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Johann van Biljon
'60 Aetna Blue 356B T5 Coupe
'94 Midnight Blue 968 Coupe - No Sunroof, RS Barn Stage 1 Chip, Airbox mod, RS Barn Cat-back, NGK irridium spark plugs - Sold
'92 Signal Red 964 Carrera 4 - Sold
'84 Burgundy 911 Carrera 3.2 Cabriolet - Sold
'90 Silver 944 Turbo S with M030 and limited slip diff - Sold
'76 Silver 911 Carrera 3.0 Targa - Sold
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[quote name='rxter' timestamp='1330750466' post='122674']
I got a pack of dynamat extreme in. I had expected a closed cell foam product, but instead the stuff looks like a huge sheet of butyl tape. And it weighs a ton. Anyone know how this stuff works? Seems like a pretty unsophisticated solution. I'm pretty sure that I don't want to add 40 pounds back into the car. Has anyone tried dynaliner instead of dynamat? They say that dynaliner goes on top of dynamat.
[/quote]
What you are looking at is not an unsophisticated solution. You expected closed cell foam, because foam is commonly used to absorb sound waves. But, the small holes in foam only work on higher frequencies. In order to absorb frequencies below 100 Hz, our anechoic chamber had foam pyramids that stuck out from the walls and ceiling about 30 inches.
But if you know what components are turning the energy into noise (i.e. constitute the speakers), then it is better to dampen them. I'm not familiar with dynamat, when I worked in this field we used a lot of EAR products. As I see Dynamat in these pictures, it looks to me like an unconstrained layer damping application. It appears to be foil backed, but would need to have a much thicker metal layer to be an effective constrained layer damping application. As I recall, butyl is a decent viscoelastic material with reasonable damping properties in the temp range of interest. We often added products that came with the layer of damping material, with foam attached to it. If you put the dynaliner on top of the dynamat you'd have a similar product. It serves to dampen, as well as to absorb.
Finally, since I was cleaning this part yesterday, has anyone noticed that the sheetmetal clutch access cover is made from two layers of steel. I'd bet that there is some sort of viscolastic material in between the two sheetmetal plates. Looks like a typical constrained layer damping application to me.
'92 Midnight Blue 968 Coupe
'94 ProbeGT, Eaton SC@9psi, Quaife, TecGT ECU, 300+HP, body sold, parting out
'98 3000GT VR-4, 400+HP AWD beast, didn't fit w/race helmet, Sold
'93 Bone Stock MX-6 Sold (in '05) sadly to the crusher in 2010
'61 Triumph TR-3, White with red leather interior; My First Car
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Best way to deal with the "drone"? Put on some music you love and TURN IT UP!!!! The Grateful Dead station on my XM radio does the job quite nicely! Of course I suspect the dynamat lining in my doors helps. <img src="/forum/images/smilies/968/rock.gif" class="smilie" alt="" />
Bill
'93 Horizon Blue Metallic Cab
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Flash, don't know how to respond to your inputs above. I am pleased that there has been some experimentation and success among members on this site improving the noise quality in our cars. I plan to take advantage of this knowledge at some point. None of my comments were aimed at changing the methods that I've seen on this site. I was responding to the unsophisticated comment.
Technically I can't completely agree with all your comments, some I do. For instance its not really true that it "lowers the amount of energy transmitted to the sheet metal". The sheet metal and the applied material act together. They are still subjected to the same amount of energy. But viscoelastic materials have the unique quality that they can absorb a lot of energy (usually as the long chain molecules microscopically slide back and forth over one another). Since the viscoelastic mat'l absorbs a lot of energy the total amount of vibration amplitude of the sandwich assembly is greatly reduced. An applied "elastic" material will not be very effective. And the way that lead worked was moreso for its mass to change natural frequencies of the sheetmetal. It was not really applied for it's ability to absorb energy, although it is much better than steel, but still not in the same class as polymers that have good viscoelastic properties.
If it seemed like it, I was not suggesting adding the foam to the back of the dynamat. Doing that inside the door would likely do very to absorb the noise that is already being transmitted to the interior of the car via many other sources. The soft materials in the car help some with that.
And finally, I was not referring to the cast aluminum access cover that we use to change the clutch. Although this cover also has what looks to me to be an applied nonconstrained layer damping material on the outside, and uses foam on the inside for apparent absorbtion of noise from inside the bell housing.
I was referring to the sheet metal cover that fits in front of the bell housing. It is part #29 on the parts list and is listed as "protective plate". Check it out. I don't often see applications of constrained layer damping, but this looks to be an example.
'92 Midnight Blue 968 Coupe
'94 ProbeGT, Eaton SC@9psi, Quaife, TecGT ECU, 300+HP, body sold, parting out
'98 3000GT VR-4, 400+HP AWD beast, didn't fit w/race helmet, Sold
'93 Bone Stock MX-6 Sold (in '05) sadly to the crusher in 2010
'61 Triumph TR-3, White with red leather interior; My First Car
(This post was last modified: 03-04-2012, 12:21 AM by
MB968.)
