Sub cancellation

[02dodgeram 10+ year member]

Let me start with some background and as much information as I can present so as to get the most complete answer I can. I've got an 02 dodge ram quad cab (the newer style), with a custom made under the seat ported box with 1.7 cf of airspace tuned around 39 hz. Its single chamber housing 2 10" infinity perfect 10.1 with a 4 ohm SVC. They're powered by an infinity 611a monoblock rated 657 RMS @ 2ohms.

My problem is more for the benefit of passengers sitting back there. Basically the ports are attached to the exterior of the box (made out of ABS plastic) very small (about 14.5 inches by 6 inches by 1.25 inches x 2 ports) but I'm very limited on space under my seats. I've already raised them up by about 2 inches to fit the box, so I really can't go any higher.

The box itself is made out of 5/8" ABS plastic from a mold to custom fit my truck with a 3/4" MDF top. I've stuffed it with polyfill to try to give it more airspace and lower the tuning frequency a little, but again, I'm very limited in my options. I haven't sound deadend anything except for directly behind some MDF baffles created for my front 6x9s, but I plan on stocking up on second skin damplifier pro and dropping in about 200 sq ft of deadener when my cashflow permits.

My problems are:

1. In the back seat, I'm getting some pretty severe cancellation (gets decently loud up front, but in the back you can only feel the bass and hardly hear it). The subs are firing upward into the seats, as thats the only place for them to go.

2. My subs bottom out pretty quickly (if I had to guess I'd say around 30 hz). Is there any way to correct for this? I understand that tuned at 39 hz + polyfill should be acting like its around 37, but there's some pretty severe excursion starting at about 30 and the low end disappears. Am I up the creek without a paddle since I'm tuned so high, or is there any way to trick the subs/box?

3. Is there any more permenant way to secure my rear view mirror? I've wrapped it with rubberbands, and it still vibrates like crazy (virtually unusable).

I'd love to wall off my back seat and throw in some 15s with around 2k rms, but my wallet would get pissed at me and go on strike.

Before I knew any better I would have guessed I needed a bigger amp, but after snooping around here the last few weeks, I realize adding more power to try to compensate for the low end would probably result in some pissed off subs. Would I be better off going sealed, and if so, would a bigger amp be in order to try to make up for the lost SPL. I bought the perfects off crutchfield during their BOGO deal because I want to maintain some SQ for when I don't feel like a wigger, but obviously now that I've gotten adjusted to having subs, I've been bitten by the SPL bug.

If swapping gear is my only option, I'm open to recommendations, and since car audio has now consumed me, I don't mind saving up for something impressive. Obviously, as with the 100s of other threads typed in all caps and with no respect for grammer or spelling, I want the best for the least amount of money, but man does reading those threads get annoying, so the sky is the limit and if it takes me 6 months to save up, so be it. I've already got my eye on some CDT comps for my frontstage as my infinity kappa 6x9s simply DON'T HAVE midbass.

Thanks for any input! I tried to be as thorough as I could, but if I left anything out, let me know. I'm sure I can find a digital camera if pictures would help.

Click to read more...

 

[02dodgeram 10+ year member]

didn't realize it got that long. Sorry!

 

[reneeb7363 10+ year member]

lol..... my stupid lil input...... are you sure they arent wired out of phase. are the ports on the same plane as the subwoofers face or are they 180 degrees off? Definately use the search tool on this one.... just a few thoughts that came to my lil pea brain...

 

[JimJ 5,000+ posts]

1. In the back seat, I'm getting some pretty severe cancellation (gets decently loud up front, but in the back you can only feel the bass and hardly hear it). The subs are firing upward into the seats, as thats the only place for them to go.

Try downfiring instead //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

2. My subs bottom out pretty quickly (if I had to guess I'd say around 30 hz).

Because playing music with content that low means your drivers will be "uncontrolled" by the enclosure...39Hz is awfully high for a daily driver. I'm not surprised your subs are bottoming out at 30Hz...you need a subsonic filter to attenuate the lower frequencies, or tune lower.

and it still vibrates like crazy (virtually unusable).

Unless you turn it down, get used to it...

 

[reneeb7363 10+ year member]

are you trying to pimp your postings there jim? LOL! tired of being in fourth?

 

[02dodgeram 10+ year member]

"Try downfiring instead "

Perhaps I don't understand the meaning of downfiring, but wouldn't that mean mounting them to the bottom of the box? They're under my rear seats, and its quite impossible to downfire them if my understanding of the term is correct.

"Because playing music with content that low means your drivers will be "uncontrolled" by the enclosure...39Hz is awfully high for a daily driver. I'm not surprised your subs are bottoming out at 30Hz...you need a subsonic filter to attenuate the lower frequencies, or tune lower."

My question was is there any way to rig something up that will lower the tuning frequency? There is nowhere else for the port to go. I don't have many options for an ideal box without taking out the back seats, or cutting out a blowthrough and throwing the subs in the bed of the truck. I've considered a center console box, but I'd rather use that as a last resort, since I often have people sitting in that middle seat, plus finishing it to an OEM look would require quite a bit of work.

"Unless you turn it down, get used to it..."

I'm used to it, but was hoping some of you "geniuses of the boom" had some input as to a solution.

Thanks for the response though. I've got a little more knowledge than is required to work at a best buy or at Crutchfield, but not enough to consider myself well versed.

 

[02dodgeram 10+ year member]

working on a picture to illustrate....

 

[02dodgeram 10+ year member]

hope that illustrates well enough.

 

[JimJ 5,000+ posts]

A downfiring sub enclosure has spacers or "feet" to provide clearance for the cone travel, of course //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

My question was is there any way to rig something up that will lower the tuning frequency?

Not easily, and it will take up more room.

Have you considered sealed instead? Sounds like that's the better way to go in your case...

 

[matrxx dude 5,000+ posts]

the port is under the seat?

 

[02dodgeram 10+ year member]

Yes the port is external to the regular box. It is basically formed by putting a rounded off rectangular piece on top with two 6" by 1.25" slits. The box would essentially be a generic fiberglass sealed box, but it has this piece on top of it which directs the air coming through the port forward (comes out at a person sitting in the middle seat's legs).

 

[02dodgeram 10+ year member]

I may wind up going sealed, but the output is already relatively low on these subs (granted they are SQ subs). Would throwing more power at them sealed possibly make up for some of the lost SPL? The recommended sealed box would be 1.2 according to infinity specs, and I could probably figure out a way to take off the top piece of MDF and redo it.

Sealed at least if I don't get an amazing amount of output, I'd have some pleasent sound.