my experience with dynamat and reducing drone---with actual dB testing
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!!! :flag: :flag: |
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? |
Nice write-up! Thanks for posting. :thumbs:
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. |
Originally Posted by mike100
(Post 1568682867)
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? :flag:
Originally Posted by Vasta
(Post 1568682886)
Nice write-up! Thanks for posting. :thumbs:
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. :thumbs: :flag: |
I don't want this to get lost on the second page just yet.....shameless ttt
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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:cheers:
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Originally Posted by peter pan
(Post 1568685145)
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:cheers:
:cheers: |
Originally Posted by bent
(Post 1568682833)
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 until 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 their 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!!! :flag: :flag: 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.:thumbs::thumbs: |
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. |
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. :thumbs:
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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.:cheers:
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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.
Originally Posted by Ratchet Thunderbolt
(Post 1568686143)
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.:thumbs::thumbs: |
Originally Posted by TLK
(Post 1568690337)
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. |
Thanks to all for the ideas and compliments. :cheers: 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.
:flag: Ratchet thunderbolt....if you don't mind my asking, what is NVH? |
I'm going to make a guess that NVH stands for noise/vibration harmonics.
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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. |
Great info.
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So what would be the best route to go for max sound deading without adding a great amount of extra weight? :bigears
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Noise reduction
Originally Posted by cmonkey713
(Post 1568706569)
So what would be the best route to go for max sound deading without adding a great amount of extra weight? :bigears
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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.
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