Episode 58: Shattering Subwoofer

Air Date: August 16, 2006

One can design an automobile sound system such that the bass can quickly shatter all the windows of the automobile.

busted

While the obnoxiously large, diesel engine-powered subwoofer that Jamie and Adam built pumped out a whopping 161 dBSPL at 16 Hz (a level comparable to those found in cars specially designed for loudness competitions), it caused the sunroof of the car to jar loose, allowing for the pressure of the sound waves to escape. Because of this leakage, not to mention the fact that the forces behind the oscillation caused the woofer to break apart, the speaker system could not possibly create the amount of intensity needed to cause all the windows to explode as the myth stated. A best-case scenario would involve only one window failing, thus creating a path for the pressure to escape.

You will get a smoother ride on a rough outback road by driving faster.

confirmed

As far as driving on non-"washboard" roads there was no solid conclusion due to a conflict of data. However, when they tested a "washboard" road, like one the myth originally states, the build team were able to confirm the theory that driving at a higher speed will indeed cause the wheels of a car to travel over just the ridges and not into the troughs, allowing for a relatively smoother ride.

33 Comments

  1. “You will get a smoother ride on a rough outback road by driving faster.”

    Same holds true when sailing over speedbumps. Ask any cab driver in Vegas that goes bombing through a valet/cab turnout at the casinos, and they’ll tell you the same thing.

  2. Ray says:

    Hahaha, I remember my brother decided to ‘glide’ over a speed ramp, which is like an elongated speed hump. Very smooth at slow speeds, namely 25 kph. He hit it at 120kph, and lost the sump, and we nearly broke our necks on the ceiling. Yes, we had our belts on.

    Still, on the dirt roads, I have also found this to be generally true, the faster I go, the smoother the ride, or so it seems.

  3. Don says:

    I agree, here in Sri Lanka the roads are rough and at about 50km/h your ride gets better than at 25km/h

  4. Co.D says:

    Speakers, windows? I’m not exactly sure what was done wrong but with enough pressure, a window WILL break, shatter twice in my case. Perhaps because of the thinner window on the rear hatch versus the position of the quad 15″ DVC seperated box. Bass works by vibrations. So, though the air pressure wouldn’t change inside the car, the vibrations on the glass CAN cause it to shatter and make you shell out $130 for a new rear shield.

    • Joely Boy says:

      you are wrong about the vibrations shattering the glass. Glass will only shatter if it is vibrating at its natural resonant frequency and at over 100 dB. because we’re talking about extremely low frequencies, if the glass didn’t break, then 16 hz wasn’t the resonant frequency of that glass, therefore it can’t break.

  5. Alain says:

    Geeeeze Come on Mythbuster Guys! Why Do you think That The Hardcore Winners of the SPL Competition have Re-inforce Body, Thicker Windows And Even With Cement Base (Yes, Its True), To get the most pressure? The idea of his speaker was a big joke. Take a Small Hatchback civic and a couple of square kicker and you’ll have yourself a good reciepe for destruction hahaha. I don’t understand why they made a bid deal out of this, because I’ve seen this happend so many time busted window, loose fender lol).

  6. Robert says:

    After seeing what joke you pulled with making your own sub i think you should really show the people what a powerful sound system can do. I mean it is kind of a dis respect to guys that have thousands of dollars in the stereo it would only serve it justice i mean i love the show but really get with someone who knows what they are doing and you will see destruction. PLEASE REVISIT THIS MYTH IT IS NOT BUSTED!!!!!

  7. Mike says:

    Alain and Robert,

    Please read the myth before commenting. Apparently you have some desire to appear cool and defend the car audio guys of the world, but the myth states “One can design an automobile sound system such that the bass can QUICKLY SHATTER ALL THE WINDOWS OF THE AUTOMOBILE.”

    You are citing instances of one window breaking, not all of them quickly shattering. That would take one bass note at an SPL that might not be attainable in a car audio system. I’ve seen many competition vehicles and have never seen one that could quickly shatter every window in the vehicle. Maybe there is one, but it is highly improbable.

  8. Tyler says:

    I agree with Mike. While damage to your car is possible, a good friend of mine actually creased his trunk lid with his system, the scene in the movie that they were trying to replicate would not be possible with any sound system. The fact is that once any gap is created the car will lose pressure and no more damage will occur. The first thing to go will be a seal or maybe a weak window, but not all at once.

  9. Andrew says:

    I think that the mythbusters were looking at the wrong aspect of the sound waves, I did only catch the last half of the episode but as far as i can tell they were only concidering the pressure. I think that it would have more to do with a med sound wave, not through the air but through the surfaces conecting the speaker to the glass. It would be something kind of like the experiment with the earthquake machine. A small to medium, constant, wave will eventually move the glass enough past its elastic potential for it to break. Maybe not all at once because it would depend on how far from the source the glass is.
    Anyways thats my two cents.
    Andrew

  10. Jonny says:

    Please Redo the sub myth. my friend blew out the rear windo on his integra first day having it with 2 MTX 12″ subs and a Rockford amp….it can happen that speaker your built was crap. put 2 jackhammer in that car and it will blow out all the glass.

