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Best Way to Brace a Box


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DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: June 24, 2012 at 9:34 AM / IP Logged  

soundnsecurity wrote:
i guess some experimentation is in order for me now. i might have to rebuild a new box for my current 15 and see what i can do to improve how it sounds in my truck because right now it's the worst part of my system by a long shot.

What driver is it, maybe I can suggest something for you...

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soundnsecurity 
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Location: Louisiana, United States
Posted: June 24, 2012 at 9:58 AM / IP Logged  
its a 15" RE audio SXX dual 2ohm. its the newer version but it has the same specs as the old one. specs can be found here
the amp is a PPI black ice 1800
right now the box is just under 3 cubic feet which is their minimum airspace
Best Way to Brace a Box - Page 3 -- posted image.
that is the box i made but its missing the very top piece in the picture. its standing up in my truck with the port on the bottom and facing the back of the drivers seat.
the problems i have with it now is mainly the response seems to be all over the place. it will play some notes with nice volume but it wont have any detail to it. and other notes sound good but are barely audible. if i turn it up to hear the good notes then it also amplifies the bad notes which overpower the rest of my system. so i turn the amp up but i turn the LPF way down, i usually like my low pass set around 90Hz and mine is set to about 50Hz right now.
i listen to a lot of rock and heavy metal that has very fast drum beats and a lot of bass guitar so i need my sub to be fast and detailed, SPL is optional.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: June 24, 2012 at 11:18 AM / IP Logged  
Sounds like you have a boom issue with might very well be caused by the effects we've been discussing.  Let me model that driver.  Be back in a sec.
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DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: June 24, 2012 at 11:29 AM / IP Logged  
Looks to me like 3cuft (85 liters) should be vented at 31.6 Hz.  In that alignment your peak output is at 79.4 Hz, which can sound quite boomy inside a vehicle.  What is the tuning frequency of your current enclosure?  This driver also models very nicely in a sealed enclosure of about 1.8 cuft (50.7 liters).
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soundnsecurity 
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Location: Louisiana, United States
Posted: June 24, 2012 at 12:27 PM / IP Logged  
i wanted it tuned to 32Hz but i dont think i got there. from what it sounds like i maybe botched the tuning a little and im thinking its closer to 36Hz. my problem was that i only wanted to take up a certain amount of space directly behind the drivers seat. my back seat is a 70/30 split so i took the 30 side out and i also didnt want to pass the window line.
i couldnt tune that low because the port would take too much volume from the overall box volume. tuning to 32Hz would have left me with about 2.5Ft^3. the port itself is 2" X 15.5" X 21". the 2" is actually 2 and 1/8 because of a lazy cut and by the time i found out about it it was too late to re cut that day so i just went with it.
i forgot to mention that the box is also stuffed with 1 cubic foot of poly in an attempt to make it more listenable until i figured out what i should do next.
i might do sealed since you say it models nicely in 1.8 even though it isnt recommended by RE. ive never been a big fan of sealed boxes but it would help me maintain my space needs because i really dont want to take the rest of my seat out in the name of sound.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: June 24, 2012 at 1:07 PM / IP Logged  
Before you do anything else, I suggest blocking the vent and see what happens.  Take a towel and stuff it into the vent hole, filling as much of the opening as you can.  Set your Xovers to 80Hz.  Can't hurt to try, right?
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soundnsecurity 
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Posted: June 24, 2012 at 1:25 PM / IP Logged  
i shall try it.
soundnsecurity 
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Location: Louisiana, United States
Posted: June 24, 2012 at 1:46 PM / IP Logged  
just did it. stuffed a towel into the port and played some familiar music to compare and it definitely toned down the boominess but it also dropped some low frequency response too. with the crossover up to 80Hz it was a little to much so i backed off to 70Hz and changed the slope to -6db instead of -12db and it was very listenable.
so filling the port would have made this about a 3cuft sealed box, how would this compare to the 1.8 you suggested?
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: June 24, 2012 at 2:03 PM / IP Logged  
It didn't seal it exactly, but by stuffing the port you reduce the port's output (which is why the low freq extension was reduced) and you reduce the strength of the sound wave that causes group delay as well as dampen port resonance.  You also remove the SPL that may be added due to "chuffing" or air coming out of the port at a high enough velocity to be heard.  By experimenting with the amount and density of stuffing you could find a sweet spot that gives you a sound you can live with.  A 3cuft sealed enclosure will create a system Q of around 0.6 as opposed to 0.7 in 1.8 cuft.  The difference would be subtle: higher Q means higher output at system resonance, with a Qtc of 0.707 being the most efficient trade-off between peak output and low-end response. 
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soundnsecurity 
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Posted: June 24, 2012 at 3:20 PM / IP Logged  
na i dont think ill try to fix this box. i dont want a sound i can live with, i want a sound that i cant get enough of. ill try out the sealed box first since its relatively easy to build one. i still think ill end up building a bigger ported box than what i have now just to have more bottom end but we shall see. i should be able to build that box sometime this week so ill let you know how it goes.
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