Questionhey there,
first of, i want to thank you for sharing your knowlege with those of us who dont have the experince others may have. so on to my question, i own a 1992 chevy camaro, and i recently upgraded my subwoofers to 2 12inch Kicker L7 dual 4 ohm subs, i am running a hifonics amplifier, no my problem is, as you may know, i dont have much room for a box, the subs require a min. of 1.75 cu. ft. each. i would like to go bigger and get it tuned as low as possible (34 hz or lower) for high spl. would you recomend doing a "wall" setup, a fiberglass box, etc. i have only built a very simple mdf box before, so i am still new to this. where could i get a cut sheet for such an enclouser.
thanks again,
brandon
AnswerThe strength of the box is the most important thing for the box; when the sides bow from pressure inside the box it soaks up energy. So, for example, the ideal would be a box constructed of steel reinforced cement but that is impractical. A reasonable compromise material is 3/4 plywood which is properly reinforced at the corners and very rigid. Any air openings (other than the port) should be properly sealed.
As to size, as a general rule the larger the box the better will be the response and the efficiency.
However, here is the dilemma that you face. For most woofers the optimum size of the box - or at least big enough to benefit from the acoustic parameters of the system - is larger than is practical for the size of most cars. For example, most woofers of the 10", 12" variety in order to get the top performance out of them you need a box that is 5 to 7 cubic feet - very large, indeed.
BUT: You are in luck because when a woofer is force fed at low frequencies into another big closed box, like the inside of the car cabin, the laws of physics change and it becomes, primarily, a pressure device and does not operate strictly on the acoustic principles - much to the dismay of car system designers! Under these conditions the energy you can get out of the system becomes a function of the volume of the car and the volume of the box and the power amplifier driving the system.
I have never seen a computational system that will optimize the design of performance using the parameters of the speaker AND the cubic volume of the speaker enclosure AND the cubic volume of the inside of the car/truck. It takes some experimentation. One box will not yield the same results from car to car. Most installers who work with different cars daily learn, from their experience, which ones are the best, etc.
For your system I would recommend you try two or three different boxes and see which one works the best. Your trial and error approach will go far.
The L7 has a sensitivity of only 88db which means you want to get a bigger box if you can and drive it with as much power as you can get into it. If you go to crutchfield.com on this speaker they will give you some box recommendations, too, that are worthwhile looking at because the engineers at crutchfield have very good experience about these things. They recommend 3 box sizes for this driver that make good sense to me.
Lastly, a vented box will probably be the best in terms of getting optimum bass output; the problem is designing the vent/port. It may take some experimentation and/or measurements to perfect it.
Hope this helps.
PS: I had a Firebird - same as a camaro in terms of space - and found after much trialing with many different speakers and boxes that a pair of 8" woofers each in a 1.0 cu ft box tucked into the small trunk cavity in the back had a profound performance - much to the dismay of others who had crowded 10s, 12s, and even 15s into the car. The 8s I used were JBL but I don't remember the model number; they had the white foam surround edge on them so probably they were the LE8s - no longer available. Just me personal experience.
