic motion of the surrounding air. A comparison of the results between these two approaches shows them to be consistent. In addition to mechanically induced noise, the air-flow induced noise is also explored in the present study by applying flow pressure fluctuations in the interior air. The overall sound level is determined by superposition of both air-flow and mechanical excitations. In particular, this paper addresses the structural acoustics of an isolated engine valve cover where elastomer isolators and gaskets are used to isolate the cover through viscous damping. The frequency-dependent damping and dynamic modulus used are based on experimental measurements. The results obtained show that the radiated sound level of an isolated cover is noticeably lower than that of a hard-mount one.


In a joking way, I felt that I needed to convert to the silicone gaskets to drop a bit of the radiated sound from this part of the engine!!!! (all said tongue-in-cheek..) As many already know,..the sky's the limit here. There are many sources of noise, as ID'd by Randy. The list is endless..The vehicle is essentially a collection of devices that are waiting to be excited by particular frequencies of energy and they are going to make noise, for sure. ...a symphony of sound sources!!!!!!!! In a perfect world, you'd attempt to isolate the engine.....anywaze,...so much for vibration dampening. ...now ,.. on to noise reduction...ala' lightwweight (as Randy's thread is pointing).

I'll report back to the group with any data I can garner (that is: measurements/readings) that may contribute to the thread.

The projects undertaken by several here are great undertakings..it would be quite nice to quantify the (wideband) noise reduction improvements after the work is done.

Hope to have some nice waterfall plots to post soon!!!

I offer my apologies to the group for any diversions from Randy's original thread point. I'll do my best to not head into the heavy engineering side of reality and keep it at a ground level.

My best to all,

Doyle

Glad to hear that for both of you.

I'd say the first order of business is to get a power spectrum on the car while driving from the driver's seat. (We can ignore the passenger - or try to. My studies have shown that the passenger is often a source of unwanted noise - tho that can change once a hotel for the night is reached.)

P AG knows all about the valve cover issue - that was one reason they changed to plastic ones on the 3.6L motors. But... do _we_ like that noise or not??

Wow, I'm glad we have stand up knowledgeable members like Doyle... This area of sound engineering is way over my head, so thanks to all that are contributing...

Personally I can live with the music from the engine room, it's the wind and road noise that can wear on me...

I can feel the love..;) So, are the newer cars [porsche] using different materials for sound deadening? I confess I haven't had a test drive in a new car but I'm wondering how quiet they have become.

..so how bout them Giants, eh (ahem). Before this thread starts to sound like a Bud Lite "I love you man" commercial, and if it did, Randy already sounds like Charton Heston in the later version, I think the lower exhaust valve covers on Porsches are not the type to resonate. In fact, they are so stiff on the 3.2 and the reinforcing ribs are so deep, I would not be surprised if the things absorb some level of sound rather than say, make their own sound. The top valve covers hmm....may be a different story.

I think I'll try taping up my drip rails this weekend on the way to the coast to see if there is less wind noise.

and you can have my Bud Light, but I'm keeping my Anchor Steam

As to tire noise (and my take on attempting to suppress at the source where possible), I've read where some vendors are now providing wheelwell liner material that have noise reduction properties. Noting that many European wheel well systems provide these types of materials, whereas in the US, you have (more or less) an injection mold approach with wheel house liner materials that have minimal (if ANY) acoustical absorption properties. The principle is, by going closer to the noise source, in this case, the meeting point of road and tire, noises are absorbed there.

Just a thought as to wheel wells/tire noises................


And another good read, as to glass:

"We are seeing an increase in North America for laminated side glazing on certain vehicles provided by a variety of suppliers," said Rob Vandal, director of advanced product development, Guardian Automotive Products. "At an industry level, there is a gradual increase in product fitment. The North American trend has been that some high-end vehicles are getting it for security and acoustical benefits but the latest high volume adoptions have been in mid range vehicles for acoustic benefit. As soon as you laminate side glazing then you obtain an acoustic benefit, especially in the frequencies at which the human ear is sensitive, i.e. 3,000 - 5,000 hertz range. But then if you add to that standard laminate an acoustic interlayer material then you simply improve the gain. Realistically the gain going from a tempered to standard laminated side glass is a much bigger step than the additional gain of upgrading from laminated standard to laminated acoustic. Yet there are some vehicles that have it."
A theoretical model is made to investigate the coupling effects of the trim and air gap on the frequency response characteristics of a passenger compartment. With the model, a parametric study is carried out to understand the relation between the acoustic response of the cavity and the design variables associated with the roof, trim, and air gap between the two. The validity of theoretical formulations is verified through a comparison between the theoretical results and the finite element analysis results. Finally, an experiment for a simplified compartment cavity model is performed to confirm the theoretical results. This study reveals that the resonance peak level of an acoustic mode, which has a nodal surface parallel to the trim, can be significantly reduced by properly designing the trim mass and the gap thickness of the trim-air gap system.

Onward with the data gathering... lotsa good reads out there, especially with regards to Noise and Vibration Reduction (NVH) Materials.

I will soon be applying a noise reduction technique (used by MANY here) insofar as engine noise,..it's called a "valve adjustment",....as I've one that's become a bit noisy ;)....crossing my fingers on this one.



My best,

Doyle

From Jim727: Agree also on tires - harder/cheaper and tires with high inflation pressures have to be noisier. There also has to be significant noise transmission through the suspension. I just replaced all my suspension bushings with Neatrix and find that the car is noticeably quieter (but not "quiet") now that the bushings are healthier. Not wanting to turn the suspension into that of a Lincoln, however, I'm hoping that once the noise is transmitted to the body shell some of the sound coatings will make a difference. I think they work by reducing the sheet metal's efficiency as a sound radiator??

...dead on , Jim727.......you'd want to try to minimize the actual transmission path (before it's coupled...again: "decoupling the source,..more of an active approach than a "passive" approach.)

Forgive me for this (please): In many cases within the studio world, we've completely sawed concrete pads to decouple the control room from the capture room.....I know, I know,..not a 911 point of discussion but a point made as to decoupling structural transmissions.

...back to 911's......

Best,

Doyle

Some great reads from the SAE (hold on tightly):

http://www.sae.org/servlets/PaperEvents?OBJECT_TYPE=PaperEventsInfo&PAGE=getPa pers&GEN_NUM=144830&TOPIC=Noise/Vibration/Harshness%20(NVH)&TECH_CD=NOISE

Best,

Doyle