posted
http://newport.pmel.noaa.gov/whales/acoustics.html this is a GREAT link to research for those of you that would like to learn even more about sound pressure. the link is about intrduction to UNDERWATER acoustics but contains all information for the conversions for sound pressure in water to sound pressure in air. this site is EXTREMELY informative and IMO...is a must read(as well as the loudspeaker cookbook) for those that maybe less knowledgable about acoustics and sound reproduction, that want to know more about sound and how it works in different enviroments. also, this site has led me to other interesting research in acoustical sciences. please visit the site and take from it what you can..
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[This message has been edited by ecm_3 (edited 05-29-2000).]
Posts: 122 | From: St.Louis, MO | Registered: Feb 2000
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posted
Talking about where the motor structures of different drivers fail, and where others exceede is pretty easy if they give you the right specs. First BL is needed so you know the magnetic force of the magnet on the coil. Then you need electical xmax which is (coil length - gap height) /2. This is all descibed in the Loud Speaker Design Cookbook. The farther past true xmax you push a driver the more the BL drops and the less linear (more distorted) the travel of the cone becomes.
------------------ Knowledge=SPL As does and open mind Team Hertz Canada Pres Hertz Audio
Posts: 221 | From: Calgary, AB | Registered: Nov 1999
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posted
ok ive got a comment about spl ok people hit 170s inside the port or box so why is it that we are trying to do spl with the subs firing into the cabin when we can hit 170s all day long with a box design of the subs firing into the rear of the car and use the front of the car as the internal box volume just a thought i know this has been known to work before personaly i havent tryed it yet hummm mabey i will hehe like to see a 1-2 woofer car do 175 i hope i just made sense let me know what u think
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Posts: 118 | From: spl city | Registered: May 2000
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posted
That would be a good idea, since the car acts as an enclosure anyway, BUT, the car is an extremely crappy enclosure. It flexes, resonates, and so on.
Here's an idea, mount the drivers on the surface of the car, with the boxes on the outside.
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Posts: 323 | From: Great Falls, Montana | Registered: Feb 2000
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posted
Wouldn't you create a higher pressure level by having a greater difference b/t the high and lower pressure levels in the air (sound). Like, a sonic boom is the low level and high level pressure areas slamming back together. So what would make greater spl: moving a ton of air (say from a woofer w/ a 3" excersion), or a short burst w/ large differences b/t the low and highlevel pressures of the wave? Or to put that simply, move a lot of air, or have a powerful blast of air? As far as easier to pressurize a cabin w/ different temperatures, i'm stumped, but on hot days the waves will travel slower due to the lack of particles to xfer the energy (longer "flight time"). The speed of sound changes w/ the temperature. I could get out my physics book and get the exact values for ya =). However, i doubt the speed of the waves have much to do with how much pressure you can create. Also, 2 subs will not be 2x as loud as 1 sub, unless the waves hit each other PERFECTLY. Due to the fact that sound waves go in all directions, it's awfully hard to get the waves to line up with each other. You need either the troughs or crests of each wave to line up, but if you get a trough and a crest, they will cancel out, which lowers your pressure. My theory is that if you create a parabolic shape going from the woofer (woofer facing the parabola, or the back of the car) and point the parabola towards the dash, you could direct all of the waves to one point, that point being the mic. I know this works with light (your headlights), and the easiest way to position your speakers is to say "what you see is what you hear".. have fun kiddies =) sorry its alot, but i'm posting from everything i read. hehe
------------------ It aint bass till your dash falls in your lap.
posted
I'm going to try to answer the original post. You're thinking that when the cone moves back in, then air will be sucked back into the box, decreasing pressure.
Well a sealed box would do the exact same thing when the cone either goes to the point of rest or moves back into the basket. It would increase the volume of the cabin therefore decreasing pressure.
So having air sucked into the port would be no different than a sealed sub moving back and forth.
Does that sound right?
-------------------- E-no-skips ECD-414 RF 800a2 + bd1000a1 CDT HD642-DT w/ metal tweets Eclipse 8815DVC LA 1F Cap and wire
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Posts: 86 | From: Omaha, NE | Registered: Jan 2000
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posted
The way I understand it, a port does not actually move air in and out of the box. It simply acts like another speaker. Just so happens that it uses air to create the wave instead of paper or whatever. Easy way to describe it is a passive radiator made out of air. That is why a bigger area port is more efficient. Just like bigger area speakers.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
woah there.... sound is created by movement.. a port has no moving parts... even a false speaker still moves. sound might come out of the port, but that sound is made by the speaker.. unless you have port noise, which you don't want to begin with....
