RF3112 Enclosure Help

I followed my manual's recomendation for 1.0cu ft sealed for each RF3112 driver, but it just REALLY sounded bad to me, my 3 RF 4212's installed sealed in a shared 4.0 cu foot sealed destroyed what I heard, but a RF Elite memeber buddy told me once that the 3112's need 38 hz ported enclosure if I want them to work right. I have re-read my DVC manual and read that 2.5 cu ported with RF's recomended (2) 4" x 12.65" ports *thats 40hz), I want them tuned to 38hz (so the ports will be a tad bit different) is the way to go. Due to the usuable space in the ride, I'm generating 2.50427 cubic feet by designing each subs enclosure with the dimentions of; 15." wide (speaker face plate firing into the 2nd row seats of a ford expedition) x 15.25" tall (up) x 24.8125" deep (twords the rear hatch).

Now, with those dimentions, the port or ports could only be mounted on the rear deck, behind the sub, theres depth room to basically place them anywhere on the back face. My cookbook actually tells me "in fact, the midrange leakage from the vent of a rear vented speaker will tend to be less noticeable. Ideally it should be held captive inside the box so any of it that leaks out constitutes "distortion". A rear located vent reduces the audibility of this "distortion". For rear vents just make sure you don't violate the "1/4 wave" rule". Reading goes on to tell me that the 1/4 wave rule at 38hz means that the port must be placed no greater than 7 feet from the driver (no problem), and the basic rule of at least 1/4" of clearance around the port.

The main reason I am asking this question is because every ported box I have ever bought (I have never built on and am sure that is why they have all stunk) has used square ports and was NOT custom designed for the sub, they all had port noise that I could not stand, flapping, passing air noise.

RF recomends (2) 4" ports, where as some reading states to go with as big of a port diameter as possible, the larger diameter will help eliminate the noise I am talking about, however, the cookbook statement from above states that my placement on the rear deck in itself reduces the audibility of this distortion.

Using the 12volt.com formula ((14630000*(D/2)*(D/2))/((Fb*Fb*Vb*1728)-(1463*(D/2)))) with a 6" port states I need a 6" ID pipe that is 16.68 inches long, that would be 1 port per sub. Same formula with (1) 4" ID pipe states 6.4391 inches long (MUCH diffrent than the (2) 4" x 17.28" size RF recomends). Anyone care to comment what the diffrence length gives and why RF wants (2) at this length. (I assume that there is a sound diffrence?) Anyways, I'm starting to get a little confused, and need someones recomendation here. I'm looking for comments on the box size, which size port to use, as well as just education on the reason/diffrence/characteristics of the port length diffrence between RF recomendations, and common math equations giving VERY diffrent recomendations.

This forum is visited by guys that know their stuff, One friend even recomended that I stop thinking and simply ask, (here I am). Someone here has done this all before with the exact sub, care to comment, only cant be changed variable is that I just need to stick to the above wide x tall x deep dimentions.

Thanks a million...

John

There are two ways to reduce port noise.  The first is to increase the port diameter, adn the second is to use ports with flared ends.  The reason why you will get different results with different formulas is because all audio designers have different theories about what sounds best.  There is no one "right" solution in most cases.  Vent geometry will be different with very subtle changes in how the Fs and Fb as wella s the Qts and the system Q are utilized in the formula.  Most manufacturer recomendations are based on general average listening at moderate volumes, and may not be intended to maximize woofer performance.  Indeed, most manufacturer's will recomend specs they know the sub will handle all day long to avoid warranty issues.  You can always pretty much be certain you are safe using their recomendations.

Rear mounted vents can help with so-called mid-range leakage (ringing), that is true, but in most cases, it is at a sacrifice of SQ and in many cases it leads to acoustic cancellation (since the port and the woofer face oposite directions.)  It works best in home audio where the sub system can be placed in a corner or at a preset distance from a wall... it is generally not the best solution for car audio.  I highly recomend you place your ports on the same baffle as the driver.

I thought that was a simple question 

Any other comments, not being able to put the ports on the rear baffle means NOT building the box. I have the 47 inch wide (door to door) x 15.25 inches tall(deck to headliner) by 26 inches deep (rear seats to hatch) to work with. There are two RF bd1000's syndc as power source.

SO far have tried 3.5 cuft (shared volume no internal seperators) sealed with 3 RF 4212 DVC subs, and 3 RF 3112 DVC subs each in a cuft sealed. The 3112's sounded like sh*t, and the 4212's sound like less sh*t, so I got sh*t and bigger sh*t for sound. Box sets hit okay through about 1/4 volume, at higher playing levels the 3112's , well they DONT. The 4212's play about twice as loud as the 3112's before they distort and basically start to sound like too much power is going to them (I used to run the 4212's in the same box off of 1 bd1000 amp in a 4 runner, where its performace was 200% better than I am getting now, so I can only asume it they are over powered).

Im sick of buying the wrong stuff here, based on 2 rd bd1000's synced and the above 47x15.25x26 space then, someone want to make a sub and enslosure recomendation? Or comment on the rear baffle mounted ports on sized boxes I mention above.

Plugging the 3112's specifics into term pro, I came up with  (2) 4"x18.07" ports per woofer as the best size/qty for ports for the original 2.5cuft (15.5" x 15" x 24.8125") enclouses, ports would be installed on the rear deck baffle, opposite the subs.

Thanks

Don't get me wrong, you CAN put the ports in the rear baffle, it just makes your setup much more difficult to get right.  You have to pay very close attention to reflections and acoustic cancellation.  Positioning is everything, because if you are not careful you will end up with a net DECREASE in SPL at the port tuning frequency rather than the normal +3 to +6db increase.  Do you have an RTA?

As a general rule of thumb, I highly recomend never using shared volume sealed enclosures.  The subtle differences between subs and electrical differences in the hookups and amps can cause all sorts of unwanted cancellation effects and the subs can physically dampen one another.  In a worst case condition, they can actually cancel each other out completely at certain frequencies, or "fight" each other so much you end up frying a voice coil.

RF 3112's... well, what can I say.  I'm not sure what you want out of your sound, but these are not exactly high SQ subs.  The 3112 is a much better speaker than the 4112, by the way.  But if yu want SQ, I would say don't use Rockford woofers.  Get JBL, Planet Audio, Nakamichi, Eclipse, IDQ...

I set out on this build to build a street SPL truck. Something to rattle the "homies" playing Little John in the civic with my music (Korn, Slayer). My collection includes everything from bushwick bill to Toby keith, but again this was really created to bring out the worst in urban white thrash music (Korn). I respect everyone and travel at moderate volumes, but who am I kidding, I want the ability to have fun with SPL when I want to...

No realtime analyzer.

That help?

Thanks