posted
The fact that larger boxes with larger vents yeild higher SPL levels is well known. It seems there are 3 main waysinvolving the system directly in which you can increase SPL - Increase cone area, increase power, or increase enclosure size. Take Jay Gold for example he kept hte same two USA2000X's and 2 Stroker 15's and by simply building larger enclosure after enclosure he went on a steady trip from the low 150's to breaking 160 and into the low 160's.
What are the physics behind the larger box volume theory? More cone area obviously compresses more air, thus raising SPL. More wattage pushes the pistons harder and further thus compressing more air and raising SPL. I believe ports, being the larger they are the more surface area they have, and when they hit tuning frequency and the air rides in phase with the woofer, the larger the port the greater the piston or "cone" area of the port is, and it yeilds the same basic result of increased cone area of woofers.
Higher tuning frequency gets more strokes of the woofer cone down in a given second and rapidly compresses the air before it has time to depressurize, thus higher tuning yeilds higher SPL...
Now these are my thoughts if I am wrong please correct me on the above. But in God's name I can not logically figure out why loudness is increased as BOX VOLUME goes up. Is there a certain point where you hit diminishing return?(which for ports is when you equal the woofer cone area right?)
THe only thing I can think of is larger box volume lends a spongier cushion of air behind the woofer cone, thus it is closer and closer to free air like conditions, and can therefore stroke further with less power, thus in turn pushing more air. Those subwoofer in open ended barrel setups firing back into a box with all the open area serving as the port, I am not familiar with other than that they lay down heavy numbers, but the woofers are flapping around with no cushinoning basically right, so they hit extremly high excursion pushing more air.
Ok I will shut up, but thats my brainstorming can someone please tell me the physics how it is and why increased vented box volume really increases SPL. Thanks!
Posts: 841 | From: Pennsylvania | Registered: Feb 2002
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posted
your about on the money! when you have a large vented box you force the air within that box out into the cab area,the more vent area the more output because the vent becomes a sub,there is a stopping point tuning,and compression,the sub must compress air,and do so very fast in a burst! subs that have muti spyders and other upgrades work better and will come back for more when using massive power,single spyders take less power to move to get a stroke,but fail more when using big power aka coil flying,ripped spyder,etc.your cab is like a ballon,your box is the air into the ballon,which works faster,you blowing into the ballon or and air compressor?
-------------------- 2006 IDBL 2ND PLACE WORLD FINALS 2008 World Records TBA LiL Scrappy The Louddest Honda 600 in The World! www.quadaudio.net Posts: 1629 | From: Palm Springs,CA | Registered: May 2002
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SPL is the measurement of sound pressure. Where in a speaker system is the most pressure going to be? That would be the smallest area in the system. So.............. If you have a small speaker enclosure and a huge interior, the most pressure is going to be in the enclosure. That isn't what we want. Now, if you take a huge enclosure and a small interior, the most pressure will be in the interior. This is better, why? Where is the mic?
-------------------- 2005 Black VW Golf TDI Alpine/DEI/Image Dynamics/CDT Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
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Elemental Designs
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--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Lafayette, LA | Registered: Sep 1999
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quote:Originally posted by Stevie: Don't you just love the blind leading the blind.
Go read a book on loudspeaker design before you push the Send button.
huh? who are you referring to?
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Lafayette, LA | Registered: Sep 1999
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posted
i have a cook book,its called over 13years in car audio real world testing! all that you read is not true?
-------------------- 2006 IDBL 2ND PLACE WORLD FINALS 2008 World Records TBA LiL Scrappy The Louddest Honda 600 in The World! www.quadaudio.net Posts: 1629 | From: Palm Springs,CA | Registered: May 2002
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posted
updated - a few things were re-worded to make more sense...
