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glassing MDF enclosure

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I think what he trying to convey is they excite the air rather than move it from one place to another like a pump. The pump could/would create vacuum. It is still movement, I just think that's how he's envisioning it.

Thank you, that is exactly what i was trying to say.

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Waves in the ocean don't move water. Ocean waves move up and down.

I had to.

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Funny. They propagate not unlike sound waves.

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a wave is a movement of water.

a sound wave is a movement of air.

a wave in any forum is an excitement of molecules. it is a frequency of the transmission of energy, whether that be acoustic, radiation, photonic, or aquatic, they are all in the same boat. when you throw a rock into a pond you have displaced the water (matter consisting of moliquies) in that location and force it outwards. the water that resided where that rock is now moving through to reach the bottom is pushed outwards and mixed with its surrounding water. the same happens with sound waves, the air is mixed, turned, and pushed from one point to another. if you place a rubber duck in the ocean it does not stay in one spot, it is pushed and moves along the waves. to say that water or any matter does not move because its not being directly bull dozed in one direction is false. a subwoffer does not evacuate all the air with in its box upon every bass note, nor does it even evacuate all of the air in its port chamber on every note but this air does move and does change. if you fill a box with smoke and play bass you will see the smoke dissipate as it is being moved in and out of the box along with new air.

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no need to continue arguing, i still feel you all are incorrect, but my method of trying to convey what i mean apparently needs to progress. i will leave this link to this video, that sums up what i was trying to say, at the 14 and 17 minute marks. http://www.youtube.com/watch?v=mjGLN_iMm9M

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Where in the video does it describe something at all related to what you are trying to say? Not interested in a 20min video...

In my past job, I had to teach a 200 level Waves class so pretty sure I can translate the confusion if you point out where.

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I can not tell you who is right or wrong because I have not taken enough courses or have experience in this subject, but I will take M5's word for it.

 

Can you really argue with someone who has a degree and many years of work experience in this particular subject?

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I can not tell you who is right or wrong because I have not taken enough courses or have experience in this subject, but I will take M5's word for it.

Can you really argue with someone who has a degree and many years of work experience in this particular subject?

Like i said, my method of conveying what im trying to say is lacking. Ill be more specific. Sound waves do not move air, as in they do not force air to travel from where the speaker is to where the user is, the energy from the speaker travels through the medium, in this case air. They do move air molecules, as in they vibrate, or oscillate, the molecules, which is compression and rarefaction, so the air molecules move back and forth from where they are. Now, the greater the amplitude, or energy, the more molecules that are compressed.

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The confusion stems from your use of air as a medium at different scales. 

 

here's an example:

 

 

Sound waves do not move air, as in they do not force air to travel from where the speaker is to where the user is, the energy from the speaker travels through the medium, in this case air. They do move air molecules, as in they vibrate, or oscillate, the molecules, which is compression and rarefaction, so the air molecules move back and forth from where they are.

So in the first sentence you're saying that air, on a macro level (large scale), is not moving but simply transporting the energy of the speaker.  Thats fine but on a micro level (smaller scale) air molecules are moving, which you understand as the means for which sound travels. 

So getting back to you original post:
 

 

 

Correct me if im wrong, but on the whole vacuum thing, is that not completely irrelevant? A vacuum sucks in air, so it is able to move air through the pores of the mdf. With a subwoofer however, it does not move air at all, it is exciting the air molecules and basically there is a transfer of energy from one molecule to the next. So, since it is not actually moving air like a vacuum, then it is not anywhere near capable of producing the same results, making the argument of using resin in the whole enclosure invalid? Or is my extremely basic understanding of physics incorrect? 

 

Vacuum moves air molecules and speakers move air molecules so yes air can be forced through the pores in the mdf in either case. 

 

feast your eyes on this beautiful piece of educational art. 

krs6HS0.png

Edited by lithium

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You changed one other thing now as well. In your first post you literally state, "With a subwoofer however, it does not move air at all". Obviously this isn't the case.

At the same time, your premise is also wrong. Waves do move what they interact with. Vibrating is motion but they also propagate.

I do think we aren't following what you are trying to convey though. I would like to understand what it is though.

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Btw, for work I regularly measure lamb waves. I've done this with acoustically excited material as well. These sound waves even move metal. Obviously a bit harder to move than air.

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i believe the confusion lies not only in scale but in controlled mediums for examples. such as the slinky and rope bridge thing they used in teh video to describe how a wave moves are both ridged and tethered mediums for the wave to pass through. in much the same way that you see a concrete building ripple in an earth quake you see the examples in the video move up and down to transfer the waves energy from one side to another but you do not see the medium moving out of its horizontal spacial location.

the second aspect is what you feel when you hear a speaker. take a massive speaker with large excursion in a ported box. i do not think the argument would be made that the air coming from the port is not moving. you could say that its not if you attempt to factor in combined movement through out a full reference wave length but that would again be misinterpreting the effects. when the sub pushes or pulls and you are close to the speaker you can feel the air blow in or out from the port and from teh cone. when you get farther away you no longer feel the air motion so you assume the air is no longer moving. this goes right back to the issue of scale. however the air movement is what enables you to hear the sound wave so far away and just like stated above the air is not bound to anything. the weak and strong forces that govern the movement of atoms play a part but its not like the air itself is in any way tethered like the example mediums used in teh start of hte video.

the third aspect i think may be a confusion is the very definition of "movement". if we have air being blown by a leaf blower or air carrying a sound wave in both situations the air is moving but with a different amount of force and in a slightly different interaction. still both of these constitute as "air movement" however.

