quote:

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Originally posted by Hammer One:

I have a parabolic wall in my car . It hasn't been finished in it's current state for long so I have LOTS of messing about to do yet to get the best out of it , but already a strange thing ( to me anyway !! ) is happening .

It gets to 155 - 156 almost straight away ( ie. volume levels at one third of max and amp gains almost min ) with quite a wide frequency range ( 47 - 65 hz ) but seems to hit a ' brick wall ' where increasing the volume = no gain I haven't messed with much yet - am I missing something obvious or has anyone else experienced this ???

Andy

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How much power are you running to the subs? I would check the voltage going to the subs while you are measuring spl. If the voltage isn't going up dramaticallly after you hit "the brick wall", you have ran out of power(you gains are to high is why it happens at 1/3 volume). IF the voltage goes up substantially past that point and the spl doesn't increase, the problem lies in your box/speaker setup. IF this happens you are probably to the point of max excusion where most motor structures have little control (BL factor)over the cones. I don't think that the size of the wave(amplitude) would be causing it, the cancellation would be present at all volumes to a lesser degree, and it wouldn't hit a brick wall. You would just start to reach a point of diminishing returns were a very large amount of input difference would make a small amount of output difference. but you would still have an increase.

PS the testing i mentioned earlier would be even more accurate if you where to use an O-scope too. that way you could check the waveform for squarewaving.

Anyone else have any thoughts on this?

See Ya

I'm running about 400w to each sub ( amps rated higher but my batteries are seriously in need of a change !! ) I'll definately try the 'scope test this weekend - thanks .

Last weekend I took out 2 of the subs , blocked up the old slot ports ( which were too small by far ) , and let it run with the 2 holes left from removing the subs acting as the ports . So I was 2 subs less , and 2 amps less , but with WAAAY more port area than before - gained 1.7db ???

Does this change your theories ....

Many Thanks

Andy

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www.sounddomain.com/22904

quote:

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Originally posted by Hammer One:
Thanks for the input on this .

I'm running about 400w to each sub ( amps rated higher but my batteries are seriously in need of a change !! ) I'll definately try the 'scope test this weekend - thanks .

Last weekend I took out 2 of the subs , blocked up the old slot ports ( which were too small by far ) , and let it run with the 2 holes left from removing the subs acting as the ports . So I was 2 subs less , and 2 amps less , but with WAAAY more port area than before - gained 1.7db ???

Does this change your theories ....

Many Thanks

Andy

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Not really, what you did was change the port area and box tuning to make it more efficient, so it will get louder. If you are still hitting "the brick wall" at the same volume, on the head unit, You still have the same problem, just more efficient. I would still try the test. Let me know what happened. Kinda curious

see ya

I'll do the test on Saturday and let you know .

Once again thanks

Andy

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They are Focal 33k subs .

Thanks

Andy

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Also- When you took out the subs and got more port area, that tuned the box to a high(er) frequency, I'd imagine, which almost always gives you a bigger number

ShadowStar

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All I have to say is you guys are on the brink!!

Air pressure is created by air molecules hitting whatever surface is effected by it, be that your body, your ear drums, or the membrane of the SPL mic. So to get a higher pressure you either have to make more molecules hit that surface or make them hit with a greater force. Well force is Mass times acceleration. The acceleration would most properly be called a Deceleration because it's the rate at which the molecules stop. That is almost and instantanious stop so it's a very very large number. Yet the mass is a very very small number. So the greater the velocity of the particle the greater the deceleration. So what we know so far is there is a few things we can try to do to increase the pressure.

first you can speed up the particle itself. This will make the deceleration of the particle greater when it hits the surface and therefore raise the force creating a higher pressure. The speed of the wave itself it dependend on the medium though which it travels. So if your air is more dense then it should travel faster.

Second you can increase the mass part of the force equation. Do do this you need do have a heavier particle hitting the surface. An oxygen molecule is much lighter than say an Xeon Gas molecule. Does this mean that maybe you could fill your car with Xeon gas and that could help? I don't know.

