Scott is the owner of Dynamat, the noise- and vibration-proofing product. He’s also an accomplished car designer and builder. We have an interesting chat about noise dampening and then we look at his vintage-styled Dynaliner coupe!
Podcast: Play in new window | Download
Show Credits
Producer: Jeff Fox
Audio Engineer: Chris Laxamana
httpv://youtu.be/fZf5jzfPE-8
[nggallery id=300]
The Tacoma Narrows Bridge was doing just what happens with a swing. You push it and it rocks back and forth, a certain number of times, per minute. You push harder, but in time with the natural number of swings per minute (the frequency), then the kid goes higher and faster, but the same number of swings per minute. The height is the amplitude. Resonance is the same frequency, but jumping up in amplitude. It’s how you can jump octaves in music, hitting a G note, but jumping up in octaves. The bridge jumped up in octaves and began to flex with the increased wave heights. Avoiding it, (simplistically), requires adding in some breaks and stiff spots that keep the structure from behaving like a guitar string. It takes a tiny pressure from one pinky to make a guitar string just fuzz out.
BTW, Matt was right,, that the vibration had to travel all the way down the bridge, then come back, (the second push) It was just purely by accident that the bridge had a natural frequency for swinging, plus the exact length, to allow the return vibration to double the wave heights. Possibly a one in a million chance. In most cases, the return vibration would actually work against resonance and dampen the wave, just as pushing a swing at the wrong time would cause the swing to practically stop.
And, just ’cause we had one, Adam forgot about the Matador’s 4-door cousin, the Ambassador:
http://en.wikipedia.org/wiki/AMC_Ambassador
We had the 1971 station wagon when I was a kid, with the gigantic 390 ci, 325 hp engine. And everybody that drove it said something like, “This is like driving a cardboard box on wheels!” Apparently, suspension and steering were not factors in the design.
Thanks, Scott and the rest!
Thanks Chris!
Bobby Allison and Mark Donohue won a few races in those Matador piles of junk. The “6.6L V8” was 401 ci. I was thinking they might have used Chrysler 400 B block engines, but those were 399 ci. Only knew one owner of that car my whole life, family of 4 down the street when I was a kid. Guess it was a good thing that the children were small girls at the time.
https://en.wikipedia.org/wiki/AMC_Matador#NASCAR_racing
Great show as usual guys!