------------------ It aint bass till your dash falls in your lap.
posted
Me thinks you are both right. A port seems to be an indirect radiator- it produces sound but from an external source. Maybe I am wrong, maybe I am right.
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Posts: 7866 | From: Charlotte,NC USA | Registered: May 1999
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posted
An other idea is to modify a car interior to get a reverberant chamber(like the inverse of an anecoic room), by building no parallel wall, top and buttom and calculating the exact place to put the speakers and the mic...
This method(i think...) will create in very specific points some sound wave in perfect phase and other point in total cancellation...
------------------ Show me the bass !
Posts: 643 | From: Quebec city | Registered: Mar 2000
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posted
If you could do that precisely I am sure some very big numbers are possible.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
Ohh, and a port does have moving "parts". The part that moves is the pocket of air thats inside the port. It transfers the energy that was created by the back of the speaker to the outside world. It works under almost the exact same principle as a passive radiator. You tune it by making it longer/shorter bigger/smaller which really just adds and removes to the mass of the air in the port. You tune passive radiators by adding and removeing mass to the cone. Correct me if I am wrong but that's the way I have always thought of it. A passive radiator made out of air. Just to clear things up, by saying "it acts like another speaker" I didn't mean an active speaker, I meant a passive one. That's why I said "like a passive radiator" lower in the post.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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I still want someone to use a VW bug as an SPL car, using the roof to reflect the sound waves and converge them at one specific point (satellite dish style ) :-)
ShadowStar
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
so just make a big parabola and stick it in your car... and for anyone who doesn't know what a parabola is, a satallite dish acts as a parabolic reflector to the waves coming in from space.. waves you say?? yes, waves... hehe.
about the port speaker. a passive radiator still moves due to the air pressure inside the box, and it makes sound by pushing air out. a port just directs how the air flows, while the active speaker is doin the pushing.
------------------ It aint bass till your dash falls in your lap.
posted
Sound Pressure is more than just "air flow". It is waves of acoustic energy flowing through air or whatever other medium. The port doesn't actually move much of any air in and out of the box it simply transfers the energy which is in the format of waves to the world outside the enclosure. If you put your hand in front of a port it does feel like there is a lot of air moving in and out of the box. What your actually feeling is not air flowing out of the box your feeling waves moving through the air.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
No matter how much all of this makes sense, I still don't get why it feels like a port is sucking in air. You say it's waves, but that still doesn't click. Am I just being dumb?
Parabola is fun to say! Try it. Pa-ra-bo-la.
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Posts: 323 | From: Great Falls, Montana | Registered: Feb 2000
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posted
You can put your hand infront of the cone of the speaker and you feel the same sort of thing. Goto the web page at the top of page 3 in this post and you can see a animation of it.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
Actually it was a different page I was thinking of. Here is a good link to look at: http://www.kettering.edu/~drussell/Demos/waves/Lwave.gif Notice how few of the molecules actually move more than the distance between the waves.
[This message has been edited by TGuY (edited 06-18-2000).]
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
My friend just bought a '63 VW Bug. I see what you mean about the parabola. Right now there's no fabric on the inside, the radio sounds like it's in a pipe factory.
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Posts: 323 | From: Great Falls, Montana | Registered: Feb 2000
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quote:Originally posted by [meph]: so just make a big parabola and stick it in your car...
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 ???
quote: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
well.. could be the size of the waves. no, not lengths.. the more powerful the waves are the widthier they get. if thats a word. the waves always have the same period, but the amplitude of the wave increases as you apply more power to it. your problem could be that the waves are just too big to reflect correctly off your wall. that or you could be getting some serious cancellation. just my thoughts...
------------------ It aint bass till your dash falls in your lap.
posted
I Know this might be a strange analogy but bear with me
My brother competes in world championship sailing and he was telling me what they do in terms of optimum acceleration of air. In the boats, there's an optimum 'slot' that you create (between jib and mainsail) to speed the wind up for maximum flow without stalling it. So how do you know when its stalled? - well, stalling creates mini-vortexes coming from the edge of the slot. You can see these by attaching 'tell-tails' to the edge of the sail - if they stream nicely, it means that the air isn't stalling - if they flap around, they've stalled!! The remedy was to open the slot slightly more as the wind speed increased.
Is this why the majority of big hitters are using very large ports ?? And in relation to my problem ( see a couple of posts above ) - does anyone think that my ports could be too small and restricting air flow ??
posted
The really big ports act like another speaker or three. But when ports get that big, they tend to lose the ability to play music very well- peaky output and the ports acting as tuned pipes like in a church pipe organ.
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Posts: 7866 | From: Charlotte,NC USA | Registered: May 1999
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