posted
this post is aimed toward street and super street no wall hatchback cars with stock interiors. i have noticed that alot of spl competitors believe that every car has a limit to how much spl can be created within the cabin of a given vehicle. i find it hard to believe without some type of hard proof to back it up. to me, that would be like believing in magic, or the tooth fairy. i do know that as pressure inside of a stock cabin increases, the structure of the cabin weakens, thus translating into minimum gains, or "diminishing returns" as i call them. but, alot of competitors believe in a magical "brick wall" that we hatchback owners seem to run into at 160-163db. (last years termlab) now, i have run into a point of "no returns" in my hatchback, and i am really looking into some answers as to why. i do not wish to do the carbon copy thing, and just go buy a van and copy everyone elses box since it seems everyone who has a particular vehicle runs the same style enclosure. those who have switched to vans have surpassed their hatchback scores by 3db minimum. hence, everyone seems to take the easy way out and buy a van, and copy the same box they saw someone else build. that's just not me. i wish to figure this thing out, and take my vehicle to the next level. i have a theory of what is going on in my particular situation. and i just wanted to run this by someone else to get a second opinion. here's a brief explanation for my "brick wall": subs running into power compression, amps near clipping, limited power supply, and cabin interior panel flexing = the magic brick wall. now, i can fix the power supply problem as easily as switching my 6 interstate batts out to 6 batcaps. (it's a money thing though) and with a stronger power supply, comes more amplifier output before clipping. and then, a little enclosure voodoo can get me slightly more output in theory. but i am still lleft with my flimsy cabin. so now, i am back at this brick wall. give me some opinions on what you all think about this theory that stock interior cars have an spl limit.
-------------------- Team Livewire Posts: 2199 | From: columbus, ohio | Registered: Mar 2001
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posted
First off I am not claiming to be an expert at all in the spl field, and you may already know all about this, but I am just telling you what I have heard and seen. At last years db drag world finals they talked about the spl vehicles burping, that you are not actually hearing the sound of the subwoofers on the outside, but the metal of the vehicles vibrating. I heard some systems hitting 155 db that were louder sounding than the world record holders "team bs" hitting 177.7 db. That means that team bs had reinforced their car better so that the immense sound pressure inside would not flex the vehicle walls resulting in higher SPL. I also heard that they had switched out their alternators a couple days before to a new brand and it yielded 2 more decibels. All that I know that you could do is change to new more efficient woofers, or find a way to get more available power from caps, or new alternators. You may gain a couple or so decibels from this. As for reinforcing your car all I know is concrete, bulletproofing windows, and bracing of large metal panels. Again I am not an expert at all about any of this, but I hope this helps.
Posts: 18 | From: Milton, TN | Registered: Feb 2003
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posted
My last reply didn`t cover the stock interrior spl limit theory. All I know is when the inside of the car is pressurised enough from the woofers the walls begin to flex to relieve pressure. This reduces spl capability. If the woofers are pushed harder there would be more pressure created, but if the cabin walls and windows are not very secure the pressure will be relieved somewhat. So the spl would not go up, does this sound right? What spl has to do with is sound pressure so if the cabin air cannot be compressed enough due to flexing walls the spl should not go up.
Posts: 18 | From: Milton, TN | Registered: Feb 2003
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posted
yea, but I've seen alot of cars that gain from having the windows down.. or doors open in a competition (Obviously not a DB drag)... the pressure it has to hold in has to DRASTICALLY change.......
hmmmmmmmm
-------------------- Sid Grace likes to edit my signature. Posts: 445 | From: Upstate, NY | Registered: Apr 2002
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posted
SPL is not just pressure though, it is fluctuations between compression and rareification. so a certain amount of panel flex could theoretically help your score, like having your windows down.
posted
And we had discovered that a 'fresh air' vent was easliy opened by the pressure we generated which resulted in a weird tuning sequence- at low volume gaining - a nice number, and at higher levels- a porting to the outside ruined a good score. We had to replace the vaccum actuator so the dam thing would stay sealed!! But- that was ss 1-2 also! The point being, after you generate good pressure and wear things out, all cars are subject to "leak" air- hmmm - a brick wall to me! You can only pump up a flat tire so much.