  11. nick says:

    ok guys your subwoofer hit 161 decibel’s right? well digital designs makes a subwoofer that hit a record breaking 181.5 decibels from just one sub! that will shatter a window! it was constructed in a volvo station wagon, and the trunk was concrete filled! this is true! so take 2 of these subs and “burp” them at about 20,000 watts a piece and i garuntee you that something will break! please redo this myth!

  12. Rick says:

    If there is in fact a myth that a stereo can destroy all the windows in a car at all. I think the Mythbusters are taking liberties with some myths lately. They seem to be fabricating some of these themselves. The stereo myth is bogus anyway, because its not air pressure that anyone is concerned with. Its sound waves that break a window in a car, not a diesel powered air baffle with a mixing bowl in the center. An actual car stereo producing enough vibration will easily break the windows in a car. Maybe not all at once, but who’s myth is that anyway?

  13. scott says:

    this is one i would also like 2 see redone.i think it would of done ALOT better if there was a cylinder wall like in an engine 4 surport.(to keep it moving strait up and down)i did like the diffrent aproch just wanna c what would happen going through the gears.theres always more to the storie.

  14. lavender says:

    The conflict of data seen between the shocks and accelerometer on the rough-road myth surely just proves the shocks are doing their job. They are moving, yes – that’s a part of what gives you a smooth ride in the end. The glasses are the only real contradiction, but I guess at higher speeds the inertia is greater getting up to/down from speed.

  15. chris says:

    you guys chouls use a compathion styal suba and amps ans see what you get then you will have a diffrent resalt other that one you made your self

  16. Chris says:

    I think a redo on the “One can design an automobile sound system such that the bass can quickly shatter all the windows of the automobile.” should be done. Jamie and Adam should use multiple competition subs because I believe it can be done.

  17. Nic says:

    While a redo might yield different results, I doubt that it would “un-bust” the myth. Those claiming that the pressure level is not to blame and it’s the sound waves (ie: the frequency) should recheck their info. To shatter a glass object would require several seconds of high frequency sound perfectly matched to its natural resonant frequency. Couple the two facts that a cheap $6 glass cup has a resonant frequency of about 800hz (most subs don’t play above 200hz) and the fact that each window in the car would likely have different resonant frequencies do to being differing thicknesses and sizes, and you’d see that it’s not likely to work, even if it were the “sound waves” that were breaking the window.

  18. Faat Jointz says:

    I think the speaker myth should be revisited. They should go to a bass competition and get an expert to design an actual sound system. What was that thing they had in the middle of the car anyway? Who listens to one of those? How can you “bust” a myth that states, “One can design an automobile sound system such that the bass can quickly shatter all the windows of the automobile” when you don’t even try to use a sound system? They could possibly place at least one of the most powerful subs behind each window to vibrate the glass and see what happens.

  19. phill says:

    Can you retry this myth with the MTX Jackhammer subwoofer…it is so powerfull that can will broke the windows of the car…

  20. mark says:

    every day I drive over a washboard road here in nebraska, I remember show about driving on all that angle iron, you couldn’t find a washboard road??? I’ve had a few scares of flipping over sideways, or loseing control in my pick-up, when I drove to fast. Granted faster maybe smoother, as long as your still upwright. Washboard roads are never even like your angle iron road.

  21. Tim says:

    I remember this episode 58 about bass shattering all the windows in a car. The Mythbusters are correct. Low frequency bass cannot shatter all of the windows in a car, not even Ultra Low can. Sure, you can pop a seal, loosen up a fender, shake down a poorly secured rear view mirror, cause a minor nose bleed in some people, pop open a sun roof, cause a girls hair to fly around, and cause hearing damage, but it can’t shatter all of the windows. Why? Wrong resonance. Doesn’t anybody remember the goblet shattering experiment in high school?… You need a much higher tone (~800Hz+) at around 140db with a constant sweeping pitch to shatter glass. And the best part is you only need a 150 watt system to do it with a commercial loudspeaker horn sitting close to the glass. The thicker the glass, the more power you need to do it.

    Car glass is pretty thick and reinforced to take the vibrations. It’s usually the window seals that fail first in a car, not the glass itself. Bad seals + ultra low bass = broken glass, but Only tuned resonant upper freqs can shatter glass directly. Using a sine wave generator would be the best way to do it.

    See, those bass stereo heads have been going about it all the wrong way. If they want to shatter neighborhood glass ALL the time, then they should be looking for a 2500 watt midrange horn… ha ha ha.

