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2 inverted, 2 regular subs, same enclosure


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downstarinc 
Copper - Posts: 119
Copper spacespace
Joined: October 22, 2005
Location: United States
Posted: January 14, 2006 at 3:39 AM / IP Logged  
ok imma build a sealed fiberglass box soon...i want to put 2 subs inverted (magnets up) and put 2 regular(cone up)..but i wanna build one enclosure..would that be a problem??
jl audio..nuff said
boardinbum 
Silver - Posts: 358
Silver spacespace
Joined: February 07, 2005
Location: United States
Posted: January 14, 2006 at 4:39 AM / IP Logged  
As long as you divide the single enclosure into 4 seperate chambers (one for each sub) all of equal net volume (since the volume will need a hair bit bigger for the normal mounted subs, and a hair bit smaller for the inverted subs), then it should work fine.
stevdart 
Platinum - Posts: 5,816
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: January 14, 2006 at 8:25 AM / IP Logged  

I have a different opinion on this.  All four subs can share the same enclosure.  You will be adding volume displaced by only two subs, though, when you're calculating box volume.  And the cone areas of the inverted subs will indeed add to the overall volume, so bear that in mind.  Of course you'll want to figure in some internal bracing on this enclosure, and that displacement would have to be added up as well.

Inverted subs have to be wired on the opposite polarity than the normally mounted subs.  Here's a way to make that easier:  temporarily stick a piece of masking tape on the terminals of the inverted subs, marking the tape with the polarity symbol that is opposite of where it's put.  Then just wire the four subs according to the diagram that you are going to use, using the polarity on the tape as the rule.  The tape can be pulled off once everything is set up and tested.

2 inverted, 2 regular subs, same enclosure -- posted image.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
kirktcashalini 
Silver - Posts: 492
Silver spacespace
Joined: November 13, 2005
Location: United States
Posted: January 14, 2006 at 9:33 AM / IP Logged  
yes i was going to say make sure as hell they are wired reverse what it says, that way all 4 cones will push air the same way together, other than fighting each other. very important
99 Blazer LT.   Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)
forbidden 
Platinum - Posts: 5,352
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Location: Alberta, Canada
Posted: January 14, 2006 at 1:06 PM / IP Logged  
Stevdart nailed it properly for all to understand, however, you also need to consider this fact. If you blow one sub, then the entire system is down until it is replaced. Without some kind of divider on the inside of the box, it will also make a fairly weak baffle board (the part the subs attach to). So if this were my box, I would go the much harder route of making the box into either 2 or 4 chambers so as to separate the subs in the event of a failure, one pair could still be played or if 4 chambers then 3 could still be played. It would also help to strengthen the box that with 4 drivers in it will be wanting to flex absolutely everywhere. A box that is flexing loses an absurd amount of output, make sure the box is hella strong and secured down even better to get everything out of the subs that you can.
Top Secret, I can tell you but then my wife will kill me.
crzycreations 
Copper - Posts: 52
Copper spacespace
Joined: February 22, 2005
Location: United States
Posted: January 14, 2006 at 5:00 PM / IP Logged  

doesn't it also matter on how he wires the subs to the amp? For example: if he wires them all in parallel and one is blown, then he would need to replace/repair the sub before playing the music again to prevent damage to the amp and/or the other subs. so if what I'm thinking is correct, then in certain circumstances you would have to wait till the system gets repaired before playing it at all regardless of it being a single dual, or quad chamber enclosure. Please correct me if I'm wrong, because I'm not a professional at this kind of stuff, I just thought this might be relevant

Now thinking in the opposite direction, if he had a four-channel amplifier, one channel going to each sub, then the quad chamber may come in handy.

-Don't buy it, Build it-
stevdart 
Platinum - Posts: 5,816
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: January 14, 2006 at 11:25 PM / IP Logged  

I'm not one to worry about a sub failing and causing a problem in a sealed box situation.  Look at it this way, and I'll use nice round numbers to make this simple:  you have 4 subs in a sealed 4 cu ft box, each sub getting 1 cu ft of air to work with.  For some reason, one sub fails, the wires come off, something happens to it and it quits working.  Now there are three subs using the 4 cu ft, which gives each one 1 1/3 cu ft.  Would this ruin the other subs?  No way.  They'll be fine until you fix the broken sub.  The sound would suffer in the meantime.

Just look at the amount of play in cubic feet you have in building sealed boxes for any given subwoofer.  But if this case were a vented enclosure, it would be another story altogether.

Rob drove home the importance of building rigidity into a 4-sub enclosure, and using separate complete baffles assures the strongest box, as he suggested.  With sealed boxes there is a lot of forgiveness in air space volume...but with vented boxes there is no leeway.  This case is a sealed box, and it is entirely up to the designer whether the subs share airspace or work within their own.

crazycreations, you're talking about there being a difference in impedance load on the amp if the wires slip off one of the subs.  That is true, but the load won't become lower in a paralleled wiring scheme.  If one sub out of the group is removed, the impedance will go up...not down.  (Play around with the parallel and series calculators found in the left column to see what I mean.)

An amp will go into protection mode if the load gets too low at high output levels...but you would most likely hear the difference caused by a sub failure immediately.  And in all cases where one of your drivers fails, an immediate fix is necessary. 

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
downstarinc 
Copper - Posts: 119
Copper spacespace
Joined: October 22, 2005
Location: United States
Posted: January 14, 2006 at 11:37 PM / IP Logged  
so lemmie get this straight...4 subs, one enclosure, 2 regular, 2 inverted (out of phase)= no problem? im not worried about blowing subs, i have 4 jl audio w6v2's and 2 jl audio 1000/1's...and i never abuse my stuff..the inverted subs would basically be for looks only...
jl audio..nuff said
tracker bass 
Member - Posts: 4
Member spacespace
Joined: January 15, 2006
Location: United States
Posted: January 15, 2006 at 1:46 PM / IP Logged  
Hey guys i have a question i would appreciate help
i have 2 12" 1800 wat poweracoustiks and i built them a ported box it is a total of 6.1 cubic feet. and it is built well but when i play my subs it sounds like theres paper inside the box flapping around i cant fiqure out what the noise it some help
thanx
downstarinc 
Copper - Posts: 119
Copper spacespace
Joined: October 22, 2005
Location: United States
Posted: January 15, 2006 at 2:15 PM / IP Logged  
if you have a multi-meter check the ohms of each voice coil..sounds like a blown sub to me..
jl audio..nuff said
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