The website: http://www.sounddeadenershowdown.com/

The writer didn't cover the liquid coating materials. However, the test results makes choosing mat-type insulation less confusing.

Sherwood

Interesting. Where did you read that? If you go to the quietcar.net they specifically state the product should be applied to metal surfaces. Perhaps "over" was used in place of "versus"?

Thx for that detailed post, Jon. Yo didn't happen to weigh the gallon did you?

Assuming a gallon of paint is mot much more than a gallon of water (8 lbs.); x your 25% guestimate; /2 for the amt. used.... gives maybe 4-5 lbs. of liquid. The wt. will be less than that guesstimate as the liquid fraction evaporates.

So, we might have 3,4,5 lbs. that you think is "at least as effective" in noise reduction as the 30 or so lbs. of stock padding...

Also, did you get any sense of a resonant frequency? i.e. louder at a certain rpm?

Unfortunately, I'm one of the 0.001% of the population that does not own a bathroom scale so I don't have exact numbers (or any numbers for that matter). Regarding resonant frequency, I would say that the paint does a better job than the factory insulation. At about 5k rpms things used to get really raucous in my car (aurally speaking), but my sense is that things have improved. Overall, the interior is quieter throughout the rpm range and under varying levels of throttle (less resonance). One other thing that I should mention is that my road tests were conducted with both windows down (it was pretty toasty outside yesterday), but I drove to and from LA with both windows down as well. I'll get out today for a drive with the windows up.

Rusnak... a change in sound level of 3 db or 3 decibels is typically what is required for a human to detect that there has been a change in volume. The golden ears folks will say they can hear 1.5 db changes.
I found a sound spec for a boxster S ..50 db at idle and 70db at 120km/h. Now normal conversation about 60 dB and a lawnmower is around 90 dB. Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. You know that you are listening to an 85 dB sound if you have to raise your voice to be heard by somebody else...typically what I do in my targa when I'm talking to my wife.
I'm going to keep searching I recall seeing interior noise level specs for 911's somewhere.

2007 GT3
INTERIOR NOISE
Idle (dBA): 57
Full throttle (dBA): 92
Steady 60 mph (dBA): 72

Jon -

That QuietCar sounds outstanding. You say the brush-application method is ugly; any chance of a pic? I'm thinking that eventually I would want to apply a sound absorbent material to all the areas that show grey in emptyo's pic. For now, however, gutting the interior of my car is not something I find appealing until a resto is in order (it's 30 years old and looks great - would probably cause too much damage trying to pull/replace it). In the interim, the floors could be a good candidate, so that pic would be really helpful.

Also, I've been mentally debating the benefits - or lack of - in applying this to the door panels on the inside, then something like dynamat to replace the plastic sheet behind the upholstery. Since you have experience with the QuietCar, what's your opinion of this?

If the headliner ever comes out, the roof will definitely get a coating of this stuff.

Many thanks for posting your results.

Jim

No pics, but if you're going to put carpet down over it then it's not really an issue. What makes it ugly is the fact that you can see brush strokes, so it's not a nice even appearance like you would get if you sprayed on the paint. It does self-level to a certain extent. You could also sand the paint smooth after it hardens and then apply a top coat of paint. The only time that I remove my floor carpet is to thoroughly clean the interior or for a track day, so personally I wouldn't hesitate applying the stuff on the floors.

The plastic sheet behind the door panels is a moisture barrier and is what keeps water from warping the panels. When the car gets wet, water can (and does) get in the doors. If I were you I would remove the panels and the sheeting (carefully) and apply the paint to the inside of the doors. I plan to do this too.

Great! Looks like I can just brush it on top of the rubbery coating already on the floor.

I know about the water path within the doors so I'm planning a couple of days in there to find and kill any rust that might be forming. Definitely will do the QuietCar treatment in the doors when they get to the top of the do-list.

While I was thinking about all of this I recalled that the last time we took the 911 camping I put the sleeping bags in the back seat - the car was noticeably quieter, so that would likely be a prime location to apply a sound absorbent coating for anyone who can get under the upholstery.

Thanks again, Jon.

Ron,

Thanks for the explanation re: sound levels. I think +/- two or three decibels is ok for our use. I'll see if I can get one at Radio Shack and let you know how loud my 911 is.

