Physics question of the Day?

[joshpoints 10+ year member]

Why is it that the back side of the box doesn't have much if any vibration at all, yet every other component in the car is rattling? As contradictory as the thought seems the back of the box seems like it is the easiest on your amps.

Can anyone explain this?

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[RandyJ 10+ year member]

In a ported box?? Only thing I can think of is the difference in refraction and reflection of waves inside the cabin compared to those insider the box. Ya knwo what I mean???

 

[joshpoints 10+ year member]

In a ported box?? Only thing I can think of is the difference in refraction and reflection of waves inside the cabin compared to those insider the box. Ya knwo what I mean???

No a sealed box actually.

 

[RandyJ 10+ year member]

Well, the waves properties inside and the waves properties outside would still be different.

 

[joshpoints 10+ year member]

Well, the waves properties inside and the waves properties outside would still be different.

I don't get what you're saying, or what you're getting at. Please explain further.

I would think that if everything in the car is vibrating and it is far from the sub that the back side of the box should be violent yet it isn't.

There's some kind of explanation. I'm just not sure what it is.

 

[RandyJ 10+ year member]

Air pressure inside the box is different then outside the box. ALSO, the box is solid as hell (should be) and the things in the car are not as solid as the box, which is why they vibrate so much, and the box doesnt...

 

[joshpoints 10+ year member]

Air pressure inside the box is different then outside the box. ALSO, the box is solid as hell (should be) and the things in the car are not as solid as the box, which is why they vibrate so much, and the box doesnt...

Sorry still doesn't make sense to me. I just turned my shelf system up in my room and went outside my room. The door is solid 2" thick and it was vibrating as much as the back side of my car audio box which uses 3/4" wood and has 2 10's inside of it.

Can you explain the air pressure part a little further. Maybe this is the main factor.

 

[RandyJ 10+ year member]

LOL, have you taken Physics yet? It is kind of hard for me to break things down this much. The air pressure inside a sealed enclosure will be different then that of the air inside the cabin. Just like when you roll the windows down the air pressure inside the cabin changes and the waves properties are different.

As for the comparison with the two inch door, are you asking why it did rattle or why it did not????

 

[smokeoff 10+ year member]

inside the box the air pressure changes as the sub moves, when the sub goes in the air pressure goes up, when the sub goes out the air pressure goes down. It would be just the oppsite for the cabin of your car. What this means is things in your car are always expanding and contracting/ inside the box as well as out. now with that stated it simply comes down to this, the more rigid something is the less it will flex a.k.a rattle. The wood your box is made out of should very rigid, most of the sheet metal on your car is not as rigid as that. and most of the move movment comes from thing that are not sealed solid, like your trunk lid that will move up and down as the air pressure changes. Where your box should be solid enough that the only thing moving is the sub its self. which brings us to your door, deffently not a 100% solid seal, when the speakers in you room move the air the door being a week seal is a good place for the air to try and equalize its self. speaker moves out air pressure goes up door gets pushed on, speaker goes in air pressure goes down door gets pulled on, done with a rapidly moving speaker it causes the door to move in and out, or "rattle". Leave your open just a crack on a windy day and open a window, bet you can get it to close.

hope this helped and also hope all info is correct. basicly comes down to air movement vs. rigidity.

 

[smokeoff 10+ year member]

one more thing, if you put a sizemagraph(sp?) on your box you would see that it moves a fair amount it self just nothing major. because the cone on your subwoofer weighs less that the box it weight movement is not enough to move the box.

if your box is secured to the car it will shake as much as what it is secured to causeing to look like it is not shaking that much, once again it is normally the week metal and non-secured stuff that shakes.