    • art says:

      wrong. car glass is different. what they did was perfect they need a larger cone and durability. it would have eventually destroyed that car but windows will not go out at once. which is not part of the myth. you need insane amount of pressure INSANE 200+ db ( like a stick of dynamite). no subwoofer even the jackhammers carbon cone can hold up to that pressure, not one brand can creates a cone that can hold up to that pressure.
      you say to buy a woofer to perform a real test with a real sound system, hire someone to design and fab a box for it? will you provide the money for this? they can try the same method but like someone else had said here, use a cylinder to have direct up an down strokes and build the cone stronger and try again. surely results will be the same but the windows will eventually succumb to the vibration warp of the steel.

  22. Killshot says:

    lavender was correct to point out that the suspension test results were misinterpreted. To demonstrate the suspension gauge, Tory pushed down on the car to show how the needle reflected the movement of the car in relation to the body. The suspension is designed to force the wheels down to meet the road when the body of the car is coasting on a level plain. Large variances in the needle only mean that the suspension is working, it doesn’t explain why it’s working. As for the water test, it was shown that Grant had lost control of the vehicle at the faster speed and had water all over his pants. That’d clear be from side-to-side motion, not the up-and-down bumpy motion described in the myth.

    • Math teacher says:

      Maybe a little late. I believe the results vary because when checking bumpyness we look at acceration(up and down). This is the change in which the needle moves, not how far it moves. If the needles speed changes quickly (jerkyness). So using the accelerometer is the best way to check bumpyness.

  23. Tyler says:

    http://www.youtube.com/watch?v=lxScxOaAuzY&feature=related this is not even the loudest competitor and he broke his shield in seconds!!

  24. Mircea says:

    Although the size was impressive,the manufacturing of the woofer was not.The only thing wrong with it,and the reason the myth was busted,is the irregular play of the membrane.On a normal speaker,the up-and-down of the membrane is controlled and very precise,because it’s a linear movementd.Obviously,it wasn’t the case or the worry for these guys.The membrane broke ONLY because of this movement.Try redoing it and controlling the movement,so that the mebrane goes up and down all around the diameter at the same time.However,the idea for the movement by shaft was impressive.

  25. Ytsoc says:

    I agree , the subwoofer was poorely designed; the surround was way too stretched, the transmision was a joke. They should have given more attention to how a real woofer works.
    The ideea to connect it to the engine was good, but poorely put in practice

  26. Roger Sagert says:

    Come on mythbusters you got the speaker construction wrong, your speaker diaphragm wobbled because you did not guide it, look at the video, the speaker is not vibrating in and out it is wobbling as it moves in and out, you allowed the connecting rod push to deflect the speaker diaphragm. Hint! Place guides on the center of back side of speaker and on the outer perimeter.
    hit it.

  27. Kurt says:

    Adam & Jamie,
    There are a few problems that I see with the subwoofer myth. First I admire your attempt to build a competition type sound system but you had errors in a few areas. Your subwoofer that you built was impressive as far as being a unique design, however there are a few problems that you need to address before considering the myth busted. Your subwoofer reportedly hit 161dB at 16hz. The decibel level while respectable in some classes of competition is hardly the sound pressure created by competitors at the higest competitive levels. There are several instances of competition vehicles hitting over 180 dB, which with the way that sound pressure is measured (essentially doubles with every increase of 3 dB) means that they are generating over 64 times the pressure you were. Also when designing a competition sound system the goal is to tune it to the resonant frequency of the vehicle (not the glass as several people have talked about on here). Your subwoofer was reportedly playing at 16hz, this is VERY low, most subwoofers are designed to play tones over 20hz and the resonant frequency of most vehicles falls between 40hz-50hz. Also conducting a test like this in a vehicle with a sunroof (something you will not see from serious competitors in bass competitions) was also counter productive. If you would like to revisit this myth in the future I would gladly offer the services of my store (King Konc Custom Audio and Accessories in Albuquerque, NM) to help you design and build a professional quality sound system worthy of truly testing this myth. While I am not 100% convinced that it will blow all of the windows out simultaneously due to the fact that they will likely have different different structural weaknesses (and once one window is gone that will let enough of the pressure out to likely save the others) I think that it still maybe possible if you “burp” a system that is capable of creating a high enough sound pressure level immediately playing a test tone derived from the resonant frequency of the vehicle. I think it would be fun if you guys are interested let me know!!

  28. Alexander says:

    The woofer used in the subwoofer myth had absolutely no linearity to it, a true woofer has absolutely no travel to the left or right. Thats the purpose of a spider. I have seen vehicles obliterate the windshield and doors within 3 minutes. I’ve seen vehicles make the windshield hemorrhage glass within seconds.
    These systems are capable of the upper band in the 60s, most vehicles in car audio competitions these days average in the low to high 150s, there are systems out there that can do well over 170db.
    Simply get a high pressure system designed and try squeezing a 160 without adding deadener.. you’ll lose stuff.

  29. David says:

    Clearly the windows of the car in the movie were not tempered as they shatter like normal untreated glass.

Leave a Reply

(required)