I'm hoping to suffer some hearing loss, because I am one of those people who get headaches from burglar alarms at banks, computer hard drives, and I can hear most older style garage door openers.

I don't think most of the sound comes through the floor to be honest, you guys. I think most of the sound comes from the engine through the firewall and center tunnel, and from the tires through the wheel wells. Thats were I would focus my sound deadenting materials. Also, as I mentioned you need a sweetly adjusted door and window frame to cut down on wind noise from the mirrors and rain drip rails.

Ok, info from Paul Frere's Porsche 911 story. A 1979 SC at 100 kph [62 mph] has a noise level of 73 dbA and at 140kph [86 mph] a noise level of 79 dbA. Mister Frere states that the lower noise levels [as compared to earlier models [2.4 911S 76 dbA and 81 dbA respectively] had to due with improved sound deadening and higher gearing. I would bet the readings are a bit optimistic and taken on a good day in a car with a cloth interior.

sound might come from the floor on a wet road or a bumpy one if the bumps are a certain size

when I was a kid, my dad had a 911E with the oil filler on the rear fender [Edit: the 911E I'm told was a '72, thanks, jac]. He sold it when someone sideswiped it, then got a '78 SC. He complained that he could barely hear the motor. He still has that SC, but rarely ever drives it. I use it as a time capsule reference car on my 3.2. Comparing back to back, the time capsule car is quieter. I have no reference to 79-81 db. Once I know, I'd have it locked in and I'll know if my car is lower or higher than that.

At least we're moving toward quantifying our numbers.

Factory right rear fender oil filler door only on the 1972.

The early cars are definitely louder. A friend bought a 71T in Colorado and drove it home to Oklahoma, around 750 miles. His ears were ringing when he arrived.

Now, on long trips the radio sees less use than earplugs...

JR

The early cars are definitely louder. A friend bought a 71T in Colorado and drove it home to Oklahoma, around 750 miles. His ears were ringing when he arrived.

Now, on long trips the radio sees less use than earplugs...

JR

Thanks for the dB post Ron. Let's back up a bit and make sure we all have the basics down. I edited some of my lecture notes on vertebrate sensory systems to give an overview of what we are talking about here:

What is Sound?

Sound is just pressure waves of compression and rarefaction in an elastic medium; can travel in gas, liquid, or solid.

Speed in dry air at sea level = 330 m/s (travels faster in liquids or solids).

2 Properties of Sound contain everything about a sound wave:

Frequency (Hz) -- number of waves per second (or wavelength)

Amplitude (W or db, decibels) -- size of each wave

Humans hear from about 20 Hz to 20 kHz (children) or up to 16 kHz (adults); below 20 Hz is subsonic (rumble); above is supersonic


I don’t want this to get too physiological, but for the engineers out there, I will mention that a structure called the basilar membrane can do a Fourrier transform right there in the inner ear.

Auditory Threshold (softest sound) -- 10-17 Watt, right at noise level of ear

If ear were more sensitive, would hear air molecules crashing into the ear drums all the time ---> selection has pushed evolution to the physical limit.

the ear has a huge Dynamic Range ~~ 120 dB

Can Resolve changes of 0.1 to 0.5 dB, depending on type of signal

The human ear is most sensitive to sounds in what we call the mid-range, and less sensitive to higher and lower frequencies. There are two weighting scales in common use for measuring sound intensity – the A scale and the C scale. We only need to worry about the A scale. for more info Google on these terms and the names Munson & Fletcher.

dBA (note the proper caps are shown here, though often dbA is used) is the most commonly used unit of sound intensity (aka, sound pressure level, aka SPL). It means we are measuring in “deci” (or tenths in SI units) of a Bell (the real or base SI unit for SPL) and using the A scale.

So, xx dbA means xx deci-Bells of an amount or intensity of sound, and it is weighted for the sensitivity of the human ear.

Actually, this involves the logarithmic ratio of different numbers, but I am gonna KIS. We need to compress the measurement scale (which is what you do when take the log of something) because of the huge dynamic range of the ear noted above. What this means for us, is that a dB scale is all relative. We usually set it as relative to the faintest sound that a model human can detect - not your Grandpa who used to crawl inside the speakers at rock concerts and then got struck by lightening by operating a jack-hammer - a young human with 'perfect' hearing.

