bent

Well, as I stated in another thread, I was unhappy with the drone that I started experiencing with my B&B Fusions (it didn't start untill about a month after putting them on). Anyway, the drone wasn't unbearable, it's just that I would have had to raise my voice slightly to be louder than the car when cruising on the interstate, so I decided to try a little experiment. I went to Circuit City's going out of business sale, and picked up some dynamat extreme for almost 50% off. I bought one of the big trunk kits (12 sq. ft.) and two of thier door kits. Grand total was about $150. Anyway, I installed it this evening and put everything back together no problem.

Here's where it gets interesting....I did some before and after SPL testing to see if there was any improvement. I tested with the butterfly valves open and closed at 55,60,65,70,and 75 mph.
Here are the results

BEFORE

______Open.....................Closed
55mph 94...........................92
60mph 100.........................96
65mph 103.........................97
70mph 104.........................98
75mph 105.........................99.5

AFTER Dynamat Extreme

55mph 93...........................91
60mph 96.5........................92
65mph 100.........................95.5
70mph 103.........................97.5
75mph 103.........................97.5

As you can see, there is an average of 2dB drop in SPL which is noticible. There have been numerous threads in which people claim that the sound deadeners do not do any good for controling drone, but I say that they do help. Now, you must consider that it won't be a big enough of a difference to make any type of bullet muffler bearable on the highway---there is just nothing that can be done for that. If you have a mild aftermarket system that you want to tone down just a smidge....doing the dynamat treatment in the rear is what you want.
After reviewing the dB numbers posted on B&B's website, my numbers don't come anywhere close to being the same....they show 80/78 ( O/C) @ 75MPH.....I can only assume that this is on a car with stock manifolds and cats....I have LG Pro headers and aftermarket cats. It should also be mentioned that every SPL meter is different, depending on which brand and which weighting is used. I used my trusty old Radio Shack analog sound level meter set on "C" weighting and "slow"response.

I hope this info will help somebody!!!

mike100

How do you feel it would help a stock system? Obviously the sound engineers have made a pipe that doesn't drone, but I like the idea of noise reduction that doesn't choke off the engine output in any way.

How many lbs was the dynamat?

Vasta

Nice write-up! Thanks for posting.

I had my car fitted with sound deadener, not dynamat but Crazy Cowboys stuff. To my ears it has helped. Car seems a little more solid now.

bent

I didn't think that the stock system could get any quieter!! Seriously though, I think that the lower volume sounds (road noise/stock exhaust) would see a more noticible improvement than someone trying to tame an aftermarket exhaust. If you went the extra mile ($) and did underneath and behind the seats as well as the rear, you would think you were driving a totaly different car! As far as weight goes...I would guess that I added about 20lbs to the car. Dynamat Extreme is very thin. There are thicker/denser products out there that would add more weight, but they would also be more efficient at quieting any noise. Choose wisely.

bent

I don't want this to get lost on the second page just yet.....shameless ttt

peter pan

I know putting in the dynamat in my C5 made little difference in the cabin noise. The good thing on my C5 is that my Corsa's do not drone like B&Bs. I had Route 66s on the C6 for about a week and the wife hated the drone and told me to get the off her car, so I guess her Vette will stay with the extremely quiet stock setup

bent

Hmm, that's interesting. I didn't think that the Route 66 was supposed to drone.....then agin, I didn't think that my Fusions were supposed to either.

Ratchet Thunderbolt

Great post and good information but I have to try and qualify your results. You are the first person posting, that I have read, that has attempted to qualify sound deadening material before and after installation. Again good job. I have to make a few points though.

You must have had a half way decent sound level meter because it had different weightings.

"C" weighting is not the number that you want to report for your tests. C weighting still lets in large amounts of low frequency noise into the measurement that your ears never hear.

You should be reporting "A" weighted results. This weighting curve is exactly what your ear hears. I'm sure your number would be somewhere in the 70dB range using A weight. You might also find that the delta between before and after might be somewhat larger than with C weight. That's because your measurement is contaminated with spl's that you don't hear and aren't reduced by the dyno mat.

You should also report microphone position, like driver right ear or something.

You mention your result varied from someone else's. Could be road surface conditions or wind, all play into the measurement.

You have put a lot of hard work into the install, testing and posting of your results. I enjoyed reading it. If you ever want to discuss interior car noise or testing methods please pm me. I'm always open to NVH measurements discussions.

Once again, great post and testing. You must enjoy your Vette a lot to do all the work. I enjoy mine.

glenB

If you're feeling energetic, pull the mufflers done and remove the heat shield, attach the dynamat to the underside of the trunk area as well as to the top side of the heat shield.