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You changed one other thing now as well. In your first post you literally state, "With a subwoofer however, it does not move air at all". Obviously this isn't the case.

At the same time, your premise is also wrong. Waves do move what they interact with. Vibrating is motion but they also propagate.

I do think we aren't following what you are trying to convey though. I would like to understand what it is though.

i tried to convey what i was meaning by it does not move air. i did not mean it doesnt move air at all, i meant that it does not force air to travel from the subwoofer in the back of the vehicle to the front of the vehicle; it is a tranfer of energy. so, the air molecules vibrate, they are pushed until they hit another molecule, after they hit that molecule, they are pushed with equal force in the opposite direction and the next molecule continues the process. is that not the third law of motion?

 

i believe the confusion lies not only in scale but in controlled mediums for examples. such as the slinky and rope bridge thing they used in teh video to describe how a wave moves are both ridged and tethered mediums for the wave to pass through. in much the same way that you see a concrete building ripple in an earth quake you see the examples in the video move up and down to transfer the waves energy from one side to another but you do not see the medium moving out of its horizontal spacial location.

the second aspect is what you feel when you hear a speaker. take a massive speaker with large excursion in a ported box. i do not think the argument would be made that the air coming from the port is not moving. you could say that its not if you attempt to factor in combined movement through out a full reference wave length but that would again be misinterpreting the effects. when the sub pushes or pulls and you are close to the speaker you can feel the air blow in or out from the port and from teh cone. when you get farther away you no longer feel the air motion so you assume the air is no longer moving. this goes right back to the issue of scale. however the air movement is what enables you to hear the sound wave so far away and just like stated above the air is not bound to anything. the weak and strong forces that govern the movement of atoms play a part but its not like the air itself is in any way tethered like the example mediums used in teh start of hte video.

the third aspect i think may be a confusion is the very definition of "movement". if we have air being blown by a leaf blower or air carrying a sound wave in both situations the air is moving but with a different amount of force and in a slightly different interaction. still both of these constitute as "air movement" however.

i think your confusion lies in the assumption that sound waves and wind are some how equivalent. if the subwoofer moved air, as in it pushed it and the air near the sub was moved to where the driver was, then it would be similar to the wind. so, if that was true, people would not be able to levitate objects, such as cups or paper, at their windows.

here is a linke, http://www.mediacollege.com/audio/01/sound-waves.html and in there you will see there it says, "Note that air molecules do not actually travel from the loudspeaker to the ear (that would be wind). Each individual molecule only moves a small distance as it vibrates, but it causes the adjacent molecules to vibrate in a rippling effect all the way to the ear."

 

if i am incorrect, that would mean that physics is completely incorrect and you should invest some time in rewriting physics books and be the next newton. now, i am not denying that my terminology and description of what i mean is lacking. also, i am not saying that the air within the vehicle will not be moving, or circulating, while the sub is transfering energy, just that the air is not circulating due to the sub.

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Each individual molecule only moves a small distance as it vibrates, but it causes the adjacent molecules to vibrate in a rippling effect all the way to the ear."

Just to make this easy, that "rippling effect" is wave propagation.

Wind isn't a good analogy as it is regularly DC motion. You can make it AC, but that is another discussion. Water is a perfect analogy though as water waves and electrical waves are mathematically identical.

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One other tidbit

 

 

 

i did not mean it doesnt move air at all, i meant that it does not force air to travel from the subwoofer in the back of the vehicle to the front of the vehicle; it is a tranfer of energy.

You stated it didn't move air before. Obviously I think this is more of a communication concern than right/wrong. As for the clarification you cited, if it doesn't move air then "hair tricks" won't work. If you see this differently though I would like to understand why.

Generically speaking there are two ways to "move" things. The first is with a forcing function, F=ma (2nd law btw) and the other is to excite a resonant response. I've measured the resonance of every part of the human body and generically speaking hair resonance doesn't fall into the realm of what a subwoofer plays. And yes, even with resonance you need some forcing function, it is just it takes an awful lot less energy to do the work you are trying to accomplish (or more likely avoid).

As for NCC's response, sure boundary conditions alter how things are perceived and actually what happens, but they don't change the laws of Physics or how waves operate.