Now, here is a relative table of familiar sounds. Note: these are NOT adjusted for "annoyance value" - some sounds or patterns of sounds are more annoying than others, even at the same SPL (examples might include a baby crying, a teenager whining, your wife asking for a home repair for the 11th time, chalk scratching across a blackboard, etc.)

http://forums.pelicanparts.com/uploa...1216149280.gif

Here is the info Ron posted in table form; compare this with the familiar noises table above.


http://forums.pelicanparts.com/uploa...1216149590.gif

BTW -
[1] hearing loss can occur at sustained SPLs as low as the 85 or so.
[2] There is no way to repair hearing loss.
[3] Hearing loss occurs BEFORE you feel pain from the noise.
[4] Louder mufflers sometimes make LESS hp on a motor than quieter ones.

Just a safety message... We had a kid die here yesterday in one of the rivers. This was just after I cautioned another kid (these were both college student "kids") about her tubing trip down the exact same spot in the river. The guy that died was a top athlete & football player and apparently very nice guy and level headed. He did not appear to hit his head, but the river caught him anyway.

So be careful and be careful with your loud noises. If you are setting off car alarms you are surely damaging your own hearing.

Here are some actual measurements presented by various magazines on noise levels under different conditions in various 911 models.- unfortunately the methodology was not given (direction mic was facing; averaging; position of windows, etc.). Methods likely differ among sources; methods would likely be the same for any single source of data.

But, FWIW:

http://forums.pelicanparts.com/uploa...1217565660.jpg



http://forums.pelicanparts.com/uploa...1217565689.jpg


The data are for all noises combined of course. Note the deep reduction in noise levels for the SC compared with the early S, and the reductions for the GT3 at idle without much reduction at speed or under acceleration.

I. Overview
Engine noise is something we all like. Individuals may differ in how much engine noise they want to hear, and in which components they like to hear (exhaust, vs. induction howl, vs. chain noise, vs. fan noise). There will also likely be differences for each person depending upon situations. As you age, you may want less noise – for example, even Bruce Anderson eventually got rid of his 911 and bought a Boxster, though not all of that was noise issues. You may want less noise on a long freeway trip, if you are taking a female companion on a long trip, or are driving through a neighborhood. Cutouts offer a way to lower the noise level selectively.

Other noises are almost always “bad” – that includes wind noise, tire noise, noise from rock or grit strikes on the underbody, and noise from the transmission, wheel bearings and CV joints. Maybe some people like transmission whine??

II. A Noise History for the 911
The early cars have very high wind noise and most magazine testers complained about it at the time. The difference between an early 911 and a well sealed modern car is even more glaring. The engine also made a lot more noise than the later SC, and there was likely more tire noise also, since modern finite element models for tire noise reduction were not implemented until about the late 1970s (nor did anybody have the computer power to run them).

There is not much an end user can do about tire noise except to change to a lower performance type of tire, such as the ones for performance sedans like BMW. Engine noise is often something we want to keep, so let’s talk about wind noise for a bit.

Wind noise is generated by turbulence – when the air breaks away from a smooth flow over the body (or loops back in an eddy). Noise is also generated when air passes through a hole for the same reasons.

Later, Porsche greatly reduced wind noise:

“Porsche has really gotten its act together regarding noise. [engine noise so low it's eerie]
... the dreaded wind noise that has plagued 911s since Day One is gone. Even the noise around the mirrors is subdued. [car is so tight now that it takes 2-3 tries to close the doors]”
- Road & Track, Porsche 911SC - What Could be Better?- April 1978 (last page of article).

So, why is the SC so much better? The thick and rounded edges of the mirrors no doubt play a part. The SC’s also have an “extra” door seal. A friend of mine added that seal to his 1970 E. He is a very careful guy, but he reports that although the extra seal reduced the wind noise, it is still high – and higher than an SC belonging to a friend of his. So there must be something else about the SC that lowers the wind noise. Perhaps it is the closer fit of the doors…

See also the graphs above - I updated them today also.

Good work Randy... Now tell us how to fix our old cars!

