Dual Pockets
i have 2 12"solobaric l7 and the only good sound i hear is the insode bass?
i have a big box that came with the kickers (dual box)someone told me there might be too much air space or too tight!and i have a ma audio 2000 watt amp its sounds ok but my cousin installed the music . i wanted some advice before ipay out of pocket what could be wrong? my box is _o___o___ (somewhat like that)
It's hard to know exactly what the problem you are facing without being there. Still, in regard to the actual system, there are several things to consider here:
the 12L7's, though having specs for sealed enclosures, really do well in a ported enclosure of about 2.96 cubic feet including the displacement with the vent. I cant recall the exact vent size... something like 2.5 inches wide by 10? inches long, by 17? inches deep... I used to build them all the time and it worked well in many applications. Naturally, its not the only vented size that works well, just one of many that have been done and one that worked exceptionally well in my experience. If the box is sealed, you may still get a good response but it wont be as loud and "boomy" as what a vented/ported box would be. In either case, the box must be air tight (save the opening of the port).
You have 2 12L7's... what ohm load are you running to the amp? If it's an 8 ohm load, then you arent getting the power you should. If it's 2 ohms or lower, you may be getting too much out of the amp and could damage the amp. You noted that its an MA Audio brand amp... what model amp is it? This would give me some more specific info on the amp. I'm presuming the amp is wired correctly but if not (as indicated above), many other problems can occur. However, capacitors are not necessarily needed. They may help but its not mandatory. Loose grounds can definately cause problems but really, you would have a lot more issues than just it only sounding good inside. If the amp was wired poorly, you may have other intermittent, if not constant problems such as the amp going into thermal shutdown, become very hot, fuses blowing, or strange sounds coming from the subs.
In regard to amps too, many ppl think that the max rating on the amp is what the amp will continuously put out but that is far from the case. I dont want to ridicule your choice of amp but to be honest, MA Audio (Mobile Authority Audio is what they were called in the early 90's) is not that good of a company to begin with. The quality of their components is not comparable to better brands such as JL Audio, Kicker, Phoenix Gold, or Boston Acoustics, to name a few. At best, that amp is probably doing 1000watts rms, if that much. That means that each sub, **at best**, is getting 500watts, but most likely considerably less. Unfortunately for your system, the 12L7 takes more power than that, usually as much as 700 to 900watts if not more (I've pushed them with as much as 900 watts per speaker without problem). In my work truck, I have one 10L7 seeing 725watts RMS all day and does really well (sealed downfire box). My wife has 2 12L7's in her 04 Impala with a Memphis Car Audio ST-1000D pushing both at 1 ohm. That's a little more than 1200watts going to them both, if not more as Memphis is known to underrate the RMS rating of the amp, and it's still not enough. I've also run 1000watts RMS to EACH VOICE COIL of 4 15L7's in vented enclosures, (2000watts rms per speaker, amp gains were matched). The system slammed but could have held more even.
One thing important to note is that Kicker 12L7's only need about .85 to 1.0 cubic feet for a really good sealed enclosure, (maybe even as small as .70 with high, high power going to them; no bigger than 1.25 before the output starts to decline in quality). If you have a really big box and its not ported then it's quite likely that you have the wrong size box. Having too much air will drastically impair the performance of a sub.
There are more things also that you could look at such as internal acoustics, the use of dynamat or other sound deadener, adequate power wire going to the amp coming from the amp to the woofer (12 guage is adequate for 95% of the installs out there. I dont recommend smaller), etc. If you are having rattling that's heard outside, make sure whatever bolts or screws or panels that you can physically reach with a rachet or screwdriver are tight. You can use some form of sound deadener on the underside of the trunk too, that may help.
I could probably add more to this but I think you have enough here to start with. I dont know what your experience with box design/building is so to lend a hand a bit, I'm going to put the instructions for calculating the air space of a rectangle/square box. To calculate the air space, you...
1) first want to know what size material the box is made out of. Most are made out of 3/4 inch material, typically medium density fiberboard (MDF).
2) Next, take measurements of the box: the length, the width, and the height (or depth depending on how you want to look at it).
3) You have to account for the material the box is made out of; if not, you will over-calculate your volume. So, if it's made out of 3/4 inch material, you have to double it for each measurement (3/4 inch thick wall on one side + 3/4 inch thick wall on the other side = 1 1/2 inches, or 1.5 inches). If it's 5/8 inch (another common thickness, do the same thing (5/8 = .625, doubled = 1 1/4 or 1.25)
4) Subtract the doubled amount (1.5 in the example) from each measurement and that will give you your internal dimensions.
5) Multiply the internal dimensions together, that will give you the total cubic inches.
6) Divide that number by 1728 (or divide by 12 three times, same thing) and that will give you the internal volume. The result will be a reasonably close approximate as you arent accounting for speaker displacement or the internal divider, if present. They will be very accurate though, no more than a few hundreds of a cubic foot off (which isnt enough to be noticable by anyone).
Good Luck!
~G~
