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Old 4th December 2007, 03:29 AM   #1
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Default Small parameters for a small free-air sub

I want to get two 8" free-air subs for a project in the SUV I own. I am having issues finding an adequate sub for this. Do you guys have any recommendations for T/S parameters theat would work? I would not mind using home audio subs.
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Old 4th December 2007, 04:16 AM   #2
jpruden is offline jpruden  United States
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I think it has more to do with suspension than T/S parameters...

JL Audio used to make an 8" free air sub. Here is the parameter page for that driver (warning: opens a PDF)

http://mobile.jlaudio.com/pdfs/8-12IB4_BDS.pdf

The only common spec that you'll probably be looking for is a driver with a relatively high Qts... the JL Audio driver had a Qts of 0.684.

Honestly, though, not every high Qts driver is suited for use as a small sub... the driver also needs to have a really robust suspension and a decent throw to get any sort of air moving...
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Old 4th December 2007, 04:31 AM   #3
jol50 is offline jol50  United States
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What kind of power, or what kind of use will this be for? It is always better to go larger in size or number of subs with IB if you want a lot of output....if you have room.
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Old 4th December 2007, 12:13 PM   #4
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I have several amps to choose from.

a JBL bp600. 600 watts I think?

zapco AG360 60x4 or...

a orion cobalt 265 60ishx2

a 10inch may fit but I was just going to use 2 8's mainly for sound reinforcement' not necessarily boom. although it would be nice.
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Old 4th December 2007, 03:45 PM   #5
jol50 is offline jol50  United States
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You should not need much power, IB just can't take it you hit xmax. I have 4 12" infinity 1242 IB in my car now. The sub manual actually says IB is ok at half rated wattage, so they are 300rms that would be 150wrms. I have a kicker that is 420wrms running at 2 ohm on all 4...so 105wrms each. Indeed, the amp runs out of power before the subs. You need tighter suspension to return the sub to center as there is no box to help, yet if too much it will raise the Fs way up and again you have no box to tune the sub otherwise. You can model subs in winISD with a super huge sealed box to show it, and remember your crossover will slope the opposite way of rolloff. For 8s I would look for lower Fs to keep the sound, suspension not too loose Q around .6 is good give or take. If they are weaker they will put out more....but go out of control sooner. Xmax is the limit, an amp with subsonic filter might help a little. Check some forums like ssa and search for IB/free air to get an idea what drivers work. Could also ask places like partsexpress on the tech page. You can also use aperiodic to help power handling, where you just mount a filter/cloth behind the sub...that slows it down and helps keep it out of xmax as much. You got to watch the subs to know your max point, its not like boxes. You may know much of this, just trying to help. Some say go big xmax, not sure I agree as they have harder time staying in control and centering. These infinity are fairly good, but they don't move much until I max the amp out, really the travel does me no good at all. And then they are less efficient, so you get less and have to put more power to them.
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