If you want to squirm further back, attach some above the pipes as well.

cmonkey713

The rear tire noise is the main reason to sound deaden. If you are still running the Goodyear runcraps the tire noise is terrible. I have Borlas, longtubes and cats, the drone is very noticeable but the noise from the rear tires is much more annoying. If you have a bone stock C-6 coupe the tire noise is very annoying at speeds above 60 MPH.Forget about the exhaust it's the tires that drive me crazy.

BlackMark

Don't overlook the liquid sound deadeners. In talking to Anthony from Second Skin he explained that the best sound reduction and drone reduction in particular is achieved by sandwiching the body panels with material. Using Dynamat Extreme on the heat shields underneath I also found to help alot, as well as four or more coats of the liquid on the underneath. I have only the hatch area finished so far with Dynamat Extreme and the Crazy Cowboy kit and it has really mellowed the sound of the Flowmaster system on my C6. The above decibel reduction info is great and will make an outstanding addition to the archives.

TLK

Actually, "C" level measuring on the RS meter is best. The reason is that the "A" weighting rolls off very sharply, essentially excluding any bass sounds below 500 Hz. It is important to cover this ground because you can hear it and this includes the booming, rattling and droning.

"A" weighting was federally mandated for supposed environmental hazard testing, but noone has proved that it is particularly good for that other than that it was federally mandated so all meters have it and can make comparable measurements.

Ratchet Thunderbolt

I disagree regarding C versus A measurements. A weighting is a curve that very closely matches the human ear. C weighting is very close to linear, no weighting, but drops off below 100 hz. If you were to graph a measurement to look at you would want to do it A weighted so you could look at what you were listening to. If you wanted to listen to a recorded noise you would record it linear or C weighted so when you replay it to listen to it you would not double A weight it, once on the tape and once when you listen to it. A weight is what you hear and the numbers are representative of what you listen to. The human ear rolls off quite sharply after 500hz, it is down 10db at 250hz. The human ear hears nothing under 35hz, you feel it instead of hear it. I work in the NVH area with Superchargers, it's a great field. If you would like to discuss NVH and Corvettes I would enjoy it. Please pm me if you would like.

bent

Thanks to all for the ideas and compliments. I actually couldn't remember the difference between A and C weighting...so I just left it where I had it set (I was previously using a Rives test cd designed to work specifically with this meter to determine room response and subwoofer placement) Anyway, I held the meter (i know, i know...) with the mic facing the rear of the car and centered between the seats about 1" above the console lid. While my wife was driving, I had her set the cruise control at given speeds. I held the mic in the same position for each reading and averaged the reading between the high and low swings, ignoring the lowest readings when the car must have been coasting on a slight down hill and also the highest readings when it was accelerating. I wasn't extremely scientific about it, but I only wanted a general idea of wether or not the mat was worth the expense. For $150 and an afternoon's work, I would have rather seen better results but at least it wasn't all for nothing. I will eventually make more efforts to quieten the drone, but I hope to eventually stab in a 3.15 or 3.42 which should put my crusing rpm's out of drone range.



Ratchet thunderbolt....if you don't mind my asking, what is NVH?

gota07

I'm going to make a guess that NVH stands for noise/vibration harmonics.

Wayne O

Good post...I appreciate your efforts, your testing and the results you posted. I might have been inclined to eliminate the source of the drone rather than trying to muffle it but installing Dynamat is beneficial for a number of reasons.

You might try using a carpet cargo 'mat' as well. A carpet mat doesn't cover the wheel wells but they look good and I bet it would further enhance the results you're looking for.

danl72

Great info.

cmonkey713

So what would be the best route to go for max sound deading without adding a great amount of extra weight?

Ratchet Thunderbolt

It's a trade off. You can kill high frequencies with very little mass, something like fiberglass will work. Stick your hand between you ear and a tweeter speaker, it will kill the sound. High frequencies are very directional and have little energy. On the other hand low frequencies like engine firing frequencies are hard to kill. At 1500 rpm the engine firing frequency is 100hertz, that' slow. It take mass to really block them. A sub woofer in you house can be placed anywhere in the room because the bass goes everywhere and through everything. So, its a trade off, the more mass, weight, the better you can kill low frequency. Dynamat has mass plus it adheres to the surface it's on which also kill the vibration of the part it's on. So you are actually blocking the noise and stopping the part from vibrating at that frequency. The bad part is the weight. I probably didn't answer your question but you might be able to make a better decision about what you want to do.

davekp78

The OP showed about 3 db reduction after the dynamat installation. Trouble is, 3db, while noticeable, is not extremely dramatic. You need 10db to be half as loud. I don't think that is practical with add-on dampeners.