Having used the JL stealth subs in my e46, I wonder why we have not been using a infinite baffle Sub in the back hatch of our X5. It is sealed off from the cabin, you have more airspace, and the install is a lot cheaper and much easier, and most like better sounding. Seems like you have to cut that lid anyway to add a grill in a lot of the installations, so why not pop a infinite baffle subwoofer in there and a grill>?
Infinite Baffle
Infinite baffles (IB), often termed "Free Air", are possibly the simplest enclosures to build, and a great way to conserve space. This design is defined as an enclosure that contains a greater volume of air than the Vas of the speaker. Applying an infinite baffle system in an automobile is relatively easy. The concept of an infinite baffle is to isolate the sound wave produced by the front of a speaker from the back wave. This normally involves mounting the speaker(s) on a board that seals off just behind the rear seat while using the trunk of the vehicle as the enclosure. When all is said and done, an IB enclosure is truly quite large.

Trade-offs come in many forms when working with IB enclosures. Sure, using IB enclosures conserves a lot of space, especially in the trunks of smaller cars. However, there are some losses to be noted. The most prominent is efficiency. Without a solid structure built around the woofer, it is difficult to reinforce the sound. Trunk interiors are filled with flimsy panels, thin sheet metal, and usually a measly spare tire -- none too pleasing for sound reproduction. This same issue holds value with the speaker's power handling. As much as 50% of the nominal power handling of a woofer can be lost when placed in an infinite baffle. Another anomaly that plagues IB enclosures is the tendency to lose control of cone movement when played below the Fs (resonance frequency of the driver), much like ported systems when played below the tuning frequency. For this reason, it may be desirable to utilize a subsonic filter below the Fs of the speaker.


When purchasing IB speakers, keep in mind the following parameters to assure that the speaker is right for the application. The first is the Qts (the total resistance of the driver at its resonance). Speakers with a Qts greater than 0.6 typically work well in an IB environment. The second is the Vas (the volume of air having the same compliance as the driver's suspension). The Vas should be smaller than the total volume of the environment the speaker(s) are being placed in.

Good: minimal space consumption; generally easy to build.Bad: poor efficiency; sometimes difficult to isolate front and back wave; limited cone control below speakers fs.




A True Infinite Baffle Subwoofer