When I first got my car it had the original windshield gasket that was very dry and had shrunk, in fact you could have nearly stick your finger through the bottom part of the gasket. Even now with a new gasket I wonder how much wind noise I'm getting. I keep meaning when I have less things to do to the car is to run some duct tape around the W/S to see if the wind noise is reduced. Has anyone tried that?

Has anyone found the later style mirrors reduce the wind noise?

yes duct tape around the entire seal will surely reduce noise - it would be similar to a flush mount windshield

Randy,

Then you're saying it's not that the W/S gasket is leaking air, it's the aero dynamic affects of the cross section that makes the noise... I might have run a test and deduced that the masking tape was holding out the wind and then silicone the gasket and still had the problem.

Thanks,

no both cause noise - eddy formation of certain sizes & close to the window will create more noise than the "wrong" sized eddies created far away

- this is all based on the pioneering aerodynamics work of Prof. Edward E. Size

One way to reduce noise is to rid the car of air leaks. Not nly that but they are annoying.

The rubber seals around the blue plastic lines above the pedal cluster area have gaps in them. The gaps are hard to see without shoving your hear way up into the compartment floor.http://forums.pelicanparts.com/uploa...1233989374.jpg

They also can allow water and road groddu to enter the interior and cause rust (of course, it may not have been the brightest idea in the world to pierce the interior for the master cyl. and its mounting bolts either...)

An easy way to detect the gaps is to stuff a drop light up under the steering rack in this area and then look for light from inside the car.

This is a closeup of the area shown above:

http://forums.pelicanparts.com/uploa...1233989562.jpg

When thinking about panels of sheet metal, like the body of the 911 is made from, you have to realize that sound doesn't just go thru the panel and out the other side.

Instead, sound hits the panel, and some of it bounces back off the way it came; some of the sound will be absorbed into the panel and excite it. This means the panel will vibrate and radiate sound on both sides. The panel will vibrate just the way it did in your sophomore physics class textbook...

In other words, it will vibrate the most at certain resonant frequencies. This link shows some examples (using a panel that is specifically designed to vibrate nicely):
Harold A Conklin Jr: Piano design factors

Another example would be the head of a drum. The panel is the drumhead.

In your car, a crimp in the panel will change the way it vibrates - basically it will make the panel act like two smaller panels.

One thing you can do is to put a pad on the side of the panel where the sound comes from (incident side) -- e.g. inside of the engine compartment. This has the advantage of preventing some sound from even exciting the panel in the first place.

Second, you can put some gum on that drumhead. You can demonstrate how effective this is at a concert some time. Go sticka nice wad of gum on the drum head and wait for the drummer to strike it - you will note that the sound is considerable attenuated. (Note also that drummers often have pretty strong forearms, so take care to not get caught when doing this.) It only takes a small amount of gum to .. ah.. gum up the works of the acoustical panel.

So, when using a dampening material on a panel, one trick is to only put a piece in the middle of the panel. The amplitude of the sound will be reduced and the frequencies produced will be spread out (i.e. the "Q" will be lowered).

25% coverage is what I usually see quoted for how much to cover.

some background:
http://en.wikipedia.org/wiki/Resonance#Q_factor

Third, you can put something on the inside of the panel (same side as your ear) to absorb any sound generated.

The pic in this thread shows an idea about what to do - I might do it a little differently in the details but the general idea is correct for the Mexico Blue car.

http://forums.pelicanparts.com/porsche-911-technical-forum/320515-sound-deadening-question.html

True, Kemosabe. Good info.

However, one must realize the muffler skin is also a major contributor to the decibels created. Using a more rigid shell might result in better noise control. In the end, droning is perhaps the trade off in exchange for a relatively lightweight muffler.

Sherwood

This is one of my favorite noise reduction threads, keep coming back to it when I search.

Single biggest improvement I have made to my car noise wise - replace cheap aftermarket engine mounts with genuine Porsche parts. No weight penalty, in fact my wallet is a bit lighter!!

Quite true - a light wt. muffler (using Ti and CF) is shown for the GS car made by Robert Linton. Go to RennList 964 section, and IIRC the thread is pinned to the top. Obviously, it is not something that ordinary mortals can do, but that thread is well worth reading in its entirely.