Sound Reduction with Minimal Wt. Penalty

[RWebb]

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.

[RWebb]

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

[David]

Great thread, subscribed!

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

[dipso]

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.

[Jim727]

Originally Posted by RWebb

rather than one up each other on the loudness of our airplanes, which can be done in OT, can we stick to the issue of materials to attenuate noise?

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

[RWebb]

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.

[Jim727]

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??

[Mitch Leland]

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.

[RWebb]

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.

[Mysterytrain]

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?

[dshepp806]

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

[javadog]

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

[dshepp806]

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

[RWebb]

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??

[Mitch Leland]

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...

[Mysterytrain]

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.

[rusnak]

..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

[dshepp806]

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

[dshepp806]

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

[dshepp806]

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

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

Best,

Doyle