efficency - how to make your subs "happy"
a bigger box has more compliance, which lowers the frequency at which the speaker will resonate at
you have a few different factors -
the motor is trying to move the cone the suspension is pushing back on the cone, to prevent the coil from being pushed too far - a speakers motor strength is not linear, and when it gets pushed to its limits, it has less force to bring it back - this is where multiple spiders help, to mirror the BL curve - as the motor gets weaker, the suspension gets stiffer
Tip - compare different Qts/Qes values, Fs and Vas - and look at the impedance curve changes, remember that when you make the suspension stiffer, the VAS goes down and the Qes/Qts and Fs go up - also try different box volumes
next you have the box volume - a small box has a low compliance - it is a stiff spring, - the box makes the woofer "tight", as it likes to resonate more at the higher frequencys than the lower ones - eg a high Q sealed box
TIP - look at the impedance curves of a high Q sealed box
a bigger box has more compliance - is a looser spring, also the bigger box likes to resonate at lower frequencys
again, look at the impedance curves
next you have the port
a port acts as a spring, that delays the back wave of the sub so it comes out more in phase with the front wave
the most air comes out of the port at the tuning frequency, however the wave is only delayed by 90 more degrees - its 90 degrees ahead of the next wave, hence the theory of +3dB
(the wave starts off 180 degrees behind, then is delayed a further 90 degrees, so 270 degrees behind the first wave, or 90 ahead of the next wave)
at the tuning frequency, the woofer is resonates less, since most of the motor strength is transfered to moving air out of the port
above the tuning frequency, the port becomes more in phase with the woofer, but there is less output out of the port - but more motor strength is transferred to the cone, rather than the port, so the cone moves more
below the tuning frequency, the woofer goes increasingly out of phase, with the woofer - to 180 degrees
again, look at the impedance curve and a impedance phase graph, and also cone excursion
somewhere above the tuning frequency, the port/sub will naturally resonate more (ie the summed output from the port + sub will be greater) at, and give a peak - note, that most box programs frequency response plots aren't accurate enough for you to pick the tuning frequency using that graph
port surface area...
remember that a ports output is determined by the subs cone area, cone excursion and the frequency played in relation to the tuning frequency
a larger port is more linear - the air couples with the cabin a little better - there are less frictional losses - of course, really HUGE ports - much larger than the subs cone area, can be unneccesary
-------------------------------
box size vs cone excursion, and there is a compromise between acceleration of the cone due to the box (ie due to resonance), vs the motor, remembering that a bigger box is a looser air spring and likes to resonate at lower frequencys and vice versa (the port also changes that a bit)
between the suspension stiffness vs motor strength and amount of resonance vs frequency and in relation to box size
and between the port output vs cone excursion and determining the best tuning frequency
------------------------
I'll let you draw your own conclusions - testing with a LinearX measuring system - trying all of the variables and looking at the SPL vs impedance curves etc, would be a great advantage..
of course, not all of us can afford one, or put in the time for testing (me included...)
otherwise, any testing is good - and post your findings here if you can
quote:Originally posted by TGuY: I always thought about it this way:
SPL is the measurement of sound pressure. Where in a speaker system is the most pressure going to be? That would be the smallest area in the system. So.............. If you have a small speaker enclosure and a huge interior, the most pressure is going to be in the enclosure. That isn't what we want. Now, if you take a huge enclosure and a small interior, the most pressure will be in the interior. This is better, why? Where is the mic?
Your rationale is correct, in some ways. However, SPL is not static pressure, it is pressure variance. So your reasoning has to skew a little, especially in a ported situation.
And Stevie: No need for all that ruckus up in here.
posted
hey stevie, if you are such a big brain please state what you THINK.now i dont know everything to this but when you post somethin like that you must think you know everything. As a matter of fact where do you see the send button.i dont see one.i dont think i even see the word send.do you?so what does that tell ya.go get some glasses.
Posts: 64 | From: metairie,la | Registered: Jul 2002
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-------------------- Visit www.tunablecompacts.com for ALL of your styling and performance needs! Posts: 14 | From: Bangor, ME | Registered: Apr 2002
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posted
My latest trial for higher spl has led me to discover, that we had more input power available to our subs than our current box design will allow. That leads me to believe, that too much volume is limiting our subs at a specific spl level. Back to the cutting room!
posted
Fairly easy question. A larger enclosure simply acts as a higher Q resonator, same as having a larger port does. If you have less damping on the system the peak is larger. After a point the air becomes non linear and the coupling between woofer and air lessens, so yes there is a point where it starts to lose it.
C
-------------------- *hmm need to think of a new sig* Posts: 2999 | From: England | Registered: Oct 2000
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you say a larger box with a single spider sub will take less power then in a smaller box were you can feed it more power ? well close to this not exact. :-)
well I have done a few designs with a lightning audio bolt series sub, and tests shows that I can feed it 300 daily , which it is only rated for 150 rms and 300 max, and burp it with 1200 at my peak freq. Interesting I think since the smaller box I tested would only take 150 daily and burp at 700.
yes both are ported at the same freq for my application, and yes the larger box provided the best spl, which I hit at a comp last sat.
