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Shattering Subwoofer/Rough Road Driving Episode # 58 Origianl Air Date: August 16, 2006
The Myth: You can make a car speaker so powerful that it can blow up the car with the amount of decibels it puts out.
The Experts:
Wayne Harris (president – dB Drag Racing) helps Adam and Jamie test their rig.
Mike Bartells (Extreme Audio) explains to Tory just how loud a car speaker can be.
Memorable/Quotable Moments:
Jamie: Well, it better work – my shirt’s all dirty!
Rob Lee: Dr. Jamie Frankenstein is as happy as can be!
Adam: Inexplicably, Adam’s wearing chain mail!
The Science Behind the Myth:
Rob Lee: Speakers produce sound by switching an electromagnet on and off and vibrating the speaker cone. This moves air back and forth, creating waves of pressure. This pressure is measured in decibels.
The Action/Results:
Jamie and Adam decided that, for this myth, there would be no small scale testing - they would just get right into it. So, they got a car and started tearing everything out of it. They wanted to be able to fit the biggest speaker possible inside of this car. It turns out that the speaker is fifty-one inches in diameter. The speaker is diesel-powered; in other words, the guys made a crankshaft to attach to the transmission of the car. A push rod moves the speaker cone up and down to create the vibrations.
While the guys were slaving away on the speaker, Tory was down in Daytona Beach to do some research. There is a contest called the Spring Break Nationals, in which people compete to see who has the loudest car stereo. Tory visited many different vehicles and chatted with their owners. He didn’t see any cars blow up, but he did notice that many of the cars were reinforced to keep the sound in the car.
Finally, the big day arrived for the guys. Wayne Harris from dB Drag Racing came to M5 to help the guys test the car. Adam did a quick test, to see if the rig worked, and the speaker oscillated just fine. It was finally time! The guys let it rip! After a few seconds, the “mythwoofer” ripped itself to bits. Wayne Harris did manage to get a reading, and the “mythwoofer” put out 161.3 decibels at 16 Hertz. The car did not blow up, but the sound waves did rip the sunroof off its rails. This myth is BUSTED.
Rough Road Driving
The Myth: Driving fast on a washboard road will give you a smoother ride than driving slowly.
The Experts: Grant, Tory, and Kari
Memorable/Quotable Moments:
Grant: (holding the car keys) Ok, so I am giving you these, and I expect you to act responsibly, be home by eleven, and have it gassed up.
Tory: All right, Mom!
The Action/Results:
Grant, Tory and Kari decided to tackle the myth of driving on rough roads by putting together three different ways to measure the roughness of the ride. Grant put an accelerometer that measured all three axes of movement in the car. Tory welded a rod to the suspension, and made a gauge to measure the displacement of that rod on the hood of the car. Kari made a pyramid of wine glasses, and filled them all with water. The test run, through a parking lot with many speed bumps, showed that all three measurement methods recorded the bumpiness of the ride quite nicely.
For the real test, the gang left town and went to the Prairie City State Vehicle Recreation Center. There, they found a dirt access road to drive on. The first test, with Grant driving at 20 miles per hour, showed a maximum deflection on the suspension of 3 inches and a loss of 3.5 liters of water. The second run, at 45 miles per hour, resulted in a maximum deflection of 6 inches and a loss of 4.5 liters of water. Then Tory was given the keys! He kicked it up to 70 miles per hour! The deflection reading was off the scale. But, when the team went back to the shop to see the accelerometer readings, they found something interesting. The accelerometer showed fewer peaks at 70 miles per hour than 20 miles per hour over the part of the course that was described as the most uniform. This was confusing, so the team decided that they needed more data.
They built their own washboard road this time, using angle iron welded to a steel bar. Then they measured everything again, using both Kari’s glasses and Grant’s accelerometer. The results from these two instruments, plus the high speed camera, showed that the tires were skipping from peak to peak on the simulated washboard, just as the myth suggested. Less water was spilled and fewer peaks were measured at 70 miles per hour than at 5 miles per hour. Myth CONFIRMED!
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