This is going to be long winded, and unfortunately, strewn with subjective, and vague descriptions, but hopefully, I can get some help amidst all my vague "expectations".

I installed a sub system in my "Winter 'Vette" ('92 Dodge Stealth RT/TT) to augment the factory system, which is better than the factory system in my C6...except that it lacked bass badly. I bought a 3/4" piece of plywood and cut it to fit snugly in the back of the car, over the spare tire area. I removed the spare tire, jack, etc and the board I made basically replaces a fiber board that originally covered the spare tire area. The area is approximately 3' x 2.5' x 8". I used 3/4" adheasive weather stripping around the entire perimiter of the board to seal it as best I could to the rear interior plastic.

*Subs used are JL Audio 12IB4, Two of them
*Amp is a Soundstream 500 SX
*Signal to the amp comes from the rear channels of the factory (Mitsubishi) head unit, via a "Directed" brand, Line Output Converter.

That's pretty much the system. First the expectation then the results. Here's where it gets really subjective.

The expectation comes from a Trans Am I had years ago. I did pretty much the same thing; removed the rear storage lid, and replaced it w/a carpeted, 1" plywood board with:
*two JL 12WO4 subs
*powered by a Sounds stream 300SX amp
*Signal was direct from an Alpine 7534s head unit.
Now this system IMO, pounded. When cranked up, it felt like you were going to damage something; either your body, or the car. Friends all agreed that the power and quality of the sound was awesome (so it wasn't just my opinion). If you opened the rear hatch and played the system, lot's of bass was apparent, even from a distance. The system seemed to perform effortlessly too. That's what my expectation for the new system is. Adjectives I'd use to describe the performance of the Trans Am's system are:
POWER
Depth
"3D" sound (yes, the bass sounded/felt 3D)
Effortless

The problem: The current system doesn't sound like the system in the TA...at all. The bass is fairly tight, but not strong at all. This is hard to describe, but it's WAY better than it was before I installed the subs and amp, but it just seems like something is missing....because something must be "wrong". Arguments about my hardware selection and implementation asside, the thing should impress the average person and it won't, currently.

Settings: I have the LOC turned up about 1/2 way, and I have the line level input selector switch on the amp set to "high" or 0-5v. I have the crossover switch set to "low pass" and the speakers are sired in parallel, for 2 phm load. I have the gain on the amp turned all the way up, as high as it will go, and the crossover turned all the way down to "45" (hz?). If I raise the crossover at all, the midbass get overwhelming real quick, and it's annoying sounding. Overall, adjectives I'd use to describe the performance are:
Weak
Colored sound
unimpressive
strained
Not DEEP/no depth

1. How do you know what voltage is coming from the LOC based on the settings of the pots?
2. Are the 12IB4's comparable to the 12WO4's?
3. How do I know what to set the input voltage at on the amp?
4. Power from a 500sx should KILL. Why do I have to have the gain cranked, just to get bass that is notably better than stock?
5. How would I know if something is out of phase (either the LOC wires or speaker wires)? -I know the speakers wires aren't out of phase, BTW.
6. Something is out of whack. Any input please?

 

wrong box size, cancellation, box flex, subwoofer position..

 

alot of this has to do with box size or not bein in a box at all

 

The "IB" stands for infinite baffle, which means those subs are designed for NO enclosure. While I have no experience with those kinds of drivers you're certainly not using them as they are intended and by putting them in an enclosure you could very well be causing the problems you're hearing.

 

Thanks for replying.

All "problems" that would have also existed in the Trans Am as far as I can tell. I didn't think woofer position mattered much (at all). Isn't bass omnidirectional? Also, when you open the hatch or the doors, out side or in the garage, you can hear some bass...but it's not like the TA was...not at all. And this car has a bigger amp. If the issue were cancellation, or woofer position, stepping out of, or moving inside the car would "fix" or change that...would it not?

That's right. I got the IB's because even w/the weather stripping, I'm going to have "leakage" all over the place...just like I did in the Trans Am. The speakers I had for the TA; the 12WO4 were supposedly ALSO an infinite baffle speaker, and the 12IB4's are supposedly the replacement for that application. I hear you about putting them in a "box", but please realize that I got them because all the box really does, is "separate" the listening area from the magnet area -for lack of a better term. There is still going to be "pressure" leakage throught the interior plastic mouldings.

The more I sit here and think about this, the more I think the speakers are out of phase. Of the amp is defective. The sound quality is just not right. It's not a little off the mark, like a messed up box would be...it's WAY off the mark.

 

TTT Please...

 

Looks pretty simple to me.

The older JL 12WO4 subs were good in an enclosure from 1.5 ft^3 sealed or 2.5 ft^3 ported. In that space you described in your TA, it was probably 'close enough' to work properly.

