It's not a thread about wall vibration. It's about the stuff that comes out of the speaker cone, courtesy of internal cavity effects.
The thing that's difficult about conceptualizing areas of velocity vs pressure is that air molecules are essentially elastic in their collisions. So they should bounce off the wall without slowing down except at collision.
But as some here have mentioned it seems that in a given cabinet there are areas of average higher velocity, and areas of average higher pressure.
This must be because the waves are on average more in rarefaction than they are in compression in certain positions. This will also change with frequency. So its a very complicated situation.
As far as lining the walls, I can't say scientifically why this is wrong, but I would try to use uneven surfaces like an anechoic chamber. The reason is that afaik sound waves can reflect off an impedance change. This is similar to seeing light reflect off water.
Further there is issues when the material doesn't evenly absorb certain frequencies. Its also possible that something in center helps funnel the sound away from drivers better. Look at how tweeter chambers are designed.
But as some here have mentioned it seems that in a given cabinet there are areas of average higher velocity, and areas of average higher pressure.
This must be because the waves are on average more in rarefaction than they are in compression in certain positions. This will also change with frequency. So its a very complicated situation.
As far as lining the walls, I can't say scientifically why this is wrong, but I would try to use uneven surfaces like an anechoic chamber. The reason is that afaik sound waves can reflect off an impedance change. This is similar to seeing light reflect off water.
Further there is issues when the material doesn't evenly absorb certain frequencies. Its also possible that something in center helps funnel the sound away from drivers better. Look at how tweeter chambers are designed.
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Yes you see some odd things if you look too close, but you still have a point. As a child on a swing goes back and motional energy is invested against gravity, so the air molecules put theirs into a region of pressure. This is a gradual effect, yet at some point the swing reverses direction, and is therefore considered to have passed through 0m/s.
Good question
The question of standing waves and comb filters comes up when reflections are off flat surfaces, not surfaces that reflect off in different directions (which are the side walls of a speaker box). This has got to be the biggest issue in terms of insulation and diffusing of potential standing waves.
The flat wall first reflection points in a speaker box can only be the backwall and the flat walls at the top and at the sides of the protruding driver. In those cases the potential is a wave/s of sound reflect in a equal way off the wall to the back of the driver. It is in those places that having insulation off the walls more and or changing the shape of the wall will make a difference in terms of reducing the worst of the problems.
That is how I would make sense of comments about adding more stuffing around the driver, and I have seen on this site some treatment of the back wall to alter the flatness, and how you make sense of speaker designs with rounded backs.
May I whine?
I refer to normal acoustic theory in my replies. And read a lot of misunderstandings about the sound field in enclosed spaces. And my knowledge of acoustics really is quite basic.Such as the standing wave with wavelength four times the distance from front to back of the enclosure. I think someone posed that the moving diaphragm could act as an open end of a transmission line with the corresponding phase shift. Or something like that. Assumptions and simplifications that don't work.
Heres my understanding of standing waves. Sound waves are longitudinal as someone else here has said. So then you have compression and rarefaction, right?
So then lets take a sound wave in a long tube. When the tube is the right length relative to the soundwave, then the compression and rarefaction will line up. This is resonance. This is exactly like a quater wave pipe. right?
So then in a speaker box the high pressure areas are where you have more average compression and the velocity areas you have more rarefaction. So then its not that the sound is traveling at a different speed. Its the same speed just different parts of the wave.
So sound travels at a constant speed, but the air molecules in the wave have a changing speed. They get faster and slower as part of the wave.
So then lets take a sound wave in a long tube. When the tube is the right length relative to the soundwave, then the compression and rarefaction will line up. This is resonance. This is exactly like a quater wave pipe. right?
So then in a speaker box the high pressure areas are where you have more average compression and the velocity areas you have more rarefaction. So then its not that the sound is traveling at a different speed. Its the same speed just different parts of the wave.
So sound travels at a constant speed, but the air molecules in the wave have a changing speed. They get faster and slower as part of the wave.
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You are beginning to grasp it In a propagating sound wave, air molecules only move a little bit, the propagation stems from the interaction of the particles. The result can be described in terms of pressure and in terms of motion.
In the case of a standing wave, the molecules behave in a different way: near boundaries their movement is constrained by the boundary on one side and the (varying) pressure on the other (of course this is a representation in one dimension, but we have three). The pressure variations here are high, the particle movement low. Whereas the particle movement on other fixed places (so-called pressure nodes) is on its maximum. It all is really like a guitar string (on which you can play flageolets too).
In a propagating sound wave, air molecules only move a little bit, the propagation stems from the interaction of the particles. The result can be described in terms of pressure and in terms of motion. In the case of a standing wave, the molecules behave in a different way: near boundaries their movement is constrained by the boundary on one side and the (varying) pressure on the other (of course this is a representation in one dimension, but we have three). The pressure variations here are high, the particle movement low. Whereas the particle movement on other fixed places (so-called pressure nodes) is on its maximum. It all is really like a guitar string (on which you can play flageolets too).
I would say the movement of the air molecules is like a guitar string, in that you have motion in the middle and pressure at the ends. So a low frequency wave is a longer string. But this is always true no matter what.
You mean putting the material on the walls? I can say the burrito sounds better. I believe that its more effective, and I also think that there are numerous reasons for this. You want to funnel the sound away from the driver.
You mean putting the material on the walls? I can say the burrito sounds better. I believe that its more effective, and I also think that there are numerous reasons for this. You want to funnel the sound away from the driver.
More resonant jaw-jaw to the people.
Standing waves do not carry signals. Reflections (anything that moves) have frequency (velocity).
There are not (m)any standing waves in speaker boxes.
There is an abundance of insufficiently damped vibrations and diaphragm resonances.
Excessive (high amplitude) vibrations can be seen as electric forces losing battle against magnetic forces at the molecular level.
Standing waves do not carry signals. Reflections (anything that moves) have frequency (velocity).
There are not (m)any standing waves in speaker boxes.
There is an abundance of insufficiently damped vibrations and diaphragm resonances.
Excessive (high amplitude) vibrations can be seen as electric forces losing battle against magnetic forces at the molecular level.
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May I add: even in a spherical enclosure standing waves can exist, given excitation.
I believe stuffing the whole enclosure with appropriate absorption is the safest way of taming resonances, i.e. when you cannot evaluate results by measurements, revert to this method. It will tame the (wanted) resonance of reflex or TL speakers too, to some extent.
I believe also that less than appropriate stuffing will do in most domestic applications, because your listening room probably has far bigger issues regarding resonances. Weakest chain link.
The burrito solution will work better than traditional wall covering. Just because it is more effective at lower frequencies, where a lot of enclosure issues exist. But without checking the results, you could be missing a few problems with this approach. Just as with every other partial filling of the enclosure.
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