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2005 Silverado Z71 Ext Cab


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Big Dog 
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Joined: May 02, 2002
Location: Quebec, Canada
Posted: January 05, 2007 at 7:46 AM / IP Logged  
The compression while firing downwards would create a nice tight snap and besides, you'll feel the bass as well as hear it...
Prepare your future. It wasn't the lack of stones that killed the stone age.
djorgensen3 
Member - Posts: 6
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Joined: December 29, 2006
Location: United States
Posted: January 05, 2007 at 8:04 PM / IP Logged  

I just thought firing up would be easier to make the enclosure size correct but I will just make it wider for the one sub.  So downfire it is.  Thanks to everyone for your help!!

schmiddy 
Member - Posts: 5
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Joined: January 04, 2007
Location: United States
Posted: January 06, 2007 at 7:05 AM / IP Logged  

The enclosure size should be the same whether the driver is firing up, down, forward or backward.  I would recommend learning a bit more about speaker design before moving ahead- relatively small differences in enclosure size can make a huge difference in sound.  There are tons of resources on the internet; I would check the DIY speaker sites, as most car audio sites don't dig into this level of detail.

All drivers have a resonant frequency.  The main reason for an enclosure is to counteract the resonance of the speaker at that frequency and smooth the overall response.  A sealed enclosure is basically an air spring the dampens the driver at that frequency; the size of the enclosure is pretty forgiving.  There is an "optimal" size for accurate bass; a box smaller than that will sound boomier, a box larger than that will sound "faster" but have poorer low frequency extension.  A vented enclosure is basically a resonator that acts out-of-phase with the driver at the resonant frequency; there really is only one correct box size and port length to let it do it's job properly.  If this is your first sub design, I would stick with a sealed enclosure because it's much more forgiving.

A properly designed sub should not sound any different whether the driver is pointing up, down, forward or backwards; sound radiates more or less equally in all directions at low frequencies, provided that the front of the driver has several inches of clearance.  In theory, the sound would actually be cleaner with the sub facing forward/backward because gravity would not cause the cone to sag in one direction; however, my understanding is that most car audio subs have lower-compliance designs that minimize this effect.  There is a way to calculate this from the Theile-Small parameters, but I forget how.  It is related to the moving mass of the cone, and the stiffness of the suspension.

I hope I'm not confusing the issue too much, but these are basics that you should understand if you want a good result with your sub design.

djorgensen3 
Member - Posts: 6
Member spacespace
Joined: December 29, 2006
Location: United States
Posted: January 06, 2007 at 8:33 PM / IP Logged  
I understand everything you have said.  My point was to have the best quality low bass sound.  I have already used several online enclosure calculators and have come up with several different volumes dependent upon which calculator I used.  And those answers were different from the manufacturers recommendations.  It seems that the online calculators suggest a much larger enclosure.  It isn't my first sub enclosure but I have been out of it for quite a long time.  So far what I've come up with is to build my own enclosure similar to the prefab boxes large enough for two subs but only use one.  It will be as large as the manufacturers smallest ported recommendation but with the ability to try it sealed, as suggested by the online calculators, then ported  to determine the best sound for my taste.  I just wanted to know if firing up through the seat would muffle or muddy the sound from the sub.  I realize sub bass is omnidirectional by I want good sound and some feel.
dsintia 
Member - Posts: 1
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Joined: January 05, 2007
Location: United States
Posted: January 06, 2007 at 11:19 PM / IP Logged  
I just dealt with the same issue this past weekend, you know the four kids and two adult thing... I fired downward in a forward staged sealed enlcosure with just over 1.1ft3 vas on an infinity perfect 12" with an alpine amp and it produces really tight bass.  Good luck.
schmiddy 
Member - Posts: 5
Member spacespace
Joined: January 04, 2007
Location: United States
Posted: January 07, 2007 at 8:14 AM / IP Logged  
Good deal... I think I misread your earlier post about a different sized enclosure for down vs. up-firing.  Sounds like you've thought it through.  One other thing to think about; if the enclosure is large enough to serve as a ported enclosure, it will most likely be very big for a sealed enclosure- very low Q.  The bass will sound fast and tight (low group delay), but you won't have very good low extension and you'll need lots of power to drive it to sufficient volume.  If you haven't tried WinISD yet, you might want to give it a whirl- there's a good tutorial on this site.
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