Well its off to the drawing board for the next design to be built and testing to be done.
posted
you will find that larger and smaller boxes need different tuning frequencys for the box to peak at your cars resonant frequency
since the tuning frequency was the same (the boxes will be peaking at different frequencys) then its hard to say which was better
Posts: 358 | From: .. | Registered: Apr 2002
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posted
the formula for the mathematical equation: first you must define the equation for the relative theoretical viscosal changes which induces the linear expansion of the polypropexalinearglassonite of the fiberistical surfaces in which the box yields. Once that is defined you then divide the equation by 2, add back the surface of the molecular portion resulting in a greater area of mass, which going undistrubed by the contraining velocity of the air turbulance induces the higher SPL?
Or something like that.
Have a great day!
Posts: 5534 | From: CO | Registered: Apr 2001
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-------------------- Visit www.tunablecompacts.com for ALL of your styling and performance needs! Posts: 14 | From: Bangor, ME | Registered: Apr 2002
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posted
i just got a memphis 1000d (1100w) on my kicker xpl 15's in a sealed box @ 600w rms per sub so 1100w/1200w i hit 142.7 with a 300w kenwood. What do you think my spl wil increase too there are no meters withing like 1-2 hour distance. the local audio shop sold theirs.
-------------------- 97 eclipse fosgate wires sony cd/md deck 2 kicker 15's memphis amp 142.7 db (with 300w kenwood) http://members.sounddomain.com/arsenicx Posts: 47 | From: Kansas City | Registered: Oct 2002
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posted
I think everyone has the right idea. I also think it’s the kind of question that doesn’t have a simple answer. There are a few important things for spl that nobody mentioned though. Even in a car, It is very important to load the sub as much as possible. And Yes, cancellation does occur in cars. I've proven it in mine. It plays a big role in loading/unloading the sub, and is frequency dependent. At a certain frequencies it will be loaded more than others.
As Bassaholic_au said, at tuning the ports output in dB is max and 90 degrees out of phase. Actually it’s 270 degrees behind. Same thing basic thing though. One way around this is to build baffles in the box so the air has to travel 1/4 of the wavelength of the ports resonance frequency from the sub to the port. Then it will be in phase at tuning or 360 degrees behind. This also further loads the sub.
How much air you can move or compress with your sub is limited. To maximize this at one frequency as much as it can be maximized you need to tune the sub and port to the same resonance frequency. This will show up on your impedance curve looking like a sealed box. At this frequency, the cone movement is minimized while the port will be just humming. So by the time you reach maximum excursion, your moving a $hitload of air! A Note: doing this takes away your choice in size of box or tuning frequency. You may need a lighter or heavier cone to get what is right for your situation.
Now, I keep saying, “ load the sub”. Two very important things for Gain. 1. If the sub and port have the same resonance frequency, the impedance at this frequency will be very high. Again, very high. this is good! 2. Also, as you increase the load on the sub, its impedance rises. Example placing a box in a car trunk will cause the entire impedance curve to rise. This is why people can run their amps at lower impedance’s then they are rated. A 4-ohm sub might become an 8-ohm sub.
Putting this together. Say we have a 0.25-ohm sub. Tuning the sub and port to the same resonance frequency will give maybe a 2.5 ohm load at resonance. The baffling will increase it further to maybe 3.5. Then placement of it loading it further by not allowing cancellation at that frequency will further increase it. So now we have a 0.25-ohm sub with a 4-ohm impedance at its peak frequency. Now take a 2000x that can do 120v rms output. Into 4 ohms, that’s 3600 watts. But subs sensivity is with respect to voltage not power. So your amp is only delivering 3600 watts, but your sub will respond to it like its still a 0.25 ohms sub.
So know you have 120*120 /0.25ohms = 57,600 watts. The total amplifier gain is 10 *log (57600) = 47dB.
Lets compare this to an amp that’s rated at 3600 watts at 0.25ohms The total gain here is 10 *log (3600) = 35dB.
The difference is +12db for this case.
It’s normal in my experience that you always end up with a sensitivity of 120-123 dB in car at 1watt.
123+47 = 170dB 123+35 = 158dB
This is how people can hit 170+dB with only one Sub!
Posts: 1247 | From: Fullerton. CA ,USA | Registered: Oct 1999
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