posted
I think an important point to bring up is what perspective are we taking when we look at whats going on inside the cabin. #1 are we creating a pocket of air trapped inside a metal chamber and the woofer cones (and port air mass) are squeezing and relieveing this pressure as you would a baloon....this air compressor theory as I think of it as would make perfect sense then that the brick wall is the sheet metal etc flexing. But if you take the other perspective as #2 the woofer cones are moving forward and backward quickly creating a little "disturbance" or pressure "packet" which then radiates away from the cone untill it hits a barrier such as the dash (the reason i believe that if you move a mic around the score will change drastically). That point at which it hits the barrier or a little distance backwards, a standing wave will develop in which the compression is higher than any other waves or points within the air mass being pressurized. I think both of these theories actually occur in any setup, however This theory #2 I think is whats happening MORE in hatch back or trunk cars (reflection setups) where the theory 1 "pressure cooker theory lol" is whats occuring more so in a wall type setup where you effectively created a chamber so much more divided, and so much closer to (or more so) then the woofer enclosure volume, that you effectively get an actually air squeezing action of the whole air mass as a whole along with the waves. I think this whole air mass compression results in less microphone disturbance than would traveling rarefaction/compression packets.
I am just babling but this is what I think. Honestly I dont think there is any brick walls if you eliminate equipment fatigue. I beleive if you add more watts and more driver capability the SPL WILL HAVE TO go up. I don't care how flimsy the car is, if the drivers stroke harder or further (more power, equipment advances, technology) the SPL must go up...untill the ruptures and the waves have nothing to hit. Its just a matter of WHAT can we do with the equipment we have available now. If you took the car and turned it into a metal tube, then you placed a big piston in it like a giant syringe, then you connected a hydraulic arm to the piston and rammed it up and down at 20 HZ with enough force and linear travel that the air pressure compression/rarefaction was a difference of 50,000,000 PSI......you get the point. This is what I love about this hobby is its totally insane . Try to talk about this stuff to a normal non-stereo person who views a stereo as something in a car to listen to when driving Below I am checking areas of compression and rarefaction, and I think I found an area of high compression Posts: 841 | From: Pennsylvania | Registered: Feb 2002
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quote: I beleive if you add more watts and more driver capability the SPL WILL HAVE TO go up. I don't care how flimsy the car is, if the drivers stroke harder or further (more power, equipment advances, technology) the SPL must go up...
exactly my point. though i do know that as the pressure increases, you will experiance diminishing returns. but never a "no returns" or "brick wall"
-------------------- Team Livewire Posts: 2199 | From: columbus, ohio | Registered: Mar 2001
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posted
Yeah thats what i think man, that theres no definite point but it will keep getting harder and harder as you go up, like a bottleneck type effect or whatnot. But if you can supply enough muscle to squeez further it will go...just keeps needing more and more muscle. Like if you could get drivers with 400 pound magnets, 4 gauge voice coils and throws of 12 inches then tuned your enclosure to 60 HZ and went to a multi million watt transfer station at a power plant and slammed double ought speaker wire right to the big terminals that comeoff a 200 kilovolt transformer fromt he nuclear generator i dont doubt you would do 180+ Db, hell the car would probabaly tear apart at the welds but you'd probly do it lol Posts: 841 | From: Pennsylvania | Registered: Feb 2002
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posted
Sorry, i just got finished studying for my math exams, but...
Sounds like an asymptote type thing. Where that little curved line get infinitely closer to the imaginary straight line, but never touches it. The curved line would be your recorded SPL, and the imaginary line is your maximum theoretical SPL. You'll never actually reach a max, but even if you quadruple your cone area and increase power by ten, you still won't hit or cross that line.
Sorry guys, i shouldn't have done that...
-------------------- 1995 Grand Am GT Nakamichi CD-45z Pair of Audiocontrol EQT's Audiocontrol 4XS Crossfire TEK100.2 Illusion Audio ND-6 Crossfire VR142 Image Dynamics CD1E V.2
Looking for the following: Image Dynamics IDMAX 12" Crossfire BMF1000d or VR1000d Posts: 48 | From: Buffalo | Registered: Oct 2002
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That's a good point.., and if i can add my 2 cent, i would say, that air compresion with a cone is not linear fonction regarding dBs...
In other words, when cone compress air in front of the woofer, the air mass on rear of it became uncompressed, and lost density(lower pressure)
The fact is that when you compress air, the density increase, ok!... but on the other side, the air loose density..