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I think that at higher frequencies it would be about the transfer of energy from one molecule to another at that scale (as far as feeling/knowing the air is moving), but not with sub bass frequencies. When someone is demoing a big system and it's doing hair tricks and the like what's moving if it's not the air? It's not continuous movement as the argument about a vacuum has been stated but when the pressure inside the enclosure is lower than outside the enclosure that lower pressure is by definition a vacuum and the air at the higher atmospheric pressure outside the enclosure is going to move into the enclosure even if it's only for the split second. The opposite will happen when the cone of the driver moves on the rearward stroke and pressurizes the air inside the enclosure.

I just have a hard time understanding the purpose behind the debate at this point. Sure, the molecules get excited and transfer the energy from one to the other. That excitement means they're moving into each other. They are air molecules right? So I'm still not understanding how the air isn't moving. Albeit in very small amounts (compared to wind or a vacuum), bidirectionally, and at high speeds. If the air didn't move how would the smoke rings in

be possible? The very science behind that phenomena is that the air is directed through the hole causing a vortex. It's a drum, the sound of which we hear is no different than the sound the driver reproduces. If the air didn't move it couldn't create the vortex to make the smoke ring.

Okay, that's it. I'm done with this thread.

Vacuum - as defined by the dictionary, "an enclosed space from which matter, especially air, has been partially removed

so that the matter or gas remaining in the space exerts less pressure than the atmosphere (opposed to plenum )."

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One other tidbit

i did not mean it doesnt move air at all, i meant that it does not force air to travel from the subwoofer in the back of the vehicle to the front of the vehicle; it is a tranfer of energy.

You stated it didn't move air before. Obviously I think this is more of a communication concern than right/wrong. As for the clarification you cited, if it doesn't move air then "hair tricks" won't work. If you see this differently though I would like to understand why.

Generically speaking there are two ways to "move" things. The first is with a forcing function, F=ma (2nd law btw) and the other is to excite a resonant response. I've measured the resonance of every part of the human body and generically speaking hair resonance doesn't fall into the realm of what a subwoofer plays. And yes, even with resonance you need some forcing function, it is just it takes an awful lot less energy to do the work you are trying to accomplish (or more likely avoid).

As for NCC's response, sure boundary conditions alter how things are perceived and actually what happens, but they don't change the laws of Physics or how waves operate.

Hairtricks would be the same as someone levitating an object, such as a cup or a piece of paper,in their window. The sound wave is energy, the energy can pass from one medium to another. So, some of the energy that is in the air is tranfered to the air, causing it to vibrate like the air molecules. Same with an echo, when the echo reaches a barrier, part of the energy is transfered into the barrier and some is reflected back to the person.

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What type of energy is that?

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What type of energy is that?

Kinetic?

 

Now we are getting somewhere.

Ek = 1/2 mv2

 

Notice the v in the equation, it's velocity.  Pretty sure if you look up the definition of velocity that you will find it is motion which means it is moving.

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What type of energy is that?

Kinetic?

Now we are getting somewhere.

Ek = 1/2 mv2

Notice the v in the equation, it's velocity. Pretty sure if you look up the definition of velocity that you will find it is motion which means it is moving.

You are still stuck on what i am meaning by movement. Yes, subwoofer moves air, as in it vibrates the air molecules; they move back and forth, they oscillate from a given point, but they do not force the air to travel from one point to another.

Im pretty sure an anemometer wont measure the winds from a speaker system since they do not create wind. This video shows what i am stating when it comes to waves from a speaker, albeit, not for very long, but it shows it.

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Why are you calling DC motion movement and AC motion not?  Why do you assume that both can't happen at the same time?

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Why are you calling DC motion movement and AC motion not? Why do you assume that both can't happen at the same time?

Do you not comprehend what i am trying to convey? If you do, then please, enlighten me on what you would deem as the correct way.

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I absolutely have no idea why you are confused.  Nor do I understand at all what you are trying to say.  Stating that a speaker doesn't move air is completely confusing to me.  I'd like to understand so I can clarify for you.  Subwoofers absolutely move air.  ANY device that is moved in any medium will also cause that medium to move.  Newton's 3rd law makes that very clear.  For some reason I see you stating his law falls down, but don't see why you think so.

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I absolutely have no idea why you are confused. Nor do I understand at all what you are trying to say. Stating that a speaker doesn't move air is completely confusing to me. I'd like to understand so I can clarify for you. Subwoofers absolutely move air. ANY device that is moved in any medium will also cause that medium to move. Newton's 3rd law makes that very clear. For some reason I see you stating his law falls down, but don't see why you think so.

Everything i have posted link wise conveys what i am trying to say, which is what physics states. The air molecules move but the air molecules do not travel, as in, from the sub to the persons ear, the energy that travels through the air does. So, the energy travels until it vibrates air molecules that are near and in our ears, causing the ear drum to vibrate with the air molecules, which goes into the cochlea, which has tiny hair like cells that convert the vibrations into electrical impulses, then they are sent to the brain. That is the process, that is how it works, if you have an issue with understanding it, then im not sure what to tell you.

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