The JL 12IB4 is designed for an infinite baffle style mount. If you put it in a box, it needs AT LEAST EIGHT ft^3 per driver.

Given the dimensions in your post, the subs only get 2.5 ft^3 each... it's no wonder that they won't play low.

Top it off with a crossover point of 45 Hz and you are doing nothing but sending massive amounts of current to a driver that cannot perform below 45 hz, and the power ends up as heat loss. Nothing more, because the sub cannot physically recreate the lower frequencies because the box restricts it's movement.

Turn your gains down and set your crossover for 80 hz and watch what happens: I bet it's loud and it's really boomy, and doesn't sound right... because those subs are designed to be in a very large enclosure.

Swap your subs with something that can work in a 5 ft^3 enclosure (of less if you want to tune a box to size) and you will see the results you are looking for.

Let me know if you have any questions or need further clarification.

Mark

 

Now that's a post that I can understand, plus you referenced my old 12WO4's for comparison. Thanks.

That sucks though, that I have to buy more subs. What would happen if I ported the board? Argh! That's a crappy solution...if it's any solution at all.

-Tom

 

Well, if you are looking for the cheapest way out, you could try and clamshell them (isobaric). That cuts the airspace they need in half, though your efficiency takes a dump... worth a shot if you want to save some dough...

 

What does that mean? To "Clamshell" them?


Clearly, I just got lucky w/my old Trans Am and the components that came together in it...'cause I obviously don't know what I'm doing here.

-Tom

 

Crude drawing:


seal off one of your sub holes with a chunk of wood and load the woofers together as in the picture in the other hole. Make sure the surrounds don't touch (you may have to separated them with a spacer). On your bridged mono amp, run the negative terminal of the sub that is outside of the "enclosure" to the positive side of the amp and the positive side of that sub to the negative side of the amp and wire the sub inside of the enclosure positive to positive at the amp and negative to negative at the amp.

Give it a shot, it might be a cheap fix as it is just your winter car.

If it doesn't work well, get yourself into a good sub in a proper sealed, vented, or even bandpass enclosure. Sell the other subs or hook em up to a wall socket and enjoy the smoke ...

 

"Enjoy the smoke." -LOL!

That 's crazy about the isobaric idea. I've never seen anything like that before.

As a "Winter beater", that idea doesn't really fly (for me), because I need as much usable space in the rear as possible. That's why I pursued the "baffle board" in the first place; it didn't sacrifice ANY hatch area volume at all...other than where the spare tire used to be. I can still throw skis boots, poles, gear, etc in the back no problem, and not have to worry about moving/removing a sub box all the time.

I guess I need to figure out what the best woofers are for that contraption that I've built.







I did some more accurate measuring and calculating of the volume of the "enclosure":
The dimensions are ROUGHLY 50" x 27" x 5". I say roughly because it isn't symetrically shaped, and the floor isn't totally flat. Additionally, even though it's well sealed against the interior plastic trim, the plastic trim itself isn't sealed to anything else (floor pan, rear wall, etc -just like in an F-body)...so that would allow some leakage -I would think. I don't know how that affects the "real volume" of the space though... There is a chunk "missing" from the area that is an Isosceles, 90* triangle; 11" x 11" -or 60.5" sq. Knowing this, I calculate the volume as such:
50 x 27 = 1350" sq
1350 - 60 = 1290" sq
1290 x 5 = 6450" Cubed
6450/1728= 3.73 cubic feet, or 1.87 cubic feet per sub. Roughly.

 

I did a couple changes, including the one that you recommended: turning the gain down. In the pics below you'll see the amps settings, as they were when I first posted. Yesterday, I switched the input level from "high" (.5v-5v) to "Low".2v-2v. That allowed me to lower the input gain to about 1/2, and still have the same volume (if not a little more). I turned the crossover up and played w/it for a llittle while. If I set it at just over 60Hz, it sounds WAY louder, but not much boomier. -It was still "boomy" when set at 45Hz, IMO. Once you go over about 80Hz on the dial though....OMG it gets SUPER annoying sounding. ALL HUM!

So I left it set at just a smidge over 60Hz on the dial, and put it back together. It sounds a lot better/stronger...but still, nothing like my old car did. I on board w/the idea that I've got the wrong woof's, which bums me out.

One thing I still don't get though; Even thoguh the enclosure I built is too small for the woofers I have, on paper, the enclosure has leakage all over the place. For example, I tried to get a good seal between the board, and the interior platic mouldings, and I think I did...but the air can very easily travel past the plastic below the board, and above it. Wouldn't that make the space "behave" like a larger space?