Third you can increase the number of particles hitting the surface. That is where cone area comes in. Trying to have as tightly compressed (dense) little "pocket" of air hit the microphone. This is where shape of a cone may or may not make a difference. The main goal I think is to get a driver to compress as much air as it can into each of those little "pockets" of air in each pulse of the wave. Just for imagination's sake say you set a marble on your speaker and it is thrown directly on the membrane of the microphone...you would get amazing pressure levels. This is because of the mass and number of particles that hit that membrane. I hope that was a good analagy.

My personal opinion on ported boxes...keeping in mind my lack of experiance is that they are more efficient because the air inside the box does work as a spring of sorts...that spring resists the motion of the speaker but makes it come back much easier. in a sealed box this spring is the tightest...especially in a small sealed box. Therefore you get snappy bass at high notes and no low extention because the sub can't move far enough to create the low frequencies. This Spring is created because when the speaker pushes out it creates a vaccume of sorts and with a higher pressure outside the box than inside then you get outside air pushing the speaker back down and resisting it's outward movement. When you port a box you give it a way to equalize the pressure in the box. the bigger the port the more equalized it is. Well the more equalized it is the less outside air resists the movement of the sub. So less resistance = more efficient. That's just my theory. I have no Idea anything about tuning frequencies or any of that.

one thing I did notice someone said something about feeling the wave...just to clear that up what you feel is the particles hitting your skin. Waves are basically imaginary

As for the idea about a parabolic shaped box it sounds good. Such as your Satellite dish... or it could be eliptical too. The way a satellite dish works is that reciever that sticks out in the middle is at what is called the focal point. Which is, if I remember correctly, the point at which any thing that hits the dish will bouce back to that point. There are some mathematical relations there, if you want to know them look up Conic Sections. But the way I figure it...if you made...say...the dash in that shape (I don't know if the rules would allow you) and you got all your speakers the same distance from the point on that elipsis so that the waves from all of them hit the focal point at the same time then you could really get something out of it. Sounds like an expensive experiment though.

and I have no idea if this is true but it seems to me that the reason that a higher Xmax helps is that the driver itself moves with more force and faster but at the same frequency. So to get it to move with more force and speed yet at the same frequency it needs to move farther on each "stroke" i guess you could call it.

I have been into this kind of stuff for a long time yet I still feel I am just a beginner. Heck I believe that my love for audio systems is what made me choose my major of Electrical Engineering. The point to telling this to you is I want to that you all for this wonderful forum and topics like this...it really sparks my intrests and mind. I hope to see a lot more ideas from you guys...I'm eager to learn what I can...hope I helped a little...Sorry it was so long...I'm kinda a rambling idiot at some times.

Jared

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Originally posted by JBrod:

>first you can speed up the particle itself. >This will make the deceleration of the >particle greater when it hits the surface >and therefore raise the force creating a >higher pressure. The speed of the wave >itself it dependend on the medium though >which it travels. So if your air is more >dense then it should travel faster.

That is how the Navy is getting 215 dB from an underwater sonar array.

>Second you can increase the mass part of the >force equation. Do do this you need do have >a heavier particle hitting the surface. An >oxygen molecule is much lighter than say an >Xeon Gas molecule. Does this mean that >maybe you could fill your car with Xeon gas >and that could help? I don't know.

Illegal by dB Drag rules, but in theroy would work.

>Third you can increase the number of >particles hitting the surface. That is >where cone area comes in. Trying to have as >tightly compressed (dense) little "pocket" >of air hit the microphone. This is where >shape of a cone may or may not make a >difference. The main goal I think is to get >a driver to compress as much air as it can >into each of those little "pockets" of air >in each pulse of the wave. Just for >imagination's sake say you set a marble on >your speaker and it is thrown directly on >the membrane of the microphone...you would >get amazing pressure levels. This is >because of the mass and number of particles >that hit that membrane. I hope that was a >good analogy.

Supposedly the way the truck from Sweden hit 162 hit a single Punch XLC 18.

>My personal opinion on ported >boxes...keeping in mind my lack of >experiance is that they are more efficient >because the air inside the box does work as >a spring of sorts...that spring resists the >motion of the speaker but makes it come back >much easier.

At or above the tuned frequency.

>in a sealed box this spring is the >tightest...especially in a small sealed box. >Therefore you get snappy bass at high notes >and no low extention because the sub can't >move far enough to create the low >frequencies.

The tightness of the bass is caused by the midbass interaction, along with interactions with the other drivers. Has little to do with being a sealed or ported box.