Just imagine that you only have to compress it to do dB.. (the sound come from just one variation of pressure in front of the speaker) the pressure diferential with atmospheric presure is in theory higher then the diferential measured on rear of the cone because in front, the density of air became higher...
Now, if we compare with the other case, measuring diferential pressure on rear of the cone, the air density decrease.
What i mean is that we all know or already heard that extreem vehicule like 165-175dB have more diffucult to double their dB by just doubling power and woofer then in 140 range
Non linearity of air characteristic occur...
I think that the atm pressure is the responsible.....
If it would be doubled, the non linearity slope of air density vs diferential pressure should offset..
dB is created with repeated cycle of increasing pressure(more air molecule) and with decreasing air pressure(lower number of molecule then atm)
As you increase dB, as the step when decreasing number of air molecule create non linearity(second phase of a complete cycle)
We use these two cycle to do dB because as you know woofer cone travel in two direction
but i think that the phase when compressing air is linear, but the phase when decompressing is'nt.
just for the reason that quantity of air molecule used is'nt the same for the first phase then for the second...
compressing air posibility is higher then uncompresing it, because when uncompressing, you can't go under zero PSI...
suppose that you have a car able to do 194dB (atm pressure). just IMAGINE!!
This pressure diferential is composed fo variation from 14 to 0 to 14 to 28 to 14 psi for one cycle.
the phase able to increase the number of dB will be only the phase compressing air. The other phase will reach 14psi to 0psi and will not be able to go under zero...
but you will always able to go upper 14psi.. like 28, 42.. etc..
That's my concept...
please correct it, if i'm wrong.. ?
-------------------- Street A "not legal but not outlaw!" Score in my integra: -152.34 dB 51Hz TL sensor -157,1dB 51Hz AC mic
2005-2006 Street A Champion in Quebec province!
CRAZY TESTs: ||||||THE ONLY 6.5" TO SCORE 168.9dB(TL)OUTLAW IN THE WORLD with 6 Watts.|||||| -Crazy 5.25 Bose sub 1.1cu box: 138.0dB TL mic 55Hz with ONLY 100W ! ---------------------------------- www.teamxmax.com Posts: 643 | From: Quebec city | Registered: Mar 2000
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posted
a lot of people think about this subject the wrong way. spl vehicles actually create very little static air pressure in the vehicle. all the pressure is created in the form of a wave. the definition of a wave from dictionary.com "A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself." aka, you're not creating any real static pressure. it is only transferring pressure from one medium to another. aka, the panels flexing in a vehicle aren't really creating a pressure drop in the cabin, they are simply absorbing energy from the waves hitting them. energy is constant, it cannot be destroyed, only converted. so, if you have sound energy changing into kinetic or heat energy, you're creating an efficiency drop. to keep the wave from loosing energy, you must keep all the energy in a sound wave form. that is why extreme vehicles are more capable. not to mention their simplified interiors. this plays a big role. you must remember, when a wave refracts off of a surface, the phase changes. one the phase of your wave starts to change the interaction between waves causes cancellation. that is the biggest reason why opening doors/windows helps. it doesn't effect the static pressure, because there is none. it simply allows the waves to escape, so rather than them bouncing around in the interior very likely causing some sort of cancellation at some point, they escape. really though, for huge output you do need a controlled environment. the loudest vehicles are the one that have the best path for the waves to travel. the best not necessary meaning the right length to tune it well, but more a path more resilient to cancellation. if you could create a system where there is no cancellation, and many waves could be focused where ever the mic is positioned, you would see HUGE gains. almost unlimited. just think of how a parabolic dish works. this is the same principle. the only problem is, to make something like this in the frequency range the db drag org is limited to, would be near impossible. if done, it could mean incredible output at the focal point though. HUGE output.... in other words, more power is good. more displacement is good. the real gains come from making a system that has a controlled environment. too bad there is no way to visualize sound waves and phase inside our vehicles. it would be so much easier. if you don't believe me, just look at systems and how they have progressed. the reason why you see so many people doing well with a small number of woofers over a large number is because of how much more simplified things get. simple is good. enough rambling from me.
-------------------- 2005 Black VW Golf TDI Alpine/DEI/Image Dynamics/CDT Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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The idea is that up to 140 Dbs, you gain 3 db by doubling power. higher, and you'll gain like 2.5 for every double, then 2, then 1.5 then 1 then .5, etc, etc.
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