>This Spring is created because when the >speaker pushes out it creates a vaccume of >sorts and with a higher pressure outside the >box than inside then you get outside air >pushing the speaker back down and resisting >it's outward movement. When you port a box >you give it a way to equalize the pressure >in the box. the bigger the port the more >equalized it is. Well the more equalized it >is the less outside air resists the movement >of the sub. So less resistance = more >efficient. That's just my theory. I have >no Idea anything about tuning frequencies or >any of that.

At or above the tuned frequency of the box, the back wave is in phase with the speaker, making the box "sealed." Below the tuned frequency the wave is out of phase, thus allowing the woofer to unload. This is the reason why you don't want to EQ too heavily below the tuned frequency of the box. You will shread your woofer.

>one thing I did notice someone said >something about feeling the wave...just to >clear that up what you feel is the particles >hitting your skin. Waves are basically >imaginary

So are particles for that matter. Quantum mechanics has unified the two.

>As for the idea about a parabolic shaped box >it sounds good. Such as your Satellite >dish... or it could be eliptical too. The >way a satellite dish works is that reciever >that sticks out in the middle is at what is >called the focal point. Which is, if I >remember correctly, the point at which any >thing that hits the dish will bouce back to >that point. There are some mathematical >relations there, if you want to know them >look up Conic Sections. But the way I >figure it...if you made...say...the dash in >that shape (I don't know if the rules would >allow you) and you got all your speakers the >same distance from the point on that elipsis >so that the waves from all of them hit the >focal point at the same time then you could >really get something out of it. Sounds like >an expensive experiment though.

How the truck from Sweden hit 162 with a single 18.

>and I have no idea if this is true but it >seems to me that the reason that a higher >Xmax helps is that the driver itself moves >with more force and faster but at the same >frequency. So to get it to move with more >force and speed yet at the same frequency it >needs to move farther on each "stroke" i >guess you could call it.

XMAX has nothing to do with the force the cone moves. In a ported box, XMAX is the lowest at the tuned frequency, which is generally the loudest frequency for that car when we talk about SPL cars. The force at which the cone is driven is a factor of the BL- the motor strenght. Look at the old posts in the Alma Gates part of the forum, I talked about that in the L7 topic. Along with why ported boxes aren't going to break 180 dB.

Jared
[/B]

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also. couldn't you get a perfect seal in your car and just pressurize it before a comp =).. hehe. "wow. ur at 120 and your subs aren't even on yet!" but then again. that would'nt work unless the diaphram of the mic seperated the cabin from the outside.

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Eli, I think the answer to your question is both. Air is both at the same time- that is how air acts as a spring. But air is not a linear spring. As we compress the air more and more, the tighter the spring gets, and the more work it takes to compress it. This is why ported boxes will not work in the high 70s or 180 dB level. Or so I'm told.

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All things are made up of atoms...that's something I think we can all agree on. Well "air" is just a bunch of atoms loosely spaced, floating around in our atmosphere. held down by gravity (why there is no air in space) All gasses are just atoms loosely spaced, liquids are tightly spaced atoms. And solids are atoms that are very tightly packed. If I remember I think our "air" is 65% nitrogen, 25% oxygen, and 10% other. I can't remember the actual numbers but that's the basic idea. And if you compress any gas enough you can turn it into a liquid and then a solid. Solid Carbon Dioxide is Dry Ice. They use Liquid Oxygen and liquid Hydrogen in space shuttles. I hope that explains it a little clearer.

But if you want to get to the quantum level of things, ALL atoms from everything are in constant motion, exchanging with every atom around it. So my atoms are exchanging with the computer's atoms, which is exchanging with the desk's atoms, so we are all one in a way. We are here and not here at the same time- know anything about someone's "cat"? It is when we observe an object, motion, speed, location is zero.

But that is just a tangent...

But an explaination on how air can act as both waves and particles- if you do some reading. Which this brings us back full circle to an old question in SPL- is achieving a high SPL solely a function of raw pressure, or "getting the wave" on the dash? But that is another topic all together.

flames aren't plasma... flames are just heat energy and light energy. the different colors observed are due to the type of matter and the temperature. plasma is for the most part only found on the sun. and in extremely small portions nad for small amounts of time on earth.